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Need Your Assistance - Audire Andante
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Old 8th August 2019, 10:52 PM   #1
GKTAUDIO is offline GKTAUDIO  United States
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Default Need Your Assistance - Audire Andante

This project has been really challenging me.

It's a very interesting design with really high-quality components, but really difficult to work on, because it is two mirrored channel boards that sandwich a central chassis backplane. Access to the bottom of the boards must be made by completely opening it up like opening a sandwich. I am guessing Julius knew how to test the boards in situ, but any repairs require opening it up completely. The unit had been repaired twice by Julius, the second time it appears, with one board being replaced. I haven't been able to find a schematic.

When I got it from my brother, who bought it new from Julius, it had blown out his Otez amp, and in testing I found that it had high DC offset in one channel. I found it also had some electrolytic caps that had leaked onto one board, and one sealed Clarostat volume pot with a damaged trace. There were some flux accumulations and a few dodgy solder joints. It appears the pots, with their board mounting legs, are long out of production, so I'm still trying to determine the best fix for that pot, but only if I can fix the larger problem.

I started with the caps, replacing all of the electrolytics with then went through and measured and tested every component I could test. I cleaned up solder joints, removed flux, and cleaned jacks and switches. I have one channel working perfectly, but the other channel still has high enough DC to trigger the protection in one of my amps, and blow the rail fuse in my other amp.

I have not figured out how identify, let alone troubleshoot the JFETs, and what voltages they should be seeing. I'm hoping it's just a matter of adjusting the trimmers on the boards, but I'm not sure if I'm taking voltage readings at the right points (or transistor legs), or even if I'm upsetting voltages on the JFETs with my Fluke meter. Also, it looks like some of the metal can transistors may have been house parts for Audire because many don't have part numbers that show up online anywhere; some look like they had original mfr. numbers, but were printed over with house part numbers.

I am not a trained tech or engineer, but electronics has been my hobby for 50 years, and I've built many tube guitar amps, repaired guitar amps, built tube mono block audio amps, and have been teaching myself (with much reading from you folks here at diyaudio) how to service, repair and upgrade solid state audio gear. I've bought and am reading a half dozen books on audio design, troubleshooting, and repair, but my troubleshooting skills are just not up to the task of tracking down one remaining problem with this beautiful preamp.

It is such a rare and interesting preamp with great personal history for my brother, that I'd really like to fix it, and improve my abilities at the same time. I've attached some photos and can post more.

Thank you
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File Type: jpg DSCN5320a.jpg (912.7 KB, 210 views)
File Type: jpg Andante_Bottom_Both.jpg (889.7 KB, 210 views)
File Type: jpg DSCN5305.jpg (713.4 KB, 193 views)
File Type: jpg DSCN5299.jpg (615.7 KB, 195 views)

Last edited by GKTAUDIO; 8th August 2019 at 11:09 PM.
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Old 9th August 2019, 04:55 PM   #2
GKTAUDIO is offline GKTAUDIO  United States
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Default More photos

More photos...
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Old 10th August 2019, 02:04 PM   #3
GKTAUDIO is offline GKTAUDIO  United States
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Really hoping someone here can offer suggestions...
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Old 10th August 2019, 02:18 PM   #4
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Without a schematics it is very difficult to help...
Fab
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Old 10th August 2019, 02:37 PM   #5
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Need Your Assistance - Audire Andante
Hi Greg,
Can you post pictures of the unit's face plate and rear chassis? Someone may recognize it.

-Chris
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Old 10th August 2019, 04:08 PM   #6
GKTAUDIO is offline GKTAUDIO  United States
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Hi Fab,
Yes, that's for sure. I've searched for months for a schematic, but no joy.

Chris,
Great idea, thank you.
Greg
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File Type: jpg Andante_Face_Full.jpg (127.6 KB, 63 views)
File Type: jpg Andante_Face_R.jpg (261.1 KB, 67 views)
File Type: jpg Andante_Rear_Full.jpg (159.7 KB, 60 views)
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Old 10th August 2019, 06:48 PM   #7
anatech is offline anatech  Canada
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Need Your Assistance - Audire Andante
The metalwork looks like an SAE.

I did find another model that might show you how they thought. The Legato phono preamplifier schematic from HiFi Engine ...

I hope this helps.

-Chris
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Old 10th August 2019, 07:25 PM   #8
GKTAUDIO is offline GKTAUDIO  United States
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Thank you, Chris. I found that back in December 2018, but it is a later design using op amps instead of discrete JFETs, among other differences, including no tone controls, and I suspect the problem with DC offset in this unit is related to the tone control circuit.

That is based on a couple of times when it was connected to an amp and powered up, I switched the tone controls either out or in, and the amp protection would pop on the right channel.

Is it possible to get reliable voltage readings from JFETs without the loading from my Fluke causing inaccuracy?
Cheers,


Greg
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Old 10th August 2019, 07:39 PM   #9
anatech is offline anatech  Canada
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Need Your Assistance - Audire Andante
Hi Greg,
Yup, no problem with JFets. If you're worried, you can use your oscilloscope. The voltages will not be precise, you only need to know approximate values. The gate-source voltage would be of the most interest to you. Your drain-source voltages should indicate linear operation, except for muting transistors where they drive them into cut-off or saturation. I would expect to see diff pairs using a JFet as a constant current source for tail current.

I wish it was on my bench as we could have gone through it together.

-Chris
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Old 10th August 2019, 10:43 PM   #10
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Hi Chris,

I appreciate your time trying to help an ignoramus. It must be a real challenge trying to convey things that must be rudimentary to you.

My supposition is that the dual can transistors are dual JFET complimentary pairs, and that is what part number U404 seems to be, even though my Atlas DCA Pro 75 is calling them voltage regulators. The two connected to the trimmers just read as two diode junctions, or as not detected at all. The part numbers U1732 and 6808 on those parts don't come up on a web search. The numbers on top appear to be Audire's numbers for their location in the circuit. Am I on the right track thinking those trimmers are for adjusting CSS voltage?

Due to the unknown part number I'm not sure which legs are D,S, or G, and my 'scope skills are very rudimentary, so I'm not even sure where to connect the probes but infer from your instruction that I would probe two legs, if I can determine D,S and G?


I really do appreciate your time, Chris - thank you.


My wife just said we should take a vacation to Canada and put this on your bench!

Cheers,
Greg
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