1

MU524 Vari-Mu Tube Compressor / Re: Light Hiss/Noise

« on: February 27, 2024, 02:26:34 AM »

Yes, the hiss would clear after removing the cover, and only reappear when securing the screws to the posts I mentioned.

2

MU524 Vari-Mu Tube Compressor / Re: Light Hiss/Noise

« on: February 24, 2024, 07:45:02 PM »

JPK,

Thanks for the suggestions. As far as I can read with my meter, it was around 1mVAC.

I tried different slots, and a different 500 chassis with no changes. I was also sure to check, and then check again, the DC converters were different considering stereo usage.

However, in the process of testing one of the units today, while taking off the panel, I noticed a decease in the hiss I am concerned about. Through some more testing, I had to isolate two of the four screws that secures the cover plate from making contact with the plate. I isolated the points on the plate from the posts and screws. Those were the screws near U2 and the one near TP5. Both devices exhibited this noise, one way worse than the other.

It was odd though. Only the screw near TP5 did this at first, and once I isolated that screw, the screw near U2 started doing the same thing, so I isolated it as well. Luckily, there were no further surprises.

I did look under the main PCB to see if perhaps some unwanted contact was being made when tightening the screw. None found. I even tested this by taping off the whole underside of the cover plate thinking perhaps some intermittent contact was taking place along the plate. I couldn't find an issue there either.

In the end, I applied isolating electrical tape on the cover holes (both sides) near TP5 and U2 in order to isolate the screw from the plate, on both devices.

Any ideas why this might be?

Connecting this back into my system, I found upping the output of the MP556 and lowering the output of the MU524, reduced audibly, any remaining noise -  aka better gain staging.

3

MU524 Vari-Mu Tube Compressor / Light Hiss/Noise

« on: February 11, 2024, 09:30:57 PM »

My intention for the pair of MU524s was as a subtle buss compressor for mixes.

I noticed that there's a light, but audible, hiss/noise coming from these devices.

I understand this may be inherent to analog, especially tube/valve, devices, but is there anything to look out for that may cause this noise?

Thank You,

Ed

4

MP566 Tube microphone preamplifier / P1/P2 100K LogB Pots

« on: February 11, 2024, 08:51:07 PM »

Is it possible to purchase a couple of these (P1/P2 100K LogB) pots from Sound Skulptor?

The "Out" pot on one of my MPU566 has gone intermittent where I need to tilt the post (i.e. wedge a guitar pick under the knob) in a particular direction for it to function. 

I reflowed all solder points on the pot to eliminate a cold joint. No such luck. It seems my pot is bad.

Thank You,

Ed

5

MU524 Vari-Mu Tube Compressor / Re: Is a THAT1246 a Suitable Substitute for OPA2134?

« on: December 16, 2023, 11:31:03 PM »

I received the replacement OPA2134...and minus my resistor mistake, once corrected, everything works!

6

MP566 Tube microphone preamplifier / Re: LED Goes Green, But Not Red

« on: December 16, 2023, 11:29:56 PM »

I was able to get a replacement from Digikey...all is working.

Thank you.

7

MU524 Vari-Mu Tube Compressor / Re: Tone Imbalance Between Two MU524

« on: December 16, 2023, 08:51:07 PM »

Figured it out.

I had the wrong value resistor at R18. The right value is 470k ohm.

Interestingly, my second kit came with two 470 ohm resistors per the BOM. There should only be one.

When it came time to install R18, I mistakenly used the extra 470 ohm in its place.

I did a 'stare and compare' between my first build and second, and with the BOM, was able to confirm 470k was the proper resistor for R18. Clearly, I had the wrong resistor installed.

Sound test completed: only a .5dB level difference, with a pretty much exact tonal response through both.

8

MU524 Vari-Mu Tube Compressor / Re: Tone Imbalance Between Two MU524

« on: December 16, 2023, 08:25:09 AM »

I've performed the setup again on both units - same issue. One has a higher frequency output than the other.

I've also tried new cables, different slots pairs...it seems related to one MU524.

Ideas would be appreciated.

Thank you.

9

MU524 Vari-Mu Tube Compressor / Tone Imbalance Between Two MU524

« on: December 15, 2023, 03:12:24 PM »

Running my two 524s in stereo, I notice about a 13dB difference in level around 10k. The levels stay parallel until around 700Hz, then gradually differ in the higher spectrum.

I'm thinking I need to redo the setup on both.

Is there anything in the circuit that would most affect the high frequency content?

10

MU524 Vari-Mu Tube Compressor / Re: Proper Stereo Use

« on: December 15, 2023, 03:09:41 PM »

Thank You, JPK!

11

MU524 Vari-Mu Tube Compressor / Proper Stereo Use

« on: December 15, 2023, 08:02:28 AM »

I was able to get both MU524s working...whew!

I'm using a Midas L6, which has a "comp bus" link between pairs of slots.

Should  I be using the Midas' link function along with the Link switches on the 524s?

Is only the detector slaved between the two units when linked?

Are the controls independent despite the link enabled?

Thank You,

Ed

12

First Aid / Re: MP566 - Missing DPDT Switches

« on: December 09, 2023, 08:02:10 PM »

Thank you!

13

First Aid / Re: MP566 - Missing DPDT Switches

« on: December 07, 2023, 04:37:41 PM »

JPK,

Can I get the manufacturer's part number on the DPDT switches for the MP566, please?

Thank You,

Ed

14

Discussions about the products / MP566 & MU524 - Sonic Delight!

« on: December 07, 2023, 02:52:14 AM »

I just finished one each, MP566 and MU524 (building a pair of each) and I must say, they sound frickin' AMAZING!

As a part of the audio testing, I ran a drum loop out of Cubase as an external plugin insert, through the MP566, then into the MU524 (and then back into Cubase) and was blown away with how big and round the sound was. The MP566 boosted the level some, not into saturation, and then the MU524...which, is a REALLY nice compressor for gentle averaging...it's not snappy, and it doesn't pump...but wow, does it really bring the whole signal to life.

Thank you, Sound Skulptor....great stuff!

15

MP566 Tube microphone preamplifier / Re: LED Goes Green, But Not Red

« on: December 06, 2023, 10:17:46 PM »

Bad LED.

When I jumped R46, there was no change.

So, I was able to clip onto the bad LED legs (i.e. signal right off the PCB) and clip onto the LED from my second kit, and it lit RED as expected: when saturated.

Not sure if I damaged it, or bad from the factory.

How can I replace this?

Thank you again, Jean-Pierre!

16

MP566 Tube microphone preamplifier / Re: LED Goes Green, But Not Red

« on: December 06, 2023, 01:22:46 AM »

Input was 1VAC 1kHz sine (from the Signal check):

1. -14.08
2. 13.57
3. 4.82
4. 15.27
5. -0.18
6. 4.82
7. -14.08
8. -8.6
9. 4.83
10. -0.05
11. -15.33
12. 4.83
13. 3.27
14. 14.19

17

MU524 Vari-Mu Tube Compressor / Re: Is a THAT1246 a Suitable Substitute for OPA2134?

« on: December 05, 2023, 07:57:37 AM »

Thank you, once again, Jean-Pierre!

18

MP566 Tube microphone preamplifier / Re: LED Goes Green, But Not Red

« on: December 03, 2023, 06:54:05 AM »

Something wrong around U3, R36...R46, D5...D11.
Check components value, direction and solder joints.

Thank you Jean-Pierre.


I did find D9 was reversed, but correcting it made no difference. I double-checked the value of all components in the vicinity of the U3, and D11 and R46...reflowed solder over everything there, but the LED would not turn red, just turn off. Lowering the gain made the LED green so, I can only conclude I must have damaged U3, or another component, in some way.

The preamp is functional (still - despite my rework, whew!), so, I'm just going to live with it the way it is.

On the next MP566 I'm building, waiting in the box, I will be more careful.

Thanks again!

Ed

19

MU524 Vari-Mu Tube Compressor / Is a THAT1246 a Suitable Substitute for OPA2134?

« on: December 02, 2023, 04:19:24 PM »

I was taking inventory of the parts for the MU524 I just received and there were only two OP2134 in the kit...and there was a third IC next to it which is a THAT1246.

Checking the spec sheets, it doesn't look like the THAT1246 would be a pin-for-pin equivalent replacement for an OP2134.

Does Sound Skulptor substitute a THAT1246 for a OP2134 when low on OP2134?

If that's a mistake, may I get a replacement OP2134?

Thank You,

Ed

20

MP566 Tube microphone preamplifier / LED Goes Green, But Not Red

« on: December 02, 2023, 07:03:25 AM »

Everything passed the signal check...but during that test (#5), I noticed as the gain increased, the green would go out...the led dark, but the voltage increased as expected.

Any ideas?

21

First Aid / Re: MP566 - Missing DPDT Switches

« on: November 30, 2023, 06:02:54 PM »

Thank you, Jean-Pierre!

Ed

22

First Aid / MP566 - Missing DPDT Switches

« on: November 30, 2023, 08:15:56 AM »

Hello,

I just received two MP566 kits and found that each kit is missing one DPDT switch.

May I have those replaced, please?

Thank You,

Ed Gelmetti