1

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by JPK on November 05, 2024, 04:41:21 PM »

You need first to find out in which section the level change takes place:
- input section: you can measure the signal level on tranformer T1 pin7 (against TP2),
- preamp section: measure the signal level on TP1 (against TP2),
- ouput amp section: measure the signal level on tranformer T2 (between yellow and brown wires).
This should narrow the search scope.

2

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by Dolbah on November 04, 2024, 08:43:42 PM »

Yes, possible. This switch activates 2 different relays: RLY2 and RLY3.

I switch both Relays now, same issue afterwards.

3

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by JPK on November 03, 2024, 05:53:39 PM »

Yes, possible. This switch activates 2 different relays: RLY2 and RLY3.

4

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by Dolbah on November 03, 2024, 02:26:59 PM »

How about you send it to us for verification? I'm a bit out of ideas...

I'll concider it, but it's not tempting to use more € on this. Buying replacement for broken relay alone cost 50€ inkl. freight and import.

The "new" way of resetting the issue is now to fip the Ohm switch back and forth a couple of times.Could this also be relay issue?

5

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by JPK on October 30, 2024, 05:39:30 PM »

How about you send it to us for verification? I'm a bit out of ideas...

6

LA502 Optical Compressor / Re: LA502 setup question / potential problem

« Last post by JPK on October 30, 2024, 08:31:08 AM »

You could reduce the gain of the side chain by decreasing the value of R21 from 47k to 22k or 10k.

7

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by Dolbah on October 28, 2024, 06:53:39 PM »

Unit 1: output transformer yellow wire: 8.4VAC (Gain=40, TRIM=Min).
unit 2: output transformer yellow wire: 8.4VAC (Gain=40, TRIM=Min).

Both units have the same level on the output transformer primary.
The issue must be the transformer or post transformer: R25/C9, R26, the phase switch or the finger connector.

Check the solder joints of R26 and the phase switch.
Can you plug the other output transformer to this unit to check if the transformer is the culprit?

I desoldered all joints on R25/C9, R26, the phase switch and I inspected the the finger connector.
I then cleaned all surfaces with isopropyl ans desoldered with fresh tin.

Just to be sure I switched output transformers between the units.

Still same issue.

One thing I have noticed. At sometime during my search for this issue, unit 2 has stopped "resetting" itself, like it did earlier when the the output slowly rised after the output transformer was disconnected for a while. This seem to have stopped and now the volum is higher regardless.



But none og the units have the unity gain that you told me about though.

Update: This issue might have been 2-sided. After testing yesterday, i turned some switches on both unit, to see if anything weird happened. And on unit 1, when selecting 300 ohm and then back to 1200 ohm, i suddenly gpt a volume difference.there too, but on this, the volume was lower. So i reflowed all suspects around the switch and i now have stable sound on both.  So it might seem like i hade a increasing issue on unit 2 and a decreasing issue on unit 1.

Tested a while yesterday, and i have a steady signal going into both now for 15 minutes with no isuues 🎉 Will leave the signal on while working today, and check in now and then.

I shorted the U1 pins today. When i reasembled the modules, the uneven volume came back. I have now found a way to recerate the issue. It seem that the P1 gain knob might be the issue, but its still a bit weird.

Unit 1
Step 1. With the module powered, i can unplug the Output transformer and plug it back in, and this wil reset the issue. Volume goes back to high/normal
Step 2. If i wiggle the P1 gain pot, the volume goes down a lot, in steps. For each wiggle i loose a little. This happens every time. I just wiggle back and forth and i loose volume. The thing is that i can not wiggle the volume back again,  to get volume i need to redo step 1.

I have desoldered and resoldered P1, it did not help.

UPDATE: Desoldere P1, and sprayed som cleaner into the pot. It made it a tad looser on the twiddle, but seem to have solved the problem.

No, it didnt. Problem back today.

Unplugging output transformer still resets the volume, but it slowly goes down after a while. This time the P1 knob doeas not provoke the issue anymore.

Suggestions?

8

LA502 Optical Compressor / Re: LA502 setup question / potential problem

« Last post by MaurizioFratello on October 28, 2024, 12:10:44 PM »

Hi JPK, 

thanks for the clarification! I have redone the adjustment and get good values across all measurement points. Then it seems everything is ok. 

One remaining question would be the rather sensitive "PEAK" potentiometer. Is there a way to make the side chain less sensitive, so you can cover more poti travel before the compressor kicks in and make compressing percussive instruments with high attack e.g. Fender Rhodes, Clarinet more precise and more subtle (currently it is more like an "on/off" thing...)?

Best
Moritz

9

MC624 Monitor Controller / Re: high offset on u2/u5

« Last post by mcdavis on October 26, 2024, 06:40:42 PM »

I think you were right about the offset, I checked later and everything seemed fine and I was able to zero them out.

I still check for shorts on the IC/pins thank you!

10

MP573 Microphone preamplifier / Re: 300 Ohm not working + suddenly change in output volune

« Last post by Dolbah on October 26, 2024, 05:28:54 PM »

Unit 1: output transformer yellow wire: 8.4VAC (Gain=40, TRIM=Min).
unit 2: output transformer yellow wire: 8.4VAC (Gain=40, TRIM=Min).

Both units have the same level on the output transformer primary.
The issue must be the transformer or post transformer: R25/C9, R26, the phase switch or the finger connector.

Check the solder joints of R26 and the phase switch.
Can you plug the other output transformer to this unit to check if the transformer is the culprit?

I desoldered all joints on R25/C9, R26, the phase switch and I inspected the the finger connector.
I then cleaned all surfaces with isopropyl ans desoldered with fresh tin.

Just to be sure I switched output transformers between the units.

Still same issue.

One thing I have noticed. At sometime during my search for this issue, unit 2 has stopped "resetting" itself, like it did earlier when the the output slowly rised after the output transformer was disconnected for a while. This seem to have stopped and now the volum is higher regardless.



But none og the units have the unity gain that you told me about though.

Update: This issue might have been 2-sided. After testing yesterday, i turned some switches on both unit, to see if anything weird happened. And on unit 1, when selecting 300 ohm and then back to 1200 ohm, i suddenly gpt a volume difference.there too, but on this, the volume was lower. So i reflowed all suspects around the switch and i now have stable sound on both.  So it might seem like i hade a increasing issue on unit 2 and a decreasing issue on unit 1.

Tested a while yesterday, and i have a steady signal going into both now for 15 minutes with no isuues 🎉 Will leave the signal on while working today, and check in now and then.

I shorted the U1 pins today. When i reasembled the modules, the uneven volume came back. I have now found a way to recerate the issue. It seem that the P1 gain knob might be the issue, but its still a bit weird.

Unit 1
Step 1. With the module powered, i can unplug the Output transformer and plug it back in, and this wil reset the issue. Volume goes back to high/normal
Step 2. If i wiggle the P1 gain pot, the volume goes down a lot, in steps. For each wiggle i loose a little. This happens every time. I just wiggle back and forth and i loose volume. The thing is that i can not wiggle the volume back again,  to get volume i need to redo step 1.

I have desoldered and resoldered P1, it did not help.

UPDATE: Desoldere P1, and sprayed som cleaner into the pot. It made it a tad looser on the twiddle, but seem to have solved the problem.