Build Thread:MS PQ76

[Gustav]

MSPQ76

I had some requests for a non-tube PeQ version, so this is it. I used the 1176 output stage to make it a little interesting to work with for me, rather than copying something else 100%. MS processing is included. To control the gain, I cheated and added a simple opamp control.

rev 2 PCBs avaliable
Documents at the bottom

https://pcbgrinder.com/index.php?route=product/product&path=59_70&product_id=214

This is a new project, so there is no FAQ and maybe some possible issues I haven't even thought about, but Ill do my best to help out if you have any questions, or if some error I did not catch shows up. This is how these things usually work....

Gustav

 

[Gustav]

A Physical object.

 

[evilcat]

Hi Gustav,

Interesting piece we have here!!! Do you have some samples?

Best,

Ben

 

[Gustav]

Hi Gustav,

Interesting piece we have here!!! Do you have some samples?

Best,

Ben

Thanks, and nope, no samples

Gustav

 

[Mraihala]

Hello!

Lundahl LL4202 or LL2801 for this, what do you think?

http://www.lundahl.se/faq-items/ll3815-is-a-small-mu-metal-core-microphone-line-input-transformer-turns-ratio-11-5-2/
http://www.lundahl.se/faq-items/i-have-some-ll2801-what-are-they-used-for-and-is-there-any-datasheet-available-sorry-but-there-is-no-data-sheet-for-the-ll2801/

Best,
-Mikko

 

[TwentyTrees]

Hi Mikko,

Gustav's recommending the LL5402 output transformer, and the PCB is silk screened accordingly - finished mine using those and they sound grand, slightly scooped emphasis in a very pleasing way! I don't know the ones you suggested tho, so I can't say whether they'd work as well. Is there a particular reason why you're interested in them, rather than the LL5402?

There's not much out there on the MSPQ76 yet, so I'll say straight up that it's a  really fun build and sounds brilliant. I'm going to swap out the gain pots for a pair of Valab switched attenuators for better L/R control on the stereo bus (when those arrive from Taiwan), then will post in more detail about my experienece building and using it. Happy to answer questions in the mean time!

Andy (first post!)

 

[Gustav]

Hi Mikko,

Gustav's recommending the LL5402 output transformer, and the PCB is silk screened accordingly - finished mine using those and they sound grand, slightly scooped emphasis in a very pleasing way! I don't know the ones you suggested tho, so I can't say whether they'd work as well. Is there a particular reason why you're interested in them, rather than the LL5402?

There's not much out there on the MSPQ76 yet, so I'll say straight up that it's a  really fun build and sounds brilliant. I'm going to swap out the gain pots for a pair of Valab switched attenuators for better L/R control on the stereo bus (when those arrive from Taiwan), then will post in more detail about my experienece building and using it. Happy to answer questions in the mean time!

Andy (first post!)

Hi Andy.

Glad to hear you got a completed build, and the EQ is to your liking

Gustav

 

[Mraihala]

Thank you for your response Andy!

I happen to have a few vintage  LL4202 and LL2801 and was wondering if they could be used on this project, ignoring that they wouldn't fit in the PCB. Seems very interesting project indeed, like all the PCB Grinder projects at the moment 

 

[TwentyTrees]

Gustav - yep, it's lovely! Will send you more detailed feedback when I get it properly finished up, but very happy so far.

Mikko - ah, that makes sense, and is a good question! I know nothing about substituting transformers but hopefully someone more knowledgeable will chip in. I've been thinking myself that I'd like to try something else in there (maybe Cinemag) if I make another at some point...  8)

Andy

 

[hotmouthrecords]

Hello,  I have to clear up a few things maybe you already know and can chime in.  ANYBODY

on the main board:    TP1 , TP2, and TP3 are not for any soldered component right? TEST POINT?

Also the com connections are just basic 1 to 1 , 2 to 2........etc.    IF SO,  THE KITS COM COLORS ARE REVERSED FROM THE BUILD GUIDE PICTURES!!  FYI.    so.......go by number not color.?

Lastly,  the bottom pin of the MS switch also goes to nothing?        sorry if these are too basic but thanks !

HOTMOUTH RECORDS
SAN MARCOS, TEXAS

 

[Gustav]

Hello,  I have to clear up a few things maybe you already know and can chime in.  ANYBODY

on the main board:    TP1 , TP2, and TP3 are not for any soldered component right? TEST POINT?

Yes - you can reference the all-populated picture for these kinds of doubts. .

Also the com connections are just basic 1 to 1 , 2 to 2........etc.    IF SO,  THE KITS COM COLORS ARE REVERSED FROM THE BUILD GUIDE PICTURES!!  FYI.    so.......go by number not color.?

1 to 1, 2 to 2 etc. Conenctor for the molex can be turned 180 degrees, which means the colours of the cable can go either way. If you check the guide again, you may find that the colours on your build are in reverse order both on send and return compared to the pictures!?

Lastly,  the bottom pin of the MS switch also goes to nothing?

Check the schematic or board layout.  You are sending 12V to the relays when the switch is in, you are sending nothing nothing when the switch is out.

Hope that helps!

Gustav

 

[hotmouthrecords]

i have 1 quick question about the install for the frequency 2 x 6 switches.      should pole A    be on bottom?  so that pin 1 of the switch goes into hole A1 on the silk screen?    or will they work the same if flipped 180 degrees?
sorry if this is dumb but its my last step and i got really nervous that is would make a mistake this close

 

[Gustav]

i have 1 quick question about the install for the frequency 2 x 6 switches.      should pole A    be on bottom?  so that pin 1 of the switch goes into hole A1 on the silk screen?    or will they work the same if flipped 180 degrees?
sorry if this is dumb but its my last step and i got really nervous that is would make a mistake this close

The switches are symmetrical, so (from the assembly guide) - "Mount any direction".

Hope that helps!

Gustav

 

[hotmouthrecords]

My EQ is alive  but acting wierd!    all is well on bypass.    putting it in adds 4 db of gain.    then when I switch to left/right i loose the right channel.

Mid/side sound pretty good but gain pots seem to do very little.      does anyone have any good testing ideas .
What should I see at the TP's?  I am using low level link noise,    When I engage Mid/side I loose a side on the spectrum analysis too!
And I triple checked everything but still feel like i wired the pots  backwards too!    I need the master!!!
 

 

[Gustav]

My EQ is alive  but acting wierd!    all is well on bypass.    putting it in adds 4 db of gain.    then when I switch to left/right i loose the right channel.

Mid/side sound pretty good but gain pots seem to do very little.      does anyone have any good testing ideas .
What should I see at the TP's?  I am using low level link noise,    When I engage Mid/side I loose a side on the spectrum analysis too!
And I triple checked everything but still feel like i wired the pots  backwards too!    I need the master!!!

First off, you shouldn't trouble shoot it with stereo material or in MS. Get one channel working at a time, using one in/output at a time.

Second:Check the voltages on the PSU and on the board input.

Third: Would you mind sharing a few pictures of your work? (Solder & component side both). Seems like you have a few problems, so a picture may be a good start.

Gustav

 

[hotmouthrecords]

I will post a few posts to get in a few pics.      My EQ power supply is as follows , almost as labeled :    -15.1      +14.4     
+29.5      +11.8.  those are the same at board input.  both pots are doing almost nothing. 

 

[hotmouthrecords]

This is pic angle 2

 

[Gustav]

This is pic angle 2

Soldering work looks fine, impossible to see the cabling on the pictures, though.

So, now I would recommend that you check one channel at a time, MS switched out.

Gustav

 

[hotmouthrecords]

this looks like page 31 of the build guide but page 33 has a different wiring .      left only works when wired like so in picture.
Right side is totally dead.  what do i look for ?    starting point?    or what should I see  voltage wise when the unit is totaly opperational.

 

[Gustav]

this looks like page 31 of the build guide but page 33 has a different wiring .

What we know..

As I have understood your feedback, the supply voltages are good, and your bypass is working, so that gets an "ok"

Judging by your pictures, the soldering work is solid, but you can go over it to check for any bad solder points just to make sure. I am not leaning in that direction, but its best not to rule it out as a possible problem.

Unless I read your feedback incorrectly, you were getting M in both outputs when trying to run i in MS. This means the right channel output section is working, and we can concentrate on the input and gain section.

If you wired the gain pot backwards, it will just turn the "wrong" way, so unless you've moved the middle pin to a side on the pot, it should not cause the channel to misbehave or cut the signal completely.


What we can do.

I can't tell how you made your wiring at all. It seems like you pieced together wires of different color, so I can't follow them (In any case, its best that you check it yourself). Since you have a channel passing signal, you can compare the wiring on the good channel to the wiring on the one not passing signal.

These are random guesses, but you may have..

1. Wired the filter board incorrectly. You can check this visually by comparing to the good channel, but checking with your meter set to continuity would be the best solution.

2. Programmed the switches incorrectly. I think theres mention of this in the guide. Make sure to remove the programming ring, and rotate the switches fully CCW before setting i. If one of the frequency selectors is caught on the wrong side of the throw we are using.

As a test, you can take the filter board out of the equation by shorting pin 1 and 2 on the filter board connector on the main board instead of connecting the filter.


---

You asked about this earlier, but Ill repeat it just to make sure you saw the reply.

1 goes to 1, 2 goes to 2, 3 goes to 3.

---

If none of these issues "fix" it, you have to feed the bum channel a signal and check to see where it gets lost. You can see in the schematic where the test points are placed in the chain.

TP1 is on the input, TP2 is after the filter. Remember, the filter drops the signal by about 20dB when you check TP2.

If you have bypass "working" on both channels (not in MS mode), we can narrow the problem down even further and conclude the input is good.


....and after that long ramble, my short answer is, check the filter board connector. 1 to 1, 2 to 2, 3 to 3!

Gustav