91

MP573 Microphone preamplifier / Re: MP573 unstable, volume drop

« Last post by Co on May 06, 2024, 11:48:54 AM »

I just the following:
I also have a second MP573/EQ573 combo in another rack, that workes without problems. I switched them out, so the combo, that was in the IGS rack before is now in the API rack and vice versa, so I can rule out, if the power supply might cause the problem.
I repeated the test and now bothe units work perfectly. I have no explanation for this.
Do you have any clue, what could have caused this?

92

MP573 Microphone preamplifier / MP573 unstable, volume drop

« Last post by Co on May 06, 2024, 09:27:28 AM »

Hi JP,
My MP573 started to develop some strange behavior. After working normally for a couple of minutes, the gain starts to become unstable, going down and up again a few dB. Then after ca. 46min the gain drops considerably. The gain then very slowly goes up again.
When I use the gain switch (48min), the preamp starts working normally again, but the problem accurs again after a couple of minutes.
This problem alway occurs, no matter, what gain I set and no matter, if the EQ is in or out.
The file from the screenshot was recorded with a digital 100Hz sine.
It would be great, if you could help me with this.

93

CP4500 Stereo Bus Compressor / CP4500 meter intermittently unresponsive

« Last post by kokopel on May 04, 2024, 07:42:13 PM »

Hi

I purchased a second hand CP4500, it is very well built and mostly everything works/is calibrated perfectly.  

There is one small problem with the compression meter though...

Every now and again it's as though it is "stuck" at the zero position only moving very slightly like 1-2mm even though high compression is going on as expected.  When this happens if I raise the level of the signal being fed into the compressor by a large margin it becomes "unstuck" and works as normal (for a while) even when the input signal is back to normal.

I should say this is only happening around 10% of the time it is in use.

It is compressing correctly and when the meter works it shows the correct amount of compression.

Could this be a mechanical problem with the meter itself or could it be the driver circuit?  Are there any other components to look at which could be causing this?

Many thanks in advance.

94

CP4500 Stereo Bus Compressor / Re: Compression happening randomly

« Last post by JPK on April 29, 2024, 11:58:47 AM »

95

MU524 Vari-Mu Tube Compressor / Re: Cant find problem in my build

« Last post by JPK on April 29, 2024, 11:58:07 AM »

Your values on TP4 and output are good. The error was mine and I have corrected the values in this page. I am sorry for the confusion.
The noise in the output shown in your video comes from bad balance settings on trimmers TR1 and TR2.

96

MU524 Vari-Mu Tube Compressor / Re: Cant find problem in my build

« Last post by dr.arturs on April 27, 2024, 11:56:40 AM »

The unrealistic output level of 22.67VAC could be caused by the DMM.

*I don't think that DMM is a problem at this time.

* In changed conditions meter shows -6dB

Have you tried to listen to the output. How does it sounds?

* I think compressor is not working properly. Here are links to the two videos i made. One is with voice and one is with sine wave.
https://failiem.lv/u/ymfec8jdsq

https://failiem.lv/u/kt74mcexdq

97

CP4500 Stereo Bus Compressor / Re: Compression happening randomly

« Last post by Mr. Burns on April 27, 2024, 01:06:16 AM »

You were right! It was a bad solder joint on U10. Thanks for the help

98

MU524 Vari-Mu Tube Compressor / Re: Cant find problem in my build

« Last post by JPK on April 26, 2024, 04:27:09 PM »

The unrealistic output level of 22.67VAC could be caused by the DMM.
What says the dB meter in the changed conditions. It should show -6dB.
Have you tried to listen to the output. How does it sounds?

99

MU524 Vari-Mu Tube Compressor / Re: Cant find problem in my build

« Last post by dr.arturs on April 23, 2024, 08:05:37 PM »

Yes, sine wave value is 1VAC when compressor is connected. P2= 2.505kohm (when U1 and U2 are removed)
R16=219.7ohm

100

MU524 Vari-Mu Tube Compressor / Re: Cant find problem in my build

« Last post by JPK on April 23, 2024, 06:05:49 PM »

Your values look better.
It is only  the output AC volatge that seems a little high.
Are you sure about the input voltage of  1VAC? It should be measured with the compressor connected.
Check the total resistor value of P2, between the 2 side pins (remove U1 and U2 for this measurement).
Check the value of R16.