Master volume for Dynaco power amp

[Leevi]

Any ideas how a working master volume could be installed in the following
circuit? I have tried a traditional pot before the grid resistors but it didn't not work.
/Leevi

http://www.google.fi/imgres?imgurl=http://www.triodeel.com/dynamk3.gif&imgrefurl=http://www.diyaudio.com/forums/tubes-valves/155095-sophia-electric-el34-schematic.html&usg=__hjF5J3ruja0KIGGP-5pRlq6ujgI=&h=1056&w=825&sz=27&hl=fi&start=0&zoom=1&tbnid=sfKWouR1MUHzZM:&tbnh=157&tbnw=123&prev=/images%3Fq%3Ddynaco%2Bkit%2Bschematic%26um%3D1%26hl%3Dfi%26sa%3DN%26biw%3D1024%26bih%3D649%26tbs%3Disch:1&um=1&itbs=1&iact=hc&vpx=359&vpy=306&dur=2&hovh=254&hovw=198&tx=129&ty=243&ei=4Dz7TNXaF82YOqb2odUK&oei=bDz7TI_KKsWv8gObyIzsBg&esq=5&page=1&ndsp=12&ved=1t:429,r:9,s:0

[FYL]

This link is shorter: http://www.triodeel.com/dynamk3.gif

Classic Dyna MKIII.

There are four possible approaches : input volume control (very hifi, with a 100K pot max.), bootstrapped PI MV (simple and very effective), PPIMV (traditional), crossline PPIMV (not recommended here).

[Leevi]

I have used a 50K pot instead of 470K resistor at input which works fine.

bootstrapped PI MV (simple and very effective)

How do you add this to the circuit?
Leevi

[FYL]

How do you add this to the circuit?

Good question. It's very simple with an AC-coupled cathodyne, much more complex here with a DC-coupled version.

[tubenit]

There is a thread in ARCHIVES on different types of Master Volumes that may possibly be useful to you?

http://www.el34world.com/Forum/index.php?topic=3496.0

With respect, Tubenit

[Geezer]

FYL wrote:

bootstrapped PI MV (simple and very effective)

Can you show some examples (or describe, in detail please) the PI MV that you often mention. I did a search of your past posts on the subject & didn't come up with anything. I believe it can be applied to both LTP & cathodyne, correct?

TIA, G

[sluckey]

Here's the boostrap PI mv. I don't see any advantage over the simple input mv that you used, at least for this circuit. However, depending on what you intend to do with this power amp, I might use a 500K input mv rather than your 50K.

EDIT... hold on. I left a resistor off. added corrected drawing.

[Leevi]

Post-phase inverter 'cross-line' master volume didn't work. It behaves like an On/Off VOL.

I have not tried Post-phase inverter master volume but it will probably not work, see above

Boostrap PI mv might work but since there is printed board used in the amp it's quite difficult to implement.

Actually what I'm using right now is pre-phase inverter master volume which seems to be enough
like sluckey stated

I don't see any advantage over the simple input mv that you used

Thanks
Leevi

[FYL]

Can you show some examples (or describe, in detail please) the PI MV that you often mention. I did a search of your past posts on the subject & didn't come up with anything. I believe it can be applied to both LTP & cathodyne, correct?

Yes, the same approach can be applied to LTP or cathodyne PIs. Here are two examples as partial schemos. The first is a modded 5E3 with an AC-coupled cathodyne and a BMV - only one pot is required. The scond one is a typical LTP with a BMV using a dual-ganged pot.

[HotBluePlates]

If this amp were to be used for reproducing recorded music, I would use only the input volume control. However, I would probably replace the input 470k resistor with a 500k pot.

My choice would be based on the multiple nested feedback loops in this amp, and the unpredictability of what result you'd get by having a master inside those feedback loops. 2 of the loops run from the output transformer secondary and from the screen tap of the OT primary to the input tube cathode.

That makes the typical hi-fi input volume control the only point outside of the loops.

Besides, all the feedback (and the tpyical hi-fi architecture with the split-load inverter) means this amp would barely have enough gain to boost a guitar signal without an external preamp. Of course, the original was intended to be used with a preamp for music reproduction...

The McIntosh MC-30's I have use the input volume control, and it works quite well, even if I'm running a CD output straight into the input volume control with no preamp.

[Leevi]

I would probably replace the input 470k resistor with a 500k pot

I started  with 500k pot and changed it finally to 50k which used better the range of the pot.
Maybe 70-80K could have been the most optimal but I didn't have any.
/Leevi