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

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

Post by danman » Mon Nov 18, 2019 6:25 pm

@bmwfreq...you can replace the nfb resistor with a potentiometer of a lower value than the resistor. Wire it as a variable resistor and not a voltage divider. This will allow you to dial in a bit of extra nfb voltage when you turn the ppimv down. You will want to add a small resistor in series with the pot to prevent you from dialing in too much nfb. From memory I believe that I have used a 10k (linear) pot with a 5k series resistor with good results.

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

Post by novosibir » Mon Nov 18, 2019 8:00 pm

The NFB resistor value has to be at least twice of the resistor's value below the slope R to ground, otherwise the poweramp will oscillate
The fault almost always is sitting in front of the amp :wink:

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

Post by djseban » Wed May 27, 2020 10:40 pm

Hey there,

In my 2203 I recently moved PPIMV to the front (left from Presence pot above the filter cap with 56K resistors on it), but since this I experience problems with oscillation - when I slowly increase PPIMV pot, the amp starts to do these windy noises/crackling and sometimes pops. Usually I don't go above 25-30%. Does anyone have idea on what might be the culprit? I use very fine shielded wire. I also tried relocating the PPIMV pot to the back - problem totally gone, dimed the pot without an issue. I'd be grateful for any insight on this. I thought about interference with filter cap and presence pot, but I am not sure, maybe the wires going to swampers (5k6) on EL34s are too long?
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Re: The PPIMV (Post-PI-Master-Volume) thread.

Post by danman » Thu May 28, 2020 6:34 pm

The wire leading from the board to the presence pot can cause problems in a stock amp if it's not routed properly. It may be that your PPIMV pot being so close to the presence pot is causing the issue. It's weird since you did use shielded wire but that's the only thing that I can think of.

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

Post by ESR » Fri May 29, 2020 11:32 am

djseban wrote:
Wed May 27, 2020 10:40 pm
Hey there,

In my 2203 I recently moved PPIMV to the front (left from Presence pot above the filter cap with 56K resistors on it), but since this I experience problems with oscillation - when I slowly increase PPIMV pot, the amp starts to do these windy noises/crackling and sometimes pops. Usually I don't go above 25-30%. Does anyone have idea on what might be the culprit? I use very fine shielded wire. I also tried relocating the PPIMV pot to the back - problem totally gone, dimed the pot without an issue. I'd be grateful for any insight on this. I thought about interference with filter cap and presence pot, but I am not sure, maybe the wires going to swampers (5k6) on EL34s are too long?
I hope Danman's response it helpful to you. On a different note, I've been curious for a while about how a PPIMV would sound on a Master Volume circuit. So, am I correct in assuming that you have your PPIMV wired in as an *additional* master on top of the original stock master on the front panel? In other words, you've got a preamp gain knob, an original master volume control, AND a PPIMV... yes?

So, if this is the case, I've always thought that you can use the preamp gain knob to adjust how much "sizzle" you want, while using the "stock" master volume to slam your phase inverter with the full onslaught of the preamp... then use your PPIMV to dictate overall volume output of the amp...

Is that how yours works? Good results? Details?

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

Post by novosibir » Fri May 29, 2020 12:00 pm

@ djseban - you haven't specified, what kind of PPIMV you've installed, what pot value.
Keep in mind, that a PPIMV's pot value of 2*500K is much more sensitive and hence much more prone for cross talk or picking up stray fields than a 2*250K pot like i.e. the LarMar PPIMV

And yes, keep an eye to the routing of the violet Presence wire and keep it far away of the PPIMV's wiper and their cable as well as far away of the OT's primaries.
The fault almost always is sitting in front of the amp :wink:

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

Post by djseban » Sun Jun 07, 2020 1:49 pm

ESR wrote:
Fri May 29, 2020 11:32 am
I hope Danman's response it helpful to you. On a different note, I've been curious for a while about how a PPIMV would sound on a Master Volume circuit. So, am I correct in assuming that you have your PPIMV wired in as an *additional* master on top of the original stock master on the front panel? In other words, you've got a preamp gain knob, an original master volume control, AND a PPIMV... yes?

So, if this is the case, I've always thought that you can use the preamp gain knob to adjust how much "sizzle" you want, while using the "stock" master volume to slam your phase inverter with the full onslaught of the preamp... then use your PPIMV to dictate overall volume output of the amp...

Is that how yours works? Good results? Details?
Yeah, that's basically how it's done - regulating the signal coming out from PI to power amp, everything before that can be as stock as it gets. Personally, preamp-wise, I have hot-rodded 2203/#34/#36 modes in preamp and I can say PI distortion is vital for attaining the tone I want. Of course, having master on 7 and PPIMV rolled to 3 won't sound like full-blown master on 7, nevertheless it's still better than having no PPIMV. Recently I played on my friend's stock 2203 clone with MV and Gain dimed and I'd say it was one step away from being considered high-gainish.
novosibir wrote:
Fri May 29, 2020 12:00 pm
@ djseban - you haven't specified, what kind of PPIMV you've installed, what pot value.
Keep in mind, that a PPIMV's pot value of 2*500K is much more sensitive and hence much more prone for cross talk or picking up stray fields than a 2*250K pot like i.e. the LarMar PPIMV

And yes, keep an eye to the routing of the violet Presence wire and keep it far away of the PPIMV's wiper and their cable as well as far away of the OT's primaries.
Hi Larry, I've got LarMar type installed. I also didn't specify that my 2203 is a clone. I resolved the issue by eliminating everything in equation: I switched OT and choke with my other amp and basically rewired entire amp with new components (including filter caps) - the issue was still present and was random af. Once I moved PPIMV back to the backplate the issue stopped, but shortly after it continued to do the noises. I've got 2 quadros of JJ EL34s on which I always tested my amp and recently I borrowed EHs from my friend and it turns out my JJs were in the end of their lifespan. To get JJs to 34mA of resting current I had to set bias to about -38V, when I put in EHs I had to dime bias pot to -45V, and even with that the weakest tube had like 38mA) - I played the amp for a good hour on EHs and there were no issues whatsoever. Turns out that entire thing with moving PPIMV to frontplate and amp starting to crackle/oscillate was a coincidence.
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Re: The PPIMV (Post-PI-Master-Volume) thread.

Post by ESR » Thu Jul 30, 2020 3:21 pm

djseban wrote:
Sun Jun 07, 2020 1:49 pm
Hi Larry, I've got LarMar type installed. I also didn't specify that my 2203 is a clone. I resolved the issue by eliminating everything in equation: I switched OT and choke with my other amp and basically rewired entire amp with new components (including filter caps) - the issue was still present and was random af. Once I moved PPIMV back to the backplate the issue stopped, but shortly after it continued to do the noises. I've got 2 quadros of JJ EL34s on which I always tested my amp and recently I borrowed EHs from my friend and it turns out my JJs were in the end of their lifespan. To get JJs to 34mA of resting current I had to set bias to about -38V, when I put in EHs I had to dime bias pot to -45V, and even with that the weakest tube had like 38mA) - I played the amp for a good hour on EHs and there were no issues whatsoever. Turns out that entire thing with moving PPIMV to frontplate and amp starting to crackle/oscillate was a coincidence.
djseban--

I'm finally building myself a 2204 (JCM800 layout). I've planned to put a PPIMV on it since back before I bought all my parts. (I've installed the LarMar PPIMV on my Super Lead as well as my 1987. Love it.) I like the PPIMV on my plexi's... Very excited to utilize it on the 2204.

Wanted to ask you--did you do the stock LarMar PPIMV values when you put it on your 2203? (dual gang 250k log pot, 2.2M resistors), with the 220k resistors removed...?

Also, to you or to anyone else who can answer confidently--the 5.1k grid resistors on pin 5 of each power tube should stay in place, correct?

Thanks!
-ESR

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

Post by novosibir » Thu Jul 30, 2020 4:29 pm

ESR wrote:
Thu Jul 30, 2020 3:21 pm
Also, to you or to anyone else who can answer confidently--the 5.1k grid resistors on pin 5 of each power tube should stay in place, correct?
They are 5.6K and yes they should stay as an oscillation protection
The fault almost always is sitting in front of the amp :wink:

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