troubleshooting an Aleph P

[Bill Fuss]

I,ve run into a problem with a low level buzz from one quadrant out put, and nowhere else. It possibly could have been there from day one, as I just started using the balanced outs and it is on the neg out of one channel. It appears on the scope as an upper half of a sign wave about .5ms long and repeats every 8ms or so and is about 8mv. The only thing I used differently from the original design is BC550C and 560C for the ccs, but I have put caps across them to no avail. All my voltage readings are right on for the entire board. I have swapped supply boards, systematically replaced every component in that quadrant, reflowed every solder joint, and totally isolated the board from all input and output wiring, with no change. I'm using Kristians boards with dual regs.
Could the problem be with the higher hfe of the BCs or an inherent problem with the board layout.
The unit has always performed fine but the buzz is audible using balanced outs. I guess its actually 120hz hum.

Anybody out there seen anything like this before?

Questions or comments are definately welcomed.

Bill

[Fox]

If it's a buzz and it seems like it it could be a grounding problem. Could you post something about your grounding scheme?

Just my 2$,

Fox

[Bill Fuss]

Your $2 or 2cts is appreciated at this point, Fox. With the board totally isolated from everything but the power supply I tried grounding the board directly to the chassis, and also through a .1 uf cap with no change. I also lifted the thermistor off of ground, with no change.
I'm convinced it is in the circuitry, somehow amplifying the residual ripple that's down in the microvolt range. I don't have any previous experience with constant current sources so I don't know if this is what is happening for sure, but there aren't too many things left.
Possibly radiation from the diodes affecting only that part of the board, I guess that's possible!

Bill

[rtirion]

something similar?

http://www.diyaudio.com/forums/showt...45#post1398745

[Bill Fuss]

I wish it was, as I found your post in a search and did exactly as you did, with no change.
There has to be a simple explaination, or else there really are gremlins.

Bill

[rtirion]

Did you try to test the powersupply separate from the amp board?
Specially check all power connection (solderjoints etc) between
the boards.

So with only the PS board, nothing else connected, check with
your scope (AC connected) if you find the same type of
repeating signal.

That would narrow things down a bit.

[Bill Fuss]

I didn't check the reg boards without a load, but I have a separate board for each channel. I swapped the boards channel for channel with no change. The reg board outputs are virtually identical and very clean. I haven't cascaded the scope channels as I didn't see the need to look at the residuals, but maybe I will just for kicks. I did check all the diodes on both boards, all OK.

Bill

[Fox]

Originally posted by rtirion
Did you try to test the powersupply separate from the amp board?
Specially check all power connection (solderjoints etc) between
the boards.

So with only the PS board, nothing else connected, check with
your scope (AC connected) if you find the same type of
repeating signal.

That would narrow things down a bit.

The Aleph P and BOSOZ PS-boards should never be tested without a load. If you do, they will go up in flames. Some folks at this forum can prove I am right

Fox

[rtirion]

I do not share your experience of the PS going up in flames at
no load.
However, I do use a variac when testing. And if you are in doubt
use a light test load (power resistor, led +resistor)

[Bill Fuss]

60ma isn't much of a load anyway, I'm going to try running both channels off of one reg board and see if it changes. Ordering some ZTXs today to eliminate that possibility. Anybody got any of Veteran's boards lying around that need a good home?

Bill