SOLVED!!! G1176 (mnats board H) + G9 ground problem?!?

I just finished my G1176. When I connect it with my G9 there is a HUGE 50Hz broom and lot's of hoom, but if I connect sound card out to 1176 in everything is OK. G9 also work perfectly without 1176.

They are on the same 230V outlet, I tried to remove ground from G9 output. Removing ground from 1176 also have no results.

Any ideas?

Looks like a ground loop between them. How's the ground scheme on your G9 and uour 1176?

Hmmmm, when I touch chassis on G9 broom is 50% quieter. But I don't have any problems when I connect G9 with sound card input.

One more information. Just tried to connect through computer. Mic - G9 - Sound card - 1176 - headphone amp. There is a 50Hz noise, but very quiet. Interesting thing is that noise starts when I connect (touch) RCA's positive pin, and nothing happens (good or bad) when I connect ground to.

Hope that I'm not to confusing like this situation is confusing for me!!!

First, did you scratch paint around all screws? If not, do it. Also, is your chassis steel or aluminium? Did you used shield cables for all your wiring such as di, xlr, etc? Do you ground the output xlr? If yes, remove the ground connection. Also, try moving around one of both box to see if there is one of them polluting the other (often time, when power transformer are upon each other)

OK, after lots of testing I can say that only one board from 4 working good. Biggest problem is with first one with that annoying strong BUZZ.

I check all screws etc., but nothing. Interesting thing happened when I removed ground just like Deepdark sugested to me. Buzz was still there, but with LO-CUT.  I didn't measured but i think it is around 1Khz.

All the time I had microphone connected trough G9. I can hear mic all the time, but also with lo-cut when I remove ground-

HELP PLEASE!!!  :-[

mihailojocic said:

OK, after lots of testing I can say that only one board from 4 working good. Biggest problem is with first one with that annoying strong BUZZ.

I check all screws etc., but nothing. Interesting thing happened when I removed ground just like Deepdark sugested to me. Buzz was still there, but with LO-CUT.  I didn't measured but i think it is around 1Khz.

All the time I had microphone connected trough G9. I can hear mic all the time, but also with lo-cut when I remove ground-

HELP PLEASE!!!  :-[

Click to expand...

hmmm there must be a short somewhere Inside the G9. Start with your dmm and probe all ground point to be sure they conduct well. Check your 10pins connectors to be sure all wire are all making contact and are in the good orders. Be sure your transformer shield is effective (if using oep, check continuity of the shield with the main bolt). How did you ground the G9 exactly?

I also think that there is a short, but in 1176. G9 work with excellent reliability more than 5 years. With other 1176 board everything (almost) is perfect. I check and re-check, and...

so, your G9 works fine now? Did you tried it with another piece of gear than your G1176? Just to see if the G9 interacts well with other gear. If yes, then your trouble must be into teh G1176.

Problem(s) is(are) solved! There was a short on the main board, almost invisible (thin like a hair). Maybe I just need more patience in the future in searching shorts after soldering.

Also there was a few bad soldered spots on the ratio board. That also caused buzz.

I am happy because I made 4 G1176 in the same time, so I had chance to compare with other, good working boards. Switching (changing) ratio boards from one set to other helped me to find bad ones.

Now I have other problem, but I will post that on the "All things G1176".

Cheers!!!