eBay Mystery Mixer

[Slime_Lord]

If anyone wants the knobs, they need to be cleaned but I’ve already got a bunch of this type and changed them out after cleaning the dirt off the mixer.



I took a better picture of the logo and searched with the image, no results. I’ve attached a better image of it just in case.



I’ll try to fire it up tomorrow night, the power connector appears to be a male, 10 pin connector, similar to some that I’ve seen from Amphenol -



https://www.newark.com/amphenol-ind...|&CMP=KNC-GUSA-GEN-Shopping-PMAX-Med-ROAS-S40


1 or 2 pins aren’t connected, 2 pins handling +/- and the rest are ground. Whoever wired this was meticulous with color coding connections, I’m only seeing 1 color ran for ground. I’m assuming that it’s just reference/virtual ground ran throughout but some of the connections don’t have continuity between them.



With the supply only having a positive and negative rail, should all inputs/outputs/0V ref share the same ground or should some tie to earth? I do see one connection coming from the connector tied to the chassis, same color wire (I know I shouldn’t take things at face value, hence the question ), assuming this needs to tie to earth. Being overly cautious since I’ve got no schematic, sorry if it’s a dumb question.

Edit: leaving my dumb question up for prosperities sake. I tested continuity between all grounds from the power inputs on each channel strip. Everything except the XLR outputs share the same ground. I’m sure if the power supply that was made for this were connected, there would be continuity between the XLRs and the rest of the mixer.

 

[Slime_Lord]

It powered on without issue tonight!

It sounds as good as I had hoped it would, quiet line/preamps that saturate really nice when driven, and the 3 band EQ sounds nice and punchy. I ran an 808 clone (Yocto) and a Buchla Music Easel through to see how it summed and everything was nice and clear.

For as much dirt as there was on this, 2 pots were a little bit scratchy, contact cleaner fixed that.

The mixer is mono, both mix a and b are the same but this gives me an excuse to expand on its design, possibly replicate some of the channels and learn some stuff.

 

[vitopower]

The pcb material and layout style are similar to an eq board I acquired years ago from Opamp Labs when I bought a bunch of kits from them. The logo is also similar, maybe this was an early prototype or a redesign. Great find!

 

[Slime_Lord]

The pcb material and layout style are similar to an eq board I acquired years ago from Opamp Labs when I bought a bunch of kits from them. The logo is also similar, maybe this was an early prototype or a redesign. Great find!

Do you by chance have any pictures of the boards you bought or any schematics handy of the strips?

I was running the mixer off +\-15V last night, I know it can handle more power what voltage is typical for OAL boards?

I paid $250 for the mixer, glad I went with my gut.

 

[johnk_1]

If anyone wants the knobs, they need to be cleaned but I’ve already got a bunch of this type and changed them out after cleaning the dirt off the mixer.



I took a better picture of the logo and searched with the image, no results. I’ve attached a better image of it just in case.



I’ll try to fire it up tomorrow night, the power connector appears to be a male, 10 pin connector, similar to some that I’ve seen from Amphenol -



https://www.newark.com/amphenol-ind...|&CMP=KNC-GUSA-GEN-Shopping-PMAX-Med-ROAS-S40


1 or 2 pins aren’t connected, 2 pins handling +/- and the rest are ground. Whoever wired this was meticulous with color coding connections, I’m only seeing 1 color ran for ground. I’m assuming that it’s just reference/virtual ground ran throughout but some of the connections don’t have continuity between them.



With the supply only having a positive and negative rail, should all inputs/outputs/0V ref share the same ground or should some tie to earth? I do see one connection coming from the connector tied to the chassis, same color wire (I know I shouldn’t take things at face value, hence the question ), assuming this needs to tie to earth. Being overly cautious since I’ve got no schematic, sorry if it’s a dumb question.

Edit: leaving my dumb question up for prosperities sake. I tested continuity between all grounds from the power inputs on each channel strip. Everything except the XLR outputs share the same ground. I’m sure if the power supply that was made for this were connected, there would be continuity between the XLRs and the rest of the mixer.

i'd like to get some of those knobs from you if possible.

 

[Slime_Lord]

i'd like to get some of those knobs from you if possible.

All yours, shoot me a message w your address.

 

[johnk_1]

please hold onto them for me (!) i'm waiting for the site to allow me to start conversations so i can send you my address.

 

[johnk_1]

or send me a PM and i'll respond to it. thanks!

 

[vitopower]

Do you by chance have any pictures of the boards you bought or any schematics handy of the strips?

I was running the mixer off +\-15V last night, I know it can handle more power what voltage is typical for OAL boards?

I paid $250 for the mixer, glad I went with my gut.

They are in a box in storage, its the 2 band eq kit and another eq, but the PCB is similar clear green and IIRC the mounting holes were similar cuts. The eq kits I was using were +/-24v but I remember there were different voltages on some of their plugin modules.

here's an expired listing with the 2 band schematic (not mine)
https://reverb.com/item/39934496-2-...r-sets-diy-quad-eight-electrodyne-inductor-eq

 

[Slime_Lord]

They are in a box in storage, its the 2 band eq kit and another eq, but the PCB is similar clear green and IIRC the mounting holes were similar cuts. The eq kits I was using were +/-24v but I remember there were different voltages on some of their plugin modules.

here's an expired listing with the 2 band schematic (not mine)
https://reverb.com/item/39934496-2-...r-sets-diy-quad-eight-electrodyne-inductor-eq

Perfect, thanks for sharing!

I need to check again but don’t remember seeing inductors on the EQ section.

I traded some gear last month for a Stevenson Interface Electronics 100D mixer, the EQ design is somewhat similar to the schematic in the reverb ad. i might try to compare the 2, the 100D could def sound a lot better, lol.

 

[Slime_Lord]

I just disassembled one of the boards, scanned and traced the layout. First time doing this but with the boards all being single-sided, it’s a good learning experience.

I’m going to try making an adapter board for the NE531 - 8 pin can > 8-dip, with a 2520 footprint outside of the 8-dip footprint.

I’ll share the gerbers later this week!

 

[John Kallas]

for some reason (unexplained) i can't find the message that you sent me that i responded to.

 

[Slime_Lord]

for some reason (unexplained) i can't find the message that you sent me that i responded to.

I’ll message you

 

[John Kallas]

i got it in my email but not on the website for the latest one. thanks!

 

[John Kallas]

they say that i need 10 posts so i can receive messages (so here's another one)

 

[jasonallenh]

Date code on those opamps appears to be "thirtieth week of 1974" if I am understanding it correctly. '60s it is not. Doesn't mean it isn't cool, and it does appear to be well built/wired.

"Wild inputs"? That sounds fun!

You can never get enough wild inputs!

 

[Winetree]

Could this be the the answer to the PAL in logo.
Paul Buff built the mixer and tape machine used in his studio.


Pal Recording Studio - Wikipedia

 

[jasonallenh]

Could this be the the answer to the PAL in logo.
Paul Buff built the mixer and tape machine used in his studio.


Pal Recording Studio - Wikipedia

According to this, the studio was long since closed by the time these opamps were manufactured. Doesn't mean it wasn't him, but that logo doesn't appear in any images I can find

 

[Slime_Lord]

Could this be the the answer to the PAL in logo.
Paul Buff built the mixer and tape machine used in his studio.


Pal Recording Studio - Wikipedia

I don’t think so, it looks like that studio closed it doors in 1964. Despite what the eBay seller thought, the mixer is not from the 60s.

I suspect it’s opamp labs boards put into an enclosure. The faders look very similar also.

Jasonallenh, 74ish sounds about right! Didn’t realize there was a way to figure out the manufacturing date, good to know.

I scanned the channel and ACA boards in and traced them in sprint layout. Channel rough draft (free hand trace) and most recent iteration are attached. I’d like to extend the channel so that the transformers are mounted onto the board. I’ve got 12 input transformers pulled from Yamaha PM-180 & M604. Haven’t got far enough to see if they’ll work as an input transformer for a channel though.

I’ve never done this before, there’s probably errors on the most recent iteration. Figured I’d share for feedback.

 

[Slime_Lord]

I'm merely repeating my Post #15!!! Looking at your recent images shown in Post #41 actually scares me!!!

[there’s probably errors on the most recent iteration] -- And.....it's an unfortunate "fact-of-life" that you DO NOT want to have any errors!!! That's just how things are.

Otherwise.....GOOD LUCK!!!

/

Check your PMs

I'm merely repeating my Post #15!!! Looking at your recent images shown in Post #41 actually scares me!!!

[there’s probably errors on the most recent iteration] -- And.....it's an unfortunate "fact-of-life" that you DO NOT want to have any errors!!! That's just how things are.

Otherwise.....GOOD LUCK!!!

/

i wonder if there’s something wrong with private messages, I sent you one shortly after post 15. I’m still down to have the boards reverse engineered, so feel free to get back to me when you can .