Neumann W492 equalizer DIY project (PCB docs added)

[sr1200]

@dogfaceaudio  - were the pots at CAPI not correct.  Im looking for 2 sets myself and the prices on what Jeffs got going on over there is just right as long as the pots are.  I dont mind the center detent on the freq pot and you CAN use dual where it calls for single gang (i did that on the first 2ch unit i built and stupidly lent out and even more stupidly sold.... regrets.... ).

 

[fnhscar17s]

Alright people long time lurker.

I have built many diy projects but this one has an issue that is stumping me.

Here's the deal:

First off no measurable output what so ever with a scope that measured the correct dbu coming out of the signal generator finds nothing on the output unless I activate hardwire relay bypass (which I believe may be linked to my other issue specifically since the eq is not getting it's + or - rails stable).

The other issue when I run the power supply unloaded I get 15v for the positive and the negative rail and 12v for a seperate rail to run the relays for hwb. Now when I attach or wire one or both channels my positive rail drops to 2v after a few minutes. I have already changed the power supply to another power supply because I speculated that maybe the psu regs were bad but the new psu does the same thing.

It is really strange that even when I get the rails to work I have no output what so ever.

Do you guys have any suggestions.

So far I have checked my psu wiring, the io wiring, torid wiring, measured my psu voltage and confirmed time based drop through observation (takes about 2 to 3 minutes before the pos rail drops to 2 to 3 volts). Running out of ideas hopefully someone here has some suggestions on where to go next.

 

[kante1603]

Hello,


not too many parts on this pcb.
Best too show us some clear and focussed pics of your build.
Which ICs do you have inserted,are they orientated the correct way?
If yes then remove them and measure dc on the ic sockets to rule them out of being faulty.


Best regards,


Udo.

 

[fnhscar17s]

Thanks for the response I am using the ne5532ap made by Texas instruments.

The proto board in the photo is just a breakout for the psu rails the center stripe for the case ground was disconnected by cutting traces where the black sharpie line is.

Here are some pics
Of the psu section

You will notice the psu filter board by collective cases the issue was tested with and withour this board.

 

[fnhscar17s]

Here is the hardwire relay bypass section it is the hardwire relay bypass kit from diy tubes

 

[fnhscar17s]

Here is the filter board with opamps in.

As a side note I tested once channel with no opamps and it held the power rails while I tested it didn't have much time as its getting late gotta get ready for work. Weird if it was the opamps what are the chances both channels are acting up unless my dumass put them in backwards.

 

[fnhscar17s]

More pics of the filter board

 

[fnhscar17s]

Different angle of the filter board. Let me know if you guys need any other angles I will be more than happy to shoot em for the assistance. Thank you once again for taking a look.

Thanks for the reply udo

 

[fnhscar17s]

Pin 4 to pin 8 on the boards measured 30v at each opamp socket. so combinated -15 and +15 potential difference of 30v

After checking this it seems they were oriented correctly according to datasheet.

Any other pinout on the ic sockets I should test?

 

[kante1603]

Hello,


thanks for the pics.


It is impossible for me to recognize anything in your build.
All I see is a massive bunch of colored thick wires and some bad solder joints (too much solder).


You should bring the eq back to life first.That means no modifications and no add-ons!!!
I see you have a nice JLM psu there.Good.

To sort things out:

Remove everything that does´t belong to the eq per default,so the additional filter board and the relays board should (temporarily) be disconnected.
Next step is -as you can imagine now- set it up with just the psu directly hooked up to the eq board.Nothing in between.
Do not forget the 0v connection from the JLM psu to the eq.
Without any ics inserted measure pins 8 and 4 with reference to ground.You should get +/- 15 vdc there.
If all is good  insert the ics and check if the unit passes audio.
If it does´t then you´ll have to trace through the circuit.
Generally -as always- give the board a good visual inspection (parts in correct position,correct values,solder joints etc.) first.
As you have the pots off-board you should definitely check your wiring.


Best regards,


Udo.

 

[fnhscar17s]

Thanks udo for the response.

I will take out any additions and power it up, I will double check my pot wiring and other wiring as well.

I checked the voltage going to the sockets last night it was 30v from vcc to gnd.

Psu connections to board -15 from gnd to negative lead, +15 from gnd to pos lead.

I will recheck my pots too. I will post a reply later tonight.

Thanks again.

 

[kante1603]

Thanks udo for the response.

I checked the voltage going to the sockets last night it was 30v from vcc to gnd

Thanks again.

You're welcome.
30vdc from ic socket pins to gnd is wrong,it should be +/-15vdc.Pin 4 is negative,pin 8 is positive.
Looks like a ground is missing.
Measure connectivity from JLM psu ground output to the middle psu connection (I think it was labelled "black"?),should have very close to zero ohms.
You must not power it up for this.


Best regards,


Udo.


Addendum:Have looked over the wiring diagram,"black" is the upper pad,not the middle one,pardon.

 

[fnhscar17s]

I will give you an update once I get off work.

I guess I forgot to mention the 30 volts i was measuring was from pin 4 to pin 8 which would be 30v collectively correct (measuring potential between them)? I will recheck when I get home.

 

[kante1603]

I will give you an update once I get off work.

I guess I forgot to mention the 30 volts i was measuring was from pin 4 to pin 8 which would be 30v collectively correct (measuring potential between them)? I will recheck when I get home.

30 volts between 8 & 4 is correct,but to be sure measure them with your black probe to 0v (audio/psu ground) on all ic sockets.
I recently helped a guy here with something similar,it turned out he forgot a groind connection.....
Better safe than sorry.

Best regards,


Udo.


P.S.:Where are you located,you might want to update your profile?

 

[fnhscar17s]

I am in the us located out of minnesota.

I will double check. Thanks

 

[fnhscar17s]

0v filter board to 0v on psu continuity test is good ok both boards. As well as pos and negative rails.

15v +/- on each socket tested and good

All off board pot wiring checked with continuity meter.

Pulled the psu filter and now to pull the relay boards.

 

[fnhscar17s]

Pulled the relay boards and pulled the psu filter unit came back to life super low noise all the filters work as they should.

Thanks again udo. I should of known to divide and conquer at board level first.

 

[kante1603]

Pulled the relay boards and pulled the psu filter unit came back to life super low noise all the filters work as they should.

Thanks again udo. I should of known to divide and conquer at board level first.

Good to hear/read!
Yes,kind of a golden rule,make the basic unit work first,then do your modifications.
For my taste you really don't need the additional filterboard because the JLM has heavy filtering on board anyway.
A couple of years ago I built an 8 channel unit,powered the same way as yours by a torroid and a JLM AC/DC,no issues.


Have fun,


Udo.

 

[fnhscar17s]

It is a very queit unit by itself. The collective cases psu filter is rated for additional 10db of improved signal to noise. I am friends with the designer I am talking to him to troubleshoot it. The psu filter drops the positive rail so I'll fix that here soon.

I have always been a fan of the jlm audio powerstations. I used em for a lot of my projects. I built an api 3124 with a di, impedance switch ,and mute switch worked great! 

For whatever reason I can't get the relay board to work I have triple checked the wiring for power and io. I'll figure it out eventually. Thanks for your help udo

This forum rules.

 

[Aslem]

Guys, i'm new here, i'm from Brazil, and i can't find this potentiometers here, i wanted build with rotative key with resistors... what do you think?