Yet another DOA

[clintrubber]

Ran into the schematic of the DOA as used in the output-sections of the AP System One.
Topology varies in a few places w.r.t. those already seen around here, so I thought it might be of interest.

Apologies for the page-width, but otherwise details might get lost.

Configured for/near unity gain (2k Rin & 2k Rfb).
More on how two of these amps are used to drive the output-transformer
can be found in pat#4,614,914.

Gentlemen (M/F), feel free to switchover to your 'if I had done it then I'd...' modes and unleash that accumulated wisdom :wink:

(AP-people, if you see this and think this is not right to have this on the 'net please let me know and I'll remove it)



Bye,

Peter

 

[bcarso]

Complex compensation network! Obviously it works...

One thing that stands out is the low voltage across Q4405. I'm also impressed that they get the fabled Ap performance out of those clunky (but rugged) output devices.

Of course the secret sauce is the negative resistance drive for the output transformer, stabilized by the noninductive copper resistor winding, which patent UREI licensed for some of their transformer-coupled-output equipment.

 

[Viitalahde]

What a wimpy output! :razz:

 

[clintrubber]

[quote author="Viitalahde"]What a wimpy output! :razz:[/quote]
At first I thought you were serious :wink: but FWIW then realized these TIPs are TO-220 devices, I think the 'biggest' that I've seen so far.

 

[Samuel Groner]

Thanks very much for the scan. Just found some spare time to run a few simulations:

* open loop gain systemone_gain.gif
* inverting square-wave response systemone_square-wave.gif

All done with 600 ohm load. I'm surprised how high the unity-gain bandwidth is considering the slow output devices (didn't had any appropriate models, used the much faster MJE15030/MJE15031). Is the HF noise gain one in the particular implementation?

Not wanting to appear greedy but do you think you could find time to make your scanner have a look at the analyser input amplifier and perhaps the notch filter? This would be mighty interesting, thanks.

Samuel

 

[bcarso]

You know this opens up an interesting avenue which will potentially rankle the company---DIY POOGE* on Ap System Ones. As you may know these machines have been way too reliable and successful, and the used market is thriving. Ap will no longer suppport the systems come next year, and already have discontinued the interface cards. Why? They need to sell their newer stuff!



*An acronym coined years ago in the pages of Audio Amateur, standing for Progressive Optimization Of Generic Equipment.

 

[Samuel Groner]

Just for the records here the important bits which already went into public domain:

www.google.com/patents?id=ZVwwAAAAEBAJ
www.google.com/patents?id=_dc8AAAAEBAJ
www.google.com/patents?id=Fkc0AAAAEBAJ

Samuel

 

[bcarso]

Those are most interesting. Note that they span the period when Hofer was trying to put Tektronix on the map as an audio test equipment company and they decided against, which led to Hofer (and Cabot?) leaving to form Audio Precision.

And as they say, the rest is history.

 

[clintrubber]

Yep, the middle one of those three is pat#4,614,914, and was stated in the first post of this thread already.

For my own sanity, I'll put further scanning on my to-do-some-day list, which doesn't mean that it'll never happen, but also prevents that in a few weeks time I'll have scanned the complete service doc in response to 'really-really the last one now, please' questions :wink:

Regards,

Peter

 

[Samuel Groner]

Note that they span the period when Hofer was trying to put Tektronix on the map as an audio test equipment company.

So we need the other Tektronix references (altough less interesting I think) as well:

www.google.com/patents?id=bjoxAAAAEBAJ
www.google.com/patents?id=oHwCAAAAEBAJ
www.google.com/patents?id=p2EwAAAAEBAJ

Samuel

 

[clintrubber]

For my own sanity, I'll put further scanning on my to-do-some-day list, which doesn't mean that it'll never happen, but also prevents that in a few weeks time I'll have scanned the complete service doc in response to 'really-really the last one now, please' questions  :wink:

Regards,

 Peter

From the AP-mailing of today:

One thing the end of the year does bring is the final days for System One service. As I noted earlier this year, System One has reached the end of a long life, and it's simply no longer cost-effective to service. To help System One users with the transition, Technical Support has gathered every System One reference they could and added it to a new System One Support page ( ap.com/products/s1 ) including the Service Manual and the original System One Training videos, starring a much earlier rev of the four AP founders!

I didn't see it there (yet) though; I either didn't look good enough or it isn't uploaded yet.

edit: Ah, it's there: http://ap.com/download/search?query=service+manual


Regards,

  Peter