[Bach911]

Thanks again for the correction. Bought lsk389b from trendsetter as recommended. Earlier bough 20 SK170 and tried to match with little success. Idss on 12 volts ran 0.03 to 0.15 mA. None would match below 10 percent. Maybe the lsk170 would match better than the sk170, but why take the chance. I will read all of the 29 pages from the "Is anyone building the KGSSHV?" tread so you are not having to save me from serious mistakes........not that I mind hearing from the creator of cool electronic designs and overseer of the NMR.

 

[Amarphael]

I need some help here please...
 
When my amp is hooked thru the RCA inputs it's producing a buzz on both channels, from around 9 o'clock position, and it gets louder with turning up the volume. this applies also when there's no source load connected. When hooked thru the XLR inputs there's a low level hum only when the dial is completely down (it's a DACT CT-2 quad stepper) and on all further positions it becomes very very faint.
 
I don't know if it's relevenat here but i should note, I've had some major issues with the PSU in the past which required replacing 3 of the 4 transistors and p2p soldering some connections where traces were burnt out:
 

 
 
I get stable 367V/358V stable on the postive/negetive HV rails accordingly and close to +/-0.1V on the 15V rails.  However, and this is the second issue i'd like to solve, i have a constant DC balance drift on both channels from around 0.5V to 3V and the left channel offset is drifting 3V-8V after adjustment.
 
I'm far from a techie so i'd vey much appreciate some directions where i should look in to this, primarily the buzzing problem.

 

[valve5425]

  I need some help here please...
 
When my amp is hooked thru the RCA inputs it's producing a buzz on both channels, from around 9 o'clock position, and it gets louder with turning up the volume. this applies also when there's no source load connected. When hooked thru the XLR inputs there's a low level hum only when the dial is completely down (it's a DACT CT-2 quad stepper) and on all further positions it becomes very very faint.
 
I don't know if it's relevenat here but i should note, I've had some major issues with the PSU in the past which required replacing 3 of the 4 transistors and p2p soldering some connections where traces were burnt out:
 

 
 
I get stable 367V/358V stable on the postive/negetive HV rails accordingly and close to +/-0.1V on the 15V rails.  However, and this is the second issue i'd like to solve, i have a constant DC balance drift on both channels from around 0.5V to 3V and the left channel offset is drifting 3V-8V after adjustment.
 
I'm far from a techie so i'd vey much appreciate some directions where i should look in to this, primarily the buzzing problem.

 
No offense, but I'd ditch that PCB and start again! It looks somewhat past it's best!! Can't really tell from the photo, but if you're using metal washers under your screws/bolts then you could short out the two tracks they're bridging. Could make lots of sparks!!

 

[Amarphael]

First, No offense taken and yeah i agree, replacing it makes a lot of sense and a path i'd like to take. But easier said then done... First, I have no idea where to get a replacement and fabricating my own is out of my league entriely. I don't think that the HV version would be compitable but please correct me if i'm wrong. Second, It'll be a tough desoldering work since i only have a simple desoldering copper strip and i'm afraid of damaging the transistors in the process.
 
Anyway, the PSU seems to be fine as far as rail output measurements go... Do you think it still can be related to my problems?

 

[valve5425]

Your PSU measurements seem to suggest that the boards working fine.
 
If this is happening with no source connected, then it may be a grounding issue in your amp. Does the noise change when you touch the chassis? Check all your ground connections/solder joints.

 

[Amarphael]

Sorry for the delay in response.
 
Well it's happening via the SE inputs regardless of the source connected or not. and It doesn't change if i touch the chassis. so you think it's a ground issue because the balanced inputs are unaffected? Also, if it's the problem doesn't the buzz supposed to be constant rather than be affected by the volume control?

 

[valve5425]

Hmmm. The usual problem is ground loops, but if this is happening with no source connected, then it suggests it's in the amp. If the noise increases when the volume control is increased, then the problem is more than likely before it. I'd suggest checking the wiring before the volume control. Check the soldering and also the wiring layout. You don't want signal wiring near to AC wiring or transformers. You say it's a "buzz" and not "hum". Hum is usually mains related, buzz could be anything!