Pioneer M-22 Power Amp - Epic Japanese Gear From the Past

@PTS all original output transistors from factory! If you can find some original transistors that would be great, the same transistors were used in something like sansui 771 so you can find them, I actually managed to find original matched pairs just incase I blew an output while rebuilding and testing.

As dBel84 said you can find other newer modern transistors or ones close to original specs perhaps or modify what you have now but why do that? If you can keep it as original as possible do that instead, I had to replace my filter caps they were shot and replacements were very expensive and didn't fit safely or properly, I did subtle changes not to interfere with it but to slightly improve what I already had, these amps will stand the test of time but you have to service it, change parts, check connections etc.

Currently mine is burning in and powering a set of refurbished quad ELS 57s being fed by a Krell PAM 5 preamplifier and its bloody wonderful!

 

That ripple on the underside of the pcb... is that the masking or a bunch of flux residue?

 

I wasn't too sure myself but that's where my issue was coming from, something ksut wasn't right in that specific area, whether this was due to heat, or just caused my inrush current, maybe a prior issue with the amp who knows.

Underpinning it solved so many issues and made the amp perform and behave.

 

I agree here. I'm building a couple of Naim NAP250 clones: one as close to original as possible, and one with some upgrades to see what the difference is. But even the upgraded one uses only parts available in the late 1970s.

 

Note: those BDY58s are nice 10MHz parts, but the Naim is semi-complementary so I don't know if there are PNP version of them available or not. And they're probably not that much easier to find either.

 

Did you at least clean your own flux off the board when you were done with your repairs/mods?

And it's hard to tell just from the photos, but some of those look like cold joints?

 

This is the thing with vintage amps and boards especially class a, boards are fragile, solder joints need reflowing etc.
Just to make sure i went over each component and reflowed the solder, no cold joints for sure, another thing with cleaning these boards you have to use special chemicals other wise you get reactions with the protective coating.

It's all annoying little things but stuff you may have to deal with, i can safely say that the amp is perfect its done about 35 hours of use, its just nice to know all issues have been sorted and its reliable now.

 

Sooo, one of the power caps on my pio a-0012 decided to die recently, so I'm deciding what to change them for, any recommendations?
Tech guy who is currently looking into it suggesting installing 4x Nippon KS20133L145 he has at hand, but I'm not quite sure they are good enough for this amp. Also, it does not help that I can't find any info about such model on the official Nippon website. Googling reveals only some shady online shop selling them pretty cheap.
Suitable Nichikons KG seems to cost about $80 per one, which is a bit high, and I'm not sure it is worth it.

Is there a middle ground between Nichicons and else? Where is a good place to buy them? The only trusty place I know is mouser

 

It’s a power-filter cap. What you want is very low ESR/ESL and reasonable HF response. Mystical acoustic properties aren’t a concern here, IMO. Key properties, in my preference order, are: 0) meet minimum voltage and capacitance spec, 1) modern production, 2) they physically fit, 3) reasonably low ESR, ESL, and good frequency response, and 4) consider a larger capacitance if all other parameters are met. If the amp gets hot, throw in a high temperature rating at position #3.

 

There’s a M-22 on eBay that has not been used, will it still have aged and need work? It is
$2800

 

The electrolytics will have aged and actually could be worse because regular usage provides “reforming” (see academic thesis linked in my post here.) The rest should be happy, though I’d poke around in it to be sure.

I would personally change out the orange drops for vintage ERO MKT1813 coupling caps. Huge difference in transparency. I have a few spares, so if you’re interested PM me.

 

@skem Yes, those are 8ohm Viawave tweeters. I didn't respond, because I wanted to see if you could Sherlock the answer yourself, because I've mentioned them a few times in several posts. You're an extremely smart cookie, and I hate spoon feeding.

In nearly 5 years I haven't reached a 1000 posts, and try to keep the fluff posts to a minimum. Some people don't get that and clog the useful resource threads full of crap, making sifting through information a real pain in the f'ing ass... Not directed at you though.

I really wanted to let the M-25 run in and the caps to settle before giving a a comparison. I've been using the M-25 for music and TV duties since it arrived (I rock the JBL 4312G for all TV duties 8 days a week). I started using the M-22 again during the iPhono vs Nighthawk vs EC Classic comparo last week. I can say this... The M-25 has the gusto and grip in the low end hands down, but the liquid mids and to die for treble of the M-22 has the overall championship title for sure. Even though the caps used in each refurb are not the same, which could be part of the difference in sound, and I suspect my M-22 does not sound like yours. The M25 does get surprisingly warm as I've mentioned before, probably due to the first few watts being class A before switching over, and TV use probably rarely pushes it into class B. Also using the hot XLR outputs from my DAC converted 1:1 to RCA helps bring some more to the plate volume wise with the M-22.

I could see myself selling the M25 in the future, but definitely not the Mighty Meme-22...

 

I'm pretty blown away with the quality of sound that a 45 year old design pumps out. Burn-in (after replacing caps and a lot of semis) was also a bit more noticeable than compared to other components I've tried.

One thing I'm left wondering is if the old transistors, aside from the Sanken outputs, have any impact on sound quality. I replaced all the transistors except the Sankens, and it sounds great and is very quiet. I read elsewhere that while we've improved on mass manufacturing with modern packaging, modern transistors also tend to have less overall bandwidth.

I'm sure if there is any difference, it's likely not perceptible to the human ear, but was jw if a full replacement of all components may remove some of that "magic"?

I didn't replace the resistors (except the bias pots), but I had second thoughts given how toasty it gets inside those heatsinks.

Just a random question I had while I was enjoying the beautiful music this thing puts out.

 

I recall some earlier discussion from @purr1n that the original transistors were hand matched. That being the case, I wouldn't mess with them.

 

On various russian forums, several people changed output transistors to Motorola 2n5884 2n5886 pairs and noticed major improvement across the board, especially with low-imp speakers.

Besides that, some info on other changes can be found here for instance: https://translate.yandex.ru/translate?lang=ru-en&url=http://audioes.ru/viewtopic.php?f=33&t=6769

 

An amp designer which I forgot the name recommended me 2N6338, 2N6341 for replacement. There are 40MHZ which is quite high like originals.

 

I would do a lot of research before dropping high bandwidth transistors in. Scott Frankland (a tech who's serviced M-22s for a number of SBAFers) said there's nothing like the 10Mhz Sankens on the new market. He mentioned there's a 40Mhz military spec transistor he knows of that could work, but that would take hours of bench time modification to drop in and work well. I spoke about it in more detail in post 377 on this thread.

 

You found the name I forgot. The recommendation came from Mr Frankland to use these numbers.

 

Hi Folks, my M-22 has been operating fine for quite a long time. However, now when I flick the toggle switch to turn it on, I get an immediate vibration kind of sound. This goes away when the unit warms up (after about 10-15 minutes). Anyone have that kind of issue? If so, what was the issue? Thanks in advance.

 

If works fine but is humming it’s probably the transformers coming unpotted. If it is a clicking and doesn’t work then it may be the relays, which in turn implies something in the self protect circuit. Sounds most like a transformer issue, though. Is the sound coming from one of the two big black cubes on top?