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Sansui AU-317 Amplifier Repair, Review & Rant!

Come with me this time as I repair a Sansui AU-317 integrated amplifier and discuss problems associated with the wrong approach to caring for old beauties like this.

As a friend pointed out to me the other day, this isn’t really a rant and I don’t actually rant here at Liquid Audio, but I do express my thoughts in an attempt to educate, inform and hopefully help readers make better decisions. Welcome back everyone and thanks for your patience!

I’ve just repaired this lovely Sansui AU-317, a classic integrated amplifier from the late ’70s that we will chat more about as we go. This case presents a worthwhile learning opportunity too and provides pause for owners of such equipment to carefully choose who they entrust it with.

By the way, whilst I’ve not been writing so many articles, I’ve been busy updating the FAQs and the Hall of Shame, in particular case #16, featuring one of the worst-made hi-fi products I’ve seen in a while, and a business owner who threatened me with legal action for making people aware of it. But I digress… Time to geek out a little bit at one of the best budget amplifiers ever made. Let’s go 😉

For more about this story and a nice little video summary that has gone viral, by my YouTube channel standards at least, check this out:

The Sansui AU-317

Many of you will have seen my own Sansui AU-317 in the workshop over the years. I love these amplifiers, their baby brothers the AU-117 and AU-217 and the bigger brother AU-517 and AU-717, AU-D707/AU-819 and AU-919. I repaired an AU-217 only last week and there is a lot to love about the slightly more capable AU-317. The rest of the range is of course legendary and I love these stylish, servicable and great-sounding amplifiers.

The Sansui AU-317 is a fully discrete component and full-featured design that can form the heart of a nice little system. With 50 Watts per channel and a solid 10kg build, these babies from 1977 – 1980 make modern $1000 amplifiers look like the toys they are. The AU-317 has a really good discrete phono preamplifier containing some very nice parts built in, a headphone ‘amplifier’ (really just a socket, but you know what I mean), and bypassable tone controls.

These amplifiers are completely repairable even now, more than 40 years on and virtually nothing would render an AU-317 unrepairable, so there’s a lot to love here. try repairing a Cambridge Audio CXA61 in even ten years and you’ll appreciate my enthusiasm for equipment like the AU-317.

Sansui AU-317 Specifications

Courtesy of HiFi Engine (absolute legends, BTW!)

  • Power output: 50 watts per channel into 8Ω (stereo)
  • Frequency response: 5Hz to 70kHz
  • Total harmonic distortion: 0.03%
  • Damping factor: 70
  • Input sensitivity: 20mV (mic), 2.5mV (MM), 150mV (line)
  • Signal-to-noise ratio: 77dB (MM), 100dB (line)
  • Channel separation: 65dB (MM), 73dB (line)
  • Output: 150mV (line), 1V (Pre out)
  • Speaker load impedance: 8Ω (minimum)
  • Semiconductors: 51 x transistors, 25 x diodes, 2 x FET
  • Dimensions: 430 x 110 x 340mm
  • Weight: 9.5kg
  • Year: 1978

The Right Approach

I focus on the wonderful world of classic hi-fi equipment here and I don’t want to waste too much time discussing what not to do, but the nature of my work means there’s unfortunately no avoiding it in cases like this. Those who follow my work will know that I have a particular dislike of poor workmanship, unnecessary work and ‘recappers’ parading as technicians.

There’s a ton of Sansui AU-317s around. They fail occasionally, in different ways, but repairing an AU-217, AU-317, AU-517, AU-717 etc., should be no big deal. I work on more Sansui amplifiers than just about any other brand, apart from Accuphase, Marantz and Pioneer, and I always enjoy it. Successfully working on equipment like this though is heavily dependent on a technician’s approach.

The wrong approach, so often applied to lovely pieces like this, hinges around shotgun parts replacement, applying sets of ‘improvements’ people find online, removing good parts and replacing them with junk, not testing components and circuits, and a generally non-technical, un-skilled approach that focuses on ‘what people reckon’ should be done. This approach is risky, wasteful, generally ineffectual, devalues the equipment and yet sadly, is by far the most common.

The right approach is conservative, technically focused and cares for the equipment first and foremost. It sees parts replaced where necessary or to improve the performance of the equipment, with parts that improve on original specs. This approach focuses on repairing faults and restoring perfect operation, whilst keeping to the original design intent with careful, technically correct work. This approach is also informed by an individual’s skill and experience rather than what various random people think should be done with pieces like this one. This approach is also far less common.

Sansui AU-317
Here’s the subject of today’s article, the venerable Sansui AU-317, a truly great budget-integrated amplifier. This one came sans-phono preamplifier shield, filled with bad new parts and unusable due to two faults.

“She Needs a New Flux Capacitor, Sir…”

So this Sansui AA-317 went to a local repairer, via her previous owner. The amp went in for presumably the same issues she came to me for – unlistenable distortion and DC offset that rendered the amplifier unusable. She went back to her previous owner with those problems, minus all of her original high-quality capacitors and a new set of crappy ‘Suntan’ brand caps, driver devices and trimmer potentiometers installed for no obvious reason.

The previous owner finally gave up on her at this point and upon reading the diagnosis I’m about to show you that said the amp was not repairable. The current owner, my customer, purchased her and the previous owner kindly suggested he take her to me for a look. Thank you to the previous owner!

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Suntan capacitors – not something we would ever want to see in beautiful old gear like this baby. Note also new trimpots and new NEC TO-220 driver devices. Also, note the crud on this board, remnants of which include Sansui polychloroprene glue.

What caught my attention though was the diagnosis given by the previous repairer:

“The transformer related to the power section is on its way out” and “the JFET ICs need to be replaced.”

Previous repairer

Yeah. I mean, the customer might not understand what this means but any competent technician reading this is going to think “Hang on a minute..!”. Unfortunately, none of that ‘diagnosis’ is true or even remotely accurate, nor is it even possible in this amplifier. He might as well have said, “She needs a new flux capacitor!”

flux capacitor
Yes, still available from Jaycar for just $200 000 AUD, if you need to replace your flux capacitor. Suntan doesn’t make these, thankfully.

What does “the transformer related to the power section is on its way out” mean, anyway? Is there a transformer party somewhere that this one needs to attend?! Transformers – more than meets the eye! And there is only one transformer, so why mention “the power section”? What IS the power section anyway?

As for the “JFET ICs”, there are no ICs in an AU-317, it’s one of the lovely things about the design. The service manual refers to them as ICs, but that’s where we as technicians must exercise some interpretive skills and clarify that they are dual JFET packages, definitely not integrated circuits. Anyway, I’m not much worried about the name, what bothers me is that these work perfectly!

Sansui AU-317
More Suntan and Lelon

I’m sure that someone reading this will be thinking: “Mike, none of this matters!” The thing is, it does because it’s just a complete waste of people’s time and money if we just say that the factual details don’t matter. It certainly matters to the owner and to anyone who cares about keeping beautiful equipment like this running!

This diagnosis was given because the person giving it needed to tell the owner something, and they didn’t know what to tell them, so they made it up. That’s not good practice. We’ve all had tricky repairs, this work can be complex and challenging, even after doing it for many years. But if you are sending work back unrepaired, with false, misleading or even made-up fault descriptions, that’s a real problem.

Service & Repair

The path to repairing this lovely classic AU-317 was to isolate, diagnose and repair the faults, of which there were two. That took six parts and some time.

Fault 1 – Distortion. The distortion was caused by blown current limit resistors in the bias/drive circuit that turned this amplifier into a class-B design with no driver stage. That means that huge signals would be needed to drive the output stage at all, and what you get would be badly distorted. I replaced the current limit resistors, set the bias current and bingo, the distortion was gone.

Fault 2 – DC offset in the right channel of the phono preamp. DC offsets are typically caused by leaky or drifty small signal semiconductors and the obvious pair to check in the right channel of the phono preamp is the right channel input differential pair. Sure enough, one device was bad, so I replaced both with a new hand-matched pair with improved specs.

Some critical cleaning, service and adjustment completed the work here and is what had this AU-317 running perfectly again.

Sansui AU-317
A plan view of the AU-317 as she arrived. She’s dirty and needs a deep chassis wash, general service and repair.
Sansui AU-317
The heavily flux-contaminated board must be cleaned. Note also the output device part numbers written on the board. There are neater ways of recording what goes where. These didn’t even need to be desoldered so goodness only knows what went on here.
Sansui AU-317
I’ll never understand people leaving boards looking like this. Yes, I’m helping my competitors by writing these articles!
Sansui AU-317
This is how these boards should look when properly cleaned.
Sansui AU-317
After a deep chassis wash and dry, the amplifier is on but no current is flowing through these output devices, hence the zero reading on the Flukes. This is a significant problem, yet it went unmentioned in the ‘diagnosis’. Why?
Sansui AU-317
Four small parts later and it’s a bingo! The art lies in finding those four small parts, yes, but a quick look at the schem helps and you work through some measurements from there.
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Blown current limit ‘fusible’ resistors. No new trimmers, transistors or capacitors are needed. There’s often confusion around fusible resistors. All resistors are ‘fuses’ if you think about it, but these are a little more sensitive to overcurrent and tend to drift upwards rather than fail open. That’s good, it prevents excessive current flow as it’s designed to, but often the gear will still work when these fail, but with significantly degraded performance.
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It’s always a good idea to service relays switching any meaningful amount of current.
Sansui AU-317
All this pain just to get to a couple of pesky, leaky transistors! Worth it though because it’s the only way to resolve this issue.
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Only one of these was guilty, but you would never just replace one device in a differential pair, and especially never with a different type of device… Right..?! I always replace a differential pair with two new, hand-matched devices, even if only one device fails. This assures low DC drift and offset. How’s the resolution of the iPhone camera by the way? Very impressive!
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So that’s it, this is what needed to be replaced in this amplifier to resolve its issues.
Sansui AU-317
The cleaned, repaired and serviced Sansui AU-317. Woo hoo!

Results

This Sansui AU-317 repair was particularly rewarding because her owner is such a nice guy and he appreciates the approach I’ve described in this article. He owns many Sansui amplifiers including a Sansui AU-101, AU-217, AU-555A and AU-4900, all of which I’ve serviced and repaired for him but his favourites are the AU-217 and AU-317 I recently worked on. Here’s what he told me about the AU-317:

[The] 317 sounds spot on, you are the man 🙏🏻 thanks again Mike. She sounds bloody awesome, I hate to admit its in a tight second spot for my favourite.

Michael B
Sansui AU-317

In terms of overhaul and restoration, less is more, especially with pieces in generally good condition. Overhauls by the right people are worth having done, but as always, the devil is in the details. The right technician won’t be getting their information from forums, installing Suntan capacitors or charging $1500 AUD to overhaul a basic amplifier. They will already know what to do, based on the condition of the equipment in question. Keep this in mind.

Sansui AU-317

If you want to spend that much on a vintage amplifier, I suggest you take the $1500, sell the AU-317 and put all of that money into a nice Sansui AU-717, AU-819 or AU-919. That’s going to give you a far better piece of gear and bang for your buck than going crazy with an AU-317 or AU-4900.

Sansui AU-317

The Bottom Line

Want a beautiful-looking, great-sounding, affordable, reliable, repairable moderate-power integrated amplifier? I highly recommend you consider the Sansui AU-317 if so. These are solid, well-designed, well-made pieces of Japanese hi-fi history. Nothing like this will be made again and at their current prices, you can’t go wrong. I’d take one of these over new plastic rubbish with Bluetooth integration every day of the week. Just take it to someone with the right approach when it needs service!

As always, thanks for reading and I hope you found this article informative. If you’d like me to look at your Sansui AU-317 or any other lovely Sansui amplifier, get in touch.

Sansui AU-317 Integrated Amplifier

$500 - $800 AUD
8.5

Build Quality

7.0/10

Features

8.5/10

Sound Quality

7.0/10

Servicability

10.0/10

Bang-Per-Buck

10.0/10

Pros

  • Full-featured integrated amplifer
  • Excellent phono preamplifier
  • Tape and headphone functions
  • Superbly servicable
  • A great performer in its niche

Cons

  • Lacks slam, air, refinement etc. of course, given what it is.

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10 thoughts on “Sansui AU-317 Amplifier Repair, Review & Rant!”

    1. I have an old Sansui AU 317 from my dads estate that I would like to sell if anyone is interested!? Or knows best place to move it!? It’s from my fathers estate and it’s okay condition. I am in Brisbane. Anyway I came across your article while researching this amp. I don’t know if I am out of place mentioning it here. But it be nice for it to go to someone who is interested in this. Cheers Kris

      1. Hi Kris, not at all, you are welcome to mention it here, but you’d be better advertising it via mainstream selling channels like Gumtree, Facebook marketplace, Stereonet, etc.

  1. What an unconscionable disaster was inflicted on that poor AU-317. Thank goodness the owner entrusted it to you! As always, an interesting and educational read from Mike, especially when it’s about a Sansui!!

  2. Hi Mike,

    Nice work as always, and agreed the 317 is a great “little” amp. Having repaired/restored a great deal of Sansui gear over the last 10 years or so on the east coast of Australia I can attest to the failure (drift high or go open circuit) of the “current limit/fuse resistors” in nearly every amp/receiver that has these fitted. You may not be aware, on the 317 there is also a fuse resistor fitted to each channel of the Control Amp (tone control) board – R17 and R18 68ohm 1/4W. These are also invariably high in resistance or open circuit.

    One other thing (typo I believe), the 317 doesn’t have a dedicated headphone amp, but it does have a dedicated Mike amp.

    Keep up the great work!

    Cheers
    John

    1. Hi John, thank you for the kind words and it sounds like we’ve both worked on lots of Sansui, me since 2009. You are quite right about the fusible resistors being problematic in these and many other amplifiers. I try to limit the technical detail I present in these articles a) because certain competitors seem to enjoy visiting which helps them but not me!, and b) I’m mindful of not making articles too technically ‘heavy’ for the average reader. Not a typo re the headphone amp, the whole thing essentially is a headphone amp when used with ‘phones but agreed, it doesn’t have a separate active headphone amplifier/buffer circuit. The mic amp is a classic feature I rarely mention but some will enjoy it for sure. Karaoke anyone..?!

  3. Bravo, Mike! I’m so glad that I have you looking after my current system (the best I’ve ever owned) and with several components bought from you. I’d hate to have to take my gear to anyone else. Cheers, David

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