UA 6176 / 1176 problem?..

[Johan]

hello all

this is my first post here, and not a diy-unit but a commersial one

I am sitting with a Universal Audio 6176 ( 610 pream and a 1176 in one unit )in front of me and the problem is that when I move the release-pot, with no signal, the G.R VU-meter is moving..
my initial reaction was that this shouldnt be so, but trying the same with another unit, it behaves the same way...looking at the schematic for 1176LN I cant see that this should hapen, but then, it isnt *IDENTICAL*...does anybody know..I just cant wrap my brain around it...and having two units displaying identical problems suggests to me it might not be a problem, but should be this way...?.. but still?..

thanks for any help..

Johan

 

[Johan]

thank's
..well..if I put the release pot at the 12o'klock possition and adjust the G:R meter to "0" then turn th release upp full, the meter goes up 2db and if I turn ity down the meter goes down 2db, so it would seem there is DC on the pot, but if I read the schematic correctly, only the discharginbg DC from the rectifeid signal ( wich isnt even applied here ) should go through the release pot...
...I can see how this would hapen if someone swaped the cables going to the pot from the pcb, but the unit seems to tested at the factory and is it even possible they swaped around a few cables, on several units, at the UA-factory?...( two, possibly more unit doing the same..)

thank's

Johan

 

[Steffen]

meter movement when turning the release knob seems to be "normal" with 1176 comps. due to the high impedance of the sidechain path (up to 5 MOhm, depending on release setting) the circuit is very sensitive to leakage currents and other crap which might charge the the timing cap a little.

steff

 

[Johan]

ok..I guess that explains it..

thank's guys..

johan

 

[SSLtech]

Yep. Plus the 6176 and 2-1176 units have that little tiny clear-plastic cheapo-meter, which really doesn't have that great a resolution.

We have about a dozen 2-1176's here and I've observed that they all do it rather more than the real (1 x rev D, 1 x rev F) UREI units that we also have, and also more than the two Purple/Bloo units that I have at home also.

In addition to leakage currents, dielectric absorbtion and charge re-release is a possible cause. This could probably be checked by replacing the time constant capacitor. (don't forget the release pot is in parallel with the capacitor, so short release times mean a load across the cap. Unlike most compressors, I think that the 1176 might have a static voltage across the cap, which would be the 'bias' voltage which sets -1dB gain reduction at no 'official' GR.

Keith