PRS Sonzera 20 Schematic

[bnwitt]

Hello everyone. 


I just picked up a 2020 PRS Sonzera 20 watt combo amplifier for my studio.  I read that it has two artificial heater grounds which adds some hum and also that the Mosfet effects loop adds some background hiss.  I am looking for a Schematic but PRS has told me they don't release them.  State secrets or something.  I would like to work on reducing noise in the amp and a schematic would sure make that easy.  Do any of you have any experience with this amplifier that you can offer?  I hope everyone is doing well.


Barry

[tubeswell]

First time I’ve heard of it.

Pretty stupid of them to make an amp and not release the schematic for servicing. Who do they take us for?

Have you opened it up yet?

[bnwitt]

Tubeswell,
It is their policy not to share documents.   I don't know why they think they've done something new with vacuum tubes.  I have the chassis out of the cabinet and on the bench.  Typical problems are bad rectifier diodes and grid resistors.  I don't see any overheating evidence and it doesn't look like it has a lot of run time.  The tubes are all original.  I'll post some pics this weekend.

[bnwitt]

See very blurry schem.

[shooter]

a schematic would sure make that easy.

State secrets

since they've conspired against you, time to bust out the scope, catch the hiss n hum in action, send them 8X12 glossy images and ask if they will accept an NDA to release the schematic.

If they say NO, explain how negative comments on the internet about what a suck AS..terics amp they make along with viral images.....
you're creative, be creative....


 

[sluckey]

See very blurry schem.

Any better?

     https://sluckeyamps.com/Sonzera20.png

[shooter]

Any better

i can only see maybe 100 places where hiss might hide 

[tubeswell]

DC heater filtering would be on my hit list

[bnwitt]

Any better?  Indeed!!  Thank you Steve.

[bnwitt]

a schematic would sure make that easy.

State secrets

since they've conspired against you, time to bust out the scope, catch the hiss n hum in action, send them 8X12 glossy images and ask if they will accept an NDA to release the schematic.

If they say NO, explain how negative comments on the internet about what a suck AS..terics amp they make along with viral images.....
you're creative, be creative....


 

  Shooter, you make me laugh.

[bnwitt]

DC heater filtering would be on my hit list

I see in Steve's schematic the two artificial Center Taps in the heater supplies.  One on the AC side and one on the DC side.  I can see the benefit of the DC heater supply on V2 the high gain channel but not on the V1 heaters.  Thoughts?  I'll get out my old audible signal tracer and find the source of the hiss.

[tubeswell]

The filament dc supply filtering needs to be working perfectly is what I meant. Are those 10,000uF caps enough*? Is one of them not working? Etc


(*Some DC heater supply arrangements hang a filter cap off every tube filament.)

[bnwitt]

The filament dc supply filtering needs to be working perfectly is what I meant. Are those 10,000uF caps enough*? Is one of them not working? Etc


(*Some DC heater supply arrangements hang a filter cap off every tube filament.)

I'll check all caps today.  Thank you, sir.  The Robinette DC Heater supply for (1) to (3) 12A*7 preamp tubes has (5) 3,300 uf filter caps totaling 16,500 uf.  The are in a different configuration with (2) of them in series after the dropping resistor on the power rails.  Maybe the two artificial CT 100ohm resistors R36 and R37 in the PRS 20's DC heater circuit should be changed to filter caps?


https://www.facebook.com/photo/?fbid=2803185463300384&set=a.374769951310920

[pdf64]

Both AC and DC sides of the rectifier are balanced with respect to 0V common, so 3.15V AC and +/-3.15V DC (or thereabouts).
Decoupling the DC sides (ie to 0V common) can't hurt, but may not have much benefit.