26

MP573 Microphone preamplifier / Re: Volume difference between units

« on: April 21, 2021, 04:20:33 PM »

Great job of solving the issue by yourself!

Thank you!

What are the stat on replacements for the wrong U1 parts?

27

MP573 Microphone preamplifier / Re: Volume difference between units

« on: April 21, 2021, 04:02:28 PM »

All good now!   Rookie misstake

I'll leave this thread here as fear and warning to others  

28

MP573 Microphone preamplifier / Re: Volume difference between units

« on: April 21, 2021, 03:47:05 PM »

My first thought was that i had installed it upside down, but the pins are A-symetrtical so that is not possible.

What a liar i am!

I desoldered the transformer, and it was indeed the wrong way.

Switching it around now

29

MP573 Microphone preamplifier / Re: Volume difference between units

« on: April 21, 2021, 02:56:05 PM »

So got around to test the input transformers:

Low volume unit:

CARNHILL VTB1847 (unplugged) :
• Yellow-Orange : 8,2 ohms
• Red-Brown : 6.9 ohms
• Blue-Green : 21,9 ohms
• Violet-Black : 21,8 ohms

CARNHILL VTB9045 :
• 2-4 : 149 ohms
• 3-5 : 149,3 ohms
• 7-9 : 25 ohms
• 8-10 : 24,8  ohms



High Volume unit:


CARNHILL VTB1847 (unplugged) :
• Yellow-Orange : 8,2 ohms
• Red-Brown : 6.9 ohms
• Blue-Green : 21,9 ohms
• Violet-Black : 21,9 ohms

CARNHILL VTB9045 :
• 2-4 : 25,5 ohms
• 3-5 : 25,5 ohms
• 7-9 : 135,8 ohms
• 8-10 : 135,4  ohms

So yeah, as suspected.. the low volume unit measures differently on the input transformer. Actually it measures kind of opposite.

My first thought was that i had installed it upside down, but the pins are A-symetrtical so that is not possible.

What i do see though, is that the Carnhill logo is also reversed on the transformer. Could it really have been assembled wrong at the factory?
The one to the right is the one measureing wrong:

30

MP573 Microphone preamplifier / Re: Volume difference between units

« on: April 21, 2021, 02:28:43 PM »

Also.. just FYI. The 6 step switch for SW4 in the packages i received had no small holes like these.




Most likely nothing to do with the gain difference, but just in case they are the wrong parts

31

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?

32

EQ573 Equaliser / Re: EQ573-II - High band bypass issue

« on: April 07, 2021, 12:59:13 PM »

All components are placed correctly, but i did a full reflow of the switch and R15+16  and scrubbed everything with a toothbrush and some cleaner, and now its all fine =) Thanks!



By some weird reason, SW5 is not cauing dropouts either anymore. Can't see the connection, but all well now

33

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?

34

EQ573 Equaliser / Re: EQ573-II weird VU reaction

« on: March 18, 2021, 09:58:08 PM »

I measured the output of one of the unit, it reads a spike ove 3-4 VAC.
Since the needles on the VU meters are in what looks like perfect sync, i get a feeling they are supposed to do this, but need to be sure.

35

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

36

EQ573 Equaliser / Re: EQ573 II - Low band

« on: March 16, 2021, 03:33:49 PM »

There is absolutely no need of a knife to split the PCB's.
You have probably cut a track between P2 and J7a.

Ha, now you tell me i've been afraid to break the PCBs earlier, so i've used a knife to make them separate easier.

Yes! Thats the one. 
I just scraped the circuit open on both sides of the "knife wound", and added som fluss and a dash of solder on it. Filled right up.

All good now.

side question: I manage to fuch up the threads on one of the red knobs. It sits now, but if i ever need to take it off, i might not get it back on. Are there any place i can buy replacements?

37

EQ573 Equaliser / Re: EQ573 II - Low band

« on: March 15, 2021, 08:14:55 PM »

Update: Might have figured it out.
I managed to lose track of my knife when cutting the PCBs apart

The knife made a big scratch, and thought it was only cosmetical, but it wasnt.

I will try do make a wire-bridge to fix it and test later

38

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.

39

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

« on: February 09, 2021, 10:27:31 AM »

I will.

thx!

40

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

« on: February 09, 2021, 08:51:04 AM »

Could it be that the temporary insert of 1K5 did something like this

No way.

I still believe you have had an intermittent short circuit somewhere.
And it could come back.

ok, i'll just have to keep myn eyes open.

the 1K5 resistor did not survive. Lost a leg. Could you send me an extra of that one too?
BRN-GRN-BLK-BRN-BRN

41

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

« on: February 09, 2021, 08:31:13 AM »

Sent! Thank you.

I was speculating into what could have solved the issue.  I have read about peaople using Resistors to discharge other components.
Could it be that the temporary insert of 1K5 did something like this, and thus fixed the issue? Sounds far fetched, but this is the only X-factor so far.

I calibrated PCBa successfully last night,  i am going to re-solder R72 now and calibrate PCBb and give the unit a go

42

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

« on: February 08, 2021, 10:30:54 PM »

Ok, good news!

I decided to remove the Resistor, and added a Amber LED i had.

meter dB = 0
I measure 2 VDC between the LED pins

Gonna leave it on for a while and see if it burns.

I have NO idea why it works now, i really do hope that this was not the works of 2 faulty LEDs in a row.


So, what i need:

The IN switch is no good, it has been slow since the beginning (see earlier post) And it is slow again now. And does not always pop all the way back out.

Also, I need new LED.

Can you provide this?  I am thinking about ordering more LEDs anyway, so i can buy a new one myself, if you can provde a new switch.

Is this the correct size? https://www.switchelectronics.co.uk/blue-2mm-lighthouse-diffused-led

43

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

« on: February 08, 2021, 08:54:56 PM »

What if i remove the resistor, and try to insert a new (temporary) LED again

Any LED will do, the specs are very tolerant.

You got 2 LEDs burning in a row, this shows another issue.

Ok, so where do we go from here?

44

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

« on: February 08, 2021, 07:06:59 PM »

This looks plain normal!
Nothing happens if you shake the wires to the meter a little?
I just cannot understand how the green LED may have burnt. And why the needle went to 20.
I suspected an intermittent short circuit inside the meter.

Hmm..
I'll have to shke the wires later, but i have done this allready.

But does not the 1K5 resistor we borrowed affect stuff in a positive direction? or are you saying that the LED should "resist" the equivalent of 1K5?

Are you now saying that there is not coming too much current into the LED/meter at all, even if i remove the resistor and put in a new LED or a short?

Can i safely put in the ICs and test?

Ok, lets assume the original LED was just bad. (Please send me the specs, so i can order a new one)

What if i remove the resistor, and try to insert a new (temporary) LED again. Lets just investigate their specs:

These are the ones i have available.
I tried the White one last time. It burned out, but kept the connection intact.

https://www.switchelectronics.co.uk/pure-white-3-x-2mm-rectangular-led-500mcd-100

Are there any reasone any of these LEDs wont be suitable?

45

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

« on: February 08, 2021, 05:05:55 PM »

What DC voltage across the 1k5?
What DC voltage across the meter small terminals?
What DC voltage across the relay (taken across D19)?
What DC voltage across R104?
Does the meter lights up?

What DC voltage across the 1k5?  8,6 VDC
What DC voltage across the meter small terminals?  5,7 VDC
What DC voltage across the relay (taken across D19)?  16,8 VDC
What DC voltage across R104? 1,3 VDC
Does the meter lights up? Yes

46

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

« on: February 08, 2021, 03:18:23 PM »

Can you temporarily replace the LED by a resistor of 1 to 1.5 k ?
And check if you can hear the relay clicking when you activate the compressor.

No, i do not have any spare Resistors around. i would have to de-solder one from PCBb in that case

Edit: But, why not. I'll just borrow one from PCBb. I'll take R72

I put R72 (1K5)  in the LED spot, and yes the Relay clicks whn turning the unit on.

Also, for the first time ever, the VU needle is resting at 0db

But, the resistor is taking down the exessive voltage, right? So we still need to find out where the extra voltage is coming from.

47

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

« on: February 08, 2021, 02:49:10 PM »

Can you temporarily replace the LED by a resistor of 1 to 1.5 k ?
And check if you can hear the relay clicking when you activate the compressor.

No, i do not have any spare Resistors around. i would have to de-solder one from PCBb in that case

Edit: But, why not. I'll just borrow one from PCBb. I'll take R72

48

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

« on: February 08, 2021, 01:06:40 PM »

If PCBa is disconnected i do not get a measurment.
If PCBa is connected tom PCBc, i measure 0,54  (20k on DDM) with the second down right pin. Se picture below.
Edit: I get no measurment between the corresponding pins on CN2b

So, i am looking at these.  As next suspects.

First, this is how i have been thaught to measure shorts:

I set the DDM to Ohm and 200. I measure my probes togheter and get something around 00,7
I then touch the probes between any suspected shorts on the PCB (where there should be no connection at all) And if i get a similar measurment i conclude there is a short.

Is this the correct way in your eyes?

I get no shorts between the VU+ and VU- pin on CN2a/b this way.

If i choose to increase sensitivity to 20M, i do not get a reeading between probes anymore, but now i get a reading between VU+ and VU- pins on CN2a, without PCBc connected on 0,25

Forgive my lack of experience on this specific measure, but is this a sign of short-circuit?

The visuals indicates no short at all, so i am uncartain why the 20M gives me a reading.
Here are some closeups of the VU pins

49

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

« on: February 08, 2021, 12:21:51 PM »

569 Ohm, on large terminals  and only "1" (infinite, right?) between the small ones

You must also check between the small and large terminals, in case there is a short circuit inside the meter.

I have checked this, there are no shorts between any of the meter wires.

50

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

« on: February 08, 2021, 11:36:47 AM »

- Keep the IC's removed until this is sorted out.  Done!

- Check the meter: 600 ohms between the large terminals, infinite resistance between any other terminals.
569 Ohm, on large terminals  and only "1" (infinite, right?) between the small ones



- Check the relay coil, 2800 ohms across D19.  Measuring 2.83 at 20k on the DDM


- Look for a short circuit between the CN2 Vu- pin (second down-left)and any other close pin.

If PCBa is disconnected i do not get a measurment.
If PCBa is connected tom PCBc, i measure 0,54  (20k on DDM) with the second down right pin. Se picture below. 
Edit: I get no measurment between the corresponding pins on CN2b