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Building another M-4

Discussion in 'Yamaha' started by stoutblock, May 16, 2018.

  1. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    I believe this is my sixth M-4 build?

    I'm going through my notes from my last builds and looking for parts etc. I am surprised I can't find a source for all the multi-turn Bourns P mount trimmers? I found the 100 ohm (3296P-1-1011) at Mouser but the 2.2K and 4.7k seem to be 6-9 week back orders? Anyone have a source for these?

    Most the other parts seem to be available.
     

     

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  2. zaibatsu

    zaibatsu Well-Known Member

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    595
  3. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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  4. zaibatsu

    zaibatsu Well-Known Member

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    595
  5. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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  6. DEAFASABAT

    DEAFASABAT Active Member

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    Very interesting. Would you post or PM to me more on how you approach your M4 projects?
    Do you make the boards? If so are they of better quality and robustness than the stock paper & resin originals (D-10, FR-4 etc) ?
    Thanks!
     

     

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  7. zaibatsu

    zaibatsu Well-Known Member

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    595
    In my experience it makes no difference, and I've found stock trimmers that are at least that far out of spec when there are supposed to be two the same. Note that even in modern times those are only rated to 10% tolerance.

    As long as you can hit the adjustment value you need, which is usually pretty close to the middle in a healthy amp anyway, you're good to go. For what it's worth, I have some of those on the way (5kΩ) for a project where I need 4.7kΩ myself. The stock pots measured quite close to 5 at max anyway.
     
  8. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    I have never had problems with the PCBs as long as they have not seen duress. Like a lot of this old equipment you can raise the traces if you are not careful removing components. Abused M-4s can see over heating damage on PCBs. I just try to find decent M-4s in good overall condition. If they look too abused they tend to become a carcass for later projects.

    One area of concern is the PS PCB. Make sure you use the bottom center brace to secure those big caps or the PCB can get damaged. I tend to use the longer 100mm (vs 80mm) Nichicon LKG1K153MKZ caps which do not allow the use of the upper cap support plate. I can still use the surround support brace and I fabricate a simple upper support plate. I will post some pictures.

    I was thinking the same thing as it should not be a problem as long as I don't run out of adjustment. I wonder why the shortage of Bourns multi turns out there? Never had this problem before?
     
    Last edited: May 16, 2018
  9. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    One of the areas I've had problems with on M-4 amps is the volume controls on the back. I have never had an M-4 where these don't get dirty and scratchy over time. I really think they are a weak link in this amp and can't help but wonder if they can easily deteriorate the sound quality even if they seem to be working well?

    I'm thinking on this build to bypass them with a couple of 30K resistors. I do have some concern, in order to have some volume sensitivity on the pre-amplifier, I have typically set these volume pots on the M-4 about halfway. If I bypass them I may have very little adjust-ability on my pre-amp volume?
     
    Last edited: May 16, 2018
  10. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    595
    You can bypass the pots at the equivalent of having them set at halfway (or 2/3 of max) rather than at max volume, just measure the pots at your desired permanent setting and replicate with resistors. I think if the pots are sounding clear across their entire range (and you give them a full cycle now and then to keep them that way) it's not critical to bypass them but if you're keeping the amp it's up to you, I don't see why not.

    As for the trimpots, I'd say if you're actually at the last 10% of any adjuster there's bigger problems than the pot itself. I think you'll be fine, as will I.
    On the shortage, no idea - but I've noticed a lot of other through-hole stuff out of stock lately (transistors, caps) so either this is the beginning of the end or some large orders have recently been made by big companies (seems more likely). I figure we're just little fish in the component purchasing sea so it's nice to have backup plans like the above options.
     
  11. avionic

    avionic " Black Knights " Subscriber

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    I use exclusively single turn. Good enough for OEM good enough for me.
     
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  12. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    I could not find a source for side mount single turn for all locations either? At least not in original specification numbers. The single turns are certainly much better and more stable than the factory ones.
     
  13. avionic

    avionic " Black Knights " Subscriber

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  14. avionic

    avionic " Black Knights " Subscriber

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    On the M-4 there is plenty of room to utilize side slot .
     
  15. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    ^^^ Thanks ^^^

    I like the ones that fit like the factory ones with the screw on top. They also need to fit the PCB at the same 3 pin locations. The photo in Mouser do not agree with the Bourns spec sheet in all cases, but according the the spec sheets, for the single turn this would be 3362R type which are available in 100 ohm and 4.7K ohm but not in 2.2K ohm?

    In any case, I found the multi-turn in the 100 Ohm, 2K Ohm and 5K Ohm that should work fine?
     
    Last edited: May 16, 2018
  16. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    Last edited: May 17, 2018

     

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  17. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    Got the back done today. IEC inlet, speaker binding posts and upgraded RCA jacks.

    IMG_0257 (net).jpg
     
  18. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    I think this is the final order list for me. I know the filter caps are too tall for the factory bracket but I've used them in the past successfully. They are the right diameter and they fit the PCB cutouts perfect (once you file the tabs just a little. Just make sure they are well supported!

    I was able to find most everything but I did have to go up in voltage on a few items. Also, I noted the schematic has a couple of different values as compared with the original installs I have seen? Never noticed that before?

    Mouser does not stock the 2.2uf/25V BP so I'm using one from my stash.

    Any input before I push the button?

    M-4 caps v2.jpg
     
  19. zaibatsu

    zaibatsu Well-Known Member

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    Last edited: May 18, 2018
  20. stoutblock

    stoutblock If it sounds good, it is good... Subscriber

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    Interesting. I have used the high spec WIMA caps on Nakamichi's over the years but never on a Yamaha that I can remember. Have you personally used these to replace electrolytics on a Yamaha amp?
     

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