1

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

« 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.

2

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

« 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?

3

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

« 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?

4

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

« 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.

5

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

« 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.

6

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

« on: October 22, 2024, 10:39:07 AM »

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.

7

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

« on: October 21, 2024, 07:12:12 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.

8

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

« on: October 21, 2024, 05:34:49 PM »

Can you plug the other output transformer to this unit to check if the transformer is the culprit?

This has been done several times, it follows the main board. I'll look into the areas you suggest

9

EQ573 Equaliser / Re: High pass not working EQ573-II

« on: October 17, 2024, 08:29:52 PM »

Check the values and solder joints of R26, R27, R9, J6a, J6b, C13...C22, L1, RN1, RN2.

thank you! it was somewhere on that route  All ok now

10

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

« on: October 17, 2024, 07:56:12 PM »

With the impedance set to 1200, the gain should be just a little under unity, around -0.7dB.

Ok, so the issue is still:

If i unplug the Transformer on unit 2 (the one with new Relay) for a while, the volume is normal, after a while (5-15 minutes) The volume on this unit slowly rises and ends up higher then the other.


I did some tests:
----------------

Unit 1 (The one without any apparent problem):
Output pot = 0
Gain knob: 10
Impedance 1200
Input level: -12dB
Output level: -9,79 dB

That's 2,21 dB difference

Unit 2 (The one with replaced Rly3 and gain issues):

Output pot = 0

Gain knob: 10

Impedance 1200

Input level: -12dB

Output level: -6,58 dB



That's 5,42dB difference

----------------

General powercheck:

Unit 1:
V+ and TP2
 without Transformer: 24,24 VDC
With Transformer: 24.15 VDC

Unit 2:

V+ and TP2

without Transformer: 24,35 VDC

With Transformer: 24.25 VDC




Try to follow the signal

Send a good constant sine signal on input, like 0.5VAC measured between pins 2&3 of the input XLR. Check the level with the preamp connected because the input impedance of the preamp may pull the signal down.



Connect the voltmeter black probe to TP2 and trace the signal on:


Unit 1:

• Input transformer pin 7: 0.9VAC,
• TP1: 4.669VAC (Gain=40, TRIM=Min),
• output transformer yellow wire: 8.4VAC (Gain=40, TRIM=Min).

unit 2:

• Input transformer pin 7: 0.9VAC,
• TP1: 4.68VAC (Gain=40, TRIM=Min)
• output transformer yellow wire: 8.4VAC (Gain=40, TRIM=Min).

To verify the transformers DC resistances


unit 1:

CARNHILL VTB1847 (unplugged) :

• Yellow-Orange : 7.6 ohms
• Red-Brown : 6.4 ohms
• Blue-Green : 21 ohms
• Violet-Black : 21 ohms

CARNHILL VTB9045 :

• 2-4 : 24 ohms
• 3-5 : 24 ohms
• 7-9 : 144 ohms
• 8-10 : 142 ohms

unit 2:

CARNHILL VTB1847 (unplugged) :

• Yellow-Orange : 7.6 ohms
• Red-Brown : 6.4 ohms
• Blue-Green : 21 ohms
• Violet-Black : 21 ohms

CARNHILL VTB9045 :

• 2-4 : 24 ohms
• 3-5 : 24 ohms
• 7-9 : 133 ohms
• 8-10 : 132,6 ohms

Update:

I have noe switched input tranformers between the units. The issue does not follow the transformer, so it must be somewhere on the board.

11

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

« on: October 14, 2024, 07:01:48 PM »

Got new relays today. switched RLY3 and now 300 ihm works again. The volume on the other hand is still wrong and seem to increase several dB after a while. Should i have unity gain with the small knob on 0 and the big one on 10? If not, what should the difference be on the output? 

12

EQ573 Equaliser / Re: High pass not working EQ573-II

« on: October 12, 2024, 07:09:56 PM »

Thanks! I actually misinterpreted the problem, by testing a tone with to little lowend. The actuall problem is that the unit that did not react as originaly described. actually is ok, but the other one is shaving off 3dB on all highs, when set to Hipass 360. It gradually lowers for each step on the high-pass.

13

EQ573 Equaliser / High pass not working EQ573-II

« on: October 10, 2024, 05:29:33 PM »

High pass stopped working on my EQ573-II. I have two units, and switched the mainboard between them. The problem follows the mainboard.

When turning the knob the sound just flickers on each step, but no  noticable change in the frequency spectrum. 

Any idea where to start? I have reflowed all nearby joints and then some.

14

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

« on: October 09, 2024, 08:13:50 PM »

The volume change may be caused by a faulty RLY3 relay. This relay is the one that switches the 300 ohms impedance.
You could try to replace it (TQ2-24V). To do this you will need to remove the input transformer. Follow the instructions here.


I stopped using the cable link because one of the MP73s sometimes had some kind of internal feedback problem, making a small pulse making a small "swosh swosh" sound and the led lighting up.
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.

Hi JP
Thanks! I desoldered the input transformer and reflowed all the relays just in case, but that did not help. Have ordered a small batch of new relays.
Are there any easy way to measure if the relay is ok or not?

Also, on a more superficial note,. I dig the new grey knobs on the MP73, could you give direction to where i get those?

About the EQ and the swosh sounds. It sounds like you are describing this as normal behaviour. If so, why am i only experiencing this on one unit?

Cheers!

15

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

« on: October 06, 2024, 02:52:39 PM »

UPDATE:

Today i disconnected the transformers from the mainboard for a few minutes, after reconnection them, the volume was even again.


300 ohm is still a issue.

Waiting to see which unit is changing levels.

Update:

It is the same unit that has the 300 ohm issue that also changes volume level. After 1 hour max. the volum of this unit is much higher than before.

16

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

« on: October 06, 2024, 01:56:46 PM »

UPDATE:

Today i disconnected the transformers from the mainboard for a few minutes, after reconnection them, the volume was even again.


300 ohm is still a issue.

Waiting to see which unit is changing levels.

17

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

« on: October 05, 2024, 08:35:32 PM »

I have 2 units. They outputed uneven volume for a while, so i disassembled them, reflowed some joints and measured TP2 and TP4 to check the bias of Q6.

The Q6 bias was not at 3.0 VDC, so i readjusted them and reassembled them. Tested, and i now have equal output gain from both unit.



The next day i was continuing recording with them and realized that the volume was uneven again. I forgot to pay attention to which unit it was so i am not sure if the volume was higher or lower than the other.



Both these units have been connected to EQ573-II erlier. I stopped using the cable link because one of the MP73s sometimes had some kind of internal feedback problem, making a small pulse making a small "swosh swosh" sound and the led lighting up.  This was without any audio coming in to the unit.

This doen not happen without the EQs (also have EQs affected by this problem for a god while, but i have switched the polarity. Not ure if this can help cause this?) Maybe its the same MP573 unit.





I also had LM337T instead of an LM317T for U1, and you sent replacements.
Not sure if having the LM337T can have contributet to any of the symptoms i now experience?



I will disassemble again and try to get them equal once more. But if disassembling them resetts the problem, it makes me feel like there are some electrical components needing to discharge or something to make the unit functional.



One unit has non functional 300 Ohm too, not sure if this is the same untit.



Do you have any idea where to start looking for the cause of these issues?

18

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: January 19, 2024, 10:06:01 PM »

The new VCA chips fixed the issue. Thanks JPK 🙏🏻

19

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 29, 2023, 01:39:26 PM »

I realized that the issue with not being able to trim the channel to correct volt has moved from  board 1 to board 2 since we started. I have also moved all VCAs form 1  to 2, so i took a new test switching out all VCAs from 1 to 2 again, and i found out that it is one of the That 2180A VCAs that are malfunctioning.

I'll send you an email to get this sorted.

20

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 27, 2023, 05:04:06 PM »

Usual causes for this kind of issues:
- Bad solder joint,
- Forgotten solder joint,
- Components leads cut not short enough and touching something they shouldn't,
- Conductive solder flux creating unwanted connections on the PCB.

So i have gotten a new T2 now, but still one issue remains.

Firstly:

- Bad solder joint, = reflowed all now
- Forgotten solder joint = No
- Components leads cut not short enough and touching something they shouldn't = Not an issue
- Conductive solder flux creating unwanted connections on the PCB. = both boards Cleaned with isopropanol



Board 1 is now ok, but i am left with one issue i also had at the start of this thread, which i think is the cause of the unbalance.
With 3 VAC measured when bypassed, i can only get around 2.7 VAC max with IN button activated and T2 is turned all the way up to 1K

Tests come out ok, except this:

2.3
input signal = 3VAC
Threshold on +15
Makeup on 0
Signal level (VAC) on

• TP6=1.5VAC,
• TP7=1.3VAC
• TP8=1.5VAC,
• TP9=0.06VAC

This leaves me with the original unbalance i had.  Any idea about this?

21

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 21, 2023, 07:38:46 PM »

I have added a value on 2 of the tests:
Can you check them:
Step 1.5
When Threshold goes from +15 to -15, TP5 goes from +0.35VDC to -1.2VDC

Step 2.4
DC voltage (VDC) on TP10=-1.2VDC

1.5 = 0.35 -> -1.178
2.4= 0.36 -> -1.14

But, suddenly board 1 is working now, It has been laying still since last time i measured. Weird.  The only thing "out of the ordinary" that happened, was that i touched one of the other testpins on board 2 while testing 2.4. This made the needle go all the way down to the right. After this it is ok!

Sadly no real explenation on the issue, but as with all lucky accidents i've now managed to wreck the T2 trimmer. It does simply not work anymore. I must have overturned it to maye times. New one is allready ordered

22

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 20, 2023, 09:09:38 PM »

Does the behaviour of channel 1 tell you anything about what this can be?
Sorry, no.

Threshold mutes the audio in a very steep fashion, instad of compressing it.
The signal on TP12 is the side chain signal which  directly controls the VCA's. So we need to know what is going on TP11 and TP12.

TP11 and TP12 works as they should as described in 1.5
Sorry if i was not clear enough on this. After measuring in VDC instead of wrongly setting my DDM to VAC, they checked out.

So as i said, the unit passes all tests on the "In case your CP4500 doesn't work as expected" list

1.5
Input signal = 3VAC
(measured between output XLR pins 2&3
with compressor bypassed)
Makeup on 0
Threshold goes from +15 to -15
• TP4 goes from 0.060VAC to 0.190VAC
• TP5 goes from +0.35VDC to a negative value
• TP11 goes from 0VDC to -3.5VDC
• TP12 goes from 0VDC to +3.5VDC

23

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 19, 2023, 07:08:01 PM »

My bad, these values checks out on VDC too.
Meaning the unit is passing all tests, and there is no real reason it should not work as excpected?

I don't think so:
TP11 goes from 0VDC to -3.5VDC
TP12 goes from 0VDC to +3.5VDC
This should happen when the threshold changes from +15 to -15. Is that the case?

Could it be that the trimmer is gone bad on T3?
Possible. You can check it by measuring the resistance between the 2 side pins. It should vary from 0 to 200 ohms (remove U22 before checking)3

Ok, i will check.

But could you give a feedback on what you see in the video i linked?

Does the behaviour of channel 1 tell you anything about what this can be?  Threshold mutes the audio in a very steep fashion, instad of compressing it. 
This also happens when only board 1 is active, is that normal?  If not, the chances are slim that T3 is the culoprit, as is it not even installed in the unit when testing board 1 alone.

(Edit: checked all trimmers, and they respond ok)

24

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 18, 2023, 11:02:43 PM »

When testing TP11 and TP12, my meter starts meassuring around 0.5 VAC and the meter starts decreasing in value unbtil it hits 0 VAC. Thishappen both with Threshold on -15 and +15
Here we are measuring DC voltage, not AC.

You always have the option to send us your your unit for a check. In this case, please contact us here.

My bad, these values checks out on VDC too.
Meaning the unit is passing all tests, and there is no real reason it should not work as excpected?

Not to keen on spending $$ sending the unit to France. If we can't fix this one remotley, it will sadly be discarded and put in a dusty corner. To bad, as i really really like this one.
I've buildt over 20 pc. of 500 units from various brands, only the SS TS 500 Tape module has been the one i/we gave up on.

As i said, this one worked well until i adjusted T1, T2, T3 and T4 to get it back in perfect stereo balance, then it started fritzing. Could it be that one of the trimmers have gone bad?

I tried adjusting T3 with a sine going through, and when my screwdriver touched the metal trimmerhead the audio slightly changed volume. I tried wiggelig a little and at one point the wiggeling actualy seemed to improve the issue. Both channeles now responded almost the same when adjusting threshold.
So i desoldered the T3 and inspected it. Looked fine!... and then resoldered it again = the main issue still persists, but the audio is now stable when my screwdriver hits the trimmer, and wiggeling does not help. This is all to confusing. Could it be that the trimmer is gone bad on T3? This is the trimmer i adjustet very first in the process.

I made a new video showing the issue in stereo:

https://www.dropbox.com/s/aa10nuih14c7ysq/IMG_6421.MOV?dl=0

25

CP4500 Stereo Bus Compressor / Re: Unbalanced channels + + +

« on: December 18, 2023, 10:53:49 PM »

When testing TP11 and TP12, my meter starts meassuring around 0.5 VAC and the meter starts decreasing in value unbtil it hits 0 VAC. Thishappen both with Threshold on -15 and +15
Here we are measuring DC voltage, not AC.

You always have the option to send us your your unit for a check. In this case, please contact us here.

My bad, these values checks out on VDC too.

Meaning the unit is paasing all tests, and there is no real reason it should not work as excpected?

Not to keen on spending $$ sending the unit to France. If we can
I've buildt over 20 pc. of 500 units from various brands, only the SS TS 500 Tape module has been the one i/we gave up on.
As i said, this one worked well until i adjusted T1, T2, T3 and T4 to get it back in perfect stereo balance, then it started fritzing. Could it be that one of the trimmers have gone bad? Did you watch the video i linked?