friedman post phase master design

[Suckseeder]

I have a Friedmann Plexi on the bench. Close to this but 100n
Coupling Caps ,100pf snubber

 

[RealAmpsAreDead]

I have a Friedmann Plexi on the bench. Close to this schematic, but single 250k pot cross line MV!
Coupling Caps .1 , 100pf snubber , 2M2 bias resistors



View attachment 457270

Are you sure it‘s not a dual gang pot?

 

[RealAmpsAreDead]

Absolutely, I was surprised too

Weird…How exactly is it wired then?

 

[Suckseeder]

Look at the MVC pot, same size like the others. 2 core with shielding

 

[Suckseeder]

Weird…How exactly is it wired then?

 

[Suckseeder]

The pot reduces resistance between the lines. Because the two audio signals are perfectly mirrored (180 degrees out of phase), they cancel each other out. This cleanly starves the power tubes of the signal, dropping the volume.

 

[MacMeda]

Can this be installed in a 1987X

 

[Suckseeder]

Can this be installed in a 1987X

Yes

 

[MacMeda]

Yes

I am not a tech but really could use an mv in my 1987.
Is this all I would need to show a competent tech ?
Do you feel this is a better option to the Rich or Lamar ( or anything else)
Thanks
In San Diego

 

[FourT6and2]

I am not a tech but really could use an mv in my 1987.
Is this all I would need to show a competent tech ?
Do you feel this is a better option to the Rich or Lamar ( or anything else)
Thanks
In San Diego

If a competent tech doesn't already know what Lar/Mar PPIMVs or this version are... they are not a competent tech and I would find someone else. This stuff has been around for 40-50 years. If they need a customer to tell them what it is, run.

 

[MacMeda]

If a competent tech doesn't already know what Lar/Mar PPIMVs or this version are... they are not a competent tech and I would find someone else. This stuff has been around for 40-50 years. If they need a customer to tell them what it is, run.

The guy I just spoke to asked if 1987X was a car.
Then I asked what type of MV he liked to use and he said “ The best” , I ran

 

[RealAmpsAreDead]

If a competent tech doesn't already know what Lar/Mar PPIMVs or this version are... they are not a competent tech and I would find someone else. This stuff has been around for 40-50 years. If they need a customer to tell them what it is, run.

I think his question was just what PPIMV is the best option in the end. Interesting question. Did someone compare the Friedman Plex one to the others?

 

[MacMeda]

I think his question was just what PPIMV is the best option in the end. Interesting question. Did someone compare the Friedman Plex one to the others?

Yes, thank you.
Also, I’m not looking for bedroom volumes just to knock it down a bit.

 

[harddriver]

Yes, thank you.
Also, I’m not looking for bedroom volumes just to knock it down a bit.

The traditional Lar/Mar PPIMV works well for knocking it down a bit and is tried and true. Supposedly the PPIMV used in the Plex and Suhr SL68 is a slight improvement/evolution over the Fischer/Lar/Mar PPIMV.

Both PPIMV designs will negate your negative feedback at very very low(bedroom) levels there is no way around that. But if you accept their limitations they can be used to great effect. You can use an attenuator in conjunction with your PPIMV and get some/most of your NFB back at about 30-50% volume level and then you only need to knock off -4 or -8 of DB using the attenuator before the Fletcher/Munson curves take effect can get you lower volume levels. ie: loud comfrotable bedroom levels with a tube amp.

If you need absolute Bedroom levels then you will need to run the amp into a Suhr reactive load or Suhr reactive load IR or something similar and reamp with another power amp and or use IR responses reamped through your studio montitors.

 

[harddriver]

Can this be installed in a 1987X

Yes

 

[MacMeda]

The traditional Lar/Mar PPIMV works well for knocking it down a bit and is tried and true. Supposedly the PPIMV used in the Plex and Suhr SL68 is a slight improvement/evolution over the Fischer/Lar/Mar PPIMV.

Both PPIMV designs will negate your negative feedback at very very low(bedroom) levels there is no way around that. But if you accept their limitations they can be used to great effect. You can use an attenuator in conjunction with your PPIMV and get some/most of your NFB back at about 30-50% volume level and then you only need to knock off -4 or -8 of DB using the attenuator before the Fletcher/Munson curves take effect can get you lower volume levels. ie: loud comfrotable bedroom levels with a tube amp.

If you need absolute Bedroom levels then you will need to run the amp into a Suhr reactive load or Suhr reactive load IR or something similar and reamp with another power amp and or use IR responses reamped through your studio montitors.

Good info, that explains a lot.
I felt like -8 db was the max.
Thanks

 

[harddriver]

Good info, that explains a lot.
I felt like -8 db was the max.
Thanks

You also need to take into account when you are not driving the speakers with some volume will also change the tone and how our human ears hear things.

For me using an attenuator beyond -8DB tends to sqaush the tone and that mostly due to the Fletcher Munson curves and how our ears perceive it.

The Suhr reactive load is also a nice unit and has plenty of power handling capability up to a 100 watt amp according to Suhr. I slave my 68 plexi with two tubes pulled to run it at 50 watts cranked and the Suhr doesn't even get warm so it should be able to handle up to the claimed 100 watts and it does sound better than my purely resistive loads I've used in the past.

Either way the original Lar/Mar or the new version of the Lar/Mar(used in the plex/suhr SL68 MKII) will sound great and do what you want.

 

[Suckseeder]

I stand corrected! Having the amp for only 2 hours on the bench, the size of the MV pot deceived me to believe it‘s a single pot.
After a discussion with RealAmpsAreDead, I‘m now convinced it must be a dual gang pot. So here you go, this is a new version of the Lar/Mar design, wired as a Rheostat ,not a voltage divider. Sorry for the confusion champions