friedman post phase master design

[psychodave]

Someone posted a clearer photo of the Suhr on TGP today

View attachment 389464

What value pot?

 

[psychodave]

Someone posted a clearer photo of the Suhr on TGP today

View attachment 389464

Looks exactly like what syscokid posted. Assuming the 250k pot is correct.

 

[iff]

What value pot?

They didn't say

Looks exactly like what syscokid posted. Assuming the 259k pot is correct. View attachment 389471

Yeah, just with 1.1M resistors instead of 2.2M

 

[harddriver]

Here's what 1% Metal Film resistor color bands for 220K 1M 1.1 M 1.2M and 2.2M

220K = Red Red Black Orange Brown
1M= Brown Black Black Yellow Gold and/or Brown Black Green Yellow Red
1.1M= Brown Brown Green Brown
1.2M= Brown Red Green Brown
2.2M= Red Red Black Yellow Brown


The 2.2 Meg appears to be the PI grid leak resistors on the Suhr SL68 board from that pic. Since they are not mounted between the input lug and the wiper are they still serving as compliance resistors to reference the 250K pot to 224K and also function as a safety in case the pots wipers go bad as they do in the oriignal Lar/Mar Type II. I dunno.....but I can tell you they aren't 220K.

So technically Dave Friedman isn't lying when he told that guy it's a Lar/Mar PPIMV... it's configuration is different.

Psychodave.... there should be a black ink marking on the Alpha pot metal case showing what value it is. Could your friend have a look and see if he can see it, he may need a mirror or take the pot out of the chassis to flip it over?

 

[psychodave]

Here's what 1% Metal Film resistor color bands for 220K 1M 1.1 M 1.2M and 2.2M

220K = Red Red Black Orange Brown
1M= Brown Black Black Yellow Gold and/or Brown Black Green Yellow Red
1.1M= Brown Brown Green Brown
1.2M= Brown Red Green Brown
2.2M= Red Red Black Yellow Brown


The 2.2 Meg appears to be the PI grid leak resistors on the Suhr SL68 board from that pic. Since they are not mounted between the input lug and the wiper are they still serving as compliance resistors to reference the 250K pot to 224K and also function as a safety in case the pots wipers go bad as they do in the oriignal Lar/Mar Type II. I dunno.....but I can tell you they aren't 220K.

So technically Dave Friedman isn't lying when he told that guy it's a Lar/Mar PPIMV... it's configuration is different.

Psychodave.... there should be a black ink marking on the Alpha pot metal case showing what value it is. Could your friend have a look and see if he can see it, he may need a mirror or take the pot out of the chassis to flip it over?

I'm red/green colorblind. True story...

 

[harddriver]

I'm red/green colorblind. True story...

The Brown and Green are hard to see on those blue 1% metal films anyway but the the resistors Suhr is using is definitely 2.2Meg and the standard carbon films that Friedman is using also appear to be 2.2Meg. So the only outlier is what value the dual pot is......I would venture to guess 250K either Audio log or Linear if it is indeed a Lar/Mar implemented differently.

 

[jski59]

I have an original SL67, do you guys know if could just rewire the master using the existing mv double pot?

I’ve been debating trying to mod it to mk2 specs myself…it’s cool that Suhr will do it, but I’d prefer to mount the added switches to the back and keep it stock looking.

 

[RealAmpsAreDead]

The Brown and Green are hard to see on those blue 1% metal films anyway but the the resistors Suhr is using is definitely 2.2Meg and the standard carbon films that Friedman is using also appear to be 2.2Meg. So the only outlier is what value the dual pot is......I would venture to guess 250K either Audio log or Linear if it is indeed a Lar/Mar implemented differently.

it is a 250k (and 2M2 resistors) - I have that info from that German guy on YT who analyzed the amp - no idea if log or linear.

 

[GlideOn]

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

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?

Yes, I have installed several LarMar over the years and have typically used the 2.2M in parallel with the 250k pot. Even put one in a 130w Fender UL Twin, but that one was a Dual 100k with 2.2M in parallel and had a crap ton shielded wire wrapping around 1/3 of the amp - not the most graceful install, but it is solid. Extremely useful for that amp with its ginormous headroom on tap.

The pot value and consequential paralleling resistors can be of any value so as long as it is within the max grid lead rating of the power tubes within the circuit. Personally I don't hear too dramatic a difference of the pot value, moreso the circuit preceding it. It's all a part of the sum of the whole. 220k is just a popular value carried from many, many designs and generally strikes a good balance of gain and clarity.

I'm not surprised though if there's some variance in the PI section to tame the gain a bit. It can get hairy and tubby in some amps. The Dirty Shirley/Twin Sister amps is such an example - they have a 470k coming off one of the PI Anodes to ground, but those also have a 220k in their V1 Anode pushing the gain up a bit.

However, I got the word from Mr Friedman himself, just so there's zero doubt:

 

[harddriver]

Yes, I have installed several LarMar over the years and have typically used the 2.2M in parallel with the 250k pot. Even put one in a 130w Fender UL Twin, but that one was a Dual 100k with 2.2M in parallel and had a crap ton shielded wire wrapping around 1/3 of the amp - not the most graceful install, but it is solid. Extremely useful for that amp with its ginormous headroom on tap.

The pot value and consequential paralleling resistors can be of any value so as long as it is within the max grid lead rating of the power tubes within the circuit. Personally I don't hear too dramatic a difference of the pot value, moreso the circuit preceding it. It's all a part of the sum of the whole. 220k is just a popular value carried from many, many designs and generally strikes a good balance of gain and clarity.

I'm not surprised though if there's some variance in the PI section to tame the gain a bit. It can get hairy and tubby in some amps. The Dirty Shirley/Twin Sister amps is such an example - they have a 470k coming off one of the PI Anodes to ground, but those also have a 220k in their V1 Anode pushing the gain up a bit.

However, I got the word from Mr Friedman himself, just so there's zero doubt:

I have installed quite a few Lar/Mar's as well. With the 2.2M mounted in the PI grid leak positions and the pot wired in parallel instead of in series the 2.2M resistors now essentially are bridging from the input lug to input lug and the wipers are connected via the buss wires to the bias lug to where the bias is connected so this configuration is quite different to the original Lar/Mar. I guess the 2.2M are still providing some compliance and safety functions as well which is my main concern, but if it's good enough for John Suhr and Dave Friedman I'll probably try it out again this time with the 2.2.Megs in place of the 220K PI grid leak resistors and see if it is any better than my trusty Lar/Mar Type II.

This is what John Suhr says about the new SL68MKII and the new Master Volume:

Fat-Cap, Mid-Boost & 3-Way Bright Switches​

Fat-Cap Switch: One of the only tweaks found on a very famous amp John worked on in the 80’s, the Fat-Cap, adding low-end punch and bass that’s perfect when using the ‘Treble’ channel. In the original SL series, the ‘Fat’ cap was always in the circuit. This switch allows you to remove the Fat-Cap to get closer to a ‘true’, stock vintage amp.

Mid-Boost Switch: Dial in the perfect amount of midrange punch to cut through the mix. The Mid-Boost give a bit more gain to the phase inverter and a subtle lift to the tonestack, boosting the gain to the mid range. Most usefull when dimeing the controls.

3-Way Bright Switch: Add brilliance and sparkle to your tone, with clarity and presence. This switch allows you to choose between 3 different values, ‘Off’ is the original SL series, all-the-way bright which is the stock value found in vintage amps and a middle position that is somewhere in between.


Say goodbye to the need for external attenuators. Our redesigned Master Volume circuit gives you total control over your amp’s output, preserving your tones unique character, whether you’re in a bedroom jam or commanding the stage. This type of master volume control is highly effective at transparently controlling the output of the amp. When the control is at 10, it is completely transparent and out of the circuit. Start turning it down, and the amps volume can be reduced all the way to whisper levels.

 

[harddriver]

These pictures showed up on TGP recently.....

 

[GlideOn]

It's probably likely that most of us enthusiasts who don't have factories printing out exacting PCBs will just continue to wire them in the classic point-to-point fashion.

It's really hard to improve upon the LarMar design except perhaps adding variable NFB, adjust the PI section to taste.

 

[harddriver]

It's probably likely that most of us enthusiasts who don't have factories printing out exacting PCBs will just continue to wire them in the classic point-to-point fashion.

It's really hard to improve upon the LarMar design except perhaps adding variable NFB, adjust the PI section to taste.

I hear ya.... I have been happy with my Lar/Mar for many years in my 72 SL. I had pulled my old Lar/Mar since I was already installing new filter caps.bias caps and some missing Iskras with new ones in my 72 to try this new master deisgn out originally installed this new configuration with 220K's when we thought that's what was going on and it was a fail soundwise and I re-installed a new Lar.Mar immediately.

I have some 1 watt 2.2M 1% metal films coming so I will install this new configuration again and see how it compares to John Suhr's glowing description.

Here's what it looked like with the 220K, there was no volume taper and it had some weird artifacts and it was harsh. I have since moved the Presence pot to the old polarity switch hole and re-installed a new Lar/Mar Type II in the presence pot location with shielded wire after the tryout of this new configuration failed with the 220K' as we now know are 2.2M.

 

[GlideOn]

I hear ya.... I have been happy with my Lar/Mar for many years in my 72 SL. I had pulled my old Lar/Mar since I was already installing new filter caps.bias caps and some missing Iskras with new ones in my 72 to try this new master deisgn out originally installed this new configuration with 220K's when we thought that's what was going on and it was a fail soundwise and I re-installed a new Lar.Mar immediately.

I have some 1 watt 2.2M 1% metal films coming so I will install this new configuration again and see how it compares to John Suhr's glowing description.

Here's what it looked like with the 220K, there was no volume taper and it had some weird artifacts and it was harsh. I have since moved the Presence pot to the old polarity switch hole and re-installed a new Lar/Mar Type II in the presence pot location with shielded wire after the tryout of this new configuration failed with the 220K' as we now know are 2.2M.

What was the value(s) of the dual pot you used?

I've noticed pots with 15k or more difference start to get those artifacts when down low. I currently have one with less than 4k difference an the sound is super smooth all the way to a low trickle volume.