1176's VU issue

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SaMpLeGoD

Well-known member
Joined
Jul 19, 2007
Messages
441
Location
Portugal
Hello all!
I posted this on the all 1176LN thread but, nobody answered, so I'm posting here to be more visible, I think this is a known problem...
Well, I build some 1176LN Rev D, Rev A, Rev F and Rev J and all of them has the same minor problem: The VU's needle never stays quiet in GR mode with no signal, it always slightly swing around the "0" VU... Rev A is better than the others in this case... I experienced one original 1176LN black faces (REV D) and the needle is solid as rock pointing to the "0". even when I switch between +4 and GR the needle goes back to the "0" quick and firm...
I read, read, read here in the forum, and some people say that the original do the same thing, others are talking about a eventual dirt around the FETs... well, I clean the FETs, saw the original by myself and stand the opinion that, somehow, it must have any other reason to this happens!! circuit? VU? component's placement?
I tried with Hairballs big and small VUs, tried with SIFAMs AL29WF and AL19WF... all the comps act the same!
I have the FETs perfectly matched, Q12 and Q13 matched.... used 2N5088 with HFEs between 500 to 600 (greater that the 250 asked), all done, and regulated as it should! the comps sounds and acts perfectly, but that issue annoys me a lot...
any help or ideas???

Cheers,

Eddie.
 
SaMpLeGoD said:
any help or ideas???

Yep, that's what the meter adjustment pot on the front panel does.

I believe I answered this in the 1176 thread.

It's because the meter driver circuit is unregulated and fluctuates with mains voltage. The only way to fix it is to redesign the driver circuit.

Mark
 
Biasrocks said:
SaMpLeGoD said:
any help or ideas???

Yep, that's what the meter adjustment pot on the front panel does.

I know that, but is pretty annoying do that every 30 seconds...
does the original's driver circuit equal to the clone?
humm... strange... the original don't do that.
Cheers,

Eddie
 
I have 4 rev D's and a Rev A and don't have any problems. Takes them a while to warm up then they hit 0 and stay there. I calibrate them after a LONG warmup with the lid on. I did use all 50 VA transformers tho. Don't know if that would effect anything.

John
 
Rob Flinn said:
Never bother zeroing the meter until the unit has been switched on for at least an hour.  Never bother calibrating either unless it's been switched on an hour too

Thumbs up.

It'll take up to an hour for the meter circuit to "stabilize".  If you're zero adjusting it during this time it's going to keep moving on you.

If you keep it on for long periods of time, like in a commercial studio setting it should be fine.  But every time you fire it up it's going to start at -1db and slowly climb to 0db over an hour.  Just trust it'll end up at zero eventually.

Mike
 
My one behaves a little different. It does stray on start up and eventually stabilizes to a point. Sometimes it could stabilize on 0 or somewhere between -1 or + 1.
 
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