G9 finished - but oscillation at highest gain pos.

Hi,

I finished my G9 this day... everything works, all voltages are fine. That preamp sounds great...!!!
(thank you jakob for your help)


but there's just one thing that makes some problems....


when I switch the gain switch to its highest position (11) oscillation occurs.

This behaviour is exactly the same on both channels..

when i plug an instrument into the front jack input, there's no oscillation...


I just recorded a short file... it's sounds quite interesting...
reminds me on tuning an am-radio...

http://www.cmaudio.de/g9oscillation.mp3


I'm using the newest board revision, the value of r9 and r109 is 47k


I found some posts, where some of you had a similar problem, but no solution for that...


thank you for your help...

matthias

Well i am not sure but i think i remember that somebody shielded one of the cables going to the frontpanel pcb and the oscillation disappeared. Not sure which one it was, i think the middle one ?
Better wait til somebody can confirm this.
Oh and i remember that this only happens with OEP equipped G9's ?

Flo

Hi Flo,

I used oep trafos (with can) for the input, lundahl 5402 for the output...
wima caps, Phillips JAN 5184 tubes... the ouput calbes that go across the board are shielded...

I don't hear any hum or noise... even that oscillation sounds very clean...

the cables that are going to the front pcbs are not shielded.. I think jakob(?) mentioned, that it is not necessary to shield the connectors, because the connectiopns on the front-pcbs are also not shielded..

here's a pic...





matthias

Hi matthias !
Nice Job, damned this board is full of "golden hands".
That's said I had the same osc. problem and had to remove the wires from the instruments face jacks inputs to get rid of these osc.. I've tried to shield these cables, the others, and had no chance.
This preamp is pretty fine and with the power trafos fixed outside of the case (backplate) it becomes far less noisy.

regards.

Fly

http://perso.wanadoo.fr/flyingfader/GyrafG9/index.html

Hi Matthias

I shielded the signal cables to the switching board to prevent oscillations in the left channel. Other people avoided oscillations the same way. See the link:

http://medlem.jubii.dk/klausdiy

Best, Klaus

Sorry, the channel to the right.

[quote author="matthias"]Hi,...

http://www.cmaudio.de/g9oscillation.mp3

matthias[/quote]

Hey, you can make a hit song with that sound! Just add a phat hip hop beat a'la Missy Elliot..... heheheh :grin: