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.

“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!

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!”

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!

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.

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

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.

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.

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.