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

rockstah · Post by **rockstah** » Thu Jun 08, 2006 5:44 pm

SDM wrote:
rockstah wrote:
Kuli wrote:Hi guys!

Will one of these pots do the job?

http://elektronik-lavpris.dk/eshop/show ... O_ID=95602

I know it's a 470K pot and the recommended pot is a 500K. What effect will a 470K have compared to a 500K?
it will be 30k away from 500k. when your volume is up full it will have 470k resistence. 30k away from away from being on 10 so to speak.
When you slap 500K's acrossed your 220K bias feed resistors as in a very popular version of the PPIMV your drop their value to 152.8K when the pot is cranked. With a 470K dual pot they drop to about 149.8K, only 3K difference. Either leaves you 70K short of 220K at least.

thanks Steve!

pongo316 · Post by **pongo316** » Sat Oct 21, 2006 5:02 am

So Idealy you would want to have the resistors & pot = 220K (when pot is wide open) ?

So I would need to play around with the resistor values to get this match.

Does any one know the dirference in Mod I that uses the dule 1meg pot v's ModII

Just hooked up the Mod II on my build (not that impressed)

I did rebias the amp with pot (PIMV master)maxed out (after I installed it) might have to muck around with the fixed resistors (HMM maybe change them with two pots and fine tune it)

The other thing I noticed when turning master down the out put tubes start to glow more on the plates (i take it this is normal)

rockstah · Post by **rockstah** » Mon Oct 30, 2006 12:49 pm

so im trying to get my head around this master volume.

it replaces the 220k's on the board. is there danger of having it on zero and having no resistence here in the curcuit?

im confused as to which side of the pot is fornt and whichs back

anyone tried this master volume?

novosibir · Post by **novosibir** » Mon Oct 30, 2006 1:51 pm

Don't use a dual 100Klin as shown, but a dual 250Kaudio - then put a 2.2M resistor from each wiper to each output (where the bias voltage is supplied), then you avoid tube death after a possible wiper failure.

Larry

rockstah · Post by **rockstah** » Mon Oct 30, 2006 1:52 pm

novosibir wrote:Don't use a dual 100Klin as shown, but a dual 250Kaudio - then put a 2.2M resistor from each wiper to each output (where the bias voltage is supplied), then you avoid tube death after a possible wiper failure.

Larry

i was going to use a dual 250k lin pot. will that work?>

novosibir · Post by **novosibir** » Mon Oct 30, 2006 2:11 pm

that will make a loudness jump, but works

pongo316 · Post by **pongo316** » Mon Oct 30, 2006 3:55 pm

rockstah wrote:so im trying to get my head around this master volume.

it replaces the 220k's on the board. is there danger of having it on zero and having no resistence here in the curcuit?

im confused as to which side of the pot is fornt and whichs back

anyone tried this master volume?

What book is that from ?

rockstah · Post by **rockstah** » Mon Oct 30, 2006 4:17 pm

"a desktop reference of hip vintage guitar amps" by Gerald Weber. kendrick-amplifiers.com

novosibir · Post by **novosibir** » Mon Oct 30, 2006 4:22 pm

rockstah wrote:"a desktop reference of hip vintage guitar amps" by Gerald Weber. kendrick-amplifiers.com

But the 'Trainwreck Pages' from that book.

Larry

rockstah · Post by **rockstah** » Mon Oct 30, 2006 4:24 pm

novosibir wrote:
rockstah wrote:"a desktop reference of hip vintage guitar amps" by Gerald Weber. kendrick-amplifiers.com
But the 'Trainwreck Pages' from that book.

Larry

yes indeed - it has atranwreck section in the book.
Larry talk to me more about the 250k dual pot and the 2.2m resistors - not sure where they go

novosibir · Post by **novosibir** » Mon Oct 30, 2006 4:41 pm

rockstah wrote:Larry talk to me more about the 250k dual pot and the 2.2m resistors - not sure where they go

Ok - step by step:

- The coupling caps are connected to the input lug's of the pot
- The bias supply voltage (which usually feeds the both 220K) is connected to the output lug's of the pot (of course to both)
- The pot's wipers are connected to the power tube's grids (or to their swamp resistors)
- Now simply solder each a 2.2M on each section of the pot from the wiper to the output lug - a small 1/4W resistor will do it

These are only for safety, because if the pot's wiper fails, then the output tube's grid is w/o bias voltage and will immediately jump over the Jordan.

But with the resistor applied and a failing wiper, although this side can't be regulated anymore, but nevertheless there's bias voltage on the output's grid - and the tube(s) will survive

Larry

rockstah · Post by **rockstah** » Mon Oct 30, 2006 4:50 pm

novosibir wrote:
rockstah wrote:Larry talk to me more about the 250k dual pot and the 2.2m resistors - not sure where they go
Ok - step by step:

- The coupling caps are connected to the input lug's of the pot
- The bias supply voltage (which usually feeds the both 220K) is connected to the output lug's of the pot (of course to both)
- The pot's wipers are connected to the power tube's grids (or to their swamp resistors)
- Now simply solder each a 2.2M on each section of the pot from the wiper to the output lug - a small 1/4W resistor will do it

These are only for safety, because if the pot's wiper fails, then the output tube's grid is w/o bias voltage and will immediately jump over the Jordan.

But with the resistor applied and a failing wiper, although this side can't be regulated anymore, but nevertheless there's bias voltage on the output's grid - and the tube(s) will survive

Larry

thanks Larry,

so these resistors will not effect tone? are they not input grid resistors are they? wont this change the pots value?

novosibir · Post by **novosibir** » Mon Oct 30, 2006 5:00 pm

rockstah wrote:so these resistors will not effect tone?

NO!

rockstah wrote:are they not input grid resistors are they? wont this change the pots value?

If the pot's value is exactly 250K, then dimed it drops to 224.49K

Larry

rockstah · Post by **rockstah** » Mon Oct 30, 2006 5:02 pm

novosibir wrote:
rockstah wrote:so these resistors will not effect tone?
NO!

rockstah wrote:are they not input grid resistors are they? wont this change the pots value?
If the pot's value is exactly 250K, then dimed it drops to 224.49K

Larry

great! so last the thing is, how did you come to the 2.2M value for the resistors being needed here?

Tonecat · Post by **Tonecat** » Tue Oct 31, 2006 8:27 am

So which method is better sounding? Using the 250k with no bias resistors and the 2.2M on each section of the pot, or a 500k pot with 400-430k bias resistors?