Auditronics Grandson 110-8 Story

Bob Joneson

New member
Thought I'd start a thread on this restoration project. I just completed a restoration and commission of an Auditronics 36 channel 700 series console for a friend's studio this year, and really fell in love with these things. I've been keeping an eye out over the last few months for a "candidate", and this board fit the bill to a T.

This a mid-70s Auditronics "Grandson". Auditronics bought Spectrasonics I believe in the early 70s, and their first console was based on parts from a Spectrasonics board that listed for $36k, and was called "Son of a 36 Grand". This board, the 110 was the next set of consoles they came out with known as the "Grandson".

The vast majority of these boards were 4 bus consoles, and generally short loaded with 8-16 channels.

As an 8 bus board, fully loaded with 24 channels, and 16 channel monitoring facilities, this would have been the "Cadillac" of grandsons, and I've only seen one other example in existence. That, and it includes the optional patchbay as well,

Aside from being built like a tank, with fantastic components and fully modular, the inductor based EQs in each channel and Jensen iron coupling all ins and outs make this thing a sonic wet dream as well.

I purchased the console from a husband and wife in a tiny town in Southeast Missouri, who had it sitting in there house for nearly a decade unused. They had hopes of building a studio around it, but never got around to making it happen. Previously it had been owned by an API tech in the Phoenix area who had several of these boards, and allegedly this was his "personal" console.

For it's age, it's in pretty marvelous condition. There's definitely a lot of restorative work to be done, but it's clearly been cared for.

I've got it back at my place, and have begun the process of unloading the frame to give this thing a thorough cleaning. I immediately noticed something peculiar about the input modules. All of the jensen input trannys had been replaced. 8 of them with API AP2164s, another 8 with Melcor 400-16s, and the remaining with an array of Beyerdynamic. The stock jensen are still found on all of the outputs. I'm such a fan of the Jensen iron, I'm not sure how I feel about this yet, but it does tell me someone spent a lot of hours tweaking on this board.

Much work ahead!
 

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That's a lovely board you have there. Thanks for sharing.
I have two 110a modules racked up here and they get a lot of use.

I've always found them to be great preamps with plenty of gain, but also found the first three or four clicks of the gain pots to be pretty noisy with hiss.
Is that true of your console?
I always suspected my output cards had been tinkered with. They don't seem to match pictures I've found 100%.

Congrats, and I hope to see lots of pics and info during your progress. :)

It'll be interesting to find out how those input transformers do and if there's much of a difference between the two sets.
 
I haven't even powered it on yet. These are all 110b input modules. I know they refactored the input a bit on the B revision, but in both cases, the first 3 clicks are actually a resistive pad before the transformer. I'll let you know more as I dive in.
 
Welcome, Bob! :)

I'm not familiar with these consoles so I'm looking forward to learning more.

Thanks for choosing to share your Story here! :eatpopcorn:
 
Tons of work the last couple of days. Removed all of the modules, de-knobbed, and cleaned the bujesus out of this thing. Went through at least a dozen rags and half a bottle of simple green. 45 years of grime. Fortunately, got my 12 year old son to get in on some of the work.

Debating what to do about the input configuration. There is presently a hodge-podge of different transformers from API Bridging, to beyer peanut step ups. I'm strongly considering putting Ed Anderson's EA2622s in every channel. They match the footprint, pinout, and general specs of the original jensens that would have been in the board, but would likely lend some unique flavor. That's over $1k, in transformers though, so something I'm going to experiment with before committing to.

I finally got all of the modules loaded (still need to re-knob), and the power supply wired up, and I'll be damned if it didn't fire right up. (Thankfully, no actual fire).

Most of the panel mount molex on the rear that goes to the patchbay has broken tabs, so I've ordered new connectors which should be here in the next few days. Then I'll be able to start piping some signal through and seeing just where this old beast sits.

Anyhow it's late, and I have to work in the morning. Looking forward to what the next week brings!
 

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I have discovered hell. And apparently it's broken, panel-mount molex connectors with capacitors tied directly to the chasis. :)

I'm beginning to appreciate why these consoles listed for upwards of $30k in the early 70s ($175k inflation adjusted). The hours of skilled labor that went into them is astronomical. No Chinese robots were tacking these things together on an automated assembly line. Just good ol' bust-your-ass American labor.

Good news is... I think I'm done with the rear panel molex repairs!
 

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I'm continually impressed by the engineering and craftsmanship that went into these consoles. Had I not had the chance encounter with a different auditronics console, I would never have even thought to look into them. They're just great, solid units. 5534 opamps throughout, Jensen iron, c&k switches, bourns pots. Every component is a solid workhorse.
 
Did some troubleshooting on the power supply tonight. Wasn't regulating properly. Found a faulty opamp and a bad pass transistor. Had ano opamp replacement on hand, pass transistor had to be ordered from Digikey.

Also got a set of extender cards today. Should help greatly once I get to working through the channel inputs. Got an EA2622 transformer that fits the original footprint / spec of the input modules. It's a recreation of the API 2622 by Ed Anderson.

Hope to make some major headway this weekend!
 
What is the amplitude of the audio power rails? 18V I hope? I'm a fan of the 5532 and therefore the 5534. I like how they sound...at least I like the sound of gear that uses them.

Did you find actual purpose-built extender cards, or are you fabbing some? I imagine purpose built ones would be quite rare. If that's what you got ahold of that's awesome!
 
Rails are +/- 15 per spec, but could likely be run at +/- 18. The reality is that extra 3 volts only gives you about 1.5dB of additional headroom. The 15 volt rails are good to about +22.5dBu before clipping.

I did find legit extender cards, but had to pay up for them a bit. $100 for the set. But considering what I would have into fabbing new ones, wasn't a terrible deal.
 
Waiting for parts to arrive for the power supply (should be here tomorrow), spent the evening individually scrubbing knobs, as they're still all removed. Finishing cleaning this stuff up is helping pass the time until I can move on to more functional work.

Between that and all the Molex work the last few days, my fingers and hands are shot, lol.

Monday is a holiday for me (my day job isearch working IT at a bank), so looking forward to making some serious headway the next few days!
 
Got the power supply all dialed in tonight. The main issue I had narrowed down was the pass transistor on the negative supply rail was measuring only 5 ohms collector to emitter (essentially short), this was resulting in a lack of regulation on that rail.

So, went ahead and replaced both pass transistors, and powered it on. Got a spark, and it immediately died. Upon closer inspection the new pass transistors had a slightly thinner housing, causing the mounting screws to reach just deep enough to short against the chasis. After a few expletives, determined I'd blown the bridge rectifier and a couple of other transistors. But... quickly discovered I had these components sitting in my spare parts pile from my Scully tape machines.

After getting things replaced, it fired right up. Got the voltage adjusted, and overvoltage protection calibrated, and she's regulating away now. Nice clean rails.

Started re-knobbing tonight while I let the board sit on for a few hours. Spent hours in my living room chair with a rag and simple green scrubbing every knob individually over the past couple of days.

I did pass some signal tonight as well from the on-board oscillator out the stereo bus to control room monitors. Looks promising. When passing signal to the busses, there appears to be some issues. Not sure yet if it's line output cards, or meters, or what, but I'll get there.

Once I get it all re-knobbed I'll be able to really start diving into the signal flow now that the power supply is stable. I've haven't even touched the patchbay yet or any of the wiring for that.

More to come!
 

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What value resistors do you use for your dummy loads?

And what do you consider to be clean rails? Like how many machine of ripple at the output of the supply do you consider acceptable? Did you use a scope to evaluate this? I'm asking because I want to compare notes on the power supply I'm currently working on for my prototype Tascam console...I'm wondering if I'm expecting too much from the supply and if what I'm getting is acceptable.

Enjoying this thread.

Those Mallory CGS caps for the primary filters?
 
For this test, I'm using some 50 ohm 25W wire wound resistors, simply because that's what I had laying around. The manual calls for 20 ohm, but it's what I've got. Even though they're rated for the dissipation, those suckers get HOT!

I do have a scope, and measured ripple at about 20 millivolts at the rail outputs from the supply. However, there is a ton of capacitance in the board on the rails, so that's not necessarily what we're seeing at the opamps. I'll do much more in-depth testing once I kind of get the "big pieces" stabilized. It's like painting with broad brush strokes right now. I'll slowly start using finer and finer brushes as I get further in. Kind of an analogy for how I tend to approach these things.

Yep, those are big ol' Mallory's on the main filters. 15000uF I think (I'll need to double check).

This power supply was designed and built over 40 years ago. While solid, I would expect almost any modern replacement to outperform it.
 
So I'm freaking out about 3mV ripple in the output of my Tascam power supply. Maybe I'm freaking out for nothing.

20mV seems like a lot, but yes you are absolutely right, with decent CMRR specs of most any audio opamp it should reject it. But are there any smaller value ceramics strapped from each rail to ground before it goes out to the mixer? Like 0.1uF ceramics (anything other than C0G is fine) should be there. Or if they are there but are smaller than 0.1uF you might try increasing them to 0.1uF...it might step on that HF ripple a bit.
 
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