Master volume and treble loss

[Boy Howdy]

Err it would be helpful to provide the specifics of the amp you’re asking about

It's the amp in the schematic I posted, slightly modified.

[Boy Howdy]

No treble loss

I actually have used that type of master on another amp I have. I wanted to compare the two types. I can't remember what I concluded about the differences, but the single pot version does work well, is cheaper and sounds good. I may just take out the dual master and go with the one pot master.

[Boy Howdy]

As we all know volume controls are very touchy down low on the dial. For a clean sound I'm running at about .5 (that's one-half of one) and it's a bit of a pain to get it just right. So I generally just set roughly where I want it and then use the master volume to control the actual volume.

I have a Ken Fisher type PPI master on the amp. mod101_ppimv_master_volume_mod.pdf (tubesandmore.com) The problem is that when I turn down the master, I lose treble. So then I have to do this dance of balancing the two volume controls to get the best sound, which defeats the whole purpose of using the master in the first place.

Can I install bypass caps on the master to recover the lost treble?

Yeah, I always put a bright cap on the volume control, can't live without it. This time I actually installed a 470K resistor in series with the cap to get it just right. That worked out really well. I get what I want there, as long as I don't turn down the master too low.


The dual 100K is just what the recipe called for. I didn't give a second, or even a first, thought. . . . Gulp.

[pdf64]

No treble loss

Did you see the thread where Jon Snell raised the issue of a common mode positive bias caused by the type 3 / crossline master vol? https://music-electronics-forum.com/...olume-question

[Helmholtz]

No treble loss

The OT's MV doesn't cause treble loss either (except maybe for some Fletcher- Munson effect at low volume). Don't forget pentode input capacitance is very small.

And cross-phase MVs cause bass loss at low settings.

[vintagekiki]

No treble loss

[Helmholtz]

Yes you could.

But the actual place where treble is lost in the amp is the vol pot and the input capacitance of V1b at low vol settings.
Have you tried a bright cap of 47p to 150p across the vol pot?

Also I wonder why you use a dual 100k master pot. That low value loads down the PI output. I would use a dual 470k pot instead and try 100p to 330p bright caps if necessary. But as the MV is within the NFB loop, the bright effect will be small.

[pdf64]

Err it would be helpful to provide the specifics of the amp you’re asking about

[Boy Howdy]

As we all know volume controls are very touchy down low on the dial. For a clean sound I'm running at about .5 (that's one-half of one) and it's a bit of a pain to get it just right. So I generally just set roughly where I want it and then use the master volume to control the actual volume.

I have a Ken Fisher type PPI master on the amp. mod101_ppimv_master_volume_mod.pdf (tubesandmore.com) The problem is that when I turn down the master, I lose treble. So then I have to do this dance of balancing the two volume controls to get the best sound, which defeats the whole purpose of using the master in the first place.

Can I install bypass caps on the master to recover the lost treble?