Audio Precision System One

[Audio1Man]

Hello All
I worked for AP and designed some of the products. I do repair on the Systems that AP does not support.  The major parts problems are finding the DSP, D2A  & A2D chips. If you need service, repair, DOS to ApWin contact me.

Duke  [email protected]

 

[JohnRoberts]

Hello All
I worked for AP and designed some of the products. I do repair on the Systems that AP does not support.  The major parts problems are finding the DSP, D2A  & A2D chips. If you need service, repair, DOS to ApWin contact me.

Duke  [email protected]

Hi I'm sure we'll find some questions for you...

JR

 

[bruno2000]

Hello All
I worked for AP and designed some of the products. I do repair on the Systems that AP does not support.  The major parts problems are finding the DSP, D2A  & A2D chips. If you need service, repair, DOS to ApWin contact me.

Duke  [email protected]

Welcome Duke,
Love those AP products, and thanks for your offer!
Best,
Bruno2000

 

[kilmister]

Great to have you here Duke, welcome a board!

My unit ain't passing a self test in CMRR part. The unit shows 50Hz goes just a bit over threshold limit. I've made calibration for unit but it didn't change a thing in 50HZ region. I'm suspecting those 1uF tantalum caps but haven't had yet time to change them. Can you kindly tell if you have some more hints that I should look as well?

Thanks in advance,
Paavo

 

[Samuel Groner]

Can you run a high-resolution (many steps) sweep vs. frequency for CMRR? And at various input ranges (right now I don't recall if the System One allows manual ranging--does it?)? This would be very helpful for diagnosis.

Samuel

 

[kilmister]

Hi and thanks for your reply.

I took graphs out as Samuel suggested and here they are.
Sweeps are made from 20 to 20kHz with 100 steps. Output ranges are 100mV, 300mV, 1V, 3V, 10V and 5V witch is range that unit uses for a self-test.
Output impedance was 40ohm and input 100kohm.

Please click for hi-rez.

5V self-test:


100mV:


300mV:


1V:


3V:


10V:


Thanks for your help,
Paavo

 

[Samuel Groner]

There are many measurement aretefacts in these plots... I think you should re-run with:

* a generator level of 0 dBu (no idea what you used here)
* the analyzer set to bandpass mode (track analog generator)
* slow RMS detection and sufficient settling time

The "5V self-test" plot just uses 4 points, right? There is no 5 V range, is there?

Samuel

 

[kilmister]

Hi.

I had brain-fart in my last post. I meant levels are output levels of the generator.
Output mode was in CMTST. Detector was at "Auto" and "RMS" bandpass 10Hz to 500kHz
Self-test seems to use 5 points at 50, 200, 1k, 5k and 20k.

I'm not sure what do you mean with "input range" in your earlier post?

Thanks,
Paavo

 

[Samuel Groner]

I'm not sure what do you mean with "input range" in your earlier post?

You can disable the "auto range" function of the analyzer input.

Anyway, the 3 Vrms plot suggests that the time constants of the input AC-coupling have drifted away from each other. You can verify this by temporarily shorting the AC coupling capacitors.

Samuel

 

[kilmister]

Thanks for your input Samuel.
I'll check the caps. They seem to be 1uF tantalums (C1501, C1502 in schematic) with side note they have to be matched. The exact ones I was suspecting

Cheers,
Paavo

 

[Samuel Groner]

Are you sure those are tantalum..?

Samuel

 

[kilmister]

IIRC yes they are but I might recall wrong as it's a while I had unit open on my bench.

Cheers,
Paavo

 

[kilmister]

Ok, I messed with the component numbers last time I was finding right caps from pcb. Thanks for pointing that out Samuel.

So, the caps are 1uF/200V plastics. I measured them and their values are 0.965uF and 0.978uF. Found 15nF/400V Wima and soldered it paraller with the smaller value cap. CMRR dropped back to acceptable level, around -80dB@50Hz.
Can I leave aux-cap there or is there some another problem popping up?

Cheers,
Paavo

 

[Samuel Groner]

Should be fine that way.

Samuel

 

[kilmister]

Great! Once more thanks for your help!

-Paavo

 

[jsteiger]

I just recently (last week) received an AP System One. It came from a well respected & trusted pro audio designer who says it was just fine before he shipped it. I have no reason not to believe him. Anyhow, the left generator is fine when driving a hi Z load but starts to crap out when driving a mic pre with a 1k input Z. The level drops around 2.4dB. Yes, I have the source Z set to 150R. The right channel is always good but not the left. My first step is to open it up and try re-seating cards and chips in the output stage. Just wondering if anyone has had a similar experience or not?

Cheers, Jeff

 

[Samuel Groner]

Does the level drop occur at any output voltage (try a range of say -60 dBu to +30 dBu, with an external load resistor instead of an actual preamp)? Is it accompanied with increased THD?

Samuel

 

[jsteiger]

I will investigate and report back.

 

[jsteiger]

So, I found the time to open up my AP1 today. It was easy to find 6 completely smoke R's near the A channel output. I have the pdf skiz attached. I am not sure of the cause yet. I have the R's highlighted in the skiz.

 

[mjrippe]

Personally, I'd be contacting the seller at this point and attaching a photo of the burn victims.  Once you try to fix it he will say it has been messed with and refuse to take it back or pay for repairs.  Of course if you got a great deal and think you can DIY, that's up to you.