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Thread: Auditronics Grandson 110-8 Story

  1. #11
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    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!

  2. #12
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    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.

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    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!

  5. #15
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    Good deal.

    Post allllllll the pictures you want.

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    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!
    Attached Thumbnails Attached Thumbnails 20161008_204107-jpg  

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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?

  8. #18
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    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.

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  10. #19
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    Really enjoying your progress here, Bob!
    This is going to be a such a rewarding job.
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  11. #20
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    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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