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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.

2

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?

3

CP4500 Stereo Bus Compressor / Unbalanced channels + + +

« on: December 07, 2023, 09:49:24 PM »

-----------------------------------------------------------------------------------------------------
So, this is a continuation of thread: https://www.soundskulptor.com/forum/index.php?topic=419.msg2349#msg2349
Just to politely not weddingcrash the other users questions.

So:
I have unbalanced output after a couple of years.

My issue is that whn i start calibrating the unit from start, i can not get T1 on channel one to match the 3.0 VAC signal that is present when i standby. T1 only manages to increase the voltage to 2.595 VAC.

Edit: and on channel two board i can't get T2 og T3 down to 2.595.

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

@Dolbah
Do you get TP1=1.5VAC with 3VAC at the input?
Are the VCA's socketed or SMC?

@JPK



3.0 VAC source signal gives me 1,492 VAC on TP1.

With T1 turn on max, it gives me  2.709 VAC on the unit output.


My VCAs are in sockets

EDIT:
I realized now, that when testing with only board 1 powered, i get the above results. As soon as i power both boards, board/channel 1 suddenly gets a bump and is suddenly outputting 2.95 VAC
When removing board 2, it goes down to 2.7 VAC.

EDIt 2:
I had a bunch of OPA2134PAs laying around, so startet switching them. When replacing U21, i finally was able to match the bypass and active signal. But i have no chance of getting T4 to trimm the meter to 12 dB attenuation (worked yesterday).
Also noen of the trimmers on board 2 is reacting. And i feel the threshold is very sensitiv.

4

Discussions about the products / SS CP554 Diode bridge compressor

« on: March 31, 2022, 05:48:47 PM »

So! SS CP554 Diode bridge compressor is announced.

I allready have 2xMP573 with EQ573 Mk2 and CP4500

So, of course the CP554 looks very tempting! But i look inside, and see many of the same componenets. Same transformers etc.


Would i gain anything new with the diode bridge type compression in compared to running the 573s and CP4500?


I also have a pair of JLM LA500 comps, and a API529, but my GAS is feeling the urge to collect all the various types of compression into my setup. (And also i love the build process)

But i am haveing a feeling that i'll not gain that much new sonic terrain with the CP554..

Change my mind!!

Thanks

5

MP573 Microphone preamplifier / Volume difference between units

« on: April 21, 2021, 11:20:54 AM »

Greetings

I've buildt 2 units.
FYI: Both are missing U1 and i have temporarily shorted the center and right hole as instructed (Are the replacements on the way??)

There is a volume difference between the units at 9,2 dB. This is both via XLR and the DI.
Cables and slots have been switched for cross-reference.

• Setup went flawlessly on both units
• JMP3 jumper is removed on both
• Volume has been checked with same settings on both units
• CN1 jumper i sitiated at center and right pin on CN1, both units

I have attacked this as if the one with the lowest volume has an error, so i did a Reflow of all joints on the input transformer and did a second visual and clean of the board. I have also switched output transformers, and the issue does not follow the transformer

Went over to the the pinned post, and checked values:

Low Unit (VDC):
 
A:  2,6
B: 4,1
C: 22,6
D: 13,6
E: 2,1
F: 12,9
G: 1,0
H: 4,0
I: 0,4
J: 3,5
K: 22,9
L: 2,9


Following the signal (2.0 VAC):

• Input transformer pin 7 = No measurement
• TP1 = 0,3 VAC
• output transformer yellow wire: 49,7 VAC



High unit (VDC):

A: 2,6
B: 4,1
C: 22,5
D: 13,5
E: 2,1
F: 12,9
G: 1,0
H: 4,1
I: 0,4
J: 3,5
K: 22,7
L: 3,0

Following the signal (2.0 VAC):

• Input transformer pin 7 = 0 measurement
• TP1 = 1,3 VAC
• output transformer yellow wire: 49,3 VAC




So i have issues follwing the signal as described, but this is almost the same on both units, and the high unit sound and feel pretty perfect, so cant see any issues with it.
TP1 meassures 1VAC differently on the high vs low board.   Is this the problem area?

6

EQ573 Equaliser / EQ573-II - High band bypass issue

« on: April 06, 2021, 09:34:33 PM »

I did some final testing today, and realized i have a issue with the bypass on the high-band on one of my modules. There is a big wide bell increase in the 4-5k area.
As soon as i turn the high-band on, it behaves normally. I took some screenshots of the spectrum while running a pink noise through them, to visualize it:


First picture is of the unit that works, all bands are bypassed (XLR is switched on):



Second picture is of the other unit with the issue. All bands are bypassed (XLR is switched on):



Thirs picture is also from the unit with the issue, in this one the high-band volume knob is dead center, but the frequency knob is on "10"


So you see, when the high band is on, it sound correctly, seems to be something with the bypass circuit itself, or the switch?





Also a seperate minor issue: The SW5 Low-pass switch on the one of the modules are a bit flakey. If i turn on the Low-pass and gently press the switch up or down, the sound of the module dissapears.
I have gone over the soldering of the switch and reflowed it, but the issue is still there. Not a big problem, but could the be the switch itself?

7

EQ573 Equaliser / EQ573-II weird VU reaction

« on: March 18, 2021, 01:43:20 PM »

I have VU meters in my 500 rack. I can assign them to the slots i want. 
When turning on the rack, the needle goes wild on both units for a couple of second (and they look in sync too)

There are no audio inputs to any of them.

There is also no sound comning from them.

I have switched slots, and this happen only with the EQs, not with any of my other units.

Here is a video, each VU represents a EQ-573-II module:



https://www.dropbox.com/s/wtkdhgeottkt38q/IMG_1192.MOV?dl=0

8

EQ573 Equaliser / EQ573 II - Low band

« on: March 15, 2021, 04:31:25 PM »

Hi
I cant't find dedicated tread for the EQ573 II , so i'll put my question here.

I bought 2 of these, one is working perfect but the other seem to have problems with the low band.

When turning the red knob from "Off" to "20" or any other value, the bass frequencies gets turned down and twisting the black knob or red knob results in no significant reaction to the spectrum.

Since i have two units, i have tried switching the main boards between the fronts paneles, and the problem does not follow the main board. The issue should therefore sit in one of the front panel boards.

So, i have checked everything visually, and cant find any issues.
But, these darn Film capacitors that are placed close in a row on the front panel PCB. The middle ones are impossible to check. Could this symptom be a result of one of the film capacitors being missplaced? i rather ask, before i start desoldering to check them.

9

CP4500 Stereo Bus Compressor / CP4500 went dark during setup part 6

« on: February 03, 2021, 03:57:34 PM »

Greetings
My CP4500 went dark during setup part 6 (Calibration).

It powered it on, and the In button worked and the VU meter had light (the needle popped up to 20dB).
I got correct measurments during the voltage check, and everything seemed fine.
But after i had adjustet the sinewave to 3VAC by measuring pin 2/3 on the output XLR the LED went from green to dim orange when i turned it on. I turned it off and back on and now both the VU meter anbd the led is dark.

I have taken the unit out and put it back in several time, with no luck. I have also done a visual check, but nothing seemes off. 
I have also remeasured  0v against V-, V+ , -12v and +12v and i still get the correct measurments.
Audio passes through, but nothing seems to work.

Any one got any suggestion?