Simplest Master Volume EVER

[ampdoc1]

I came up with this MV design when building my first TW clone (I wanted to tame the volume a little for home use). I won't swear it's original, but I've never seen it anywhere. The sound is pretty much flat,..nothing missing, just a little high end boost starting about 3KhZ.

David Hicks

[Craig Reid]

That is the MV from the "800" chapter of The Ultimate Tone, Volume 3.

I have used it in several amps. I agree, it works great.

Craig

[erigm]

I saw that in TUT3. I was wondering how well it worked. Thanks for the update. I think I'll try it in one of my amps!

[ampdoc1]

Thanks Craig, for giving credit where credit is due. I've never read any of Kevin's books, but obviously he "found" this before I did.
Anyway, maybe the exposure here will give a few more amp builders a new tool.

David Hicks

[Dai H.]

ooh neat! thanks!!!

[rhinson]

hello there, is it possible to post this in another format---i can't get it to work in the format it's in and free software won't open it either. thanks very much. rh

[Dai H.]

look at a 5F6-A schematic, at the phase inverter. The first 1Meg the signal sees is replaced by a pot (wiper has grid connected to it). That's it.

[rhinson]

hello there, thanks for the explanation---yeah that is easy and easy to understand! my question is since there is always dc on the grids of the p.i. (between maybe 30v and 80 or 90v depending on the rest of the circuit) doesn't a control/pot here have the scratching sound of the presence control (which also has dc on the pot)? some i'm sure would find it annoying but if you're willing to put up the scratchiness of dc on a pot you can use this principle for variation quite a few places in an amp. i know one of the 80's or 90's marshall models changed the slope resistor in the tone control to a pot (with a 10k baseline resistor and maybe a 100k pot in series)---i can't remember what they called it but i tried in an amp a few yrs. back and it works very well. also you could do this on the cathode resistor and change the gain of a stage. the zvex box the SHO is just a single gain stage boost that has as it's gain control the emitter resistor (ie---cathode in a tube stage) as a pot (dc on the pot, hence the "crackle ok" designation on the box). from a twreck point of view, this might be very effective to tune the 3rd gain stage for less gain, ie--having the set resistor as 10k in series with a 50-100k pot. the closer the cathode and plate values are to being the same, the closer a stage is to being just a buffer stage with no gain. anyway just some thoughts and thanks for explaning that the master vol. was making the grid resistor a pot----much easier than changing the file format! rh

[Omar]

JPG Version. I zip'd it b/c the original is large.

[Craig Reid]

You raise a good point about DC on the MV pot. KOC addressed that point in the 800 chapter of TUT3.

He said, "Yes, there is DC voltage on all of the EQ and Master pots, but there is no DC current "through" them. There may be a tiny leakage current thru the EQ caps, but that was always there."

The common issue with DC on pots is the "scratchy's" or worse yet a low frequency thunder as you change the DC levels seen at the grid.

Neither of these symptoms is present with this implementation, IME.

Craig

[Mark]

I did pull out my copy of TUT3 and I was reading (briefly) about K O'C take on a 50 watt and 100watt plexi amp. He does mention a way to get the tone of both amps without increasing the wattage about 50 watts.

I must confess that I didn't understand how this is possible.
I am wondering if it could possibly be an improvement/desirable variation to the tone of an Express amp?

[erigm]

Mark,

That is a good question! What would a four tube Express sound like?!

[Mark]

Dear Erigm

There is a lot of stuff in the TUT series of books which would work well in upgrading Express/Liverpool/Rocket amps.

I definitely think the biasing circuit he uses is a prime example of this. It's zener regulated too. He does tend to raise the heaters above earth too, but I'm not convinced yet that this is all it's made out to be.

[Craig Reid]

Mark

I have tried referencing the AC heaters to an elevated DC voltage ala TUT and it works great. Low noise and a lot less hassle than DC-ing heaters.

I had thought of doing a 4 tube express, but then I was worried that you might run into real estate problems if you are using the standard 17 inch wide chassis with the two trannies at the one end.

I have a Traynor Voicemaster, with a 21" chassis. I have thought about taking out the two Mallory FP's and subbing in two extra octal sockets. Any concern about running two extra EL34's with their extra 3A of heater current draw would be answered if you made it a 4 x 6V6 platform.

Hmmm...... add in Power Scaling, adjustable bias ....

Too many ideas, too little time.

Craig

[erigm]

Mark,

I have the first three of the TUT series. Kevin O'connor is awesome ... I have spoke with him on many occasions and he was very helpful! I have used many of his ideas in my own amps (mods and amps of my own design).

What I was trying to ask is what would the difference in sound be between a two tube express and a four tube express. I have never had an amp that allowed me the opportunity to try. You know ... like a head to head comparison. Everything else being equal, what would the diff in sound be?