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Old 13th October 2008, 05:19 PM   #21
anatech is offline anatech  Canada
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Hi unclejed613,
Most resistor-zener-transistor series pass regulators are not designed properly. They generally run too much current through the zener, do not include a large enough heat sink for the pass element and mount the capacitor(s) too close to heat sources. That circuit is not really failure prone at all. I'd like to add that a reverse biased diode is still required across the pass transistor for the same reasons a three terminal regulator needs them. Often not installed in commercial examples.

The output impedance is related to how much gain is used. The output impedance of a series pass regulator should be lower than a zener diode (the transistor has beta). There are times when this circuit works just fine. You really have to think about what you are doing before deciding on regulator topology and the device type. Many people don't give a regulator more than a passing thought.

Most regulators are amplifiers. They have gain of some kind, and use feedback that is rolled off with a capacitor. What is the inverse of a capacitor in the response? An inductor in series effectively. So most amplifiers and servos behave as an inductive source.

-Chris
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Old 13th October 2008, 05:32 PM   #22
anatech is offline anatech  Canada
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Hi Numbdiver,
Quote:
They certainly could of made it easier for me to get the board out though!
We had to do this consistently - at warranty rates! You get used to it. Just simply take some pictures and do it.

Quote:
I labeled everything, and decided for safety's sake, I'm doing one at a time, so I have a reference, just in case.
Good idea. Just watch you don't flex the wires often as they will eventually break off. This will probably happen as you finish installing the board. That's the way Murphy assists me in my repairs.

Quote:
Caps were absolutely leaking. Not a lot of corrosion elsewhere, which is a good sign.
You can't see that stuff. A soldering iron tip will soon tell you where the stuff went. Never assume anything, always check.

Quote:
Lastly I still need the physical location of the these resistors so I can test them:
Follow the ground from the RCA jack back, it's electrically between signal ground and the main ground. This part should be near the RCA side of the PCB. They look fine when burned out, you must test them.

Quote:
I emailed Adcom about a manual, but haven't gotten a response.
These existed in paper format. There should be some scans around and there are people selling these on Eeek Bay.

-Chris
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Old 13th October 2008, 11:36 PM   #23
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that's the great thing about DIY. the regulator can be designed from scratch. you could use an op amp that has its dominant pole at 100khz if you want to act as the error amp. yes a lot of regulators are poorly designed, most of them designed for industrial applications. the poor design is "good enough" for driving stepper motors and solenoids. then other unsuspecting souls see the schematic for these regulators, make a few tweaks to the design (without improving on the fundamental flaws of the design) and use it for other purposes. and so 90% of the regulators are terrible for audio. the same goes for the use of 3 terminal regulators. designers look at the reference designs in the data book (usually without bothering to read any related app notes) lift the reference design right off the page, and move on. youre right, not a lot of thought goes into regulators, and that can be a fatal flaw in amp and preamp design. at the same time, i don't think a preamp needs a 50 amp capable power supply (yes there is a design out there with a gigantic power supply like that). that's taking the "low impedance" power supply to extremes. i do however think that a power supply should provide a low impedance path to ground for everything but DC. it's really not difficult to do, but more than a passing thought should go into it. i just recently read about using devices as "negaive inductors" to cancel unwanted inductive behavior. i'm going to look into that subject a bit more, as it might be useful for cancelling the inductive behavior of regulators without impairing their ability to regulate.
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Old 13th October 2008, 11:38 PM   #24
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btw, if anybody wants to continue on the subject of rifles and ammo, i started this thread:

historic small arms collecting
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Old 6th November 2008, 09:42 PM   #25
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I wanted to follow up with everyone that offered their help. I'm all done, and things went great.

3 board scrubbings with Simple Green & electric toothbrush, 2 dunkings in a hot de-ionized ultrasonic cleaner, re-drill the mounting holes, new hi-temp Panny caps, new servo op-amps.

One amp has ZERO dc offset, the other hovers around .05-.07vdc.

Thanks one and all for the help! I felt confident going in that I would be successful, thanks to having all the info up front.

Now if I can just find a 4ohm 300ma fusible resistor for the power supply on my Yamaha CT-7000, I'll be set...
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Old 31st January 2009, 08:50 PM   #26
anatech is offline anatech  Canada
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Hi Numbdiver,
Just use flameproof for your Yamaha. I don't even know if they have them in stock anymore. Normally I would use the factory part.

Quote:
One amp has ZERO dc offset, the other hovers around .05-.07vdc.
You still have leakage on the other PCB. Did you clean the parts themselves? Especially the op amp.

Isn't this stuff a real pain to get rid of? It gets into everything.

-Chris
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Old 5th February 2009, 04:14 PM   #27
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Hey Chris,
I got the CT-7000 up and running. No issues there. I think I'm going to send it to Punker X for an alignment/tweak, as I've never done one, and don't have the equipment or skills to do it.

I ended up leaving the other Adcom board alone. I replaced many parts including op amps. I scrubbed with electric toothbrush and hot h20/simple green 3 times. Then gave them to a friend that has a hot, de-io board bath at his work. They were in there twice, then the board oven.

I also scraped areas I thought needed scraping.

It amazes me that it could use more. But the offset is so small, I'm leaving it. The 565s are only running 150hz and below on my IRS Gammas, so I can't believe there would be any sound benefit from the additional work.

There is still enough current rush when turning them on (bumps the woofers), that I never turn them off. They idle very cool. I haven't put an ammeter on them at idle, but I think I can afford the added electricity they are burning at idle.

I'm impressed with the hold the keep on the woofers. They make excellent low-end amps. I've never heard them on mids or highs, but the fact the Nelson Pass had a hand in them, I would guess they are quite nice considering their price.

Rick
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Old 20th February 2009, 03:06 AM   #28
a.wayne is offline a.wayne  United States
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I'm looking for a service manual for the 565 , any info would be appreciated ...
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