Sound Skulptor forums

Build help and troubleshooting => MP573 Microphone preamplifier => Topic started by: Evan Sabby on July 01, 2024, 12:57:10 AM

Title: Bias Adjust
Post by: Evan Sabby on July 01, 2024, 12:57:10 AM

I have a question about the bias adjust portion of the testing.

I place the positive (+) test probe from the DMM on TP4 and the negative (-) test probe from the DMM on TP2.  I power on the unit and adjust P2 until I read 3 volts.  My question is after I get P2 adjusted to 3 volts the voltage begins to drop very slowly and continues to drop over time.  Is this ok?  If not what do I need to do to fix it?

I appreciate any input.

Thanks,

Evan

Title: Re: Bias Adjust
Post by: JPK on July 01, 2024, 03:20:56 PM

It is normal for the voltage to drop a little, around 100mV, as the unit warms up but it should stop when it reaches its equilibrium temperature.

Title: Re: Bias Adjust
Post by: Evan Sabby on July 01, 2024, 09:11:49 PM

Thanks.  Should I wait for the voltage to settle before I adjust P2 to 3 volts or will it be ok the way I adjusted it right after I powered the unit on?

Title: Re: Bias Adjust
Post by: JPK on July 02, 2024, 03:30:21 PM

I ususally wait 5 mn before adjusting.

Title: Re: Bias Adjust
Post by: Gavin1393 on July 15, 2024, 05:43:32 PM

Did you get your issue solved Evan? I had a similar problem, my MP just kept droppong indefinitely. Turns out my Q6 (one with the 90 degree bent legs) wasnt contacting the PCB...a little more solder sorted it!