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Yamaha M-70 Thread

Discussion in 'Yamaha' started by Bratwurst7s, Jan 17, 2018.

  1. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Thank you very much for the continued interest and moral support. That's a lot of what makes this place so fun.

    I've always wanted an M-70. When I bought the M-50 at Clark AB back in '83 I had a choice. Buy a C-70 and M-70 and wait to buy some kind of input unit, or buy a C-50 and M-50 and have enough cash left over to buy a TT and tape deck to complete the system. So I went for the complete system, Pioneer PL-L100A and Teac cassette deck (don't recall which one, it was totl and had dbx).

    But as much as I've always wanted that M-70 as soon as I saw the CX-1 and MX-1 I wanted them even more. And to complicate things I really want to put together a very nice 2-channel system to give to my son next year for his 30th birthday. I now have a CX-1 for him, as well as the Speakerlab 7WA's pictured at the end of my speaker thread, but need a power amp. So he will get the M-70 and I will just have to make do with the MX-1. :D:);)

    My Speakerlab's have always been a strong love affair. And they sound better now than they ever did when new. I've actually been in love with them for longer than with my wife (please don't tell her that I said that). We didn't marry 'till '85. ;)

    There are several Yamaha threads on the horizon.
    AX-1090
    AX-890
    RX-570
    CX-1 continuation
    MX-1
    Not necessarily in that order.

    Cheers,
    James


    Cheers,
    James
     

     

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  2. Karl vd Berg

    Karl vd Berg Super Member

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    The mighty Z-7000?

    [​IMG]
     
  3. Karl vd Berg

    Karl vd Berg Super Member

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    1,967
    Maybe I missed one previous post, but here we go: how does the M-70 sound (with the CX-1)?
     
  4. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Your very welcome, you've done all the work l have have just been happy to be along for the interesting ride ;). Wish l could be as dedicated and detailed with all of mine as you are with yours.

    Makes perfect sense, you have to have a music source. Sounds like a nice system.

    Bet it will be grind to make do with the MX-1 :biggrin:. Bet your son will be very happy on his birthday, he will practically have a brand new 1983 M-70.

    I won't say a word, haha. They look great and no doubt your improvements have made them better than when new.

    Sounds like you will be a busy man. We could be doing a lot worse things than bringing these old girls back to their former glory :thumbsup:.
     
  5. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Nope. I do recall that it was not autoreverse because I wanted 3 head and the autoreverse only had 2 heads. It did have the florescent display and dual slider level adjustment (which I found that I didn't like all that much). Dolby-B only because C wasn't out yet at that point. dbx, I believe type 1 but am not sure on that. No wood.

    Darn fading memory.
    James
     
  6. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Sounds pretty damn good. Today I listened to Santana III and Waren Zevon's 1976 masterwork. I close my eyes and kinda get lost in exploring the sound stage.

    Cheers,
    James
     
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  7. Karl vd Berg

    Karl vd Berg Super Member

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    Very nice work, James. :)
     
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  8. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Thank you very much Karl. :beerchug:

    I have something over 10 hours of use into it now.

    Considering the SQ. The difference/improvement in SQ in my system was huge when I went from using my AX-1090 to using the CX-1 pre connected to the power section of the AX-1090. Now that the AX is removed entirely and the M-70 is in use the additional SQ improvement was more subtle. Mainly in the realm of a wider/taller/deeper sound stage. Clarity is improved overall but not like the large jump gained with the CX-1 over the pre-amp section of the AX. Bass is a bit tighter.

    When I was researching the switch to LEDs I came across 2 web site that are interesting. The first has a lot of photos of the front meter panel that were useful when I worked that board and has helpful info about repair there...
    http://www.vintageaudioaddict.com/Yamaha_m-70/Yamaha_m-70.htm

    The 2nd also had useful info regarding led/meter repair but also had an interesting glimpse at the main board...
    http://www.raincityaudio.us/blog/yamaha-m-70-natural-sound-amplifier-repair

    In the 3rd photo one can see SanKen 2SA1106 transistors installed. So evidence that Yamaha did indeed use 2AS1106/2SC2581 outputs in the M-70 even though they aren't shown in the SM. But the ones shown in the photo look completely different than the ones that were installed in my amp. The silk-screen PN is printed directly on the transistor face on those but the ones in my amp had a black painted field in the middle of the face with the PN printed on that.

    The seller of the amp stated that "there was a problem in the right channel but it was not the output transistors". I'm still thinking strongly that he changed the outputs with ebay fakes in an effort to find the output problem, which turned out to be a bad solder connection on R316.

    One more thought/development. I'm going to let the Cat out of the bag so to speak. When I realized that I'll need a distortion analyzer to finish the amp and started looking into buying one our very own OMGCat! contacted me and made me a very nice offer on his QA400 audio analyzer, which I gladly accepted. So that is on the way to me now. I still need to buy a differential probe to go with it but that's a small detail. So my thanks and hats-off to OMGCat! for being a stand-up guy and helping me out of a jam. This really is a pretty special community that we have here at AK.

    I've put off making another Mouser order until my MX-1 gets here and I'll order new caps for that thing and some more LEDs then.

    Cheers,
    James
     
    Last edited: Apr 22, 2018
  9. Karl vd Berg

    Karl vd Berg Super Member

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    1,967
    I guess you have Spotify, try to play "Train Song", by Holly Cole... :)
     
  10. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    I don't have any streaming services but if you are recommending the song I'll try to find it on CD and just buy it. I am guessing that Amazon will have something.

    Cheers,
    James
     
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  11. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Concerning the mounting plate for the speaker terminal posts. I used a Mitutoyo dial caliper and measured the back panel cut-outs and metal remaining between them.

    The post holes measured 18.45mm diameter. In the vertical plane I got 5.55mm of metal between the A and B posts. In the horizontal I got 3.55mm metal between the plus and minus holes and 13.55mm between the minus pairs. I drilled the holes in steps of 2.5mm, 5mm and then 10mm and then used a sinker to remove the flash and slightly bevel the holes.

    The mounting holes measured 3.4mm in dia. The metal remaining between the holes vertically is 42.45mm. They are centered between the +/- holes horizontally and I centered them vertically above and below the absolute center of the post hole sets. I used a 2.5mm drill as this is correct for tapping 3mm M-3 holes. As I mentioned earlier I used 3mm thick for the plate so there would be enough meat to tap the mounting holes and avoid needing nuts on the inside.

    So I took these numbers and a calculator and came up with the sketch that I'm posting below for future use by anyone that needs it. FWIW the numbers worked pretty well for me so I don't think that there will be and big problems using them.

    You will want to make your marks on your plate each based on the left edge and bottom edge as an absolute and not going from center to center to avoid stacked/accumulated position errors. I used my dial calipers to set a sliding 45/90° square and a fine scribe to mark them. Using a scribe works well because where the marks cross there will be just enough of a point to drop a center punch into and get a really accurate point to drop your drill bit into.

    Cheers,
    James

    M-70_Speaker_Post_Plate.jpeg

    edit: All measurements are in MM.
     
    Last edited: Apr 25, 2018
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  12. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Thanks for sharing your measurements for the benefit of anyone wanting to do the same :thumbsup:.
     
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  13. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Happy to be of service. :)

    Cheers,
    James
     
  14. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    So today is a very good day. I stopped at the post office on the way home from work to pick up some 6mm² speaker wire that I ordered. But I was surprised to see instead a box containing the audio analyzer. Double surprised because anything that goes through Customs usually takes an extra month or so and then I get to go out there and give them some money. Heh heh, I was so excited about that that I forgot to ask about the speaker wire package. I'll have to go back tomorrow.

    Now this earlier QA400 can only take a limited amount of input voltage and one has to buy a differential probe to run anything over 5v input. I was happy to get the QA400 for the price that I did and expected that I will still have to order the probe.

    Imagine my delight when I found the differential probe also in the perfectly packed box!! Dang! :banana::banana::banana: So I'm a happy camper today. A good deal just turned into a great deal. ++1 to OMGCat!.

    The MX-1 won't get here until next week so my plan at this point is to wait until it gets here, look inside and finalize my cap list for that amp and then make a large Mouser order, to include some more LED types for the M-70 power switch etc etc. After that stuff gets here I'll swap the untouched MX-1 in my system and finish the work on the M-70. So, about 2 weeks. That will let me compare the sound delivered by the uncapped MX-1 to the re-capped M-70. And then a few weeks later swap again and compare with the re-capped/re-flowed MX-1. Ought to be a rewarding experiment.

    In the mean time my son has seen and heard the CX-1/M-70 combo and thinks that it looks and sounds great. Heh heh, won't he be surprised when they are his.

    Cheers,
    James
     
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  15. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Sounds like a plan. Will be interesting to compare the M-70 and MX-1. Bet your son will be pleasantly surprised.
     
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  16. zaibatsu

    zaibatsu Well-Known Member

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    598
    Beautiful work as always.
    I'd be interested to hear a little about how to use the QA-400 and what you find with it, it sounds like a very cool toy.
    I'm sure it was a great deal but now you're stuck with the burden of telling us all about it, that sneaky 'Cat.

    Also, on the trimpots, any reason you picked the 4-turns instead of ~20-turns especially for offset? I noticed the 4-turns are much more expensive than the higher turn ones, figured there may have been a reason you did that. They do look really nice. Also, it looks like the multiturn you used has a larger footprint than the ones i've used in the past (3296 I think), which looks like it might be a bit more stable when standing upright, how do I look for those?

    I always learn something new from these builds, thanks for sharing.
     

     

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  17. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Thank you for the friendly encouragement Z. :beerchug: I'm always happy to share what I'm up to with the hope that it might be useful to someone.

    Concerning the trim-pots, unfortunately my choices at that time were based as much on availability as anything else. If I have a choice I'll opt for a 20 turn pot every time. But some of what I wanted to order showed zero inventory and a 16 week lead time. I did actually go ahead and order the 20 turn pots at that time with the hope of an early delivery but as yet none of them have shipped.

    Concerning the pot footprint, em, ah, well, I don't really know. ;) I mostly ordered what was in stock that looked like it would fit.

    Sorry if my answers are somewhat mundane and low-tech. But sometimes that's the way it is. :D

    I'm really looking forward to learning how to use the QA-400. I just hope that I'm smart enough to figure out how to use it.

    Cheers,
    James
     
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  18. morfeora

    morfeora Member

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    Location:
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    I am pretty happy with the sound after the little change on the tweeter cap from 3.9uf to 3.3uf. :) But, lets talk about the important thing know!!! You have your amp working already... What a happy surprise to come back here to see this... amazing restoration work James, I guess your system sound now as beautiful and clean as the way this amp looks after your fixes, Beautiful! I am pretty happy for you my friend.
    Cheers,
    Rodolfo.
     
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  19. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    Hi Rodolfo, and thank you very much. The system is sounding very very good now. I have at least 25 hours on the M-70 now and am liking the sound very much.

    I still look for woofers for you several times a week. Sooner or later they will turn up.

    Cheers,
    James
     
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  20. Bratwurst7s

    Bratwurst7s In The Frying Pan Subscriber

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    I missed part of this earlier. The top-adjust version of the pot that I used on the pre-drive board is 3339H and 3339P, depending on what pin orientation is needed.
    https://www.mouser.de/ProductDetail...=sGAEpiMZZMvygUB3GLcD7rufck0TIBKyHU5WzOsAMxo=
    https://www.mouser.de/ProductDetail...GAEpiMZZMvygUB3GLcD7rufck0TIBKy5o3%2bUsM0v7A=

    The 3296 is actually what I wanted to buy but they didn't have any at that time.

    Cheers,
    James
     

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