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

Eoin · Post by **Eoin** » Mon Jan 23, 2006 8:42 am

novosibir wrote:The PPIMV usually is added in parallel to the stock bias feed resistors.

Sorry, I meant parallel with respect to the PI plates and the grid resistors... I think.

In the diagram above the pot is connected so that as the resistance between the two sides of the PI is reduced, the resistance between the PI and the grids resistors of the EL34s is increased. Would it not still work if the coupling caps were still connected to the pairs of 1k5/5k6 grid resistors as per normal - and a split from the coupling caps was connected to the wipers of the dual pot while one side of th pot was connected to the point between the two bias resistors?

novosibir · Post by **novosibir** » Mon Jan 23, 2006 9:05 am

Eoin wrote:Would it not still work if the coupling caps were still connected to the pairs of 1k5/5k6 grid resistors as per normal - and a split from the coupling caps was connected to the wipers of the dual pot while one side of th pot was connected to the point between the two bias resistors?

Shure, that would work, but it would sound worse than the in this thread described solution and still worse, the more you'd crank the pot down.

There still are some other solutions to make a PPIMV, but all sound worse than the in this thread described solution, called "Rich Mod".

The simplest solution - like Matchless does it - would be simly a single 1 meg pot wired as a rheostat between both sides after the coupling caps, but when you've heared it cranked down, you'd quickly throw it out again

Larry

Eoin · Post by **Eoin** » Mon Jan 23, 2006 10:16 am

novosibir wrote:Shure, that would work, but it would sound worse than the in this thread described solution and still worse, the more you'd crank the pot down.

Ah... fair enough.

daniel · Post by **daniel** » Fri Jan 27, 2006 1:40 pm

Couldn't you just run 2 220k resistors in series since its hard to find 400kohm resistors?

MacGaden · Post by **MacGaden** » Sat Jan 28, 2006 6:51 am

If you wanted to put the PPIV master where the prescence was, and move prescence to one of the speaker jacks, what about lead dress ?
Is

Bainzy · Post by **Bainzy** » Sat Jan 28, 2006 7:20 am

My PPIMV is in the presence hole, but I've had no noise problems whatsoever. Maybe that's because I took Larry's advice and use shielded cable for all the wires leading to it.

Billy Batz · Post by **Billy Batz** » Sat Jan 28, 2006 9:44 am

MacGaden wrote:If you wanted to put the PPIV master where the prescence was, and move prescence to one of the speaker jacks, what about lead dress ?
Is´nt the wire to the prescence pot one of the more sensitive ones to pick up noise and cause squeals and hum ?

TIA

No its not sensitive, other wires are sensitive to it. All the wires carrying the AC audio signal. Any wire to and from a volume and tone pot, and the wires to the grids of the all tubes. You may actually be safer were the jack is on the back.

Guest · Post by **Guest** » Thu Feb 02, 2006 5:13 pm

As you turn down the master aren't you shorting out the 220K resistors?? Wouldn't that mess with the bias?? How about putting another set of coupling caps on the wipers?
stew

novosibir · Post by **novosibir** » Thu Feb 02, 2006 6:01 pm

Anonymous wrote:As you turn down the master aren't you shorting out the 220K resistors??

YES!

Anonymous wrote:Wouldn't that mess with the bias??

NO!

Anonymous wrote:How about putting another set of coupling caps on the wipers?

No need for that additional high-pass-filter, it doesn't make your sound better

!

Larry

joe G · Post by **joe G** » Mon Feb 06, 2006 2:22 pm

I'd REALLY like to see pics of this done to a PCB 1959 or 1987!

sam · Post by **sam** » Mon Feb 06, 2006 2:37 pm

joe G wrote:I'd REALLY like to see pics of this done to a PCB 1959 or 1987!

PPIMV with cascaded inputs

cheers

sam

Bainzy · Post by **Bainzy** » Mon Feb 06, 2006 2:43 pm

Nice clean job there Sam. That's exactly how it should be done for optimum noise free performance.

wilder · Post by **wilder** » Wed Feb 22, 2006 4:59 pm

Here's a pic of a a 1973 PCB installation:

Chris

MacGaden · Post by **MacGaden** » Wed Feb 22, 2006 5:03 pm

Thanks, Wilder (And wellcome ) !

I started this thread to collect as much info about the PPIMV as possible, because it was spread all over the place.

With your submission I think it is complete. Thanks for your contribution.

gnugear · Post by **gnugear** » Fri Feb 24, 2006 11:24 am

I replaced my dual 500k alpha with a dual 500k PEC pot and it actually improved the overall sound by opening up the tone. With the alpha it was kind of boxy and less airy. I was a bit skeptical at first but did it based on some other reports that it helped change the tone.

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

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