Hello,
I just traded a pair of speakers for a B&K ST-2140 amp and before hooking it to speakers I wanted to set the cd off-set and bias.
There are two pots on the amp board and a lucky guess got the cd voltage down to 3mv from about 50 mv Now I know which pot is the bias pot but no idea what to set it at or where to measure. Hoping someone here can provide the procedure.
A google search didn't turn anything up. Thanks.
I just traded a pair of speakers for a B&K ST-2140 amp and before hooking it to speakers I wanted to set the cd off-set and bias.
There are two pots on the amp board and a lucky guess got the cd voltage down to 3mv from about 50 mv Now I know which pot is the bias pot but no idea what to set it at or where to measure. Hoping someone here can provide the procedure.
A google search didn't turn anything up. Thanks.
I design my own amps and set the bias to just enough to get rid of crossover distortion.
Turn bias right down.
Apply a small sine wave to input.
Monitor output with scope.
Turn up bias slowly until crossover distortion goes.
Turn bias right down.
Apply a small sine wave to input.
Monitor output with scope.
Turn up bias slowly until crossover distortion goes.
Great advice if I had a scope and a signal generator. Unfortunately, I have neither.
Hoping someone here has the procedure as written by B&K.
Hoping someone here has the procedure as written by B&K.
I would leave alone in that case. Are you sure you have adjusted the offset and not the bias current? Adjusting the bias current can have a similar effect as the output transistors work more or less hard.
As I don't have any info on the amp, I can't say with certainty I adjusted the dc off set, but it felt right. And the other pot on the board had no effect on cd voltage.
I'll contact B&K to try and get info.
I called B&K and amazingly, spoke to a tech immediately. He sent me the procedure used for various B&K amps. Unfortunately, the procedure requires test equipment I don't have. Why can't it be as simple as place voltmeter probes across resistor R112 and adjust for 35mv or something similar? Oh well, guess I'll just live with it the way it is.
In general for B&K you pull one fuse on one channel, and adjust for 100mA per PN pair, and 50mA for the front end. Same for the other channel.
Two output pairs are thus set to 250mA (per channel).
Two output pairs are thus set to 250mA (per channel).
Thanks for the reply.
I can handle what you describe. My problem is, do I need to perform this adjustment with a signal applied and an 8 ohm load on the amp?
That's what the procedure recommends and I don't have a signal generator or a proper load. I could use a raw speaker but not sure it would survive.
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