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

Discussion in 'Power Amps' started by Armaegis, Mar 30, 2017.

  1. skem

    skem Friend

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    I did replace the big caps. The details are in my post and in the “ordering guide” linked from post. The replacements are Digikey 493-8972-ND. See my write up on mounting them. I have also since bypassed them with some lower ESR polypropylene film caps that I had around from my coupling-cap test, but to no noticeable effect.

    yeah, mookauto is a terrible communicator, which makes it possible for him to get away with selling dodgy things to people. He never promises anything because he doesn’t answer questions. In the end, you hope for the best and he takes your money.
     
    Last edited: Nov 30, 2019
  2. legarem

    legarem New

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    I finally bought Mookauto personal M-22. The amp is in good cosmetic (not great) condition. I placed it on the bench and turned it on all night. The heatsinks appeared cold for a class A amp. I verified the bias. Both Chanels were adjusted at 350mv which was too low. I adjusted them at 800mv and adjusted DC output at 0mv. Everything is stable. I listened the amp connected to my 3A reference 2000 speakers and I am really satisfied with the results. As is, it seems to be one of the best amp I tried in my system. I tried a lot. Image, soundstage and timbre are really great. This is also the hottest amp I had. Hotter than a Classe DR3. The temperature reach 71C (160F) on both Chanels heatsinks. I am asking what % improvement in sound I will have with a recap job. I will probably only change electrolytics and input signal cap because I don't want to change the amp personality. I will also use a decent shielded 14GA power cord. I'll also look at relays if they are dirty.
     
  3. skem

    skem Friend

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    The relays and input cap each gave big improvements.

    I can’t tell you want the other caps do because I replaced them as part of the initial repair. I never heard the amp with stock caps. Eventually I will experiment with the Miller feedback caps, but not until this summer.
     
  4. legarem

    legarem New

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    I replaced the 3 relays with 10A relays and replaced the input caps with some used Multicap PPFXS I had. The amp now has too much details in the mid high-treble. I don't like that. The original input caps lacks detail but they're at least musical or easy to listen.
     
  5. skem

    skem Friend

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    Ha. Exactly the complaint my spouse made yesterday. I find it works for speakers but is more difficult with detailed headphones. What transducer?

    for what it’s worth, I could neither measure or hear any sound difference between a 200mV and 800mV bias setting (or any level in between). Except at 800mV is certainly produces a LOT more heat. Can you hear a difference? If not, I suggest turning the bias down to where you found it.
     
    Last edited: Dec 26, 2019
  6. legarem

    legarem New

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    I use the amp with 3A reference 2000 speakers which are 4 ohms speakers with a sensitivity of 90 db/1w/1m. I will try the bias at 350mv to see if it change the sound. At 350mv, it can perhaps go in class AB instead of staying in class A ?. To voice this amp, I will try many input caps. Maybe paper in oil caps should tame the overbright sound I have with the Multicap PPFXS cap I used. As is, it can't be listened for a long time.
     
  7. legarem

    legarem New

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    Hi Skem. I try to find the capacitors sheet list and the instructions to install the new 39000 uF but I don't find them. Thanks
     
  8. skem

    skem Friend

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  9. legarem

    legarem New

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    [​IMG] Thanks for the parts list. I checked some caps today and they read better than their value. I also received ITT PMT/2R 3.3uF 100V film caps which are rather small and can be fitted on the boards This ITT cap was often recommended by Jean Hiraga and La Maison de l'Audiophile. I never had the chance to try some. Without any playing time done, the sound is simply marvelous. The Pioneer is not overbright and all the details are there. I'm simply astounded by the results and they are not broken in. They are better than MIT PPFXS, Dynamicap, Hovland I tried. All these caps made the M22 overbright and unlistenable for long term use. I had a picture to upload but it seems impossible to do this here.
     
    Last edited: Jan 11, 2020
  10. Tachikoma

    Tachikoma Almost "Made"

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    Have you tried reducing the bias already? Am keen to see if I can get away with less heat from my unit.
     
  11. legarem

    legarem New

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    I love so much the amp as is so I'm not really tempted to lower the bias. It is also amazing the volume I have with only 30 watts with my speakers. They are 4 ohms speakers so the amp delivers probably more than 30 watts at 4 ohms. I didn't measure the output with a 4 ohms load. As this amp dethroned all the other amps I tried, I will keep it in my system. Now I'm only worried by the availability for output transistors if they fail. What to use to replace the original ones ? I seriously doubt that On semi MJ15023 and MJ15025 will give the same good results as original ones. (Do someone tried them ?) Locally, I can get real 2SC1402 but no 2SA744. Problem with obsolete transistors is all the fake junk you can find everywhere.
     
  12. legarem

    legarem New

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    I wrote to Scott Frankland and he recommend me to try to adjust the bias so the temperature will go from 70*c (155*F) to 55*C (131*F). For output transistors replacement, he recommend 2N6338 / 2N6341.
     
    Last edited: Jan 20, 2020
  13. dBel84

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    I would agree that 55 to 60 degree is the sweet spot for most any Class A amp.

    I wouldn't worry about trying to stock original output devices, if something catastrophic were to happen, the likelihood that it would need to be sent to a service facility is very high and more components would likely need to be changed. It has survived a few decades and will likely do a few more.. dB
     
  14. Tachikoma

    Tachikoma Almost "Made"

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    I have Motorola transistors in my unit, makes me wonder whether I'm missing out. What was the bias he recommended? Or did he mean you should use the amp's temperature as a guide to adjust the bias?
     
  15. legarem

    legarem New

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    He didn't recommend me any bias value. The amp temperature will dictate the bias value so today or tomorrow I will try to find the bias value according to 55*C (131*F). Presently, with a bias of 800 mv, the temp reach 70*c (155*F). At first, I will lower it at 600 mv and will give you the results about temperature and sound quality.
     
  16. legarem

    legarem New

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    I readjusted the bias today at 500 mv and temperature now reach 136 F (58 C). I will listen it tomorrow.
     
  17. dBel84

    dBel84 Friend

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    what is the resistor value across the mV measurment - I am curious what the bias current is
     
  18. skem

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    Read the test point voltage as the current per transistor.

    The voltage per transistor is over 0.5 ohms making a 2:1 ratio for voltage (per emitter):current(emitter). But the test points measure over both push (+V) and pull legs (-V), so the test points automatically read 2x voltage/emitter, making it so the test voltage can be read as amps for each device directly. In fact, there’s and additional voltage divider for the test point, but it can be ignored as the error is only 0.7%. Output transistors are Q1-4 in diagram below. 0FA64C95-4E35-40CD-AA24-0F25DFBA55BB.jpeg
     
    Last edited: Jan 22, 2020
  19. dBel84

    dBel84 Friend

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    Thanks , I was expecting a higher bias given how hot the heatsinks are but 1A is very respectable.
     
  20. skem

    skem Friend

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    It’s spec’ed at 850mV on the test points. 4x850mA/transistor = 3.4A total.

    I think my explanation above wasn’t clear enough. Edited for clarity.
     

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