Sound Skulptor forums

Build help and troubleshooting => MP573 Microphone preamplifier => Topic started by: Bert Hornikx on February 28, 2022, 04:42:16 PM

Title: Calibration
Post by: Bert Hornikx on February 28, 2022, 04:42:16 PM

Hi there,

Sending the mixbus through MP573s lately, I noticed the output volume of my two units is different.
Using a mono signal, ProTools meters and Waves PAZ analyzer, I have to set the trim knobs in a different position to get a centered image.
Not a big issue, but it would be nice to match the preamps.
Is there a way to do this?

Thanks,
Bert 

Title: Re: Calibration
Post by: JPK on March 02, 2022, 11:29:45 AM

This is surely due to the gain potentiometer tolerance which is 20%.
How many dB's of level difference do you get for the same position of the pots?
Is there still a difference for the extreme positions?
You could try to play on the value of R22 on one of the units to reduce the gain difference.

Title: Re: Calibration
Post by: Bert Hornikx on March 06, 2022, 09:21:01 PM

Thanks!
At +10 the output is nearly identical.
At -10 there is about 1db of difference.
What values should I try? Is there a way to measure/calculate this?

Title: Re: Calibration
Post by: JPK on March 07, 2022, 05:53:51 PM

You can temporarily wire a 2k or 5k linear potentiometer in place of R21 (not R22 in this case) and adjust the value to get the same gain at minimum rotation. Then replace the measured value of the pot by a resistor of the closest value.

Title: Re: Calibration
Post by: Bert Hornikx on March 07, 2022, 09:50:18 PM

Thanks, JPK!
That's a doable fix.
Will try it as soon as I can and post the results..

Title: Re: Calibration
Post by: Bert Hornikx on May 31, 2022, 02:28:19 PM

So .. I finally managed to try this fix and it works perfectly.
Very happy my trim knobs on the stereo bus are matched!

One more question: can I do the same with my 5.99 and 5.12?
What resistor do I look for.

Thanks!

Title: Re: Calibration
Post by: JPK on June 02, 2022, 05:09:42 PM

For the maximum gain you can play with R15.
For the minimum gain you can play with R12 for LOW and MID gain.
For the minimum gain you can play with R11 for HIGH gain.
But there will be some interactions.

Title: Re: Calibration
Post by: sdiazmun on May 09, 2023, 02:20:30 PM

Quote from: Bert Hornikx on May 31, 2022, 02:28:19 PM

So .. I finally managed to try this fix and it works perfectly.
Very happy my trim knobs on the stereo bus are matched!

One more question: can I do the same with my 5.99 and 5.12?
What resistor do I look for.

Thanks!

Hi Bert! What value do you use finally? I understand you changed the resistor in one preamp only, did you?
Thanks!!!