Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: AlNewman on January 11, 2023, 11:02:23 pm
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Hi,
Anybody have any input on why the master volume doesn't seem to work the same as most amps? IE: even with the preamp volume maxed, I get very little breakup? Is it simply the ultralinear configuration on the OT?
Thanks
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Here the schematic;
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Ultralinear outputs are characteristically low distrotion.
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Here the schematic;
Thanks. My master pot has a dead spot in it, so I ordered a similar one, but I won't be able to replicate the control back to stock unless I source another for about $40 plus shipping in metric money. So I'm looking at other options, maybe I'll experiment with the post PI option.
Ultralinear outputs are characteristically low distrotion.
I happen to have a choke and some extra filter caps, perhaps I'll try bypassing the UL.
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Is the pull boost being engaged?
I think by far most commercial amp master volume arrangements are of the type 4, as per your SR, rather than the types 1 to 3 that you say is most common.
Though both may be quantified as ‘distortion’ I think that intentional overdrive is a different thing to the linearity of a non overdriven circuit.
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even with the preamp volume maxed, I get very little breakup?
you don't have much gain in the preamp, V1a make the signal big enough for the TS to suck it all out, V1b simply get you back to 1 gain stage.
before you get all cut'n n paste'n, maybe bet, borrow or steal a gain or OD pedal, slap it between G-tar n amp, see if that moves your needle
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Is the pull boost being engaged?
I think by far most commercial amp master volume arrangements are of the type 4, as per your SR, rather than the types 1 to 3 that you say is most common.
Though both may be quantified as ‘distortion’ I think that intentional overdrive is a different thing to the linearity of a non overdriven circuit.
It's hard to tell if or when the pull boost was engaged. I took the pot apart, and over time the wiper got sharp and wore off the coating on the bakelight. So from 1-7, the sound was thin whether the boost was out or in, than from 9-10 it got louder and deeper, and the boost seemed to have more effect. Now though I have a pot that will work, but it is only a single pole switch, so I won't be able to wire the boost as intended anyways, and it is a fairly expensive part to have a feature nobody seems to care for.
even with the preamp volume maxed, I get very little breakup?
you don't have much gain in the preamp, V1a make the signal big enough for the TS to suck it all out, V1b simply get you back to 1 gain stage.
before you get all cut'n n paste'n, maybe bet, borrow or steal a gain or OD pedal, slap it between G-tar n amp, see if that moves your needle
That's a good point, I suppose driving the input a little harder will make the existing master volume a lot more useful. Cut n paste aside though, I am going to have a nifty switch on the master volume that won't be doing anything, so it does make sense to put it to use somehow... I was thinking maybe put some resistors in parallel with the grid leaks on the PI, so I could switch them between 330k as original and 1M, blackface values. I'm also going to bypass the ground switch, so I'll have a nasty hole there, might fill that up with a presence control, or perhaps a switchable nfb ala Uncle Doug... Just kind of experimenting and coming up with ideas. It would also be interesting to try bypassing the UL just to see what it sounds like, but maybe you're right discretion may be the better part of valor.
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"Master Volume" is not real specific term. This one does control "volume of all inputs". It does not strangle the preamp enough to distort before the power amp distorts. The signal level at the MV pot is 2.2V, while the two channels can drive that point with over 20V. As the sketch notes, a for-distortion MV comes later in the chain.
Even an LPB at the input won't get you to massive preamp clipping and house-friendly output volume.
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Yeah, I'm kinda digging the master volume post PI. I'll try it like this for a while, not a big deal to change it back anyways. Can still dial it in for an overdrive or eq boost, and have lots of saturation with no pedals, too.
I jumpered the original pull boost in to see if I liked it, and it's probably not something I'd use much. Makes kind of an out of phasey weird distortion, had a way better result with the PI distortion. Now I just need to figure out what to do with my free panel space and switch.