1

MP566-II Tube microphone preamplifier with HPF / wrong voltage on testpoints and wrong c19 value

« Last post by Mischmaschine9000 on November 05, 2026, 07:52:58 AM »

I finished building one of my seven mp566-2 kits. All of the kits came with a 100n for c19 instead of a 1u that is written in the parts list. Is that an error or just a new revision? 
On the finished unit i get until point 5 in the test protocol, there i get tp5:+15v, tp6: +1.3V
I see no obvious misplaced components or solder bridges. Do you know what this could be?

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501 Single Host / Re: orientation of inductor coil

« Last post by skrzyp on November 04, 2026, 01:46:12 AM »

Thanks very much. It's working!

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501 Single Host / Re: orientation of inductor coil

« Last post by JPK on November 03, 2026, 05:37:44 PM »

Yes, correct.

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CP4500 Stereo Bus Compressor / Re: Make up gain no longer working

« Last post by JPK on November 03, 2026, 05:34:43 PM »

Check if you get the same voltage variation on TP12 (0 to 2V3) with MIX at 100% and no input.

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LA502T Tube Optical Compressor / Re: test procedure - having trouble

« Last post by JPK on November 03, 2026, 05:26:43 PM »

The values you measured on TP8 and U3-U4 are correct so you should be able to adjust the LEDs.
One possible cause of the problem could be an incorrect value for one of the resistors R29 to R33. Please double-check their values.

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501 Single Host / orientation of inductor coil

« Last post by skrzyp on November 02, 2026, 06:12:50 PM »

To be safe, just checking on this before soldering. Is the orientation pictured correct? My part is different than the one pictured in the build guide. Thanks in advance.

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CP4500 Stereo Bus Compressor / Re: Make up gain no longer working

« Last post by MRMNW on October 28, 2026, 01:41:54 PM »

Anything else I can check?

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LA502T Tube Optical Compressor / Re: test procedure - having trouble

« Last post by doktar on October 27, 2026, 08:05:58 PM »

Replaced the blown LED's.  

Repeated testing, the GR LEDS are still over what they should be, and can't adjust lower because all the trimmers are all ready at the lowest position.

Any advice or should I just live with it?

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CP4500 Stereo Bus Compressor / Re: Make up gain no longer working

« Last post by MRMNW on October 27, 2026, 10:45:20 AM »

Thank you

Yes to both of these

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CP4500 Stereo Bus Compressor / Re: Make up gain no longer working

« Last post by JPK on October 26, 2026, 05:24:59 PM »

Check if the center pin of P2 (makeup) goes from 0 to +12VDC when moving.
Next check that this voltage reaches R90 and U22 pin7 (with less amplitude 0-2V4).