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

Post by tjohn1968 » Tue Jun 28, 2022 11:59 pm

I’m installing a Lamar MV in a new 100w build. I am also going to install a Zero Loss Loop. My chassis two sets of dual speaker jacks on the back panel. I was going to use the second set of speaker jack holes for the Zero Loss Loop since it fits in the already drilled holes. I have come up with two options for the location of the MV pot. In one of the other speaker jack holes or drilling a new hole where the voltage selector switch of I had one would go.

I would rather keep my two speaker jacks by not sure if putting the pot where the voltage selector would be is a good idea. Would it be OK to install the pot there?

Thanks!

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

Post by novosibir » Wed Jun 29, 2022 6:07 am

tjohn1968 wrote:
Tue Jun 28, 2022 11:59 pm
I would rather keep my two speaker jacks by not sure if putting the pot where the voltage selector would be is a good idea. Would it be OK to install the pot there?
Twist the secondary leads to the output selector switch and keep a respectful distance of at least one inch between them and the PPIMV leads, which also have to be twisted or shielded.
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 tjohn1968 » Wed Jun 29, 2022 8:55 am

novosibir wrote:
Wed Jun 29, 2022 6:07 am
tjohn1968 wrote:
Tue Jun 28, 2022 11:59 pm
I would rather keep my two speaker jacks by not sure if putting the pot where the voltage selector would be is a good idea. Would it be OK to install the pot there?
Twist the secondary leads to the output selector switch and keep a respectful distance of at least one inch between them and the PPIMV leads, which also have to be twisted or shielded.

Twist the secondary leads to the output selector switch and keep a respectful distance of at least one inch between them and the PPIMV leads, which also have to be twisted or shielded.
[/quote

Dang it I have already installed my output selector switch and don’t have the slack in my my wires to really put any good twist in them. I suppose this is always a good thing to do. This is only my second build and haven’t twisted them it doesn’t say anything about it in the Metro build instructions.

Anyway, is it too risky to put the MV pot in the area where the voltage selector would be then? If that’s the case then I will just move it back to a speaker output hole and learn something for my next build.

Thanks Larry!

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

Post by CoffeeTones » Wed Jun 29, 2022 5:06 pm

I find it helps to include the PPIMV bias wire within the twisting of the PPIMV secondary leads (all three twisted together). Unless you use a multi conductor, shielded wire instead of separate PPIMV leads. You could shield the OT secondaries by wrapping them with an insulated ground wire, with only one end attached to ground, along with the OT secondary ground, or just extend the OT secondary ground wire and wrap it along the length of the remaining, connected OT secondaries. The grounded wrap wire you make the shield out of, should be closely and snuggly coiled around the wires you are shielding.

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

Post by novosibir » Wed Jun 29, 2022 7:23 pm

CoffeeTones wrote:
Wed Jun 29, 2022 5:06 pm
Unless you use a multi conductor, shielded wire instead of separate PPIMV leads.
If you use shielded wires, then don't 'ground' the shield, but use it to run the negative bias voltage from the board to the PPIMV pot
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 uiovbged332 » Wed Jul 06, 2022 11:00 am

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