71

MP573 Microphone preamplifier / Re: Where to check for faulty transormator?

« Last post by bobbriessinck on May 24, 2024, 10:36:11 PM »

Nice one, I'll check it out soon!
Thanks,
Bob

72

MC624 Monitor Controller / Re: Problem with headphone outputs on MC624

« Last post by meesterzee on May 24, 2024, 05:33:50 AM »

I checked everything above and finally with U6/U8 pin 7 wired to GND I was able to read 0VDC at both test points. Replaced both op-amps and everything seems to be working perfectly! Thank you so much for your help! 

73

MC624 Monitor Controller / Re: Problem with headphone outputs on MC624

« Last post by JPK on May 23, 2024, 10:04:01 AM »

There is something wrong in both channels.
The pins 6 & 7 should be at 0VDC.
Does it change something in the voltages if you remove the ribbon cables going to CN24 and CN25.
What are the DC voltages on TP9 and TP10, against 0V? Should be 0VDC.
Same question after removing U6 and U8 but with a wire connected between pin 7 and 0V.
Look for bad solder joints or solder bridges in the area U6 to U9.

74

MC624 Monitor Controller / Re: Problem with headphone outputs on MC624

« Last post by meesterzee on May 22, 2024, 01:47:36 AM »

The crackling/popping is only in the left ear. I measured the straight DC voltage (no audio being passed) on U6 and U8.


U6

• 0 vdc
• 0 vdc
• 0 vdc
• -16 vdc
• -12 vdc
• -12 vdc
• +8 vdc
• +16 vdc

U8

• 0 vdc
• 0 vdc
• 0 vdc
• -16 vdc
• 0 vdc
• +14.5 vdc
• +14.5 vdc
• +16 vdc

75

MC624 Monitor Controller / Re: Problem with headphone outputs on MC624

« Last post by JPK on May 21, 2024, 04:14:27 PM »

Do you have this issue in both ears?
Please report the DC voltages on every pins of U6 and U8 against 0V.

76

CP554 Diode bridge compressor / Re: Attack times

« Last post by JPK on May 21, 2024, 04:10:20 PM »

The front pannel attack times are more realistic in the 6 or 12 ratios.
In the lower ratios they are slower because they depend on the side chain signal level and this is by design.
The CP554 1ms position matches the originial Neve circuit which doesn't have an attack time switch. 
You can reduce all the attack times proportionnally by reducing the value of C37 but this will increase the distortion in the lower frequencies.

77

MP573 Microphone preamplifier / Re: Where to check for faulty transormator?

« Last post by JPK on May 21, 2024, 12:36:45 PM »

I think you should statrt here: https://www.soundskulptor.com/forum/index.php?topic=5.msg5#msg5

78

MC624 Monitor Controller / Problem with headphone outputs on MC624

« Last post by meesterzee on May 21, 2024, 04:29:55 AM »

I am having trouble with the headphone outputs on my MC624. Signal from headphones is non-existent unless pot is cranked all the way and then I get pops/clicking distortion. This happens on both the front and rear headphone inputs with low or high gain set in the controller. All other ins/outs appear to be functioning without issue. There is no visible heat damage and all solder joints appear fine.

Testing the headphone output showed the following:

1. Signal for left/right we correct at the high side of the headphone pot P5
2. The TAP of P5 into U6b.5 was at RAIL (not sure if it was HI or LOW rail)
3. U8b.7 was at HI rail


I'm wondering if I have a bad pair of op amps?

79

MP573 Microphone preamplifier / Where to check for faulty transormator?

« Last post by bobbriessinck on May 20, 2024, 10:14:59 PM »

Hey,
my mp573 has been working great for several years but now stopped doing it's thing. The LED shows input, but I can't seem to get audio going out of the unit. Swapped both mp573s, swapped inputs and outputs on the patch, everything seems to point towards the output stage of the preamp.

Where and what should I measure to determine the root of the problem? I do kind of smell something burned, but I might be biased thinking so since it's not working. Maybe in a working state I'd totally ignore the slight odor.

Thanks!

80

CP554 Diode bridge compressor / Attack times

« Last post by laurenz.zs on May 20, 2024, 03:56:13 PM »

Dear People,

I hope you are doing well.

a few days ago i finished puting a pair of CP554s together.

I enjoyed a lot the process; Thanks JPK for making this possible.

I think both units are doing well and I calibrated as mentioned in the guide.

A little Burn in time I started testing.

I realised that even at 0.5ms Attack my CP554s fail to catch a lot of peaks.

Out of curiosity I did a test.

The test I did is not "super" precise!

I recorded a Sine Wave with 10dB of gain Reduction at different Attack/Release settings and then by reading the waveform i decided where Attack and Release starts and ends.


This is what came out:

Gain Reduction 10 dB/Ratio 3:1

Attack 0.5ms: 10ms - Release 400: 360ms
Attack 1ms: 25ms - Release 400: 300ms
Attack 2ms: 31ms - Release 400: 260ms
Attack 4ms: 97ms - Release 400: 230ms
Attack 8ms: 142ms - Release 400: 300ms
Attack 16ms: 175ms - Release 400: 360ms

Attack 1ms: 15ms - Release 100: 150ms
Attack 1ms: 13ms - Release 400: 270ms
Attack 1ms: 25ms - Release 800: 585ms
Attack 1ms: 22ms - Release 1500: 2200ms
Attack 1ms: 35ms - Release A1: 550ms
Attack 1ms: 10ms - Release A2: 2900ms

The Attack Values I recorded are off by factor of 10-20 compared to the Values on the Faceplate.

This seems to be a lot and maybe I messed something up?

If this behavior is  normal; is there a way to speed up Attack times?


FYI: to spice things up and making the learning part a bit more fun i swaped out some components.

Resistors: Most replaced by Carbon Film Resistors (same Values but twice the wattage 0.5W instead of 0.25W/2W instead of 1W)
EL Caps: Most replaced by specs except for Voltage sometimes (example:1000u-35V replaced by 1000u-50V)
Tantulum: original
Ceramics: original
Film Caps: original
Opamps: Sparkos

Thanks a lot

Stay safe