JENSAMP-51X (Germanium Mic-Pre by Darius Kubarth)

[shabtek]

pulsating?
oscillation?
at all gain settings?
instrument input too?
with input shorted?
power supply overloaded?
maybe scope rails

 

[buckethead]

Built a pair 2-3 weeks ago, have the same problem with both of them. Oscillation starts with gain setting  at 3 o'clock or higher. Haven't had the time to further investigate that problem...
They work fine and sound great with lower gain setting, DI inputs work great too.

Best regards,
Mathias

 

[Bornhorst]

I just built one and have the same problem.

3 o'clock and above pulsating oscillation starts.

 

[kvothe]

Hi everyone,
same Problem here. Bought a pair, built one, but didn't have time to troubleshoot since. Wasn't some calibration necessary on these? (like I remember a variable resistor, or am I wrong?)
Kind regards, Kvothe

 

[Dr Gris]

Hi everyone,
same Problem here. Bought a pair, built one, but didn't have time to troubleshoot since. Wasn't some calibration necessary on these? (like I remember a variable resistor, or am I wrong?)
Kind regards, Kvothe

My kits came with a 1k trimmer insted of a 470R resistor for R6. That's the only calibration you need.
Since trimmers are usually set half way (mine was, I checked) you're probably pretty close even if you don't trim.
The calibration is to get 4.5dB of gain in the lowest gainposition without transformers.

Still haven't got the time to troubleshoot mine yet...

Best
//M

 

[tzman]

Hmm..after reading the last few posts, I built one of the two rev.4 kits I had waiting and mine has also got the same behavior...

 

[Upacesky]

OK, it seems the designer of the circuit is working on the problem. Got the info from the german forum.

 

[Winetree]

He's must have been working on it for the last four years,
because I posted the same problems in 2010.

 

[tzman]

Did you eventually change the ASY26's with the replacements Volker sent you?

 

[Winetree]

Yes, I even made sure they were mounted with a space between them and the board.
No difference as far as the posted problems. I've just given up on them.
Buried in to much going on now, but at some point I'll take another shot at them.

 

[culteousness1]

I am surprised that there are so many folks with that problem too.

Did anyone change the ASY for a BC560 on a faulty unit?
Can't try it myself as my Jensamp is at Kubi's place.

Best,
Carsten

 

[tzman]

Just got some NOS ASY26's in that'll try later tonight and report back.

 

[culteousness1]

I changed the germanium transistor once before with no luck.

Just asked because I thought of a GE-related part variance.
Maybe silicone transistors with a why hfe won't oscillate...

Carsten

 

[tzman]

Yeah, changing the ASY26 didn't change a bit...
Haven't got any 560 laying around right now. Still puzzled with this. I'm absolutely sure everything is in it's correct position, reflowed every solder joint, and checked the Grayhill switched. The sound in the first couple of gain steps as awesome though . I'm curios as to what Kubi might find out!

 

[culteousness1]

Haven't got any 560 laying around right now.

Can send you some, as I am very curious about it...

Carsten

 

[tzman]

Sure! I'll send you a PM.

 

[Dr Gris]

Has anybody with the pulsating inferno come up with a solution?
Mine sounds like the soundclip a page back 
Maybe I should just go over the entire board and ad some solder at every pad???

Cheers
//Magnus

 

[culteousness1]

Unfortunately, I couldn't send the BC560s to Tom before yesterday.
If we are lucky, he will receive them tomorrow and have a try.

If somebody has got a faulty and a functional unit, it would be
much appreciated to swap some parts like the ASY...

Carsten

 

[tzman]

Sorry guys, no mail today... I'll try the 560 and report back as soon as they arrive.

 

[tzman]

Ok, so I got the BC560's who Carsten so kindly sent to me. Result: Now all the gain settings either give a load of white noise or have the exact same ticking/oscillating noise. So none of the gain steps actually work...
I'm pretty much at a dead end here...seems this rev.04 just isn't working. To put that into a question: does anyone here (Volker?) have a working rev.04? If so, would it be possible to post some measurements on this thread so we can compare our units?