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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!

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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.

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

« Last post by JPK on October 26, 2024, 04:38:42 PM »

u2 shows around 14.8mv and u5 shows about 12.2mv
This may be the meter cable causing the IC's to oscillate. Try metering on TP6 (instead of TP2) and TP8 (instead of TP4) with the volume maxed.

also input 3 and 4 buttons, when one is pressed both LED's light up
You must have a short somewhere on U14 between pin5 and pin6. It can also be on connectors CN34a / CN34b (last 2 pins on the right)

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

« Last post by JPK on October 26, 2024, 04:21:50 PM »

The 1 VAC were measured between Pin 2 of the Soundskulptor extender and and the 0V Pin on the PCB
This is not correct because the output is transformer coupled so it is floating and not related to the 0V pin.
You must connect the voltmeter between pin 2 and pin 4 of the extender.

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MC624 Monitor Controller / high offset on u2/u5

« Last post by mcdavis on October 26, 2024, 02:06:54 AM »

the other two opamps zero'd fine, u2 shows around 14.8mv and u5 shows about 12.2mv without any more travel on the pot.

What should I look at?

also input 3 and 4 buttons, when one is pressed both LED's light up, but I can hear relays activating for each one individually. I don't actually care that much about the light assuming it works right.

Any input would be great.

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LA502 Optical Compressor / LA502 setup question / potential problem

« Last post by MaurizioFratello on October 25, 2024, 02:18:37 PM »

Hello,

I have built the first of two LA502s. Everything went smoothly (the manual is very nicely written and well done!). I have followed the setup guide meticulously but ran into a couple of problems or at least things that raise a question on my part. Maybe someone can help?

I insert a sine wave @ 1kHz and 1VAC into the unit. The 1 VAC were measured between Pin 2 of the Soundskulptor extender and and the 0V Pin on the PCB. It follows the input source nicely and I don't know which Pins on the extender I should use for measuring it otherwise. "Gain" and "Peak" potentiometers are fully ccw, all switches are left except for the bypass switch, which is center. Gain still fully cccw, I get 1,42VAC at the output. When I turn the gain all the way up, I get only 19,1VAC. The setup insists it should be at least 20VAC... All other setup steps work as described. The unit itself seems to function nicely, except for a couple of strange things:

• The "Peak" potentiometer reacts very sharply, i.e. a light compression is only achievable between 0 and may 20. This is dependent on the input level (of course) but still a bit odd as the device should handle line level easily, right?
• When Attack is set to 5ms, the LED meter reacts a lot (!) more compared to 10ms and 20ms, i.e. when 20ms is selected the GR LEDs will maybe hit 3dB reduction but when switching to 5ms attack, it will indicate 12dB gain reduction for a very short time. Is this to be expected?

I have scanned through the forum and followed most of the follow up questions for troubleshooting, especially from the troubleshooting guide (https://www.soundskulptor.com/forum/index.php?topic=19.0)

Send a good constant sine signal on input, like 1VAC measured between pins 2&3 of the input XLR. PEAK at 0. Connect the voltmeter black probe to 0V and trace the signal on:
--> I have measured 1VAC between In+ (Pin 10) of the extender and the 0V pin on the PCB (I don't have a suitable XLR cable right now).

R2 right pin: Should be at 0.7VACand follow the input voltage.

--> My measurement follows input voltage nicely but I get a reading of 1,4VAC (exactly double of the target)

REV1.4: R5 right pin should be at 0.5V. 

--> My measurement reads 0.97VAC (also exactly double of the target)

- TP1: should go above 10V when GAIN is at 100.

I measure 1V when fully ccw and 13,62 when gain is at 100

My input/output transformers seem ok:

Input transformer coil resistance:

1-5 in circuit: 2,13kOhm (target: 2 kOhm)

6-10 in circuit: 1,77kOhm (target: 2 kOhm)

Output transformer coil resistance:

1-3 in circuit: 4,9 Ohm (target: 5 Ohm)

6-8 in circuit: 4,9 Ohm (target: 5 Ohm)

9-12 in circuit: 11,3 Ohm (target: 12 Ohm)

13-16 in circuit: 11,6 Ohm (target: 12 Ohm)

Other test questions from various threads were:

• R17 is the correct one (brown, black, black, brown, brown)
• The output voltage across R17 (one probe on each side of R17) is 1,86VAC with gain fully ccw and 26VAC with gain at maximum
• The secondary DC resistance with the module unplugged between fingers 2 and 3 is 23 Ohm (target: 23 Ohm)
• I get 13,6VAC on TP1 against 0V Pin.

Especially the measurements for R2 and R5 (I get double the target voltage) lead me to believe there is a mistake. I have double checked every resistor on the board (pictures attached), they all seem fine. What could be problem and how could I troubleshoot/fix it?

Best

Moritz

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

« Last post by JPK on October 25, 2024, 11:03:56 AM »

PIN2&3, or all 3?
All 3.

How do I know if my lunchbox can take it?
It simply won't start if it cannot take it. The PSU will not power on, believing there is a short circuit on the rails.

Is there not any other ways to fix this?
The previous version of the MP573 did not have the slow start. We added it as a work around for poorly designed PSU's. If you have a good lunchbox, it is better to remove it.

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

« Last post by Dolbah on October 24, 2024, 07:55:07 PM »

This issue is caused by the inrush current limiter on the MP573. You can disable it (if your lunchbox can take the high inrush current) by shorting the pins 1&3 on U1 (LM317). You can leave the IC in place and short the 3 pins together.

Not normal but quite common. It depends on which module will power up first and it depends on components value tolerances.

I forgot about this one, and I have some questions:

• "shorting the pins 1&3 on U1 (LM317). You can leave the IC in place and short the 3 pins together." PIN2&3, or all 3?
• How do I know if my lunchbox can take it?
• What will happen if I accidentally put this in a lunchbox that can't take it?
• Since this is a common thing and not a building error, it sound like a design flaw that "might" happen if you're unlucky with your components(?). Is there not any other ways to fix this?

Just to be clear, this happens with one of the EQs, not both, and it follows the EQ if I switch slots. It does not follow the Preamp.

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AB528 Microphone preamplifier / Re: 300 vs 1200 ohms?

« Last post by JPK on October 24, 2024, 10:20:34 AM »

The mic impedance should not be higher than the preamp input impedance divided by 10.
Pre on 1200: use mics with less than 120 Ohms (most mics)
Pre on 300: use mics with less than 30 Ohms (ribbon mics generally)

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AB528 Microphone preamplifier / Re: 300 vs 1200 ohms?

« Last post by Alaska on October 23, 2024, 06:30:55 PM »

What is considered “high impedance”.  Any specific mics you would use 300 on?