Sonzera 20 v2 hiss/hum at idle…

[Rusty Shackleford]

I have a new Sonzera 20, v2. Mine is made in Indonesia. According to PRS they shifted production from china to Indonesia for this amp. Pretty cool amp. Good tone. Here’s my concern: with stand by on, my amp has nominal hiss noise, nothing more than any other amp. But with the standby off, there is a pronounced hiss/hum regardless of level, settings, etc. seems to be generated in the preamp section of the amp. I tried swapping the preamp tubes for EH 12ax7 with spiral wound heating filament which is supposed to reduce noise in amps with AC heater current. I don’t know if the Sonzera heater current is AC or DC, I suspect AC as this is easier and cheaper to make. Regardless, swapping tubes had no effect. Tried different power tubes, no change. I read a bit about this apparently common issue but wanted to post this to see if anyone has stumbled on a fix other than a noise gate or living with it! Thx!

 

[andy474x]

When you say standby off, do you mean amp in full-on “playing mode?” I notice mine has some noise in both standby and full-on modes as well, less on standby, kind of unusual for anything to come out of the speaker. Neither unreasonable though. If yours is excessively noisy in full-on, I’d pursue a return/replacement from your dealer.

I suspect the reason this happens on some PRS amps, especially the channel switching models, is because they started putting the channel master volume before the phase inverter (I think), at least in part to be able to put the MV control knob in with the other channel controls. So everything downstream of the MV is running wide open all the time, and amplifying some noise that’s being generated. Whereas with a post phase inverter MV, it wouldn’t be amplifying that noise as much unless the master was wide open.

Keep in mind, that’s all armchair amp design critique!

 

[Rusty Shackleford]

Yeah - I’d love to see a schematic for this amp. I understand the standby switch is really a mute. I understand it mutes the preamp input somewhere before the power amp. I believe that’s why there is always a bit of hiss, although when the standby is off (amp full on) the hiss/hum is quite a bit louder. The hiss/hum really sounds like not enough capacitance in the rectifier section but that kind of doesn’t make sense given the muting of the preamp section. I’m waiting on a response from PRS but I understand this is pretty common among these amps.

 

[Rusty Shackleford]

I visited Guitar Center yesterday. They had a Sonzera 20, v2, made in china. It has the same hiss/hum as mine. Again, it’s not unusable, just more than what I think an amp should have. Other interesting thing - my amp weighs about 35lbs on my bathroom scale, quite a bit less than the published spec of 42lbs. The made in china Sonzera 20, v2, at Guitar Center, felt much heavier.

 

[Rusty Shackleford]

Interesting piece regarding Sonzera 50 that seems to have the same noise floor issue. Looks like very similar amps, inside and out.