JBL 6260 amp bias setting

[jfine]

Does anyone know a step by step procedure to check and adjust the bias on a JBL 6260? I'm not certain where exactly the test points are, I do see the bias pots though. I believe the setting should be around .350mv or so, maybe a tad more. Also is there a DC offset adjustment on these?

Thanks in advance.

[RMC]

Hi jfine,

I don't have the exact answer you are looking for. However, another member here, Horn Fanatic, mentioned if I recall correctly that JBL contracted QSC to build some of their amps. Can't say if model 6260 was part of that subcontracting though, nor that its the exact same procedure.

In any event, I have the detailed service manual for my QSC amps and it DOES cover the amp bias adjustment procedure step by step.

ASSUMING this could be somewhat similar, it may be interesting for you in order to get SOME idea or insight and what it entails... I've already read this bias adjustment procedure some time ago and its not really a piece of cake. Preferrably instruments are required, like distortion analyser, oscilloscope, etc.

But there's also a less accurate crossover distortion and bias adjustment procedure given, without the use of a distortion analyzer.

The manual is almost 7 megs large and I THINK the max allowable here on Lansing Heritage is 5 megs. I see no copyright indication on the QSC service manual I have. So if you want a copy of it to get some "food for thought" on such a procedure, send me a Private Message here with an e-mail address and i'll forward the manual to you at that address. Good luck! Regards,

Richard

[grey]

Does anyone know a step by step procedure to check and adjust the bias on a JBL 6260? I'm not certain where exactly the test points are, I do see the bias pots though. I believe the setting should be around .350mv or so, maybe a tad more. Also is there a DC offset adjustment on these?

Thanks in advance.

Subwoof's post recommends measuring across the base and emitter on one of the big Sankens. The leads are conveniently labeled (E B C) on the board. Use some good mini grabber leads like the Pomona brand if you decide to do this.

They don't have an adjustment for DC offset. They few of these that I've measured have surprising low DC on the output. ~0-4mV

[grumpy]

I believe the QSC association came later.