Creek 4040s1 strong buzz in one channel

[Mario Pankov]

Hello all,

Got this little amp for a few weeks. When at a feet distance I was able to hear some light buzz in one channel. One day the buzz suddenly became strong. I can still hear the music coming out of the speaker but this buzz is there. I opened the amp and checked for faulty input transistors, checked caps and ground - all fine. I replaced the main ps cap and the smoothing caps with new ones, same brand as original, no change. PS section is with one bridge, so I guess problem is not there. What could be the problem and where would you suggest that I should look now? Is it possible to be the pot grounding?

[Mario Pankov]

No one on this?

[Mooly]

It could be many things...

Does it buzz with NO inputs connected ?
Does it buzz on any input (CD, Tuner, Tape etc)

Yes, it may well be something like pot grounding. Anything where there is the possibility of mechanical stress on the PCB can be a problem. If in doubt resolder all the pot connections.

Does the buzz respond to any physical pressure on the PCB. That is, does it seem like an intermitant connection.

[Mario Pankov]

Hello and thanks for replying. Buzz is coming from onechannel only with nothing connected to the inputs. Output smoothing caps were replaced, so no AC could be passing through. I suspected a faulty input transistor but they seem to be fine. Even so, I replaced them with new ones and buzz is still there. Transformer had bad joints and was an R-core, I ordered a nice toroid which I`ll install today. So buzz iz when:

- nothing is connected to the input
- one channel only
- buzz is not affected by the volume pot position
- tested it on two different speakers with diferent cables and sofort
- Nothing seems burned on the inside, tested output darlingtons and replaced all input trannies
- grounding is a onepoint, resoldered it even if it looked fine

[sakis]

make sure that you are working in an EMI free environment..... weird case but it is possible that you are picking up something

kind regards sakis

[Mooly]

It doesn't sound like a transistor fault. Hum and buzzes have other causes.

To be able to help specifically we need to see a circuit. I suspect this will be something like cracked print somewhere.

Depending on test gear available (scope ??) I would suggest finding the input to the power amp in question on the PCB and shorting it to ground to see if it kills the buzz but you MUST do this correctly or it could cause more damage.

[Mario Pankov]

Hello and thanks for the replies,

Yesterday I replaced the power transformer, as seen on the second photo it was not the original one but a R-core one. I bought a nice 160VA toroidal transformer ( a bit overrated than the original one ) and installed it yesterday. Now what is left is tosort out this problem with the channel.

Here is theschematics of the amp, hope Creek don`t mind that I post it here:



And a pic of the amp on the inside. Replaced the main ps cap with a Panasonic FM 6800uF and the output caps with some Rybucon 3300uF XYG for now, later I`ll drop in a pair of Elna Silmics.

[Mooly]

Too small...

[Mario Pankov]

Corrected

[Mooly]

Still a bit small to work with. If it's a pdf then you can put it in a zipped folder to post it.

Removing this cap will isolate the preamp from the power amp. I think the amp should be stable doing this from what I can see.

Or, you could short the left side of that cap to ground to remove all signal to see if hum disappears.