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Epic Accuphase P-300 Amplifier Repair & Review

Come along as we repair another stunning Accuphase P-300 power amplifier, given up as unrepairable and definitely one of the most technically involved repairs I’ve done in a while.

We’ve repaired quite a few Accuphase P-300 power amplifiers, and a ton of other Accuphase equipment. This beauty, having failed catastrophically and been shopped around to various repairers, was an involved, technical repair that took the best part of a day, back in 2020. Welcome back everyone, as we continue to work through a long catalogue of stories that need to be told!img 1241

This lovely Accuphase P-300 belonged to one of my long-term customers back in 2020. He’d recently acquired it from another fellow as I recall, in non-working condition. The previous owner had taken her to several local repairers, none of whom repaired her and she then sat gathering dust and in need of TLC for years before my customer acquired her and brought her to us.

I’ll let you in on a little secret: I really like fixing these sorts of pieces, especially gear like this beautiful old girl. I know it might sound almost ghoulish, but I get a kick out of repairing ‘lost causes’ like this. The technical challenge alone makes it worthwhile, but the fact that these things often come to us after they’ve been elsewhere makes repairing them just that little bit more satisfying.

Jobs like this are where technicians earn their keep. Nothing about this repair was easy, from diagnosing and finding the multiple faults to designing a repair solution including suitable replacement parts and getting to everything inside this cramped amplifier. We made some reliability enhancements to her, as well as to rectify poor previous work and of course, repair the faults – a blown right channel and other issues that likely caused it.

Accuphase P-300
A repair like this can involve many hours of diagnosis, fault-finding, disassembly, repair, reassembly, testing and adjustment.

Accuphase P-300 Specifications

Courtesy of HiFi Engine

Power output: 150 watts per channel into 8Ω (stereo)
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.1%
Damping factor: 60
Input sensitivity: 1V
Signal to noise ratio: 100dB
Speaker load impedance: 4Ω to 16Ω
Semiconductors: 73 x transistors, 1 x IC, 2 x thermistors
Dimensions: 445 x 152 x 355mm
Weight: 25kg

Features

The Accuphase P-300 is one of the all-time great what I would call mid-range power amplifiers. The P-300 isn’t up at the heavy hitter Gryphon / Krell / Mark Levinson end of the market, but it’s far ahead of most other contemporary manufacturers’ products and even now, is a bit of a hidden gem.

Accuphase P-300 is built like a battleship and bulletproof when properly maintained and overhauled at this age as is necessary. They also sound fantastic, with a powerful presence in any system and bags of power to drive all but the toughest loads, with finesse and subtlety to boot.

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Accuphase = quality, it’s really that simple. Everything is compartmentalized, on removable cards, perfect for service. Well, almost everything, except the deeply buried heatsink module emitter resistors!

There P-300 has a great-sounding headphone socket, filters, twin analog meters, multi-voltage capability and superb build and sound quality. It also features attenuators and front panel RCA inputs that give great flexibility and allow the P-300 to form the basis of an awesome no-preamp, line-level setup.

I won’t go into too much detail as I want to keep this mostly about working on this particular unit, but if you are looking for a super well-built, powerful and amazing-sounding amplifier, the Accuphase P-300 should definitely be on your shortlist.

Accuphase has more information about the P-300 over on their website. I’ve written about this great amplifier previously, so check that out for more.

Problems

This otherwise beautiful Accuphase P-300 had some history as mentioned and her owner confirmed that he had never listened to it, after picking it up cheaply. The blue LED power meter illumination is not my thing on an elegant old girl like this, but hey, some folks like this look and I have to say it definitely grew on me!

This Accuphase P-300 had one ashed channel, heavily fluxed boards, multiple dead components and some very ordinary previous work. It had never had the work it needed though, despite having been previously looked at and this was immediately obvious.

By an ‘ashed’ channel, I mean completely dead, killed and yet still receiving all power supply voltages. Because of various shorted semiconductors, these power supply voltages were appearing in all the wrong places, like the speaker terminals if it weren’t for protection, so a dangerous situation in some ways.

The right channel of this lovely P-300 had no intact driver or output devices. All of these devices needed replacement and, adding to my pain, so did all of the emitter resistors for these devices. Not only that, but fitting in the sorts of parts readily available was no easy job, necessitating full removal and strip-down of the problem heatsink/output device assembly.

I often find Accuphase gear has been badly worked on and I think this often comes down to misguided attempts to save money. Here’s a video I made about another bodged Accuphase P-300. Stories like this are unfortunately far too common:

Understanding what diagnostic measurements mean about which parts have failed is part of the art of electronics repair, as is knowing what replacement devices to use where and dealing with blown TO-66 devices is an excellent example of this.

This transistor form factor is NLA in almost all cases. We need to adapt packages that are available for the role, as Accuphase themselves did when these parts ceased being produced. TO-66 failures are often deemed unrepairable when in reality they usually are repairable.

Here’s a list of the issues with this particular amplifier:

  • Blown right channel
  • Failed pre-driver, driver and output devices
  • Multiple failed emitter resistors
  • Previous repair and thermal damage to the protection board
  • Amplifier hadn’t run in years

Repair

Enough waffle, let’s get into this Accuphase P-300 repair, step through the repair process and let the images tell the rest of the story. I’ll also post a video of this repair right here, soon.

As always, we start with the inspection, fault diagnosis and basic service work including cleaning of boards, components, and connectors. From there we remove bad modules and parts and repair each element as required.

Accuphase P-300
A deep clean of the driver boards allows me to see exactly what’s going on, and allows them to run better afterwards. I use a multi-step process for this, one of which includes a mild foaming surfactant.
Accuphase P-300
Much better, but further work needed.
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A transistor sitting across a high voltage rail was shorted only under load, making it hard to find the fault and putting very high voltages in all the wrong places, causing chaos. The devices in question are unreliable and I tend to replace them (and their complement) wherever I find them. We did that here, for both channels, fixing one problem and saving the other channel from potential death but there were more issues…

Accuphase P-300

Accuphase P-300
These specially selected and hand-matched replacement devices are much more robust, have a higher power rating and significantly outperform the originals. Note the clean board and neat component dress. Also, note the electrically perfect, original Elna capacitor, left in place.
Accuphase P-300
The front panel protection board shows low-quality parts and horrible parts placement. This is mostly a battle for another day, we are focused on repairing this old girl first, but we will repair a couple of faults with this board. Note also the non-standard main filter capacitors, replaced at some point in the past.
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The rear of the protection board, with bad soldering, dry joints and awful flux residue left in place, as though they don’t matter.
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The same board looking much better after cleaning and limited rework.
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This damaged resistor was hanging off the protection board. Ahigher power rated replacement now sits in its place.
Accuphase P-300
This is where the pain sets in, taking this amplifier module out and then apart is not a trivial task!
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Screws, panels, spacers, trim pieces…
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Gaining access to blown power resistors… Sigh…

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Accuphase P-300
Now I can access all the emitter resistors. Most had failed.
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Up-rated (in terms of power dissipation and reduced likelihood of failing) emitter resistors installed here. She’s coming along… for all those Supertramp fans out there 😉
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Here, I’ve installed premium Philips Vishay resistors…
Accuphase P-300
Reassembling the module before reinstalling it into the chassis.
Accuphase P-300
Here we see the original output devices in the bad channel. I’ve already removed and tested the missing TO-66 drivers.
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Never a good sign, and in this channel, all but one device was dead, an impressive result.
Accuphase P-300
Here, some new high-spec replacement parts sit ready for installation.
Accuphase P-300
This is where experience pays off. We can replace blown, obsolete TO-66 drivers with the right modern parts, carefully installed in a particular way. This failure alone is often deemed unrepairable but it’s not. The blown TO-3 output devices are replaced with modern rugged devices that offer significantly higher power handling than the originals. Parts selection is critical, all devices are mounted on premium silpads and we did the same with the working channel.
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A select group including some hard-to-access parts that transforms this Accuphase P-300 from an unusable doorstop into a fully functioning power amplifier.
Accuphase P-300
Finally, testing the rebuilt channel and whole amplifier. At this point, I’ve verified that all is running well and am now setting quiescent current as you can see from the meters reading approximately 50mV in both channels.

Results

Repairing this beautiful Accuphase P-300 and hearing her sing was particularly satisfying. A logical, methodical, technically focused approach again delivers what I consider a predictable result with this beautiful amplifier, though it’s something others weren’t able to achieve.

I reckon this P-300 sounded almost as good as new. Her reliability is enhanced by replacing unreliable semiconductors that often cause problems. Further work would include full restoration of all boards, that’s up to whoever owns her now.

Her owner was understandably very happy to have his amplifier running again. I suspect he perhaps didn’t appreciate the amount of work that went into fixing this one for him though. Perhaps this article will help!

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It’s worth mentioning a couple of points about this job. Having this Accuphase P-300 fixed properly when it originally failed would have been the ideal solution and would likely have saved a ton of time and money. We don’t know when that was or what the circumstances were, so as usual, a lack of history leaves us to speculate about exactly what happened here.

Without the right approach, complex, beautiful pieces like this classic amplifier are lost, perhaps destined for the Hall of Shame after falling into the wrong hands. It’s important to seek really good advice regarding any work on an amplifier like this.

By the way, I’m not for a moment suggesting that the right approach is only offered by Liquid Audio, but I can proudly say that we are one of a very small group of repairers offering it.

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Repair vs Replace

That’s the real question for any owner faced with a scenario like this, but I’m sure that if you made it this far, you’ll know where this is going. If you are ever faced with this question, it will likely come down to how much spare cash you have.

Replacing an Accuphase P-300 with something equivalent new, such as the current model Accuphase P-4500, will set you back around $14K AUD. That’s a gorgeous amplifier, but still only 90 Watts per channel, much less than the P-300’s 150 Watts per channel.

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Accuphase P4500 is a stunning amplifier, no doubt, but she’s the baby of Accuphase’s current range.

Alternatively, you could drop similar money on a Yamaha M-5000. The M-5000 certainly looks pretty and I’ll bet it sounds good. Still, it’s only 100 Watts per channel and for me, the P-4500 looks even better and weighs more.

M5000 scaled

I honestly think most will be surprised at just how good a well-sorted P-300 sounds. Very surprised. Forget technological advancements and other nonsense, this is an analog amplifier, and all the better for it. I’d take the P-4500 over the P-300, followed by the M-5000. In terms of power, if I needed the grunt, the Accuphase P-300 beats both.

Repairing even this very broken Accuphase P-300 was economical by comparison. Checking back over my invoice, repairs were not even 10% of that new replacement cost, despite the amount of work involved. You know what I think is the better option and I think most others would too. Besides, who’s got $15K sitting around to spend on an amplifier?!

If you own one of these wonderful amplifiers and it needs repair or overhaul, seriously consider having the work done, properly. With the right approach and experience, these beautiful amplifiers and others like them are almost always worth repairing.

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What are your thoughts on the blue LED meter backlighting? Let me know in the comments if you like them or prefer the classic straw colour of the incandescent originals.

The Bottom Line

Want a high-value, high-performance, high-feature power amplifier with a luxury pedigree that can grow with you and your system? Seriously consider the Accuphase P-300 stereo power amplifier. It’s a true thoroughbred, built like a battleship and sounds beautiful, just like she looks. Just don’t scrimp on maintenance, it’s never worth it.

Accuphase P-300
Such beautiful and timeless-looking amplifiers aren’t they?
Accuphase P-300
Honestly, I love the Accuphase P-300. Try lifting one sometime and you’ll understand part of the reason why.

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And so there we have it, another repair, straight from the Liquid Audio workshop to you. I hope you enjoyed this one, I certainly always enjoy working on Accuphase equipment.

As always, a huge thanks to my regular and new readers for stopping by and sharing the story. Don’t hesitate to let me know if you have any Accuphase or other classic hi-fi equipment you’d like us to look at for you, in the unique way that we go about this type of work.

Accuphase P-300 Power Amplifier

$1500 - $3000 AUD
9.3

Build Quality

9.5/10

Features

10.0/10

Sound Quality

8.5/10

Serviceability

9.5/10

Bang-Per-Buck

9.0/10

Pros

  • Superb Accuphase build and reliability
  • Fantastic drive, power and sonics
  • Very serviceable all these years on
  • Beautiful meters, timeless styling
  • Flexible inputs, attenuators, headphone socket

Cons

  • Needs the right care and technical attention
  • Styling may not have a high WAF

4 thoughts on “Epic Accuphase P-300 Amplifier Repair & Review”

  1. Hey Mike, nice article on the P300 (they are all nice articles!). I have a question on the P300 Versus the E202 that you repaired for me. Which is the better amp? Pardon my ignorance if it is bloody obvious! Cheers

    1. Thanks John, much appreciated! There’s a saying that the only silly questions are the ones we don’t ask, so good question I say! A power amp almost always beats an integrated amp, when other aspects are more or less equal. In this case, things are not equal, the amplifiers in the P-300 are better than those in the E-202, giving a one-two punch improvement that you’ll easily hear.

      1. As always a fun, interesting and informative article by Mike.
        Re meter illumination: I’d prefer soft white, but it might depend on the prevailing illumination in other nearby gear or the room itself. Soft green or soft yellow or amber might be other options, depending on what’s nearby. Far more important than the illumination is how it works and sounds, and I think we know the priorities of Liquid Audio in that regard!
        Cheers
        Rob

        1. Thank you Robert, glad you enjoyed this one! I like a warm/soft white in these also, I find the most pleasing light to be from the good old incandescent lamps which I stock plenty of for this purpose.

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