12AX7 stereo tube preamp only 12 volts
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- Опубліковано 26 гру 2013
- Low voltage tube / valve preamp with gain about 20db. Schematic and music samples included after description. UA-cam's audio compression does harm the sound somewhat, but the amp sounds good to me direct through my power amp.
- Наука та технологія
Just a couple of suggestions: Reduce the value of the pull-up grid resistor, and connect it to the plate. While it will slightly reduce gain, and input impedance, it will also reduce the output impedance, by introducing an element of negative feedback in the amplifier. I will guarantee, it will greatly reduce harmonic distortion. It will also improve frequency response. Another thing might be to connect another output capacitor to the plate, and connect a high value of resistance in series with it, to the control grid. That will allow negative feedback of the AC component, without affecting the DC bias. you can adjust the value of the feedback resistor, to find the happy medium between gain and distortion. Larger coupling capacitors help with the low frequency response.
It actually sounds pretty good, but it's interesting to note, that most of the harmonics you hear are artifacts in the speaker caused by resonance, rather than the amplifier. You can't hear the difference between 3% and .03% Harmonic distortion in the amplifier, because speakers typically have THD of ~20% or worse. Headphones are typically much better than speakers, but even with them, it's hard to hear differences between amplifiers.
Considering the limitations it's not bad. Tubes are high impedance devices so some distortion (including harmonics) are introduced matching low input/output devices to the amp. As hinted you had to adjust the bias to get the tube to work as a class A amp, without boosting the grid voltage it will be class B only. You have no frequency bias compensation so the natural RC filter will set the response curve. I worked with tubes since the 60's and still love the way they sound. In my opinion what I noticed is that tube amps are "warm" and solid state amps are "brilliant" sounding. Tubes can't be coupled together the same way transistors can and a different strategy is used in each case.
Kimberly Buck id love to pick your brain as im at the drawing board designing a hybrid.
Why you dont need an output transformer to adapt Z?
Great work John. Been watching your great content for a week now. Have learned a lot! I think tubes are great to play around with. Please do more stuff like this.
Valve amps still really produce warm, detailed sounds...thanks for very vivid video
Did you know the 12AX7 tube was introduced in 1945 by RCA? And we still use it. But this is amazing. I didn't know you could feed the plates a mere 12 volts and get it to work.
You pointed out something I have never seen anyone else do. You pointed out that in "normal" operation, a tube acts like a JFET (where a negative gate voltage, relative to the 'source', is needed to control the current flow by limiting what would otherwise be runaway current), as opposed to operating the tube in a low voltage situation, where it behaves more like a MOSFET, where a 'gate' voltage that is positive, relative to the 'source', is needed to entice current to flow and so control the current flow. Congratulations! It's about time someone brought that fact to light.
Well, it's not like a mosfet in that the voltage isn't actually backed by much current, so its output needs to be buffered. It's only purpose in the circuit is to add 'good' distortion to the signal.
So this circuit acts like a buffer? Im only beginnin to learn electronics. But this circuit reminds me of a ce transistor amp..
@@Axelvad That's not off the mark, but a tube ran on low voltage can't really supply much current, so it's output is then buffered by an op amp, usually with close to 1 gain, sometimes 1.25 gain.
Having the cathode follower resistor helps with thermal drift. It serves EXACTLY the same purpose as an emitter follower, or source follower.(bipolar junction transistor, field effect transistor) Besides, at this reduced voltage, it's hard to pass enough current to get the tube anywhere near it's rating.
You all make excellent points. and I mistyped when I said MOSFET - I should have said BJT. And while it is true that the current would be extremely low, that does not change the fact that when the grid has to be positive to entice the current off the cathode, it is behaving like a BJT. Even so much that there will be a small grid current analogous to the base current of a BJT.
the music recorded through preamp sound phenomenal
Beautiful "tube" sound created in a simple way with a 2 triode tube, well done.
Hi John this is really cool. Thank you so much for sharing it! I"m going to build it.
Thanks for this great video. The sound seems very good. I designed a theremin with 12AU7s that uses a B+ of 50 volts.
I am trying to learn about tubes and basic electronics again. A low-voltage tube amp is IDEAL for what I want! Thanks for providing a schematic! It will really help me get the basics down.
Thanks for watching. Using a 24 volt supply should work better for a preamp. My tube was worn, just good enough to use, so you have to tweak the bias for best performance with a new tube and 24v supply.
JohnAudioTech Seriously, thanks for uploading, but I need your help. I am really pulling out at the basics from way back. I know what components are supposed to do, but I'm still learning how they effect a circuit overall. Bias effects and tweaking are unknown to me but I'm guessing you mean something about how to maximize the electron transfer in the tubes. I would learn a lot if you could let me see a clear pic of the schematic, as I can't see the upper left. What I can see I'm not certain where the power supply fits in here completely and where the "ground" for the in/out connections would be. I'm also guessing that there is a separate simple circuit for the tube heat element. I hate to be a pain but can you help a "newbie" out? Cheers....and thanks for any help!
*****
The components in the upper left are not needed. They were for supplying the tube from an automotive electrical system. The biasing (called class A in this amp) sets the quiescent (no signal point) on the plate to around 1/2 the supply voltage which allows room for the voltage to swing up and below this halfway point as it amplifies the signal. The output, input and power negative go to the same point which is called ground and not necessarily grounded to earth. All this might not make sense to you now. I really can't give a lesson in a few words where book chapters of reading and soldering iron in hand are needed.
JohnAudioTech Hello. I understnad basic schematics and what the ground of the circuit could be, but I don't know exactly where the negative/ground of the circuit would be with certainty. So the upper left is power supply....OK. Understood. However, I don't know for certain where the ground or negative terminal would be indicated here...but I'm assuming it is the "bottom" of your schematic as it's all connected in one line opposite the many resistors? Yes?
***** Yes, you are correct. It is the bottom horizontal line that represents the negative side or common point of the circuit.
Wonderful video. Damn wonderful video.
Cheers from Indonesia
i love it buddy well done
very clean sounding
just found this made it works great cheers
Thanks for the great video. The guitar sounds wonderful. Could you please share with us in the description what mic and recorder you used to record the sound?
What many people don't know about the tube sound is that not only has the added harmonic content, but, those harmonics are also distorted, just in the same way as if you put a distortion pedal to your electric guitar.
Also, so you know, tubes distort the even and odd harmonics, but tape saturation has exactly the same behaviour, only, the odd harmonics are the ones distorted.
This harmonic distortion is low level as you can see on your oscilloscope, but, for some reason they add some richness to the sound.
They have tried to duplicate this digitally on some extent, and there are many VST plugins for music production in the market for that, some better than others, but the key is to make those low order harmonics distort, and, in real tubes, those harmonics levels change randomly over time, same as tape, which makes it more difficult to replicate.
I can tell that some warm is added just by listening the first song of your demo at 6:44.
Thank you for posting this, Im making me one of those soon, Cheers.
a good tube amp has 0.003 thd!
Its because a tube is volt amplifier,like mosfets(transistor )
A normal transistor amplifies by current,
Thats why tube s,and good mosfets sound so natural.
Best is to use tube as pre amp,and mosfet end power.
Thats the way i build now,
Active with 6 litle amps,class a single ended. distortion only sounds great in gitar amps,in audio its callt clipping,or over modulation.
The positive voltage on the grid is interesting. I tried some 12ax7 tubes in 12au7 headphone amp and one worked well but the other two didn't. I tried a 1 meg resistor from grid to 12 volts and that improved things greatly. Thanks for your help. It looks like the tube wasn't passing enough current to get a decent positive cathode in relation to the grid.
I will make this circuit to connect it as an preamplifier to my pl-504 amplifier.I am sure it will work.Bravo, 12 volt is perfect voltage.300+ CAN SENT YOU STRAIGHT TO THE OTHER WORLD.Thank you for the advise and the shematic.
300 vdc is no problem if you know what you are doing, only experienced electronic techs should use high B+ voltages I'm going to use 96 vdc from 24 vac transformer. A voltage multiplier will bring the voltage up. 73
Thanks for sharing! Cool stuff..
I'm a guitarist and I live for those harmonics
Wow, im back in time now....cheers.
@JohnAudioTech
I enjoy watching your videos and i love your icon picture of the chip man.
Always reminds me of Germany and their flag,same colours,red,black and yellow
Completely unbelievable !!! ........ AWESOME !!!!I would pay what little I have right now for one !!!!!
Sounds epic!
Planning to build this for bass guitar as a preamp in chain - bass guitar - tube preamp - TDA chip power amp,how do you think,this might work out as a instrument to line level boost?For now I am trying to get valvecaster do this,but in clean it actually dont boost my signal,but when I apply gain it is too much overdriven for a bass guitar.
Cool, whether the scheme is suitable for alteration in a tube microphone?
So good , Sir
Very nice preamp. Im very new to Vacuum Tubes and I would love to build a small headphone amp. I would have a question: would this circuit also work with a ECC81? That's currently the only tube I have (except for two EL95's)
Also may I ask what software you're using for the analysis ?
Can i use this as a preamplifier in front of a dedicated subwoofer in order to hear the tube sound???
As I understand it, the different between tubes sounding sweeter than solid state is in WHICH harmonics are being emphasized. As you go up through the harmonic series of a sound, some harmonics blend better than others with the fundamental pitch.
Hi John!
How are you doing the spectral analysis, can you write a few words on that?
Did you calculate THD, I suspect it's not that great for "warm sounding" tube amps?
Dude, could you please share the schematic with us pls? I wanna build this piece of art.
Great explanation.
That is surprisingly good for a tube not known for working well at low B+. You ought to play around with 12AT7 and 12AU7 and see what you can get You may even be able to use a more standard biasing on those tubes. Too bad plate chokes are so expensive. Would help a lot.
It would be interesting to drive it from a line level source. Your headphone output is a small power amp and so probably is more capable of supplying grid current to drive the forward biased grid.
My guitar preamp runs off 4 AA batteries (6volts) and is a cold cathode 12ax7 impedance (probably a
darlington dc configuration?) "transformer" to a high impedance bridge piezo. it is referred to as "a cool tube"
preamp..works good and really provides a warm sound for the guitar.
The tube heater runs off 6 volts. Don't know what the plate voltage would be but
I expect that it may have a doubler working off the 6 volt batteries for 12 volts.
The o/p of the preamp tube goes into so solid state circutry and being proprietary,
I don't have a schematic for it.
The music sample sounds very clean, similar to mine.
The tube filaments would normally be wired in parallel, to properly heat the tube on 6 volts, but, the heaters require .3 amps. In that configuration, the batteries would only last 8~10 hours. Running as "cool tube", the filaments are likely connected without the center tap pin, causing the heaters to run at only .08 amps, receiving 3 volts each. A tube can operate in this condition, but the circuitry around the tube must be very high impedance. Most likely, JFET op amps. The tube should last a lifetime.
where does the negative end of the 12v and the negative/positive whires of the input output go?
Very nice little circuit actually. And btw that special tube ur using seems to be a NOS Telefunken 12ax7, so I'd check this if I were you as they can be CRAZY expensive nowadays
I didn't see where the negative supply terminal connects. I assume it's the bottom rail, correct?
did know if the 12v was possible, but you showed me how. Thanks
Before transistors....all car radios were tube based and none of them had "100-150 volts on the plate."....and they ran on 6volts and 12volts...
Hey JAT, I hope you are doing good. Nice pre-amp, love the tube/valve, a dual Triode. I'm gathering parts to build a simple Fender 5F1 " Champ-amp", 5 watts = -. 5Y3, 6V6, and the 12AX7 pre-amp tube. As you may know, GT refers to 'Glass' tube. Check out Uncle Doug on UA-cam. He made one from an old signal generator, awesome job. Still check you out as am able, love your channel. Happy Year End and Holidays, all the best in 2016. C.
Sample music ... played on my solid state laptop... sounds great solid state !
Sound samples online are pointless, and yet, we still listen. LOL.
I built a class a headphone amp from one of ljohn linsley hood design and it sound excellent better than a tube headphone amplifier lent to me by a friend.
An ECC82 will perform better (and actually exhibit more gain) at such a low plate voltage. I was playing around with similar circuits several years ago, but for guitar pre-amp purposes. I kept wondering why I got less gain when going from an '82 to an '83. I initially thought the '83s I had were dud. Good thing I didn't throw 'em out! lol
If your primary purpose is to level match the output of an Mp3 player into a hifi amp, a transformer will do the trick nicely. Those headphone outs don't have much voltage, but they can drive into quite low impedance loads so a step-up transformer can work well with them.
John, I think that you could use self-bias (or cathode bias). That would require only a cathode resistor. At the grid you only need a high value resistor of about 1 M to ground. The current through the cathode resistor would put the cathode at a positive value relative to the zero volts at the grid due to the 1M to ground. So you wouldn't need the resistor going from the grid to +12V. Thus the grid voltage is at a negative voltage relative to the cathode. That's how self-bias works and the way it is usually done. Using only 12 V for the plate puts this amp in the starvation mode. All that means is that you won't have the dynamic range of signal that you would have if you used the normal 200 to 400 volts. However, your circuit seems to work well enough to boost the signal well about that of your music source. Good job!
Hi Alex, The way you described it is how I normally bias the tube with a high plate voltage. However, I had to put a positive voltage on the grid relative to the cathode to get the electrons flowing because of such a low plate voltage.
JohnAudioTech That sounds reasonable. I guess I would probably do the same thing after I experimented with it like you did. Good job.
What are the units for the caps in the schematic ?
do you happen to have this project with schematics and all somewhere on the internet ? would like to try it out myself
i have a spare tetrode ,Can i use it? Are there going to be some changes?
hi john great video. what are the cap values on the in and out please. cheers in advance
+MonkeyMagic Elecifun Given the high impedance, you can use film caps in the 0.1 or more range. Select value so frequencies 5Hz and up pass.
I notice that on some guitar pedals built for distortion they use the same valve but with a current of only 9volts. I have guitar valve amplifiers and my main stereo amplifier is also valve . You can feel the heat from them. The guitar pedal I have barely lights the valve. I find it hard to believe that such a low voltage has an effect but it most definately does.
Hello.
What avout a less volumic tuve valve ?
What's the plate voltage on that? I didn't think 12V was enough to get any gain out of a tube like that.
Sounds good, would you do a revisit on how to design a "flawless" distortion free power supply for the heaters?
VERY nice sounding preamp!!! The thing about tubes isnt WARMTH...it is DYNAMICS...you get the same warmth out of solid state...what you do not get is dynamics...the sound when it is louder will clip SLIGHTLY...or greatly..depending on how you are driving it...and be smooth and distortion free when low...so you get a constantly shifting ratio of signal to noise...this imparts life when balanced correctly...thus "WARMTH" (it can be a distracting mess when done improperly...or as bad as solid state...or as good depending on application...Jazz players tend to not prefer dynamics (hence the Jazz Chorus's popularity)...that has ALWAYS puzzled me) I have to point out here...I came back to say this...that tubes DO add harmonics...and that can be a blessing or a curse...we are talking about very rich signals to begin with ...and when you start to get into the BETTER circuits...too much harmonic content becomes really distracting...I am a long time Mesa Boogie user and find that the WORST Boogie's are REALLY harmonically dense and the better ones (the more sought after ones...the highly praised ones that the pro's spend years looking for.)..are the ones that are missing some of that REALLY dense harmonic content...so do not oversell the benefit of harmonics and downgrade the DYNAMICS of using tubes...yes the harmonic content is real but can really be too much..MOST people are happy with the sound of solid state and the life-like quality of tubes.)
I built one of these and it sounds great
Hi, I am a newbie, how would you supply the heater ? Would that be separate ac or dc voltage ?
@@hpsmoh The heater runs on 12 volts dc on pins 4 & 5. You do not need a seperate supply.
I! Can you send to my email the schematic of this peramplifier? I'm curious about it!
470k 4k7 (neg 10uf) and 100k is connecting to ground?
Thank you
excellent!
This is awesome! The audio demo sounded great and the THD figures looked respectable. Amazing that this can be done with just 12v. How is the overall freq response?
Bob H I didn't test the response, but no reason it couldn't go beyond 20KHz
JohnAudioTech
Thanks! I was just wondering flat the audio frequency response was over the audio range - no necessarily anything over 20k.
Very good
Hi John! I'm currently working on a low distortion tube input amplifier. The circuit topology requires grounded input DC operation with dual rail supply. As I noticed at high voltage grid is lower voltage than cathode. At 12V grid is much high than cathode also higher than half voltage of plate from cathode. What's the supply voltage that have the grid biased at mid point? What type of tubes are good for this? I'm looking at 12ax7 as it has higher gain. Thanks!
Wow. This was only a week ago? I achieved 0.0003% THD minimum. And 0.001% THD+N.
What was the song first played?
I just watched your video and im thinking about making a guitar preamp with this tube, as it is a double triode tube can it be used so one triode makes the clean sound and the other does the overdrive? Then the sound goes into a class D amplifier (because I like efficiency) also I have read the previous com about the input impedance (i know it's 4 months old) and it's usually fixed with a 22k resistor (at least on transistor amps) I need to study again how to wire a triode and then I think I will be able to make some cheap and gread sounding amps
Also most people put on a plate voltage about 200V and you don't, what do you do instead?
But maybe im saying something insane because it's 1am
Hi, this low voltage tube amp was more of an experiment. The gain is fairly low so you should experiment with additional stages for distortion driving. Input impedance can be low or high depending on the amplifier topology.
JohnAudioTech but 12volts as plate voltage works? (well it should, or I don't know where you get sound in the video)
I think a little chip or transistor as a pre-preamp should do the work to get enough gain (and if gain is still too low, maybe take the output signal of one triode and put it in the other triode of the tube)
A better way would be to cascade the two haves. Connect the signal to one, connect it's output to the input of the other. This amplifier inverts the signal, so running into the next stage will put it back in phase. The gain will be multiplied, making it much more sensitive. For distortion, you can delete the 10 uF capacitor that's in parallel with the cathode follower resistor. That will give a much cleaner, less distortion sound, than even this amplifier in the video. When you WANT distortion, putting the capacitor back in circuit will give enough gain, that it won't be hard at all, to get the "overdrive" or "tube stack" sound.
I did not watch the whole video so please forgive me if you answered this already but I have a question. How did you get stereo through a single tube? I have been searching but cannot find an answer anywhere. I have a headphone amp with a single 12AU7, and I was thinking about this. Are the L/R channels split between each triode? And if so, does this create an issue with imbalanced audio (one channel louder than the other)???
Yes each triode in the tube is used for a separate channel. No issues with imbalance. Some designs use one dual triode tube per channel. The output triode is in cathode follower configuration to lower the output impedance.
Cool, thanks for the reply!
Whats software is that???
Hey what do you use as your test setup? What software are you using to analyse the result of the 1kHz sine wave? What did you use to generate it?
I use the FFT spectrum analyzer in Audacity. You have to be sure your sound card can record with very low distortion (~.001%) and your signal source is also of low distortion so it won't influence the results.
I have a question. I saw a similar schematic, but am needing some help with an understanding of it.
www.cyclone-radio.com/preamp.png
If I just give this circuit 12V, I get no noise out of the other end of this. I am guessing it is because I need to bias the input? If so, what resistor value should I pull up to 12V and what should I pull down to ground? I see you used a 47K to 12V and a 470K to ground on your example. Now, assuming I go to the 30V the schematic has it labelled at, then what should I use for the bias resistors? And the last question is on the 12V rail, or in my possible case, the 30V rail, how much current do I need to source? Like, if I made a switching boost power supply to 30V, how much current would it need to be able to deliver? Are we talking a couple of milli-amps, 100's of milliamps? 1000's of milliamps? Sorry for being such a noob!
Binging on this channel.. :) I have a dac thats just too loud for my tube 6j1 preamp. how can i make this kind of preamp that still buffers controlling just the gain and not the input voltage? like 2v input to tube buffer to 0.9V output 100ohm impedance?
btw im using a 15v DC power supply
Awesome circuit & sound! , the tube looks like the monster from war of the world, how does it stay up with just few wires?
+Tennisplayer21Kim Solid core wire is stiff enough to hold it up.
What hardware and software are you using to do the spectral analysis. I assume just a sound card would do it?
From the looks on the icon on the task bar hi is using www.audacityteam.org
I think hi might just have played the 1K test signal and then taken the output and put that on the line in on teh sound card and recorded it, and THEN done a spectrum analysis on the recording.
I am working on a project whereby I only want to light up the tube filament with DC current. I am putting 6.3 through them and they light up. Not very bright though. When I put 7 to 10 volts they glow real pretty!! I only did it for a few seconds. How much current can I safely use? What happens if too much? Do they just burn up or is it dangerous?
for as far as i know , the ECC81-82-83 tubes are designed for 6,3V +- 5% heater voltage , so putting more voltage will destroy the tube over time.
According to the specifications, the heaters use 6.3 volts, 150 Milliamps each. For 6 volts, use the center tap pin, and connect the other two in parallel. The tube will draw .3 amps. for 12 volts, leave the center tap pin open, and connect each of the other pins to the battery. it will draw .15 amps at 12 volts. Running the voltages higher will make the tube work better at these low voltages, but will shorten the life of the tube.(not recommended!)
An interesting circuit which I may knock up. The audio sounds fine on youtube but as I have smashed up my hearing by shooting over the years all audio sounds good. Well not horribly distorted stuff but anything subtle just does not matter. Makes for a much cheaper listening experience.
I kinda wanna build 4 of these and sling them into series to build a gain stage for laughs... would be interesting to see how it breaks up on a 12v circuit... Might be like a less hot version of a JCM-800 lol
I wish I understood why you have a 47K resistor and a 470K in series. Is that where you're splitting the power supply?
He made a voltage divider with those two resistors
A simple boost converter with a good filter capacitor can yield a higher voltage for that 12AX7
+Kevin Roosa The entire point was to explore NOT doing that.
I have a question about the 1µF capacitor : Must they be "film" capacitor or can the be ceramic or electrolythic ?
If you're just playing around on a breadboard, you can use any capacitor type, however, I'd recommend film if you're building a finished amp.
JohnAudioTech I tried the schematic in your video, but it doesn't give a louder sound, it gives a much dimmer sound. Can you help me please?
JohnAudioTech Ok after some experimentings withe the circuit, I found a solution !! I've added a buffer circuit with an LM386 and it works really well !!!
I am a musician of over half my short life, and I swear by my tubes. What most people don't know though, Is that I also swear by GOOD solid state. both have their strong and weak points, and both have been executed poorly and amazingly. This is all IMO and I'm merely expressing my own thoughts. Nice video man, very informative.
do you have an schematic, please? i wanna build one to, but i have no experience with tubes :)
+Marian B 2:37 you see the schematic. But why not design your own? From that point your experience starts. You can use any triode tube from the junk box, that's part of the fun.
I'd like to see the full schematic too please!
Is there any chance to get a better schematic?
Thank you in advance!
yes, i would ask the same question
Yes, a good schematic. I would like to build one for my self.
I have not seen one of these run at 12V before so very interesting.
But could you simplify even further I wonder? The cathode resistor is normally there to provide the cathode with a positive voltage relative to the grid but you are having to run with a positive grid to make this work ( close to 11V from your resistor divider values). So, could you not eliminate the cathode resistor entirely and then you would obviously not need the cathode bypass capacitor either. Then adjust your grid bias voltage until your anode voltage was 6V?
Yes you could remove the cathode resistor but it also serves another purpose called cathode degeneration which provides some bias stability as supply voltage changes (battery runs down) and some negative feedback at the the cost of gain which reduces distortion. That tube I have is worn so the divider network may not work properly for a newer tube.
look at cool dude clems vids he tried three or four similar valves and he got one to amplify 80 times.
Would you be interested in running a similar experiment with spectral analysis again with a 12AE7 tube if I sent it to you?
I would really like to see if there is a similar "low order harmonics" effect like with this one.
Was a great experiment and the preamp works amazingly well!
+MAN CAVE NO.1 You would find that about any amplifier with a single active element whether transistor or tube will produce low order harmonics due to the nonlinear gain structure of the devices. If tubes or transistors has a perfectly linear gain structure, amplifiers would be a lot simpler to make!
Cool!!!!!!!
Hoka me pasarias los planos que has utilizado saludos
What's the maximum gain you can get from these at 12V? I'm struggling to get more than 30dB
+Jack Holden Not a lot of headroom to work with at such low voltage. 30dB is not bad. You might want additional stages for higher gain.
...does that mean you can basically 'bolt on' additional stages for more gain?
yes. Up to a total output voltage of 10-12V, assuming you get the grid bias correct.
it's hard though and you might need transformers between stages.
It seems the control grid bias is positive, is that right?
louipivovarova Yes, and he explained why in the video.
Is there a full shot of the schematic please?
...also, I'm guessing I can use a trim/pot for the bias?
That way I could adjust to suit??
Hi, is it possible to add a RIAA eq network to this circuit?
zeroTiza You could if you want just the equalization, but if you need it to bring the output of the cartridge up to line level w/ equalization as in a typical phono preamp, then no it does not have enough gain.
I'm seeing B+ on the grid 47k or is it part of the circuit 470k ohms grid bias is right.
That's not a mistake. With the plate voltage that low, it is actually necessary to pull the grid slightly positive of the cathode, much like the screen grid on a tetrode or pentode. As the plate voltage increases, the grid needs to go further and further negative, to maintain plate current. At high voltage, the grid is indeed pulled below the cathode, weather it's accomplished by a cathode follower resistor, or, negative bias voltage on the cathode. A typical set-up in a guitar amplifier is a 1k resistor from the cathode to ground, and a 100k resistor from the plate to positive. That does a pretty good job of splitting the voltage between the tube and load resistor, to give maximum headroom. The gain is ~100:1, and the grid can be referenced to ground,(usually 100k) without any need for input capacitor. The guitar can be connected straight to the grid. The 100 K resistor to ground is just to maintain bias when the guitar is unplugged, and the jack doesn't ground.
@@vincentrobinette1507 I remember in my 20s I would do experiments like this with 12ax7 12au7s after I got stoned I remember pins 2 and 7 are the inputs pins i and 6 plates and 3 and 8 cathode and a small negative charge in respect to ground to pins 2 and 7 like 750K ohms. I used raytheon and rca 12ax7s off an old baldwin organ good ole days.
@@TheWarped45 I got my start the same way! I used to get tubes and other passive components from old RCA television chassis, and old radios. My interest has always been amplifiers. I salvaged a tube amplifier out of an old Magnavox console, and that became my power supply for experimenting with tubes.
@@vincentrobinette1507 that is very cool right now I have 807s nos I think I will make a stereo amplifier one day I have 6l6s but 807s look cool maybe a 6cg7 6fq7 for the phase inverter ef86 in the preamp.
You can get the miniature wire-ended valves from the CCCP if your know where to look or try EBAY, It is like being in the KRONUS HIFI factory showroom in DUNGANNON Northern Ireland.
David, do you have a model in mind that is known (by experimental designs or otherwise) to create good sound? And do any of them come with a datasheet that quotes IV characteristics with a low supply voltage?
I want to make a tube preamp for plugging guitar into pc. Will it help or i need another config for guitar sound? I know that they use 12ax7 as power tubes in cabinet heads. I am an electrical engineer, but not aqustic. Thanks in advance.
With guitars, you need higher input impedance and additional stages if you want to reach tube overdrive sound.
Thanks for advice, i will measure how much impedance i need for my pickups...
When you say the gain is poor are you implying the waveform couldn’t compress and distort like a preamp tube can do in a conventional guitar amplifier? I am asking this because I own a Vox Cooltron guitar effects pedal with a 12au7 tube in the circuit being run at low voltage, 20 volts I believe. And in some literature Vox admitted it wasn’t doing much more than some amplication and any distortion effects were coming from silicon elements earlier in the circuit. And I wonder if this has to be true?
It will still compress when driven hard, it just lacks much gain.
This is incredible!
I found a similar model I'll gonna build, a guitar distortion like ehx lbp-2. I'll put that thing into a guitar. A guitar with two ecc83 glowing in the dark yeeehaaa!
That's gonna go through batteries like a glowing hot sword through margarine.
@@Abandonedmachine it'll get a stereo cable where one channel is the power
looks nice. but, how to feed the filament?
Five volts DC on the filament should do it. Some people use AC, but you can pick up a 60 Hz hum that way.
There are 3 heater pins on the tube. The filaments within the tube are in a series circuit, allowing it to be used as a common, for use at 5~6 volts, or, you leave the center tap pin open, and connect the end pins directly to the 12 volt source. The heaters are electrically isolated from the cathode pins. The cathodes of each half of the tube have their own pins. You can "google" 12AX7, and easily find the pin out, so you know which pins are what.(cathodes, grids, anodes, and filaments) All nine pins are connected in these dual triodes.
can you share the diagram of this proyect please?
Good evening my friend, can you tell me the values of the capacitors? I was very interested to carry out your project.
the capacitor's values are one the schematic itself...
1 uF?
wenderson eliecio Yes. You can use unpolarised electrolytic. If you don't have one, you can make one from two polarised ones, like this:
----)|---|(---- Make sure they're both 2uF because in series, that would equal to 1uF.
Thanks a lot, I do not know how to read capacitors, only resistors.
wenderson eliecio Even if they are marked, they are sometimes wrong. Your best bet is to take the multimeter, and set it to capacitance, and measure every cap you will use. Be sure to discharge them before you measure them!
Im new to electronics, can someone explain why there is a 100k?
how did you manage not to use any transformer, how did it work without ac voltage? and no output transformer???
This is a preamp circuit (not driving a speaker direct). The impedance on the output is high but can still drive the line input to my amplifier.
in all valve amps there is the ac mains but only to the power transformer then the voltage is rectified to dc. Unless of course you are building the preamp in question.
Great job! I am a novice and know very little regarding this, but willing to try to build the circuit by realizing the circuit is low voltage and safe to work with. Is the circuit your priority or can you share your schematic? I will understand if you tell me you wish not to do so. Thank you for a great video.
+Carl Philistine Hi, The schematic is shown in the video. You may need to tweak the biasing resistor values as my tube was worn.