friedman post phase master design

[SmashingAtom]

Instead of a single pot 'combining' the two sides together in 'diffusion' you get the double pot 'irregularities' , again using the time old faction of symmetry 'ain't going to get you there' . Think about how important it is to the tone by equating the cost of the part. Thats the facts.

 

[jasonP]

A little detour but, no matter how you slice it, all of these PPIMV designs simply turn the fixed PI output resistors (bias splitters, aka grid leak resistors) into a variable resistor (pot). This is the reason some might notice certain hot-rodded amps sound louder or fuller or more meaty than another. For example, older Ceriatone Chupacabras used 87K, newer ones use 110K, the Yeti uses 120K, Fortin uses 150K, some Marshalls with 6550s used 150K, EL34s were 220K, etc. Care should be used when messing with these resistor values and/or using a PPIMV because the total resistance the tube grid can handle should not be exceeded. This INCLUDES any grid stoppers. Although I doubt anybody is gonna go highter than 220K + grid stoppers.

I've seen Suhr use 150k's and Fortin use 100-110k's in this spot quite a bit. Absolutely makes a big difference in feel.

 

[matttornado]

I just got around to trying this while doing some tweaks to a 2203 build I just did. I kept the 220k grid resistors and used test leads to temporarily hook it up. I used a 250k audio pot. I must say, it worked and sounded pretty good. I can't really compare it because all of my other experiences with all of the PPIMV types were with PLEXI circuits, not 2203s. I would love to try this with a PLEXI circuit leaving the 220k resistors in place.
I also tried the Cross Line with a PEC 1 meg pot and that sounded like shit.

Not sure if I will implement this or not, or if it will be useful with my 2203 because it's sounding pretty good as is with the master at about 2 for practice.

 

[GlideOn]

I actually emailed Dave about this not too long ago regarding the new Plex and he confirmed it was just a 250k dual pot with 2.2M safety resistors on the pot. Alpha pot, no PEC, nothing dramatic.

It just works.

Sorry if that's anticlimactic.

 

[matttornado]

I actually emailed Dave about this not too long ago regarding the new Plex and he confirmed it was just a 250k dual pot with 2.2M safety resistors on the pot. Alpha pot, no PEC, nothing dramatic.

It just works.

Sorry if that's anticlimactic.

That's a Larmar type. What we're discussing is different. His PLEX amp originally had a Larmar for a master so that's probably what he's referring to. What I tried sounded awesome and is not a Larmar type from what I understand.

 

[GlideOn]

That's a Larmar type. What we're discussing is different. His PLEX amp originally had a Larmar for a master so that's probably what he's referring to. What I tried sounded awesome and is not a Larmar type from what I understand.

Essentially what you are doing is not dissimilar from what is also known as a RichMod, which uses a 500k dual pot and leaves the 220k grid leaks on.

You're just using a lower value pot is all.

The LarMar more or less maintains the pot value (or paralleled resistor) value through out the sweep. It more or less emulates the amp at a steady grid leak resistance.

The RichMod effectively scales the grid leak resistance when using a higher pot value - higher when volume is low and progressively scales lower when the volume is high. It is technically a 'Variable Voltage Divider.'

Increased grid leak resistance as you know makes an amp sound fatter, juicier which is very helpful at lower volume and since high voltage isn't flowing as of yet, is safe for the power tubes.

Expect that's you're using a 250k pot, which means it scales even lower and leaner than RichMod. Especially for a high gain preamp, you may like this leaner power section tone more if you're playing at moderate volumes; the amp is likely tighter and clearer by comparison.

 

[matttornado]

I tried this again but blew the Mains fuse! So maybe I jumped the gun?

 

[harddriver]

I tried this again but blew the Mains fuse! So maybe I jumped the gun?

I tried this a couple of weeks ago and wired it according to those Suhr MKII pics that were floating around the internet. I was hoping for some improvement over the Lar/Mar. I used a 250 K Audio dual pot in parallel with the 220K PI grid resistors and the master did not perform better than my Lar/Mar Type II that was in the amp for over 10 years. Granted I had installed it in the old Polarity switch hole but all the leads were twisted super tight and installation was clean but it picked up alot of noise and the master was not smooth(the volume taper was not good) and it had more artifacts than my Lar/Mar so I installed another Lar/Mar and I am quite happy with that because it's reliable and I know what to expect performancewise. I did end up moving my Presence pot to the old polarity switch hole and installed the new Lar/Mar in the presence pot location with shielded wire and all my issues that I heard with this so called new PPIMV went away. I do like having the master volume up front for a change. Maybe I will revisit this new design again but for now I'm using what I know works.

Dave Friedman described the new master as shrinking the values of the 220K PI grid resistors and having a pot in parallel would techincally do that

Maybe my layout was faulty and it works better routed straight back to the back of the chassis.......I dunno.

I am guessing Suhr and DF are doing something different on top of what we can see in the pics to make this design work.

I did come across another Type II variant called the Frondelli PPIMV that Rob Robinette likes. I don't know if it works any better than the Lar/Mar but here's a layout of it.

 

[syscokid]

wired it according to those Suhr MKII pics that were floating around the internet. I was hoping for some improvement over the Lar/Mar. I used a 250 K Audio dual pot in parallel with the 220K PI grid resistors and the master did not perform better than my Lar/Mar

I also think that the Friedman’s Plex new MV is wired differently than the Suhr’s MkII MV. But the Suhr seems to have 2.2M’s instead of the 220K’s in the grid leak position on the circuit board. None of the pics I’ve seen of the Suhr are clear enough where I can positively confirm the value of those resistors.

 

[GlideOn]

I also think that the Friedman’s Plex new MV is wired differently than the Suhr’s MkII MV. But the Suhr seems to have 2.2M’s instead of the 220K’s in the grid leak position on the circuit board. None of the pics I’ve seen of the Suhr are clear enough where I can positively confirm the value of those resistors.

2.2M parallel to 250k = 224k

Close enough to 220k grid leak.

 

[harddriver]

2.2M parallel to 250k = 224k

Close enough to 220k grid leak.

Dave said in an interview that if the dual PPIMV pot went bad all that would happen is the amp would return to a stock normal Plexi just with no master volume control. That would not be possible if the PI grid leak resistors were 2.2M on the main circuit board.

The only reason Suhr and Dave Friedman would put this master in a production amp would be that it was an improvement over the standard Lar/Mar Type II that Suhr used in the SL68/SL67 Mark 1's.

As far as I can tell it is not a 250KA in parallel with 220K PI grid leak resistors judging from the results that I got. I was really disappointed in what I heard.

I'm sure eventually the details will leak out somewhere.

 

[GlideOn]

Dave said in an interview that if the dual PPIMV pot went bad all that would happen is the amp would return to a stock normal Plexi just with no master volume control. That would not be possible if the PI grid leak resistors were 2.2M on the main circuit board.

The only reason Suhr and Dave Friedman would put this master in a production amp would be that it was an improvement over the standard Lar/Mar Type II that Suhr used in the SL68/SL67 Mark 1's.

As far as I can tell it is not a 250KA in parallel with 220K PI grid leak resistors judging from the results that I got. I was really disappointed in what I heard.

I'm sure eventually the details will leak out somewhere.

They're physically installed on the board for practicality, they are still wired in parallel configuration to the 250k pot, which is also wired to the PCB.

Don't overthink it!

 

[GlideOn]

I tried this again but blew the Mains fuse! So maybe I jumped the gun?

Do you have the ground legs of the pot properly installed to the negative bias supply?

 

[harddriver]

Do you have the ground legs of the pot properly installed to the negative bias supply?

From what I could see from his pics he had it set up exactly like the Suhr MKII pics that were floating around.

They're physically installed on the board for practicality, they are still wired in parallel configuration to the 250k pot, which is also wired to the PCB.

Don't overthink it!

I fully understand the function of the 2.2M compliance safety resistors on the Lar/Mar and that the amp would still give the amps bias some reference in case the pot's wipers failed.

Now in this new configuration that Suhr/Friedman is using if the pot was to fail and if these PI grid leak resistors are 2.2M values that would not provide the standard 220K value of a stock amp as Dave Friedman described in his interview about the plex when asked about this new PPIMV master design. Dave also said he did not design this new master but has implemented it use and somehow John Suhr also is using it so they got this design from somewhere or someone.

So the variations of the Alpha dual pots that could be used is:
1 meg audio log or Linear
500K audio log or Linear
250K audio log or Linear

The other part of the equation is what value is the PI grid leak resistors. 220K, 1 M as some think or 2.2M?

Have you installed this master using the 2.2M PI grid leaks with a 250K audio log pot?

 

[harddriver]

In any case it won't be long before Nik at Ceriatone gets a plex and reverse engineers it since there is not patent on this design and Dave F and John Suhr either lifted the design or paid licensing fees to use it. In the plex it does not look a dual 250KA pot mounted to that PCB, their does not appear to be enough room for one but the two lead shielded wire does appear to be tapping the PI grid leak resistors like a Lar/Mar.

I think I see Red Red Black Gold on the PI grid leak values when I zoom in and that does not make any sense because the value would be 22 ohms, but in the pic the third band could possibly be green and that would make the value 2.2M.

Also noted that Friedman is using standard Carbon Film resistor with the standard four band color code and Suhr is using 1% metal film with a 5 band color code.

 

[RealAmpsAreDead]

There was a video by Krampe Amps (can't find it anymore) who analyzed the Plex amp and comments below.
He said it is a 250k stereo pot, 2M2 resistors and the two capacitors are 100n instead of 22n.

 

[harddriver]

There was a video by Krampe Amps (can't find it anymore) who analyzed the Plex amp and comments below.
He said it is a 250k stereo pot, 2M2 resistors and the two capacitors are 100n instead of 22n.

So if they are 2.2M on the circuit board then this is a variant of the traditional Lar/Mar then. Also since the 2.2M resistors are in no longer between the wiper and the input lug of the pot I would imagine they no longer act like a safety resistor if the wiper of the pot fails but this design must be somewhat safe since Suhr and Dave F installed it in production amps.

I guess the next item of interest would be if the Dual pot is a 250K liner or audio log pot?

 

[psychodave]

One of these days a friend of mine will stop by with his SL68. I’ll be sure to take lots of pictures.

 

[harddriver]

One of these days a friend of mine will stop by with his SL68. I’ll be sure to take lots of pictures.

Guys with the new MKII seem to think there is a big difference between the Lar/Mar and this newer implementation of it.

 

[iff]

Someone posted a clearer photo of the Suhr on TGP today