Aleph 5 problems

[tonistefanovski]

Dear All,
I’ve “finished” Aleph 5 two mono blocks, but while listening something strange has occurred. Before listening test I’ve measure all voltages as on the original schematics. Everything was fine. DC offset bellow 10mV. Perfect. I’ve connected my speakers and enjoy for about 2 hours (excellent sound). But then appeared strange sound, sound like “broken” radio station (on both channels). Turned them off then on, but same…. I’ve disconnected output FET’s and recheck VGS again. All of them has the right VGS voltage as before. So If anyone can help please let me know. Note that the FET’s are connected to the board with Teflon-silver wires.
Thank’s to all,
Regards,
Toni

[Zen Mod]

both channels?

did you check PSU ?

if yes- disconnect one channel and work on just one at a time.

post what you found , so we can move further

ps. like I always say - KK's pcbs are made to look fine from top;
because of that , traces are nightmare ; and numerous other details on these pcbs are nightmare.

[Magura]

Originally posted by Zen Mod
both channels?

did you check PSU ?

if yes- disconnect one channel and work on just one at a time.

post what you found , so we can move further

ps. like I always say - KK's pcbs are made to look fine from top;
because of that , traces are nightmare ; and numerous other details on these pcbs are nightmare.

How about a pic of the psu ?

Does anything get hot?

Magura

[tonistefanovski]

Thank you on yours reply,
I've noticed that one FET getting very hot for about 10 seconds. In that period I was able to mesure voltage on 1 Ohm resistor connected on that FET. It's about 630mV (propably OK) and DC offset is still 7.5mV

[tonistefanovski]

Sorry, I forgot to mention. Yes I've checked PSU. I have +-37 Volts, under load +-34V.
Thank's

[tonistefanovski]

Two ours of listening without any problems!!! I don't know what could be a problem???

[Zen Mod]

puzzle is -why is same situation on both channels;
as I can see- only PSU is common for both channels ;

630mV across 1E is somewhat higher than in serv.man. but you say that outputs are matched?

anyway- do what I tell you- start with just one channel and inform us what you found

[tonistefanovski]

Voltages across all of 1R are between 600-630mV and yes they are little bit higher as from the original schematics. Any way I'll try to find what could be a problem
Thank's

[Zen Mod]

Originally posted by tonistefanovski
Voltages across all of 1R are between 600-630mV and yes they are little bit higher as from the original schematics. Any way I'll try to find what could be a problem
Thank's

these voltages are correct like this; doesn't mater if current through outs is higher than in servman ;(ask Magura for that )
what's important is that current between outs is so-so equally shared......

edit:

if your htsnks are near max temperature of 55degs , than is wiser that outs are in lower third than in upper third;

if they are cold enough like this,than is irrelevant

[mpmarino]

sound like “broken” radio station

Hmm, that's what "broken" protection zeners sound like. Maybe you got some bad ones that ended up opening??