Fantastic work, Johan. I am electrical engineer by trade and I could not have done this better myself. The way you broke the schematic down into pieces and then showed waveform excerpts relating to different nodes in the circuit was fantastic!
I really learned a lot from this video, and it refined my understanding of things that I only incompletely understood. So many posters on this subject have great technical knowledge,, but aren't great at explaining that knowledge, at anticipating their audience's questions. This presentation was very easy to follow, with a consistent level of technical sophistication all the way through. Great job Johan and thanks!
Complimenti! La vera bravura non sta nel fatto che johan conosca come funziona una SLP....ma nel fatto che lo sappia rendere comprensibile agli altri. Ancora complimenti!
Your ease of explanation allows me to believe that you understand the differences and similarities in the schematic of most Marshal amps. Which lends me to feel that the dial up if not assisted with variations in parts and labor. Are understood between takes
+JED TAYLOR I actually have a rather basic knowledge of the circuits compared to experts. And yeah back then they used whatever material they had in the shop to build the amps so the individual variation was significant.
You ve touched the very phenomenon of which I have just decided must have taken place. At times even with the same series of amps. Some built on American tubed some British and some German or Russian or different tubed but different grid dynamics. Example. The 6L6 or 5881. I hope that's the right tube for replacement recommendations. Seems like the 60s and 70s started the whole conversion effort. Away from 6v6 into kt 66 or even to military spec tubed. Or what ever was avalible. It must have been a great time for amp builders
I loved the video. Somehow I have missed it back then. I have two little corrections if I may. As you know I love your channel and this is not a criticism. It is just little correcture. Bypass caps on the cathode resistors of the preamp tubes do not roll off the bass. They are preventing internal negative feedback loop inside of the triode itself. Higher value will give it more bass actually. Bypass cap there increases efficiency and therefore it increases the gain. Smaller values help only high frequencies and as the capacitance grows it helps lower frequencies as well. Even those bypass caps on volume pot and on 470k resistor leading to the second tube grid aren't rolling off the bass. First one is notorious bright cap and it allows high frequencies to bypass the pot. Same thing is true for that second cap that allows high part of the signal to go around that 470k Ohm resistor. That cap is often omitted in the bass versions of the amplifiers. Top input on this schematic does not transfer into the top input on the amplifier it self. It's logical issue copied from the Fender schematic. Fender at least narks the inputs with one and two so you know 1 is most often the high gain input. Top input on this schematic is actually low input regarding to the gain. Lower input on this schematics has two parallel grid stopper of 68K meaning effective value is 34K Ohm. Second 68k Ohm is added by the grounding lug of the jack. Input resistance, is in this case , is 1M Ohm. this is high impedance and high gain input. Top input on the schematics has 68k grid stopper and input resistor is effectively only 136 KOhm. This value is what input sees towards the ground. So ti goes true the two 68K Ohm resistors and bypasses the 1 MOhm resistor and goes to the ground. 1MOhm resistor is not in use as it is shorted by the input jack. So this is very low impedance input and tons of the signal is sent to the ground directly there. Higher gain input is also brighter because 34K Ohm effective value is not reducing top end till some 30KHz while 68 starts rounding off the top end in the usable range of the amplifier. So low gain input is often also bit darker. So this input schematic is a trap as one general would say :) Phase inverter could be explained differently btu that is completely another story.
@JohanSegeborn if you want me, I can link up great videos explaining Fenders dual inputs as well as videos about the cathode bypass caps. The best learning channel for me was always the uncle's dough channel. Way he explained stuff she'd a light even on the stuff I knew.
I Really enjoy playing new videos from you, just to hear your "Hi(a), today we are going to Check(a)..". You are awesome & I honestly enjoy your reviews over any others. Keep up the good work, Johan, thank you!
Hi Johan, there are two little things that are not quite right in your video. 1. The cathode bypass caps do not really roll of low frequencies from the audio signal. It bypasses the cathode resistor, so low frequencies "are not seen" by the resistor - this enhances the gain of the stage. The higher the capacity of the cathode cap, the lower the cut-off frequency of the gain boost. So bass amps might have larger bypass capacitors instead of none at all. 2. The second part of the phase inverter is not only driven by the negative feedback loop. Someone can cut the feedback completly and end up with something like a vox-amp, which has no feedback at all and still operate with a push-pull-power section. It's more like that the signal is "passed" through the share cathode of both stages. To put it simply: the voltage difference from cathode to grid is amplified - so it does not matter if the grid or cathode voltage is modulated, while the other is kept constant. Nevertheless, a very good explanation! Cheers :D HaenC
Isn't the purpose of the cathode bypass cap to shunt the AC component of the signal around the cathode resistor and create a fixed bias, as opposed to letting the AC create a negative feedback? Reducing the negative feedback would increase the gain, as you mentioned.
I've seen Doug on youtube install a pot to adjust negative feedback on a fender champ circuit and it works great, but its like a set it and forget it adjustment.
Hey Johan, many thanks for that. I was thinking to suggest the comparison videos, ie. how the different circuits affect the tonality of the amp - Mesa vs. Marshall, vs. Vox, I believe many folks would dig it. Cheers!
What the cathode bypass caps on the cathode resistors of V1 do is to allow each of the triode gain-stages to operate at their highest gain, if the cathode bypass caps are removed the triode gain-stages would operate at reduced gains due to the action of local negative feedback caused by the input-signal being superimposed on the cathode, the cathode-bypass caps bypass the superimposed signal to ground, enabling the triode gain stages to operate at their maximum gain, the cathode bypass caps also do set the low-end roll-off of the triode gain-stage as well.
Hy Johan maybe you can do a few updates, the signal from grid to anode is not only an amplified copy but is shifted in phase 180°, while any signal that is injected at the cathode appears in phase at the anode. The cathode bypass caps do not roll off bass, but increase highs by taking away local negative feedback from higher frequencies. The cathode resistor acts like a deflector back to the cathode, that creates local negative feedback which keeps gain down over the entire frequency range. A resistor - bypass capacitor, shunts frequencies to ground so there is no local negative feedback anymore. A cap is a highpass so it reaches only so far to the lower frequencies, -as the size of the cap dictates. Thus lower frequencies cannot pass, remain in the local negative feedback, lowering gain in the lower range of the frequencies, while no local negative feedback in the higher frequencies, thus getting louder, also more uncontrolled and distorted.
Hey Johan, I really dig your channel. Great insights into Marshalls, Celestions and all sorts of setups. I have a question that I can't seem to find an answer for. I have a JVM 410 head, and the input brightness of my guitars is darker than on a PLEXI or a JCM. I understand that it is what it is (the JVM), BUT, if I want to hear more twang going into the amp, as I would playing through a PLEXI or JCM, which component would need to be addressed? A grid resistor value? What component and value would open up that high frequency roll-off a bit so that the amp is more true to the way my single coils or humbuckers sound? I already have a fancy input buffer, Mogami cables, no pedals. Thanks!!!
Hi Johan, nice video. It would be nice if you could explain how the pre-amp and cathode follower tone stack work when the two channels are jumped. Personally I have to go back to the schematic everytime to remind me that trick... Thanks for the good work. Dani
You missed the cathode follower circuit at the phase inverter tube, which creates the inverted signal for the push pull power tubes. The negative feed back signal from the transformer is only keeping the frequency output more linear. This feedback is tweeked by the added presence control.
How do the marshall 100w and fender twin tone filter circuits scematocs compare in components and wiring networks?? Id like to custom design between the 2 if I could just see the 2 schematics to get the thought process started
very informative! my next question (maybe you did a video on this) is how the different value components affect the "tone" of the amp? ex. ( a 100k resistor will have more/less gain than a 50k)
Incidentally, both the cathode resistor and the plate/anode resistor in a triode gain-stage set the overall gain, which is determined by the ratio of the value of the two resistors, as well as set the static, or quiescent biasing point, if you set the triode gain-stage up with a 1k cathode resistor and a 10k plate/anode resistor, the resulting gain of the triode gain-stage will be 10 (10k/1k), if you replace the 10k plate/anode resistor with a 100k, the gain will in theory be 100 (100k/1k), in practice the gain will be less than 100.
In a fully bypassed gain stage such as that including V1, the cathode resistor is removed from the formula to calculate gain, and, for a specific triode, gain is determined by the value of the plate resistor. A = -mu x Rp / (Rp +rp), where Rp is the value of the plate resistor and rp is the plate resistance of the triode.
Hey Johan! Awesome vid! I’d always understood that the tone stack came before the gain stage, but here it looks like the tone stack is arranged between V2 and V3. Is my understanding incorrect, or is V3 the main gain stage in the pre-amp? It looks like both sides of the tube are used here so I’m guessing more gain that way?
Great video, I would love to see how to properly bias’s one of these amps. Would one apply a 1khz test tone at Input at a given amplitude, and then adjust the 27k bias turnpot to the point where the sinewave output at speaker output does not show clipped top or bottom of output sinwave , and also make sure at zero volt crossover point of the two output tubes are in horizontal time alignment with the negative portion of the sine wave produced by the lower pair of output tubes? Or is biasing with 27k variable resistor done by simply turning and measuring grid to cathode current across a resistor till current is set to correct level for the amps design? Thanks
Watch guitarologist work on the super lead 100 and see why you bias at idle, and then bias with a input signal. Turns out, the tube sockets were not making good contact and had to be replaced. They were corroded.
Question for you Johan. For the Marshall JMP the Volume 1 and 2... when either of these is turned up we achieve power amp tube break up. Since there is no master on these amps and no subsequent preamp volume control is preamp tube distortion achieved only by the dials in the tone stack? For example. I have both my volumes on 7 and guitar is in the upper left input with a jumper from lower left to upper right. As I turn up the individual knobs for presence bass mid treble there comes a point around the 6 mark on the dial that more distortion is introduced. Is this preamp distortion being added? Or is it more power amp tube distortion? When volume 1 & 2 are turned up is it only pushing the power amp tubes? Is there any way preamp tube distortion can be achieved with a JMP or is it a fixed bias on the preamp tubes set to clean only?
Thanks Johan for the interesting discussion. I used to work in audio and RF electronics in the late 60s and so this really stirs up the cobwebs for me. I was wondering if having AC on the filaments of the preamp tubes might introduce some bothersome AC hum, even though twisting the leads would reduce the hum. I also wonder if replacing the carbon pack resistors with metal film resistors in the preamp gain stages might reduce the noise floor of the amp.
It does! Though there's a huge debate on carbon vs metal resistors. Carbon are noisier both good and bad - they add a "sizzle" for lack of a better word. But better money is spent on speakers, pickups, tubes than resistors. Not worth reverse engineering if an amp already has modern components. Tighter wraps also can help moderately
The rectifier bridge produces 120Hz ripple. Anode = plate. Plate resistor regulates the] amount of plate current allow a amplified voltage to be present across the plate resistor. The source of the plate current is the B+ supply leg. Cathode tone stack allows for lower voltages and therefore lower voltages to the manual controls as well. The inverter/driver tube drives the output tubes which generally operate in Class B push-pull. Bias also allows to bias the cutoff of each tube (within linear operational area) and overcoming the crossover notch distortion which is apparent in most push=pull transformer stages. Each output tube conducts through one half of the output transformer primary when the voltage is positive. When the transformer signal voltage goes negative, one power tube goes into cutoff and the other tube, now being in the correct 180 degree phase, conducts for one half audio cycle and so on. The secondary winding is a much lower voltage and impedance matched to the speaker(s).
Hey Johan, I'm just getting in to amp repair and design, I never realised you did this series.. they are great! Your voice/accent sounds very different to me in these early videos. Did you move?
Hi Johan, I’m willing to build a Marshall Major i am wondering if you know where can i get the original parts to build. I’m in USA and I already have someone to build the cabinet and chassis. Has a lots of kits for super lead i don’t know if i can use the super lead kit. I hope you can help me. Thank you
I never really had an idea how that tube thing stuff was meant to amplify a guitar signal, but this vid made it quite clear (didnt get most of the gridnegativfeedbackbabble though xD )
But totally and refreshingly free of the usual UA-cam "Hey wassup, this Joe Bloggs of XYZ dot com, Click Like if you think i look cool.." etc. To be fair, I thought you did explain the more techie bits very well, which enabled me for one, to start thinking about this a bit more deeply.
Great video, thanks. So which cascade makes overdrive clipping? I guess the second, where the signal from both channels blended together. BTW, can you share circuit?
+Johan Segeborn , and about bias circuit ??? I made a plexi but had problems with excess gain on channel 1. It was resolved with a signal drift grounding pin 2 of the valve 2 by a resistor of 82k. It solved the noise but it is not the solution I was looking for, is aware of which may be being generated this problem? Tks in advance.
This is a really cool video. I can’t believe I didn’t see it before. Very well explained and easy to understand. Do you think you could do one on fender amps? 🎸🎛
The first triode is working as a gain stage and the second triode is working as a direct coupled cathode follower. The plate voltage of the first triode is the grid voltage of the cathode follower, so no coupling cap is required to block DC. The grid of the cathode follower is at a high voltage, but current flowing in the triode and therefore in the 100k cathode load resistor develops a voltage at the cathode which is slightly higher than the grid voltage so that the grid is negative with respect to the cathode.
Johan,how does this architecture work compared to the jvm's?The JVm's have no diode distortion unlike other models(800's900's etc) and can use %100 tube saturation!.I believe and have heard a JVM pull plexi sounds easily,when used correctly(most people use to much gain when trying IME and using greenbacks or the like) what are your thoughts?
Kate Andrews Hi Kate! The JCM800 2205/2210 had diods but not the 2203/2204s and the SL-X JCM900s were the only ones without diods. The JVM has an extra preamp tube compared to the 1959, which is engaged in some of the settings in the JVM. Marshall themselves states in the manual that “CRUNCH GREEN MODEuses the same preamp topology of the classic Marshall JTM45/1959 'Plexi' models (i.e.: gain + gain + tone) but with a bit more of gain than is found in the originals” However here I used the OD2 orange mode which adds an additional gain stage compared to the 1959. Still this is in my opinion what sounds the closest to the typical aggressive but rather clean clipping sound of a vintage super lead. Cheers Johan
Except for capacitor and resistor values as well as only considering one side of the phase inverter tube as the last gain stage before hitting the power stage and thinking of one side as similar as a single ended amp, if you consider all that - this circuit topology is nearly identical to my Vox AC4C1 amp
JOHAN SEGEBORN, 1.) When you're biasing the power tubes in an amplifier circuit how do you bias the compression of the power tubes the 1dB compression point of when the power tubes start to compression? because its say to bias tubes at a 30mA bias current per tube to be safe but how do you know when the tube is compressing? 2.) Most Power tubes 6L6,EL34 use a B+450vdc on the plates, if you increase the B+ to +600vdc would this increase the AC ripple but why would it increase the AC ripple? i would think it would decrease the AC ripple because more B+ voltage mean less current draw from the power tubes. 3.) The Choke coil wire is frequency dependent which I'm not sure why they made the Choke frequency dependent in guitar amps linear power supply. Is the Chokes storing current like a reservoir like the filter capacitors or is the Choke doing something else to the AC ripple, not sure if the Choke is regulating the current? If you remove the Choke from the power supply will this add and cause harmonics from the AC ripple frequency getting added into with the guitar signal? 4.) For Fender amps. When you remove the normal channels first preamp tube, the vibrato channels preamp will have more output voltage and it changes the impedance and TONE, any reasons why? Tubes have very high impedance and aren't suppose to load down the parallel circuit. Any reasons why this changes the TONE of the vibrato channels preamp from removing the unused the first tube from the normal channels amp? its changes the impedance and frequency response techs have told me.
Kjempe bra! har selv en 77 mod 1959 som jeg har sendt til en Tech for å få den moddet til Mod5 specs. Hvor har du lært alt dette? man lærer jo ikke om rørteknologi på skolen lengre da det er "utdød" teknologi. Kunne tenkt meg å blitt mer teknisk når det kommer til forsterkere. En dag skal jeg modde min egen amp! Hilsen fra K.I
I remember doing that electric slide dance when I got zapped by 465 volts DC on a wet garage floor, barefoot, while working on a 68' Fender super reverb. I shit you not. I literally could not move my arms for 15 minutes, they were frozen in place.
Plug it in... power it up... insert guitar... turn to 10... play power chords... get a disturbing the peace summons... make court date... pay fine... repeat.
Fantastic work, Johan. I am electrical engineer by trade and I could not have done this better myself.
The way you broke the schematic down into pieces and then showed waveform excerpts relating to different nodes in the circuit was fantastic!
Pretty clear explanations ! Never understood a shit out of amp circuit, but now i do. You should do more of this.
Thanks! Really glad to hear. More are coming up :-) Cheers! Johan
Awesome way of explaining it. Bringing in 1 piece of the circuit at a time, and showing signal path. Thanks for this.
I really learned a lot from this video, and it refined my understanding of things that I only incompletely understood. So many posters on this subject have great technical knowledge,, but aren't great at explaining that knowledge, at anticipating their audience's questions. This presentation was very easy to follow, with a consistent level of technical sophistication all the way through. Great job Johan and thanks!
+James Lupo Thanks James! That's really good to hear. Cheers Johan
Great insightful explanation of amplification in a nutshell.
Thank you very much!
Thanks, really glad to hear that!
Another great video from the best guitar-related channel on YT!
+GodGunsGuitarsGadgetsGovernment Thanks! Very nice to hear that! :-)
You're welcome. I love your channel, you know what appeals to guitarists who are also technie nerds like me (us?).
Valves will still be here in another 150 years from now....love Valves !
Ed Berger Indeed! Beautiful things.
Great video! We call the output of the rectifier, pulsating dc.
Many thanks Johan. Very helpful, interesting, and to-the-point!
This is my impetus for improving my understanding. Thanks so much for the lessons and the demonstrations of all the amps your involved with
+JED TAYLOR Thanks Jed, I'm glad you like the videos!
This schematic and the oral rendering of its operation. A great lesson
Complimenti! La vera bravura non sta nel fatto che johan conosca come funziona una SLP....ma nel fatto che lo sappia rendere comprensibile agli altri. Ancora complimenti!
very interesting.. Johan, you can't stop surprising me.. 10/10
Thank you Johan for this informative video.
Absolutely excellent! Thank you for this post.
Outstanding job Johan! It is very difficult to communicate to a people without professional or specialized knowledge of a particular subject.
Thank you for the video Johan!
Your ease of explanation allows me to believe that you understand the differences and similarities in the schematic of most Marshal amps. Which lends me to feel that the dial up if not assisted with variations in parts and labor. Are understood between takes
+JED TAYLOR I actually have a rather basic knowledge of the circuits compared to experts. And yeah back then they used whatever material they had in the shop to build the amps so the individual variation was significant.
You ve touched the very phenomenon of which I have just decided must have taken place. At times even with the same series of amps. Some built on American tubed some British and some German or Russian or different tubed but different grid dynamics. Example. The 6L6 or 5881. I hope that's the right tube for replacement recommendations. Seems like the 60s and 70s started the whole conversion effort. Away from 6v6 into kt 66 or even to military spec tubed. Or what ever was avalible. It must have been a great time for amp builders
Fantastic ... keep on rollin'
I loved the video. Somehow I have missed it back then.
I have two little corrections if I may. As you know I love your channel and this is not a criticism. It is just little correcture.
Bypass caps on the cathode resistors of the preamp tubes do not roll off the bass. They are preventing internal negative feedback loop inside of the triode itself. Higher value will give it more bass actually. Bypass cap there increases efficiency and therefore it increases the gain. Smaller values help only high frequencies and as the capacitance grows it helps lower frequencies as well.
Even those bypass caps on volume pot and on 470k resistor leading to the second tube grid aren't rolling off the bass. First one is notorious bright cap and it allows high frequencies to bypass the pot. Same thing is true for that second cap that allows high part of the signal to go around that 470k Ohm resistor. That cap is often omitted in the bass versions of the amplifiers.
Top input on this schematic does not transfer into the top input on the amplifier it self. It's logical issue copied from the Fender schematic. Fender at least narks the inputs with one and two so you know 1 is most often the high gain input.
Top input on this schematic is actually low input regarding to the gain.
Lower input on this schematics has two parallel grid stopper of 68K meaning effective value is 34K Ohm. Second 68k Ohm is added by the grounding lug of the jack. Input resistance, is in this case , is 1M Ohm. this is high impedance and high gain input.
Top input on the schematics has 68k grid stopper and input resistor is effectively only 136 KOhm. This value is what input sees towards the ground. So ti goes true the two 68K Ohm resistors and bypasses the 1 MOhm resistor and goes to the ground. 1MOhm resistor is not in use as it is shorted by the input jack. So this is very low impedance input and tons of the signal is sent to the ground directly there.
Higher gain input is also brighter because 34K Ohm effective value is not reducing top end till some 30KHz while 68 starts rounding off the top end in the usable range of the amplifier. So low gain input is often also bit darker.
So this input schematic is a trap as one general would say :)
Phase inverter could be explained differently btu that is completely another story.
Thanks! Appreciate the input. I’m gonna read up on it again and make notes where needed
@JohanSegeborn if you want me, I can link up great videos explaining Fenders dual inputs as well as videos about the cathode bypass caps. The best learning channel for me was always the uncle's dough channel. Way he explained stuff she'd a light even on the stuff I knew.
Thank you for this video! Much appreciated
Thanks. Nice introduction to some complicated electronics. Now i can roughly see what my own amp is doing. Will help me fault find !!! 👍👍👍👍🙏🏻🙏🏻🙏🏻🙏🏻
Awesome I really enjoyed that information thank you
I Really enjoy playing new videos from you, just to hear your "Hi(a), today we are going to Check(a)..". You are awesome & I honestly enjoy your reviews over any others. Keep up the good work, Johan, thank you!
+Ivan Stoynev Thanks Ivan, that's so great odd to hear! Cheers
Incredible work Johan, this is very helpful. You should do one like this for the JCM800/2204!
Johan you're a fuckin legend. Been a big fan, and now I see you did THIS 7 years ago.
Hi Johan,
there are two little things that are not quite right in your video.
1. The cathode bypass caps do not really roll of low frequencies from the audio signal. It bypasses the cathode resistor, so low frequencies "are not seen" by the resistor - this enhances the gain of the stage. The higher the capacity of the cathode cap, the lower the cut-off frequency of the gain boost. So bass amps might have larger bypass capacitors instead of none at all.
2. The second part of the phase inverter is not only driven by the negative feedback loop. Someone can cut the feedback completly and end up with something like a vox-amp, which has no feedback at all and still operate with a push-pull-power section. It's more like that the signal is "passed" through the share cathode of both stages. To put it simply: the voltage difference from cathode to grid is amplified - so it does not matter if the grid or cathode voltage is modulated, while the other is kept constant.
Nevertheless, a very good explanation!
Cheers :D
HaenC
+HaenC _ You are absolutely right! Thanks for letting me know. I'm gonna modify the clip. Cheers Johan
Isn't the purpose of the cathode bypass cap to shunt the AC component of the signal around the cathode resistor and create a fixed bias, as opposed to letting the AC create a negative feedback? Reducing the negative feedback would increase the gain, as you mentioned.
Is Blackstar utilizing this " feedback cut entirely as well" and push pull section?
How can I cut out feedback on slp? Just cut out this 47k resistor?
I've seen Doug on youtube install a pot to adjust negative feedback on a fender champ circuit and it works great, but its like a set it and forget it adjustment.
fantastic video, now I understand how the amp works
Jorge Moreu Great to hear! :-)
Nicely done Johan, Your videos are great.
Chris Bradley Thanks Chris, Really glad to hear that! Cheers Johan
This is brilliant thank you!
Thank you sir for the informative video!
MrVibroverb64 Thanks! Glad to hear that. Cheers Johan
Superb video and a very clear explanation.
I have so many questions I'd like to ask :-)
Great explanation dear friend!
Hey Johan, many thanks for that. I was thinking to suggest the comparison videos, ie. how the different circuits affect the tonality of the amp - Mesa vs. Marshall, vs. Vox, I believe many folks would dig it. Cheers!
Wow! Thank you Johan once again. I would love to see the biasing explanation :)
Greetings from Ruhrarea in germany
Thanks! Greetings from Hisingen Island in Gothenburg!
What the cathode bypass caps on the cathode resistors of V1 do is to allow each of the triode gain-stages to operate at their highest gain, if the cathode bypass caps are removed the triode gain-stages would operate at reduced gains due to the action of local negative feedback caused by the input-signal being superimposed on the cathode, the cathode-bypass caps bypass the superimposed signal to ground, enabling the triode gain stages to operate at their maximum gain, the cathode bypass caps also do set the low-end roll-off of the triode gain-stage as well.
Thanks for info.
Yes! Please do explain biasing on a 1959 SLP!
Absolutely, I’ll do a video about the entire circuit.
Hy Johan maybe you can do a few updates, the signal from grid to anode is not only an amplified copy but is shifted in phase 180°, while any signal that is injected at the cathode appears in phase at the anode.
The cathode bypass caps do not roll off bass, but increase highs by taking away local negative feedback from higher frequencies.
The cathode resistor acts like a deflector back to the cathode, that creates local negative feedback which keeps gain down over the entire frequency range.
A resistor - bypass capacitor, shunts frequencies to ground so there is no local negative feedback anymore. A cap is a highpass so it reaches only so far to the lower frequencies, -as the size of the cap dictates. Thus lower frequencies cannot pass, remain in the local negative feedback, lowering gain in the lower range of the frequencies, while no local negative feedback in the higher frequencies, thus getting louder, also more uncontrolled and distorted.
Thanks Max, I’m actually gonna do a more comprehensive clip about this really soon.
How do you have time to do all these videos? I can barely get around watching them all haha.
Anyways keep them videos coming they are a treat :)
Hey Johan, I really dig your channel. Great insights into Marshalls, Celestions and all sorts of setups. I have a question that I can't seem to find an answer for. I have a JVM 410 head, and the input brightness of my guitars is darker than on a PLEXI or a JCM. I understand that it is what it is (the JVM), BUT, if I want to hear more twang going into the amp, as I would playing through a PLEXI or JCM, which component would need to be addressed? A grid resistor value? What component and value would open up that high frequency roll-off a bit so that the amp is more true to the way my single coils or humbuckers sound? I already have a fancy input buffer, Mogami cables, no pedals. Thanks!!!
Hi Johan, nice video. It would be nice if you could explain how the pre-amp and cathode follower tone stack work when the two channels are jumped. Personally I have to go back to the schematic everytime to remind me that trick...
Thanks for the good work.
Dani
do it again pointing out the components in a amp as you go,, i like how you highlighted the diagram hear. good vid. thnx
.
DANTHETUBEMAN Thanks Dan! Yeah I'm gonna compare 5 2204s between 1977 and 1983 and discuss the components. Cheers Johan
it would be great to fallow this through the board on the amp, :) il look for the new vid from you thnx.
You missed the cathode follower circuit at the phase inverter tube, which creates the inverted signal for the push pull power tubes. The negative feed back signal from the transformer is only keeping the frequency output more linear. This feedback is tweeked by the added presence control.
Awesome explanation! Could you tell us a little more about biasing and cascading preamp stages as well? Cheers, Johan!
Thanks, Gonna do those the coming fall. Cheers
Thank you Johan.
Would love to see the biasing too.
Thanks Patrick, Biasing is coming up! Cheers Johan
interesting as shit man. better then TV
How do the marshall 100w and fender twin tone filter circuits scematocs compare in components and wiring networks?? Id like to custom design between the 2 if I could just see the 2 schematics to get the thought process started
very informative!
my next question (maybe you did a video on this) is how the different value components affect the "tone" of the amp? ex. ( a 100k resistor will have more/less gain than a 50k)
A cathode-follower produces a gain of slightly less than 1, but, it also provides a low-impedance output.
Incidentally, both the cathode resistor and the plate/anode resistor in a triode gain-stage set the overall gain, which is determined by the ratio of the value of the two resistors, as well as set the static, or quiescent biasing point, if you set the triode gain-stage up with a 1k cathode resistor and a 10k plate/anode resistor, the resulting gain of the triode gain-stage will be 10 (10k/1k), if you replace the 10k plate/anode resistor with a 100k, the gain will in theory be 100 (100k/1k), in practice the gain will be less than 100.
In a fully bypassed gain stage such as that including V1, the cathode resistor is removed from the formula to calculate gain, and, for a specific triode, gain is determined by the value of the plate resistor. A = -mu x Rp / (Rp +rp), where Rp is the value of the plate resistor and rp is the plate resistance of the triode.
Hey Johan! Awesome vid! I’d always understood that the tone stack came before the gain stage, but here it looks like the tone stack is arranged between V2 and V3. Is my understanding incorrect, or is V3 the main gain stage in the pre-amp? It looks like both sides of the tube are used here so I’m guessing more gain that way?
Hi Johan, how would .0022 cap value change would affect the tone of the amp for example bugera 1960 has a .0033 cap
Great video,
I would love to see how to properly bias’s one of these amps.
Would one apply a 1khz test tone at Input at a given amplitude, and then adjust the 27k bias turnpot to the point where the sinewave output at speaker output does not show clipped top or bottom of output sinwave , and also make sure at zero volt crossover point of the two output tubes are in horizontal time alignment with the negative portion of the sine wave produced by the lower pair of output tubes? Or is biasing with 27k variable resistor done by simply turning and measuring grid to cathode current across a resistor till current is set to correct level for the amps design? Thanks
Watch guitarologist work on the super lead 100 and see why you bias at idle, and then bias with a input signal. Turns out, the tube sockets were not making good contact and had to be replaced. They were corroded.
Hello mate, great work. Where I can download that Schematic with colored lines ? I want to build it up. Thanks.
Question for you Johan. For the Marshall JMP the Volume 1 and 2... when either of these is turned up we achieve power amp tube break up. Since there is no master on these amps and no subsequent preamp volume control is preamp tube distortion achieved only by the dials in the tone stack? For example. I have both my volumes on 7 and guitar is in the upper left input with a jumper from lower left to upper right. As I turn up the individual knobs for presence bass mid treble there comes a point around the 6 mark on the dial that more distortion is introduced. Is this preamp distortion being added? Or is it more power amp tube distortion? When volume 1 & 2 are turned up is it only pushing the power amp tubes? Is there any way preamp tube distortion can be achieved with a JMP or is it a fixed bias on the preamp tubes set to clean only?
Man I really enjoyed this video. I'm looking into building my first amp and was wondering if there's any books you'd recommend on it? Thanks!
Thanks Johan for the interesting discussion. I used to work in audio and RF electronics in the late 60s and so this really stirs up the cobwebs for me. I was wondering if having AC on the filaments of the preamp tubes might introduce some bothersome AC hum, even though twisting the leads would reduce the hum. I also wonder if replacing the carbon pack resistors with metal film resistors in the preamp gain stages might reduce the noise floor of the amp.
It does! Though there's a huge debate on carbon vs metal resistors. Carbon are noisier both good and bad - they add a "sizzle" for lack of a better word. But better money is spent on speakers, pickups, tubes than resistors. Not worth reverse engineering if an amp already has modern components.
Tighter wraps also can help moderately
The rectifier bridge produces 120Hz ripple. Anode = plate. Plate resistor regulates the]
amount of plate current allow a amplified voltage to be present across the plate resistor. The source of the plate current is the B+ supply leg.
Cathode tone stack allows for lower voltages and therefore lower voltages to the
manual controls as well.
The inverter/driver tube drives the output tubes which generally operate in Class B push-pull.
Bias also allows to bias the cutoff of each tube (within linear operational area) and
overcoming the crossover notch distortion which is apparent in most push=pull transformer stages. Each output tube conducts through one half of the output
transformer primary when the voltage is positive.
When the transformer signal voltage goes negative, one power tube goes into cutoff and the other tube, now being in the correct 180 degree phase, conducts for one half audio cycle and so on.
The secondary winding is a much lower voltage and impedance matched to the
speaker(s).
Hey Johan,
I'm just getting in to amp repair and design, I never realised you did this series.. they are great!
Your voice/accent sounds very different to me in these early videos. Did you move?
Hi Johan,
I’m willing to build a Marshall Major i am wondering if you know where can i get the original parts to build. I’m in USA and I already have someone to build the cabinet and chassis. Has a lots of kits for super lead i don’t know if i can use the super lead kit. I hope you can help me. Thank you
I never really had an idea how that tube thing stuff was meant to amplify a guitar signal, but this vid made it quite clear (didnt get most of the gridnegativfeedbackbabble though xD )
+arschflugkoerper007 Thanks, great to hear that!
But totally and refreshingly free of the usual UA-cam "Hey wassup, this Joe Bloggs of XYZ dot com, Click Like if you think i look cool.." etc. To be fair, I thought you did explain the more techie bits very well, which enabled me for one, to start thinking about this a bit more deeply.
That was interesting.
Is it everything in these schematics cause its not that many parts and its just 5 sections together?
cool!
Hi Johan! Nice info as always. Are you a technichian or an engineer as well?
Great video, thanks. So which cascade makes overdrive clipping? I guess the second, where the signal from both channels blended together. BTW, can you share circuit?
+Sergey Gavrilov Hi Sergei, it is the master volume 2203 that has a cascaded preamp. Cheers Johan
Hi! Where do you find these accurate diagrams? Thanks!
Hello, this no have volumen?
have you the pdfs squematic?
And the list if components?
What the watts are this?
Thanks
+Johan Segeborn , and about bias circuit ??? I made a plexi but had problems with excess gain on channel 1. It was resolved with a signal drift grounding pin 2 of the valve 2 by a resistor of 82k. It solved the noise but it is not the solution I was looking for, is aware of which may be being generated this problem? Tks in advance.
+V8punch Thanks! Yeah that one is long overdue! This fall I'll do it. Cheers
Do you have a schematic in PDF form that I might be able to "borrow?"
Could you do one of these for the master volume circuit? That'd be awesome!
Great explanation! Are you trained in electronics?
"The Guitologist" is watching n taking notes!
Johan you sound like my Friend Ron who lives in Weert . I am in Austin Texas .
Beautiful explanation!!! this schematic works for make an clone?
This is a really cool video. I can’t believe I didn’t see it before. Very well explained and easy to understand. Do you think you could do one on fender amps? 🎸🎛
watch uncle doug and rusty
Did you delete the video comparing Marshall amp schematics to the 5F6A?
Hi Johan, why is there no coupling capacitor between the first and second stage of V2?
The first triode is working as a gain stage and the second triode is working as a direct coupled cathode follower. The plate voltage of the first triode is the grid voltage of the cathode follower, so no coupling cap is required to block DC. The grid of the cathode follower is at a high voltage, but current flowing in the triode and therefore in the 100k cathode load resistor develops a voltage at the cathode which is slightly higher than the grid voltage so that the grid is negative with respect to the cathode.
👍👍
Went fishing the other day, caught a Super Bass - true story!
This is interesting. So Johan is a mad scientist. You might want to check the local morgue for missing cadavers :)
Johan,how does this architecture work compared to the jvm's?The JVm's have no diode distortion unlike other models(800's900's etc) and can use %100 tube saturation!.I believe and have heard a JVM pull plexi sounds easily,when used correctly(most people use to much gain when trying IME and using greenbacks or the like) what are your thoughts?
Kate Andrews Hi Kate! The JCM800 2205/2210
had diods but not the 2203/2204s and the SL-X JCM900s were the only ones
without diods.
The JVM has an extra preamp tube compared to the 1959,
which is engaged in some of the settings in the JVM. Marshall themselves states
in the manual that “CRUNCH
GREEN MODEuses the same preamp topology of the classic Marshall JTM45/1959
'Plexi' models (i.e.: gain + gain + tone) but with a bit more of gain than is
found in the originals”
However
here I used the OD2 orange mode which adds an additional gain stage compared to
the 1959. Still this is in my opinion
what sounds the closest to the typical aggressive but rather clean clipping
sound of a vintage super lead.
Cheers
Johan
thank you.
I thought the JCM 900's did?,how is that distortion achieved on the 900DR's?
Hi, DR and MkIII have diods and the SL-X has an extra preamp tube.
Except for capacitor and resistor values as well as only considering one side of the phase inverter tube as the last gain stage before hitting the power stage and thinking of one side as similar as a single ended amp, if you consider all that - this circuit topology is nearly identical to my Vox AC4C1 amp
brilliant ! for me, tube amps have always been some kind of black boxes (or red levante for that matter) ... ;o)
JOHAN SEGEBORN,
1.) When you're biasing the power tubes in an amplifier circuit how do you bias the compression of the power tubes the 1dB compression point of when the power tubes start to compression? because its say to bias tubes at a 30mA bias current per tube to be safe but how do you know when the tube is compressing?
2.) Most Power tubes 6L6,EL34 use a B+450vdc on the plates, if you increase the B+ to +600vdc would this increase the AC ripple but why would it increase the AC ripple? i would think it would decrease the AC ripple because more B+ voltage mean less current draw from the power tubes.
3.) The Choke coil wire is frequency dependent which I'm not sure why they made the Choke frequency dependent in guitar amps linear power supply. Is the Chokes storing current like a reservoir like the filter capacitors or is the Choke doing something else to the AC ripple, not sure if the Choke is regulating the current? If you remove the Choke from the power supply will this add and cause harmonics from the AC ripple frequency getting added into with the guitar signal?
4.) For Fender amps. When you remove the normal channels first preamp tube, the vibrato channels preamp will have more output voltage and it changes the impedance and TONE, any reasons why? Tubes have very high impedance and aren't suppose to load down the parallel circuit. Any reasons why this changes the TONE of the vibrato channels preamp from removing the unused the first tube from the normal channels amp? its changes the impedance and frequency response techs have told me.
Can you review the circuit of the Marshall Major (The Pig) 200W amp?
Hi Richard, we did a minidocumentary about it today actually
ua-cam.com/video/t9Ep4YjKT1A/v-deo.html
+Johan Segeborn Perfect answer :-) Thank you Johan.
Why semiconductor in the rectifier stage
Kjempe bra! har selv en 77 mod 1959 som jeg har sendt til en Tech for å få den moddet til Mod5 specs. Hvor har du lært alt dette? man lærer jo ikke om rørteknologi på skolen lengre da det er "utdød" teknologi. Kunne tenkt meg å blitt mer teknisk når det kommer til forsterkere. En dag skal jeg modde min egen amp! Hilsen fra K.I
Thanks kennet! Jag have learned most of the stuff on foras. And I found a great UA-cam channel: Uncle Doug. He is a great teacher.
Hälsningar
Johan
1:18 So that's how AC/DC got the name AC/DC
Are you an electronic engineer?
Can you do a Mesa Boogie vid? :)
+Jonhattan Yeah, those are a bit more complicated though ;-)
+Johan Segeborn your channel and you are very cool. Even if you don't do it.
thanks for all your videos. :)
Download link please ;-)
It works by electric
and the magnetic witchcraft mojo that lives in the transformers
I remember doing that electric slide dance when I got zapped by 465 volts DC on a wet garage floor, barefoot, while working on a 68' Fender super reverb. I shit you not. I literally could not move my arms for 15 minutes, they were frozen in place.
Plug it in... power it up... insert guitar... turn to 10... play power chords... get a disturbing the peace summons... make court date... pay fine... repeat.
"You've got AC, 120V" this is not entirely true depends on which country you are in.
Well in Europe they still have 120V AC, they just have 2 transformer input windings instead of 1. 🤣
Duh?
thanks nice... wish you went a little slower
Christ almighty