Will Pre-PI master volume work on Tweedle-Dee?

[dannieh42]

Update...I installed the master volume the "Right Way" and I am not completely happy with it, but it works pretty well. Maybe I'm just being a perfectionist but it doesn't turn the amp all the way down. With the channel volume at 75% it turns it down to about the volume of a conversational voice, but not all the way. I know it's not a big deal, and I will probably be the only person to ever notice. But, it's things like that that will irritate me over time. So I was thinking of doing this and see how it worked. Thoughts anyone?

[sluckey]

If you do that, you need a coupling cap connected to the wiper of the pot. Otherwise, the bootstrapped bias will be upset.

You're not the only one that is aware that MV doesn't totally kill the signal. How important is that?

[pompeiisneaks]

Not sure if it's just an error on that schematic, but normally 'connected' wires need a dot like in other spots and there's no 'dot' on the joint between the wiper, screen, the NFB on top and the 1M below to the cathode. Just a nit pick.

I think the reason that some audio comes through is that in that case there's enough current coming through that it has two very low resistance paths, one to ground from the pot, the other to the grid so some still can leak. Earlier in the signal path the current is low enough it all goes to ground. Or is that a misunderstanding?

~Phil

[sluckey]

I think the reason that some audio comes through is that in that case there's enough current coming through that it has two very low resistance paths, one to ground from the pot, the other to the grid so some still can leak. Earlier in the signal path the current is low enough it all goes to ground. Or is that a misunderstanding?

The pot is not wired like that last pic. The pot does not connect to ground. It connects to the cathode circuit. So, even with the pot turned all the way to ground there is still some resistance between the pot and ground. That's why that MV does not kill all the signal. And there is no current to the grid.

[dannieh42]

Not sure if it's just an error on that schematic, but normally 'connected' wires need a dot like in other spots and there's no 'dot' on the joint between the wiper, screen, the NFB on top and the 1M below to the cathode. Just a nit pick.

I fixed the dot. Even though it is a nit, nits are important. The devil is in the details. I would hate for some other first time builder to be reading through this, a year from now and that missing dot confuse them. The experienced people on here would look at it and know that it was connected, but that can't be assumed with us new guys. I almost didn't wire up the filaments on this build, because on the schematic and layout I was working from, it was so basic that it just wasn't shown. Now I think "Well, of course I have to wire the filaments. That's how tubes work, stupid". But 3 months ago...Ah, not so much.

[dannieh42]

You're not the only one that is aware that MV doesn't totally kill the signal. How important is that?

It is not that important. I was just wondering if there was another way that might work better. Even if there was a better way, it would have to wait. Because, right now I am just enjoying playing through the amp and I can't play through it if it's taken apart on my bench.

[sluckey]

This will work without messing up the bootstrap bias on the PI. And it will take the volume all the way to zero.

[dannieh42]

Thanks! When I take a break from playing it, and remount the master volume knob in its final location I will try that.

[tictac]

Why would you want to turn your amp, "all the way down" with a master volume control?

The usual purpose of a master volume is to lower the overall volume so the preamp volume can be turned up causing "preamp distortion"

Turning the master all the way down until there is no volume doesnt really serve a purpose does it.

If you want to mute the volume you can use the preamp volume control....

I guess, "because I want it to..." is a reason, it's a free country!

my .02

TT

[M Fowler]

One will find that Master Volumes aren't all that great, but you have to discover that yourself, too subjective for blanket opinion.

I much prefer no MV and amps with less knobs. So funny to see people adding TMB pots, slope pots, mid shift pots, pre MV, PPIMV, ETC.

I did the same thing and another thing I quit adding was SS/tube recto switches, HT switching, and bias test points/bias pot on back. Those bias test points and bias pot on back have caused more amps to come back to my work bench because the owner/operators do not know what the hell they're doing.

But I am guilty of the same thing, it's all part of the fun of amp building.

Mark