Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: soggybag on July 19, 2019, 06:25:50 pm
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I built 36w TMB type amp from a kit a couple years back and have been thinking to mod it. It works well but it’s really loud and you need to crack it up before you can get a distorted tone.
How would I go about adding a master volume?
Recommend me a schematic of something similar with a master volume. I haven’t been able to find anything in the ballpark.
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Google turns up plenty of master volume schematics
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Did you check ARCHIVES: http://el34world.com/Forum/index.php?topic=3496.0
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The simple solution is to add a post phase-inverter master volume (PPIMV).
To make it even better, add some type of power scaling (or VVR).
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Go over to the 18watt.com site and take a look at the 36 watt room. I bet you will find where someone has added the Master volume. I know there is info on VVR for the 36 watt which might better suit what you are looking for. It's a Marshall, it's 36 watts. It is going to be loud.
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In Tubenit's link, there is a schematic of a amp, cathode bias that has a PPIMV. Most of the diagrams you can't open larger but this one you can. It's just two 6K6's but I bet someone here can help if needed to put this in your 36 watt TMB.
(http://el34world.com/Forum/index.php?action=dlattach;topic=3496.0;attach=41682;image)
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Thanks for the replies. I found this master volume mod.
[img]https://robrobinette.com/images/Guitar/5E3P_Build/5E3_Type-3_MV_Mod_Schematic.jpg[/
This looks easy to implement and similar to the scheme above.
Here the 1500r resistors are bridged by a 1M pot. My amp has four tubes with four 5k6 resistors in these locations would I wire this with a single pot or should use a dual gang?
The PPIMV mod above looks similar to the Type 3 MV though different. I think I could implement either of these without too much trouble.
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You can try a single 1M pot for that MV. It really should be upstream of the grid stoppers (1K5 on the 5E3, 5K6 in your case) connected at the junctions of the 1.5K and 220K in the drawing. Hopefully that makes sense without a diagram.
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Hey thanks for the reply Tony, if get you the pot would bridge at the points where the caps come off either side of the phase inverter? This would at the C2 R8 junction and the C3 R9 junction.
(https://www.tedweber.com/media/kits/6m36_schem.jpg)
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I would wire it with a dual gang 500KA pot, in place of the two 470K (take out R10 and 11) Like the LA MAR master volume. Run the 5K6's as in the diagram wiring of the pot I posted above, use the 2.2M R too. The wipers would get the 5K6's and the caps, .01 to the ends opposite of the ground.
Maybe someone would jump in to verify.
al
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I would but never found the point of a 36w amp choked to 5w, I just build a 5W n make it sound good :icon_biggrin:
but lots of folk put this together, probably something useful
http://el34world.com/Forum/index.php?topic=3496.0
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I could have built the 18w and it would have been the same. Still too loud with two less tubes to wire up.
When I ordered it I had it in my head that 18w might not be loud enough to keep up with the drummer.
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Hey thanks for the reply Tony, if get you the pot would bridge at the points where the caps come off either side of the phase inverter? This would at the C2 R8 junction and the C3 R9 junction.
Exactly.
I don't think I need to tell you that there are different ways to make a MV, each favored for different reasons. The type you're talking about is good for changing the sound of a cranked amp by introducing a little more preamp and PI distortion into the mix, but it's not as popular with players that want to really reduce output power a lot. The LAR MAR described by Dude, or even a pre-PI MV (or some combination) might work better to get down to a couple of watts output.
But don't let me discourage you from experimenting! It's easy to tack solder in a 1M pot to see how you like it.
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I'm really not into cutting down the volume to bedroom levels, like Shooter says get a SE 5W amp. Personally, my goal is to get the sound of a cranked amp at a reasonable volume level for gigging or just jamming. A 36 watt TMB is loud, to get the grind you have to crank the volume or use a pedal, not a big pedal fan either except for a lead. I have a VVR in my 18 watt TMB lowering the voltage to the power tubes only, just to lower the volume a bit, taking it down to lower levels you lose highs and some mojo, IMO, everyone is different. But you don't get the grind at lower levels with a VVR, IMO.
I never tried the LA MAR M/V in my 18 watt but thinking about it over the VVR. Seems for some reason the mosfet for the VVR blows in about year or so for me...? Plus for some reason I don't like the idea of lowering the B+ to 250v with the VVR but probably does no harm except make your EL84 last longer :icon_biggrin: .
If you try the La Mar in your 36 watt, post your results, good or bad ,I'd be interested. I know not many have a dual gang 500KA pot laying around but good to have a few, 250KA, 500KA and 1MA for your supply. Only problem is these pots are usually not balanced or equal unless you get lucky.
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I’m still wrapping my head around this. Correct me if I’m wrong or have missed something.
The Type 2 MV/La Mar is attenuated the signal from either side of the phase inverter feeding the power section. The dual pot acts as a volume control for both sides of the PI.
The Type 3 MV mixes a variable amount of signal from either side of the PI. Since the signals are out of phase they cancel each other out and the pot allows this in varying amount.
It seems that both of these mods limit the signal into the power section so they are not driving the power section to distortion. Instead the preamp section can be turned up to overdrive the input and phase PI.
I’m working from these schematics.
(https://robrobinette.com/images/Guitar/Trainwreck/Type-2orLar-Mar_Master_Volume_Schematic.png)
(https://robrobinette.com/images/Guitar/5E3P_Build/5E3_Type-3_MV_Mod_Schematic.jpg)
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You seem to understand them. Only thing left is to try them. :icon_biggrin:
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Here's some info that might answer your questions, most builders say the LaMar is one of the best. I never heard the LaMar on a cathode biased amp but with the volume and gain pots on your 36 watt TMB I would think turning the PPIMV down as little as possible and then fine tune with the gain and volume pots, you'd get what you're looking for. With my 18 watt TMB and the VVR, turned down 20%, blending the gain and volume gave me all the grit I wanted, any leads I use a modded TS-10 to 808 specs. One note, since the cheaper dual gang pots are up to 20% off, get a few, their cheap. You can always get a PEC pot, very good quality and accurate but around $30.
https://www.thegearpage.net/board/index.php?threads/please-school-me-about-the-lar-mar-ppimv.1017133/ (https://www.thegearpage.net/board/index.php?threads/please-school-me-about-the-lar-mar-ppimv.1017133/)
al