Master Volume Mod

[Johnny Cache]

Anyone ever put a Master Volume in a DRRI? Not sure I want to install one, just wondering because I had a Push/Pull Master in my '75 Twin Reverb and really liked it.

 

[Andy B]

I haveput master volume controls on many amps. I use a design learned from Craig Anderton in guitar player a million years ago which is a post PI design.

 

[Johnny Cache]

I haveput master volume controls on many amps. I use a design learned from Craig Anderton in guitar player a million years ago which is a post PI design.

I think I could figure one out, but maybe there is a better way to do it.

Do you have a schematic for it?


Was it a preamp or a post gain?

 

[Cleeve]

I like the way Matchless did the master on the Spitfire- So simple yet it's after the PI just where it belongs. Here is a link from ampage.org (link removed)

Just be aware that on the deluxe the direct bias means that all three lugs of the pot need to not be grounded to the potentiometer shell.

 

[Andy B]

I saw your post today & I will scan the master volume schematic in & post it as soon as I can

 

[Johnny Cache]

I saw your post today & I will scan the master volume schematic in & post it as soon as I can

Thanks!

 

[Johnny Cache]

I like the way Matchless did the master on the Spitfire- So simple yet it's after the PI just where it belongs. Here is a link from ampage.org (link removed)

Just be aware that on the deluxe the direct bias means that all three lugs of the pot need to not be grounded to the potentiometer shell.

Thanks.

Thats the way I thought of doing it first, but I think there is another way which includes a feed back loop or something like that.

 

[Andy B]

Johnny,

Here is a scan of the original Craig Anderton article which I've used for many Master Volumes. The good thing about this MV is that a sine wave stays a sine wave until the control most of the way down.

 

[FenderLover]

December 1982? That's the same article I started out on back in the day.

Funny thing about the Matchless - that's an example often cited on how not to do a Master Volume, yet it sounds fine on my Chieftain and people generally don't complain about Matchless.

 

[Johnny Cache]

Thanks!

 

[hotguit]

Johnny,

Here is a scan of the original Craig Anderton article which I've used for many Master Volumes. The good thing about this MV is that a sine wave stays a sine wave until the control most of the way down.

Hi
Will you be so kind to repost a better resolution image? I can not read the caps value
Thank you

 

[johnnyha]

Barry at Amp Maker makes a nice VVR unit, it's called the VCB. Just posted this photot in another thread. I've heard good things about the VVR method, there's one in the plexi kit I'm building. I ordered the VCB just to see what it's like, haven't got it yet. It's a simple little kit you put together, basically a pot with a handwired PCB and MOSFET. Hooks directly into the transformer and regulates voltage down to 0 to reduce volume.

 

[robrob]

That Matchless master volume will load the phase inverter output even at max volume.

This is a super simple post phase inverter master volume you can alligator clip into the circuit to try. I put this in my 5F6A Bassman and I'm very happy with its performance:

https://robrobinette.com/5F6A_Modifications.htm#Master_Volume

Simple But Effective Trainwreck Type 3 Post Phase Inverter Master Volume (PPIMV)



Add a 1 megaohm audio (log) pot and two wires and you've got an effective post phase inverter Master Volume. As you turn the Master Volume pot down (counterclockwise) more of the opposite phase signals from the phase inverter are mixed together which cancels the signal out. It's a good idea to twist the two wires together to the pot to minimize noise (twist not shown in diagram above). The pot is shown shaft down in the layout.

If you are anal you can completely eliminate the Type-3 from the amp circuit by adding a switch to disconnect the circuit. Use a 1MA pot with a push-pull DPDT switch and wire one leg of the master volume through the switch so when the master volume knob is down the circuit is completely disconnected. Pull the knob up to activate the master volume. To do this you would run the wire from the #1 (left) pot terminal to the upper left DPDT switch terminal, then run a wire from the middle left DPDT switch terminal to the circuit board's left 220k resistor. The wire from the #2 (wiper) pot terminal would be wired as normal to the left 220k resistor (see layout below).

 

[overlock]

Barry at Amp Maker makes a nice VVR unit, it's called the VCB. Just posted this photot in another thread. I've heard good things about the VVR method, there's one in the plexi kit I'm building. I ordered the VCB just to see what it's like, haven't got it yet. It's a simple little kit you put together, basically a pot with a handwired PCB and MOSFET. Hooks directly into the transformer and regulates voltage down to 0 to reduce volume.

View attachment 361346

I don't think that one will work for the DRRI, Johnny. With a fixed bias power amp, you need a two-ended VVR so that you can bring the bias voltage down proportionately with the Vb. The "right" VVR would have two MOSFETs and a dual-gang pot.

 

[FenderLover]

That Matchless master volume will load the phase inverter output even at max volume.

This is a super simple post phase inverter master volume you can alligator clip into the circuit to try. I put this in my 5F6A Bassman and I'm very happy with its performance:
.

Rob, what you are showing is the same as the Matchless circuit again. Whether cathode bias of fixed bias output, the two 220K go to ground (directly with cathode bias, through the bias filter cap with fixed bias) and are effectively in parallel with the 1M Master. Every post PI Master loads the PI without using a switch, but is trivial.
(I'd be more worried about blocking distortion with those huge 0.1uF coupling caps...)

 

[johnnyha]

I don't think that one will work for the DRRI, Johnny. With a fixed bias power amp, you need a two-ended VVR so that you can bring the bias voltage down proportionately with the Vb. The "right" VVR would have two MOSFETs and a dual-gang pot.

Good info thanks. I suppose then it should work on a 5E3...

 

[robrob]

Rob, what you are showing is the same as the Matchless circuit again. Whether cathode bias of fixed bias output, the two 220K go to ground (directly with cathode bias, through the bias filter cap with fixed bias) and are effectively in parallel with the 1M Master. Every post PI Master loads the PI without using a switch, but is trivial.
(I'd be more worried about blocking distortion with those huge 0.1uF coupling caps...)

You are correct, I thought the bottom of the pot in the schematic was connected to ground, not the other phase inverter output.

Johnnyha, this will work on the 5E3 too but the 5E3 is better served by a pre phase inverter master volume so you can control how hard the PI gets hit and prevent nasty double frequency distortion.

 

[robrob]

My recommended 5E3 Master Volume:

PRE Phase Inverter Master Volume


The PRE Phase Inverter Master Volume requires only a standard 1 megaohm audio (log) pot and an optional 100pF 'bright cap'. The bright cap will keep the tone from getting too dark when the master volume is turned down very low. Running the long wire from the Master Volume pin 2 to the tube socket under the circuit board can minimize noise by keeping the wire close to the metal chassis. Note the 1M grid leak resistor has been removed (or one leg clipped) from the circuit board.

The PRE Phase Inverter Master Volume is my recommended master volume modification for the 5E3. The mod simply replaces the phase inverter's (V2A) 1M grid leak resistor with a 1M log or audio pot. With the Master Volume full up the 5E3 circuit is completely normal--it's as if the MV isn't there so it won't change your amp until you dial down the volume. It also allows you to dial out nasty 'double frequency' phase inverter distortion, control the balance between preamp and power tube distortion and of course practice with dirt at lower volume.

 

[Andy B]

Hi
Will you be so kind to repost a better resolution image? I can not read the caps value
Thank you

The Craig Anderton Master Volume is the same as the Trainwreck Type One Master Volume. The cap values are .1@600VDC

 

[hotguit]

Thank you. All caps 0.1?