The PPIMV (Post-PI-Master-Volume) thread.

rockstah · Post by **rockstah** » Mon Nov 13, 2006 7:48 am

SDM wrote:You can turn the presence into a "cut" stlye control ala Vox, Matchless and others. It works regardless of negative feedback, so works with PPIMV's.

ah hah! do tell Steve, do tell.

SDM · Post by **SDM** » Mon Nov 13, 2006 8:03 am

Here's the basic idea: http://www.blueguitar.org/new/schem/vox/ac15fact.jpg
Look at the "top cut" control after the PI. Go with a 1meg pot and .001-.0068u cap (to taste) instead to keep it from having an effect on highs when you don't want it to. It can be added in addition to a presence control or instead of one.

rockstah · Post by **rockstah** » Mon Nov 13, 2006 8:17 am

SDM wrote:Here's the basic idea: http://www.blueguitar.org/new/schem/vox/ac15fact.jpg
Look at the "top cut" control after the PI. Go with a 1meg pot and .001-.005u cap (to taste) instead to keep it from having an effect on highs when you don't want it to. It can be added in addition to a presence control or instead of one.

very kewl - i had seen that before - great food for thought here in this thread.

thanks Steve!

Mark

SDM · Post by **SDM** » Mon Nov 13, 2006 8:25 am

Also if you replace the presence control with this style, the presence pot can just be replaced with a regular 4.7K-5K resistor to ground. The other end connects just as the pot did to the 10K of the PI and the NFB resistor. Slap a .1u acrossed it, and this just acts exactly like the regular old presence pot is still there and set as if dimed. Turn the cut control all the way up, that's how it'll sound, BUT the cut control has much more ability to cut those highs out, so you now can roll off much more high end with it (if you want to) than you could with the regular presence control turned all the way off. And, of course, the cut control remains working with a PPIMV in place.

rockstah · Post by **rockstah** » Mon Nov 13, 2006 8:28 am

SDM wrote:Also if you replace the presence control with this style, the presence pot can just be replaced with a regular 4.7K-5K resistor to ground. The other end connects just as the pot did to the 10K of the PI and the NFB resistor. Slap a .1u acrossed it, and this just acts exactly like the regular old presence pot is still there and set as if dimed. Turn the cut control all the way up, that's how it'll sound, BUT the cut control has much more ability to cut those highs out, so you now can roll off much more high end with it (if you want to) than you could with the regular presence control turned all the way off. And, of course, the cut control remains working with a PPIMV in place.

i got everything there except which 10k are you speaking of in the PI?

SDM · Post by **SDM** » Mon Nov 13, 2006 8:37 am

Yeah just the 10K (under the 470 ohm in the PI) that's already gonna be jumpered over to your NFB resistor on the board. Basically just imagine the presence pot transforms into a resistor, the outer two pot lugs are now the 4.7K or 5K resistor leads, and everything still connects the same there. Add that .1u cap acrossed the resistor, and you just now effectively have a dimed presence pot (though the pot is just a fixed resistor now), and the cut control now takes care off either letting all that high end presence through, or taking it out.

rockstah · Post by **rockstah** » Mon Nov 13, 2006 8:41 am

SDM wrote:Yeah just the 10K (under the 470 ohm in the PI) that's already gonna be jumpered over to your NFB resistor on the board. Basically just imagine the presence pot transforms into a resistor, the outer two pot lugs are now the 4.7K or 5K resistor leads, and everything still connects the same there. Add that .1u cap acrossed the resistor, you just have a dimed presence pot, and the cut control now takes care off either letting all that high end presence through, or taking it out.

oh that 10k!@

- i just figured, doing the mod i would put a 5k resistor with .1u cap across it straight to ground after the 47k neg feedback resistor on the board that previously lead to the pot and be done with it.

SDM · Post by **SDM** » Mon Nov 13, 2006 8:54 am

rockstah wrote: - i just figured, doing the mod i would put a 5k resistor with .1u cap across it straight to ground after the 47k neg feedback resistor on the board that previously lead to the pot and be done with it.

Yeah that'd do it too

rockstah · Post by **rockstah** » Mon Nov 13, 2006 8:57 am

SDM wrote:
rockstah wrote:
SDM wrote: - i just figured, doing the mod i would put a 5k resistor with .1u cap across it straight to ground after the 47k neg feedback resistor on the board that previously lead to the pot and be done with it.
Yeah that'd do it too

SDM · Post by **SDM** » Mon Nov 13, 2006 9:00 am

Also should mention the dimed presence pot effect goes away at low PPIMV volumes still, as that part is still feedback dependant. The cut control thus will only cut those upper frequencies at lower volumes. So if your problem with PPIMV's is too much of that high end at low volumes, it should work nicely for you. If you want more high end at low PPIMV volumes, it won't help with that.

rockstah · Post by **rockstah** » Mon Nov 13, 2006 9:06 am

SDM wrote:Also should mention the dimed presence pot effect goes away at low PPIMV volumes still, as that part is still feedback dependant. The cut control thus will only cut those upper frequencies at lower volumes. So if your problem with PPIMV's is too much of that high end at low volumes, it should work nicely for you. If you want more high end at low PPIMV volumes, it won't help with that.

makes sense to me.

novosibir · Post by **novosibir** » Mon Nov 13, 2006 1:50 pm

SDM wrote:Yeah just the 10K (under the 470 ohm in the PI) that's already gonna be jumpered over to your NFB resistor on the board.

That fragment is called 'tail resistor' - but not to confuse with another 'tail' of you guys

Larry

novosibir · Post by **novosibir** » Mon Nov 13, 2006 2:06 pm

Should be still added to the upper discussion:

Not only a PPIMV is affecting the feedback loop and therefore the presence control in the power stage, also the feedback controls which are named 'depth', 'resonance', 'reactance', 'focus', aso. are affecting this!

The more you crank the depth/reactance control, the more you lessen the feedback in the power stage - and the more you worsen the effectiveness of the presence control.

Therefore it's as inevitable, to bypass the 'bottom resistor' in the PI's cathode tail - the 4.7K - with the usual .1 presence cap! means, you're first setting the usual presence to 10 - dimed!

And then - as Steve already said above

- go from one PI's plate (there, where the fizzy cap is located) to a (my suggstion) .0022 cap, further into a 250K log pot's (my suggestion) or into a 1M log pot's output lug - and from the wiper's lug to the other PI's plate. That's like a loop around the PI's plates - like seen on this photo from my DINO amp:

http://www.larry-amplification.de/dino9" onclick="window.open(this.href);return false; ... 001-01.jpg

and your 'new' presence control is done and properly working, independent from your PPIMV's setting or a depth/reactance setting

Larry

rockstah · Post by **rockstah** » Mon Nov 13, 2006 2:19 pm

novosibir wrote:Should be still added to the upper discussion:

Not only a PPIMV is affecting the feedback loop and therefore the presence control in the power stage, also the feedback controls which are named 'depth', 'resonance', 'reactance', 'focus', aso. are affecting this!

The more you crank the depth/reactance control, the more you lessen the feedback in the power stage - and the more you worsen the effectivity of the presence control.

Therefore it's as inevitable, to bypass the 'bottom resistor' in the PI's cathode tail - the 4.7K - with the usual .1 presence cap! eans, you're first setting the usual presence to 10 - dimed!

wow - i will do this... eventually - thanks Larry!

And the - as Steve already said above - go from one PI's plate (there, where the fizzy cap is located) to a (my suggstion) .0022 cap, further into a 250K log pot's (my suggestion) or into a 1M log pot's output lug - and from the wiper's lug to the other PI's plate. That's like a loop around the PI's plates - like seen on this photo from my DINO amp:

http://www.larry-amplification.de/dino9 ... 001-01.jpg

and your 'new' presence control is done and properly working, independent from your PPIMV's setting or a depth/reactance setting

Larry

zaphod777 · Post by **zaphod777** » Tue Nov 14, 2006 3:31 pm

i posted very detailed pics of this master which is ken fishers type 2 found in the trainwreck pages. and with the help of Larry again, wired it up correctly.
further more the two 2.m resistors DO NOT replace the 220k's on the board - its the pot that does that.
the 2.2m resistors again safe guard if the pot fails and also makes it all add up to around 223k when dimed as if it wasnt in the circuit at all.
something the previous master volume didnt do!

Can I just replace the dual 1m pot with 250k, add the 2.2m resistors, and remove the two (220k)150k's in my Marshall 4140 combo. I believe it already has a ppimv. Just not sure if its exactly the same as the version your tweaking.

Tried to post a pic of just that section of my schematic, havent figured out how to do that just yet.
A link to the full schematic.
http://www.drtube.com/schematics/marshall/4140.gif

Much Thanks!!