eBay Mystery Mixer

[Slime_Lord]

I won an eBay auction yesterday for a 6-channel ‘professional custom’ mixer that, according to the seller’s description, was manufactured in the 60’s (I question the decade it was made). Each channel has an A and B path, I’m somewhat confused by this but will figure it out once it’s here.

The seller is located in California and appears to mainly sell collectibles and antiques, not sure how they came across this board.

To a certain extent, the mixer is reminiscent of Opamp Labs boards. The fader caps are triangular in shape, the VUs are identical to the ones on their tilt limiter (super generic though), and there appears to be inputs for Octal amplifiers on the side. I highly doubt it’s an OAL board though.

Cosmetically, it needs to be cleaned but the guts look pristine and meticulously wired. At a glance, the mixer appears to be discrete but the TO-18 transistors on each of the channels are can versions of the NE531.

From what I can tell, the passive components all seem to be fairly high quality, same for the edge connectors and pots (Allen Bradley). Not so sure about the faders though, considering the amount of first on the front, replacing them is probably the best option.

The PCBs don’t appear to be homemade, I see from the pics there are markings but can’t make them out.

Anyways - I’m curious if anyone recognizes this board or can ID what the PCBs used are. It’s def an oddball find and I’m totally content if it can’t be ID’d but any additional info will save me some time troubleshooting.

I’ve attached pictures of the eBay listing, just received the tracking number from the seller, should be here next week.

Appreciate any info and thanks for reading!

 

[rock soderstrom]

I like the (DIY?) building style very much, finely constructed.
Serious craftsmanship!

Do you have the power supply?

 

[Slime_Lord]

I like the (DIY?) building style very much, finely constructed.
Serious craftsmanship!

Do you have the power supply?

Of course not , but I’ve built power supplies in the past for larger consoles and have a spare Amek power supply that I might be able to use, just need to swap out the multi-pin.

The NE531 has a max voltage rating at +\-22V, so I know at least not go exceed that. I’ll more than likely try to power it up slowly with a bench power supply. I suspect one of the power rails is for the VU bulbs, will probably swap out for LEDs.

 

[rock soderstrom]

Of course not , but I’ve built power supplies in the past for larger consoles and have a spare Amek power supply that I might be able to use, just need to swap out the multi-pin.

I would keep an eye on the red tantalum caps. If they are part of the power supply, they die early, otherwise usually not.

 

[TwentyTrees]

"Wild inputs"? That sounds fun!



In all seriousness though, it does look like a nicely built piece. Curious to hear how it sounds, once you get that far.

 

[TwentyTrees]

I would keep an eye on the red tantalum caps. If they are part of the power supply, they die early, otherwise usually not.
View attachment 113317

Agreed. Thought it looks like they might be coupling caps for the A and B mix bus inputs here?

 

[Slime_Lord]

Good call out on the Tantalums - I’ll def swap them if they’re on a power rail.

I’m very excited to finally have a wild input, I’ve got more than enough wild outputs in this room to feed it .

Fingers crossed I’m able to get it up and running. I’ll report back once it’s here.

 

[k brown]

I'm wondering if 'wild' might indicate it was built for film sound (wild vs sync).

 

[cyrano]

Google tells me a "wild input" is an unattenuated input to chain mixers. Like a bus connection?

 

[Tubetec]

Seems like the 9 pin tube sockets are where the transformers sit .
its difficult to see from the pics ,
Did the unit include input transformers ?

 

[Slime_Lord]

Seems like the 9 pin tube sockets are where the transformers sit .
its difficult to see from the pics ,
Did the unit include input transformers ?

It doesn’t look like it did. I’ve got a handful of Altec line input transformers, they’re 8-pin though. It arrives next Tuesday and I’ll share some better pics of that section.

Good call out, did not see that the sockets are expecting a 9 pin input transformer. That helps narrow down what might be compatible and potentially lead to who manufactured/what this was modeled after.

Edit - I can’t count this morning, the Altec input transformers are 9 pin. The middle pin on one of mine cleanly broke off .

 

[Slime_Lord]

The mixer came today, I haven’t had a chance to go deeper into it but was able to open it up and take a look.

It’s a seriously extreme contrast between the outside and inside. I think someone dropped it in a puddle or tried to bury it, there’s dirt all over. I’m kind of into that though.

Anyways, what I thought were octal plug in amplifiers turned out to be input transformers for each channel. I’ll check for markings after work but at first glance I didn’t see any.

All of the faders are stepped. Is this more common in location sound/film boards? Considering where it came from and the unfamiliar feel, I suspect it’s main use might have been film, just a hunch though, I’ve got no way of confirming.

 

[Slime_Lord]

[The PCBs don’t appear to be homemade] -- The PCB's look to be at least 1970's, if not maybe 1980's. The fact that there isn't any soldermask or silk-screening on the PCB's shows that that was typically done on PCB's during that time-period, even on the PCB's I had designed back then. Normal and regular use of applying a soldermask and silk-screening didn't really catch on until the early 1990's!!!

EDIT: -- Once you finally receive this mixer and you are capable of carefully tracing out the PCB-routing tracks and are then also able to at least come up with a clearly hand-drawn schematic, I could take your schematic and convert it into a CAD-designed schematic suitable for a new PCB-layout!!! That is.....should you so desire for that to ever be done.

In addition, again should you ever desire to have things designed this way.....I could design a new PCB where all of the channels are on a single PCB and the new PCB would automatically come with a nifty -- soldermask -- of your color choosing, as well as a really swell-looking new -- silkscreen -- instead of the individual bare-bones ones as they are now. WHY??? Because doing so would eliminate a whole bunch of the wiring that is jumping from PCB-to-PCB and their potential connection failure points.

An-n-n-n-n-nddd.....if the chassis enclosure doesn't clean-up as well as you hope it does, I could also design a whole new chassis for you, maybe also including your new power-supply into it. Just a thought!!! Take a look:

https://app.box.com/s/ppsp38kb5rijeadt6i73q4u99nwurqqv
/

Thanks for the offer, I may take you up on that. I’d like to desolder one of the channels, scan it back in and go from there, assuming it sounds good!

A somewhat far fetched goal of mine (probably everyone’s…) is to build a console that’s tailored to my workflow. I’ve been buying smaller 70//80s mixers all year just to build some kind of reference point for channel design. At a glance, this mixer seems to tick most of the boxes, just need to hear it .

 

[Slime_Lord]

[I’d like to desolder one of the channels] -- I have had other audio-personnel either mail or UPS to me their vintage audio PCB's (like.....one guy mailed me "one each" of the PCB's from an original -- 1974 API mixing-console -- that he had bought in order to completely restore it to "New/Old" condition. This guy wanted me to completely "Reverse-Engineer" all of the original old PCB's so I could then design brand-new ones that were > IDENTICAL < to the original old ones!!! (He felt that > IDENTICAL < would maintain the "Magic Mojo" of the API circuit-boards, even though I could have improved upon the original PCB-layout).

Similarly, I once had a large aerospace firm mail me a PCB that had been originally designed in 1979 and they wanted me to not only "Reverse-Engineer" all of the circuitry and mechanical details of this PCB, but to then also design an identical PCB using all-new "Surface-Mount" components to replace all of the original old "Thru-Hole" components!!! The aerospace company later told me that they > LOVED < my new design of their ancient PCB!!! YIPPEE!!!

So.....it may actually be -- easier -- for me to "Reverse-Engineer" your existing PCB's to obtain all of the data necessary than it would be for you to accomplish the same thing, especially if you haven't done such a thing before. Just sayin'.....

/

I’ll shoot you a PM tomorrow. I’m pretty confident in my desoldering skills but I’ve also got really good at fixing damaged traces, the 2 go hand in hand .

 

[Ivan K.]

As a former film sound mixer who worked in the 70s & 80s on location, we did not use stepped attenuators. Most mixers had sealed A & B rotary pots. Some brave souls tried sliders, but rapidly found out that location environments (dust, dirt, rain, etc.) made short work of sliders (linear faders). Possibly used in post-production, but actual mix consoles in post were similar to music consoles, just bigger to accommodate 3 recording engineers for dialog, music & effects.

Did you post photos?

 

[Slime_Lord]

I’m noticing this logo underneath all the boards.

It’s hard to see from the pictures so I tried to draw it by hand.

I’m pretty sure it says PAL and not API, need to look it up.

The monitor output has R50K precision multi-turn pots. Whatever this thing is, precision and repeatability were taken into account. I’ll try to fire it up this weekend!

 

[Ivan K.]

Found photos-definitely NOT a film mixer. We rarely had any EQ except hi-pass for wind & trucks--you can't undo overdone EQ! More likely, a small location music mixer or a PA mixer for clubs.

 

[nsalis]

If you could take a much sharper image of the logo that also fills the entire image, there's a chance you could research it using Google Image.

 

[Disco Volante]

Love those knobs, they remind me of Gyraf's (beautiful) machines...
Happ tinkering!

 

[k brown]

Love those knobs, they remind me of Gyraf's (beautiful) machines...
Happ tinkering!

Believe it or not, you used to be able to buy those knobs at Radio Shack.