g1176 RevG issuses

[ChuckD]

I am just finishing up my Stereo 1176 (Mnats revG)
I have 2 main issuses:

1. I get a ground loop hum from one of the outputs. Depending on which one gets plugged in first... Difference ground loops? Should I just lift one of them?

2. One channel is way lower in volume then the other. Feels like there is something wrong here. the volume knobs still work on this low channel but it is too low to be usable. What causes the volume to drop in this circuit?

Thanks !!

-ChuckD

 

[radiance]

You probabely know this but just in case...

Maybe that groundloop has something to do with how your cables are wired.
If your cables have the shield connected on both sides there cane be a groundloop.
Check this link from Rane audio. I found it very usefull.

 

[ChuckD]

I still have a major difference in the 2 1176 channels I have built. One side doesn't seem to be as "responsive" . Meaning it doesn't react as much when ratio is turned up. Also this channel is much lower in volume the the other.

Any Ideas on what the difference could be? Where do I begin looking? They were built at the same time(component at a time) so the components are all the same.

Any help would be great!

-ChuckD

 

[gyraf]

Chuck,

Could be a wrong component in a wrong place. Could be a short or a bad solder joint. Last, it could be improperly matched/adjusted FET's in the units.

Jakob E.

 

[Arrigotti]

Yes, I just finished my 2 1176's (not stereo) and have been adjusting the units. The Q bias adjustment has a MAJOR effect on the gain. I'd try that first.

 

[radiance]

@ChuckD: I'm also building a stereo 1176. Both units are working but I have not yet tested them as a stereo pair.
Did you use shielded cable for the stereo interconnect? On de scheme the stereo interconnect is shielded but I think you should not connect both shields of both units together right?

If I have some time I will connect them and post my findings...
(B.T.W. I used two toroid transformers )

 

[ChuckD]

Ah ha !!

Right you were Jakob!!
Cold solder joint on the output jack.

Now it is all working. Stereo 1176 rev G.

HUM -> I do get a hum at -47.3 db is this low enough or should I try to isolate the ground loop problem more?

I used only one power transformer and hooked it up to both. This I think makes two loops? and that couldbe the cause....

What do you guys think/suggest?

Thanks !

-ChuckD

 

[mnats]

ChuckD - I'll ask again here: are you using a single transformer to power two complete, separate power supply circuits? That is, does the transformer go to the 24 - 0 - 24 pads on each board?

Ideally, I think you'd want to power the two boards from a single power supply circuit that provides the +30 -10V for each board. If the hum is lower when you power a single board, that same performance is possible even with two boards in the same chassis...as long as they are wired correctly.

 

[ChuckD]

I posted this question again with finished pictures...
It's just below.

Here :
http://www.groupdiy.com/index.php?topic=5549

Yes just one Torriod to power both... I didn't really think that would be an issue The grounds need to be all together anyway for stereo right?

-Chuck