Thanks to Hifiengine.com I was able to get my hands on the official service manuals and the owners manuals + every schematic!! HiFiEngine is free to register and after that you can download their entire catalog if you wanted. This gives you details on where to put volt meter terminals and check the biasing for each sides power transistors (for the Sansui). Once I did all the service manual recommended steps, I then decided to turn it on after I had torn it down to the bare chassis where the main PCB and transformers sit and flipped it upside down to remove the base (more circuits underneath).
Sansui AU-517 Semi-Conductor Count:
Zener Diodes: 10
Nothing looked suspect of being damaged or about to cause havoc after 2 hours of looking, so I hooked it up! I would advise someone dealing with similiar equipment age to use a variac, because we don’t know for sure how long it has been since it turned on last. Bad timing with an AC surge or just dirty AC can wreck havoc on compromised components. Play it safe if you can, look up how to use a 100W light bulb as a variac.
Sansui AU-517 Brochure (English PDF):
To my complete amazement.. this thing just worked out of the gate. I have roughly 20-30 hours listening time with it at this point and I haven’t experienced any downsides like distortion, not even ground hum! This thing is one impressive piece of equipment and having the speaker A+B option allows you to have dual stereo in front and behind you. This amp is almost entirely built with discrete components (DIP-8 op-amps weren’t feasible yet for audio) and it has nothing digital installed inside because it was built in 1978. This all results in a “back to the basics” kind of approach that many people in the field recommend including the “The Complete Guide to High End Audio” by Robert Harley (link).
The Sansui AU-517/717 both use DC amplification or Direct Coupled amplification, that is, without the assistance of bypass capacitors. No capacitors in the negative feedback loop at all. This means that all the transistors, FET, diodes connections can all be made directly. There are also no capacitors at the input or output (i.e. no caps in the signal path at all) and due to this Sansui calls this a “True DC design”. In 1978 there were very few engineers knowledgeable enough in audio and DC circuits, making these two models the AU-517 (featured on this site) and the slightly better AU-717 pretty unique at the time.
Due to this design these amplifiers can amplify from 0Hz (0Hz = DC), all the way to 200,000 Hz (by a scale of 10x greater than human hearing). Sansui says that due to the extreme range, this makes the performance of the audible range (20Hz – 20kHz) only that much better. One of the biggest upsides is one of the best TIM (Transient Intermodulation Distortion) ratings available at the time. Sansui says all of this is due to removing one of the biggest causes of distortion in the signal path, capacitors. Removal of the capacitors in the signal path gives the power amplifier much faster transient response. We can see this difference below in the oscilloscope captures of sending in square waves and their outputs compared to normal amplifiers at the time (1978). The power amp input is a dual-FET differential this is in place of the usual input capacitors.
One other note of interest is the fact that these amps are selling for $430-$670 on Ebay with some not much better than mine in terms of shape. They only have 3 total AU-517 on Ebay currently (Dec 16) in the United States. So I guess you can definitely say I got a nice donation amplifier!! I bet this thing will be able to be passed down to my kids haha, just needs a cap job at some point.
Sansui AU-517 Schematic (English PDF):
Inside our 1978 specimen, we have top end parts inside like all ALPS potentiometer and switches, high end power capacitors (Nichicon CEW) etc. etc. This is made to be rack mounted and used probably in conjunction with a few of them. Using it in conjunction with a home theater is pretty fun though! I recommend using stereo fronts (or center too) + the rears and you’ll have one + – that aren’t used if you go with the center. However I think this gives the best balance of sound for using the A+B option, this depends how good your center is vs. your front stereo speakers. The center channel is the most used channel for TV and movies, so my center is worth the same as both my floor standing Polk 70’s do together. I run a Definitive Technology C/L/R 2002 center channel. Don’t forget to check out the headphone output on this amplifier, it was far better than I was expecting. I have heard a few good headphone amplifiers from Schiit Audio and vintage units, this Sansui AU-517 is right up there with them.
The ideal setup:
Clean AC Power -> Music Source (CD, DAC, Vinyl) -> Pre-amp/control-amp/s+EQ(optional) -> Power Amp/s
I have included some of the harder to find info on this amplifier to help people who can’t use HifiEngine for whatever reason through out this article. I put a title in bold and underlined that all end with PDF) the next thing is the link. The files are uploaded to my site, so you should have no issues accessing them. In the chance that you do have issues accessing them, just contact me through the Contact tab and I’ll email it to you at no cost. I hope this helps someone and never underestimate the tank of an amp that is the Sansui AU-517/717!!