Lar-Mar Master Volume | How It Works, Pros & Cons
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- Опубліковано 28 лип 2024
- I've had a lot of requests to discuss the master volume circuit I put in most amps. So here such a video is.
Watching it back, I realized I said the twisted grid wires are as good as/better than shielded wires but I didn’t say why (but I have in many previous videos). We’re taking advantage of common mode cancellation. Any noise common to one wire is common to the other wire. And as the output tubes are out of phase with each other, the common noise is canceled out.
Just like a humbucker.
“Musically Useful Without Getting Evicted” is going to be the name of my next cover band.
Great idea! I claim “Circuit Collapse” for a post-punk project.
@@ColeWheeler4Lyfe That is exceptional !
@@ColeWheeler4Lyfe I vote for “ Common Mode Rejects” band name! LOL
The explanation with the schematics really helped me understand how this MV operated, thanks...
It's awesome that you posted this when you did, because I'm spreading my wings and attempting to build a Trainwreck Liverpool from scratch. Wanting to incorporate this specific MV. I need to revisit your grounding scheme videos too so I don't botch this project. Thank you for being a top-shelf resource.
That amp came out great. Your craftsmanship and attention to detail is just fantastic ,sir.
As one of the guys asking MV questions from your other recent bassman video….thanks! I often wish my Vibrolux was Deluxe powered, I see old LarMar in her future.
That's the one I particularly like. Parallel resistor formula 1/({1/X}+{1/Y)) = R 2,3,4,5,6 resistors keep adding the inverses of each resistor together and then take the inverse of the sum. A resistive attenuator network? That is a whole other kettle of fish, with some twisty eels added in for fun. That was the first actual real head scratcher for me in electronics class. 3rd level determinants and AC phase angle calculations were the next ones, with 64+ blackboards of math literally running in circles around the room. When we used up all 16 black boards on the four walls of the classroom we erased the first blackboard and just kept on a going, around and around.
Excellent overview on the Lar-Mar master volume. It seems to have the least consequences sonically of any that I have run across. Thank you 🙏.
Very cool, Lyle. I’ve often avoided post PI master volumes because I just preferred putting them before the PI. But this demo shows it works really well.
You've hit it out of the park Lyle! Thank you so much.
Thank you for sharing your knowledge and expertise with us Lyle.
thanks for sharing.... i love when an expert will take the time to share their knowledge
Outstanding. Learnt me somethin bout larmar. Totally knew it with my ears on my 5F6A thatbsweet spot where the nfb and presence (and i guess the icepick caps) start to do their thing.
Thank you soo much for sharing yor knowledge man,
Im about to build a Bassman-ish combo and wanted to brush up on the MV so i came straight to you 😊
Thanks again, you are awesome
I put this in the Mojotone 5F6A kit I built. Excellent modification, and I really don’t notice the low volume limitations.
Another piece of gold here Lyle!
Excellent Presentation!
Great video and info, as always.
I use this on my amps. I mostly cathode bias mine which makes this a little simpler. It lets you get the drive on the inverter. It sounds pretty nice. 🙂
Greatly appreciated!
Very useful, I put in a variable resistance in the feedback loop to make it a bit better when volume turned right down.
I tried the variable feedback pot as well as the presence control with switchable 1,5, 10 uF caps in a ‘69 champ amp and it gets pretty “Raw” as the NFB goes away like a tweed. Very nice!
@@tjminasi1442 The trick is more NFB when you turn down volume to keep NFB to similar levels when volume is up. Of course you can also use it to give you less NFB at higher volumes to give a rawer tone.
Nice! I usually did the shielded cable and its always been a bit of a mess so that twisted wire tip will be something I'll definately have to try next time I set one up!
In a modern amp you can use teflon coated 22AWG and end up with a very neat small diameter twisted run. But in these old Bassmen I used the cloth covered 22AWG purely for cosmetics/vibe.
Simple and effective.👌🏻
The grounded cathode output does require matched tubes. Nice circuit for the purpose it is used good video.
See the ‘67 Bassman video yesterday where I used the same MV with the Fender Bias Balance circuit. So you can fudge tube matching that way, though I always prefer matched tubes myself.
Thanks for that. I may have my amp tech do this to my ‘67 Bandmaster (AB763 circuit).
Well, the AB763 phase inverter/output tubes usually stay pretty clean, so a simple pre-PI MV ala late ‘70s Fenders can also be a good choice for those (without the dumb bright cap). Depends on how much you turn up the preamp volume. For “regular Fender use” (volume no higher than noon but you just want less output) the pre-PI works well. If you turn the volume to 8 a lot ala Bloomfield then the slightly more complex Lar-Mar is your friend.
excellent, thank you!
Love a Bassman❤
I use the simple 1 meg after the treble pot master on my Marshall inspired amp and it works ok turned halfway down....I am interested in trying this one in one of my old Bassmans
I just put one of these on a Z/28 mk one clone and it works well enough. Not a huge fan of master volumes most of the time but the #2 and #3 are nice because they don’t affect the tone when cranked all the way. The Z/28 has 100k grid leaks so 100k dual pot rather than the 250k.A pot/resistor combo to get close to 100k is probably a better option for safety, tho. The trick is finding a dual pot with a satisfying taper for MV. Might take a few tries with different brands and tapers. Edit: Just found a dual gang 100k A pot and used 4.7meg resistors and it works really well. Taper is more useful than 1 meg pot with 110k resistors which I tried first.
All the best to you and yours, as always Lyle! Can’t wait to hear what a “Lar Mar” is. I’m picturing a Python skit, but maybe that’s the Pumkin Porter talking. See ya tomorrow chief! Sláinte! Samhain looms! 👻🎃👻🎃
What I love about these, apart from the simplicity, is that I can get something like a twin to breakup "enough" to sound great with fuzz and drive pedals instead of that awful "sits on top" thing. Absolute no brainer in any of the silverface amps with a pre-phase inverter master..
Added bonus is power tubes last forever if you're a bedroom guy. 🤣
I have owned dozens of Fender tube amps, and also played every Fender under the sun, and thus far there are none that deliver good enough high gain for gigging & recording. Where they absolutely shine is shimmering cleans to slightly overdriven to growling gain ala tweed deluxe power tube breakup with the volume on 10. But for high gain, look elsewhere as there are far superior options.
"...there are pills for that..." your dry wit does not go unnoticed.
Great explanation! Could you comment on the use of frequency compensation that some amp builder's implement for this style of MV to address the impact of the loss of negative feedback? Cheers!
Thanks Pete. The frequency change is more apparent in amps that have a Presence circuit.
Trying to compensate is tricky as you don’t know how the player is using the Presence circuit. Easy to overdo it and have the amp too bright for many (but still not enough for others).
I advise clients that any MV involves some compromise, but this circuit is close to transparent over 1:00 and not objectionable between 10:00-1:00.
If they find themselves using the amp with the Master at 8:30 it’s too much amp for that stage.
Better to get a second smaller amp or look into the various reactive load attenuator devices (Suhr, Fryette, UA, etc).
There are ways to compensate within the circuit (high pass filter increases as MV is turned down, very minor treble bleed circuit incorporated, etc) but like I said, that is pretty much guesswork as to what *most* players will find good. Others will hate it.
@@PsionicAudio Thank you for the quick and thoughtful response.Much appreciated.
Sounds good. I tried a cross-line master volume and didn’t like it at all (Blackface Princeton circuit).
Awesome!! Thanks!! Just for my curiosity...could the gradual loss of NFB be somewhat compensated for by changing the NFB resistor out for a variable NFB resistor, maybe a 6-way rotary switch (with maybe one position breaking the NFB loop)? I guess I'm unclear as to what causes the loss of NFB functionality. I'm often accused of having just enough knowledge to be dangerous. Thanks for your awesome content!!
Thanks man. That’s a tail not really worth chasing, for reasons I don’t have enough coffee to get into. Let’s just say if it was doable and there was a real reason to do it, designers would have been doing it a long time.
Simple is good.
Thanks for the well deserved scolding. @@PsionicAudio
Respect your work. I have an Fender S face quad 6l6 amp with bias balance control .how does the Lar-Mar apply to it ?Do I need to run 2 x bias & unlink pot as separate ? so as four wires to the pot. Regards Tory
what is in your opinion the best candidate to convert to bass amp. for example some 100w all tube 800 style amp would be possible or OT is the issue?
Is this the similar to the later silver panel amps master volume?
If you were to mount the pot on the other end, perhaps in a blockoff plate for the auxilliary AC outlet, what precautions would you take for getting the wiring past the power feeds? Would just trying to make sure they cross at 90° from the leads coming out of the transformer be enough to ensure no noise is picked up from there? Is this even a concern? As far as the blockoff plate; is bonding a concern at all or would the potential isolation be even better? Thanks Lyle!
You want to steer signal away from high voltage/current AC as much as possible. Certainly away from the mains.
Hey Lyle. Thanks for your video and explanations. I installed a Trainwreck Type-3 PPIMV including a switch to completely eliminate the master volume pot on demand on my 65 DDRI. Couldnot source a dual pot here in Germany at the time I installed it. Is the difference between Type-3 and Type-2 Lar-Mar Circuit noticeable/discernible? What is your opinion? Thx in advance. Keep up your good work and greetings from Germany
Thanks. Type 3 (crossline) doesn’t have a very good taper and sounds a bit fizzy in comparison. I’m not a fan, but for minor volume reduction it can be OK.
PS no disrespect to Ken, but the Type 2 version in my schematic is better to what he showed as I (like others) include a fallback resistor.
@@PsionicAudio Sir you are right. The taper with an 1MA pot was horrible, tried 250KA and 100KA pots. Kept the 100KA one. Your videos and the AB763 Mods page from rob robinette helped me a lot working on my amp. Thank you very much again! I'm looking forward for your next livestream. Maybe you could talk a little about the SLO cirucuit and your opinion. Here in Europe there is a nice source for a SLO Kit and I'm intrigued in building a 30 Watt one as a high gain amp since my clean tones are well covered with the DRRI. Cheers from Germany
Would a type 2 style MV be a viable mod for an AC30C2?
Thanx again Teacher... Iffin I could bring you an apple...
In your opinion, does this 'ppimv' compare with an attenuator tone-wise?
Thanx again
Given that no attenuator and no MV are “perfect” the best solution for “transparency” would be to use both at once, each just doing a little volume reduction. Say MV at 1:00 and attenuator doing -6dB. So neither is really changing the sound. But you get a very noticeable level reduction.
But this kind of MV is much more “transparent” than people think. The gear forums are full of hyperbole. Nothing ever has some weakness - IT SUX. Nothing ever has some advantages - IT RULZ.
Hi Lyle. Thanks a lot for the great video and explanation. Could you advise re the values of each pot in the dual gang. Is there any issues when they don’t match ?
E.g one pot reads 251 and the others reads 266
Thanks a lot
It doesn’t really matter if the difference is 10% or less. That’s something I’ve tested with matched and unmatched dual gangs. The high pass frequency difference is negligible, and the effect on bias isn’t enough to cause hum/noise. So long as each gang’s taper is the same (and they usually are as that’s consistent in production) the MV works the same.
I spent a lot of time down that rabbit hole.
Brilliant. Thanks a lot for that. Much appreciated.
Sounds great. Not related but... My Supersonic 22 reverb is rather benign, as in, barely noticeable. Will a new tank help or is that a circuit thing?
It shouldn't be a circuit thing as mine can get really cavernous when you turn it up. Maybe check your V3 tube, which is the reverb driver and should be a 12AT7. V4 is the reverb recovery tube so that could possibly have something to do with it too.
How can it be that this Bassman has much firmer and crisper distortion than my Bassman even though the circuts are very similar except for the master volume?
The character of the distortion did not change much when the master volume was turned down. Does that mean that it was mostly preamp and pi distortion?
Would this work on an amp with a direct coupled long tailed pair phase inverter? (EF86 into a 12ax7, with a bias voltage on the 12ax7’s grids) And the OT negative feedback fed into said ef86, and not the power tubes?
I’d want to see the schematic before answering.
Thanks Lyle! What schematic editor are you using mate?
KiCad
@@PsionicAudio thank you
Ken Fisher - Trainwreck Pages - Type 2 (except Ken actually had 100k-B dual ganged pot in there).
Thanks. Linear can sometimes be better in cathode biased amps. Audio works better in fixed bias in my experience. The value will depend on the value of the coupling cap before it, but in general use the closest match to the existing bias/grid leaks.
This circuit is comparable to the rockerverb 50 attenuator?
Not at all the same circuit but IMO comparable sound with fewer parts and no heat.
If a PPIMV is installed on say a 50w 2204, when the added knob is all the way up, doesn’t that basically make the amp act as if it’s not there ….giving full control to the original master volume on the front of the amp ? I have some type of PPIMV on an ‘87 2204 and I feel like it’s simply “not as loud” as it should be with all volumes up.
The Lar-Mar is out of circuit when at full volume. The type 3/crossline usually always attenuates slightly.
Do you know the difference between this design and Friedman's design?
What is your process for checking in amps for repair/mods? I can't find a phone number.
"Things go south"... I remember it as "Better Buy Resistors Or Your Grid Bias Voltages Go West"
Didn't you also have another master volume that was a bit of a secret? I think I saw it on a Marshall or something? You had covered it up with paper. It's not this, I guess?
I share an awful lot. I don’t, however, share everything. ;)
The best Lorimar show was Mama's Family
Only rich people can afford this stuff. Within 5 years they will not exist. Don't bother.