Rebuilding 300DC. I love this amp...

Discussion in 'Marantz Audio' started by Salbreth1, Jul 5, 2016.

  1. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

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    I triple that. Also, Thanks for documenting this.

    The info {BF423z I ended up using ZTX957. These match the transition frequency and higher gain of the original 2sa879r.}
    This info would have saved me hours of time researching subs, . I ended up buying originals on ebay.

    Damn, Now I am going to have to put them nice looking bournes in.:D

    Nice work as usual.:thumbsup:
    John
     
  2. Salbreth1

    Salbreth1 AK Subscriber Subscriber

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    Thanks, yea those pots add a nice look. Im glad to see you have one, I have this one paired to my 2245 which is built. I cant get tired of listening to it. :music:
     
  3. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

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    Mine is still apart waiting for me to finish it. It was not a good idea for me to buy its twin, the esotec sm7, because i am listening to it instead of finishing the 300dc. I think the SM7 is due for a recap, so it should be interesting to compare the two when i am done.
    Your thread inspires me to finish mine. i actually forgot i started a thread on restoring mine. I will see if i can dig it up and see were i ended off. I know the pictures came in handy after a few wires broke off. I made a stupid mistake and had two filters backwards because one of the originals had the cover twisted around and i missed it. I ended up with a DBT flagging it, so i installed new rectifiers, and a few weeks ago i was playing with bypassing them. I want to find a nice way to attach them to the chassis without making it look like " I " did it:thumbsdown: I found a grounding bracket that should show up in the picture. i have to lengthen the orange wire and solder the bypasses in and see if it will now pass the dbt.

    Now that i am newly inspired by your nice work, i will get back on it. The shop has been swamped and i am hoping to busticate my phone somehow, so i can catch up and do some fun stuff for a change.
     

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  4. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

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    I found it. Looks like its been apart for 6 months. I had a few issues that knocked me on my ass, but i'm starting to feel better so i guess its time to put this project to rest. Thanks for your excellent thread. I may be asking for info on pt numbers and Also have the thank the Doctor for the suggestion to upgrade a few wire sizes on this thing. Here is were i was at before i shocked the rectifiers...
    http://www.audiokarma.org/forums/index.php?threads/were-did-that-marantz-300dc-come-from.699011/
     
  5. Salbreth1

    Salbreth1 AK Subscriber Subscriber

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    I checked out your thread. If you revive it I will start posting there. Let me know if you need any part numbers. I have a replacement for almost everything in there. Also, if your replacing the rectifiers I would definitely get some new pp caps to bypass them with. Unless that an old picture.
     
  6. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

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    I used wima .1uf polyester for replacing the stock ceramics, they are hiding down in the picture. Then i jumped to .01uf with the brown silver mica's, At least i believe they are silver mica's. so they are in parallel. I figured i would do an ear test without the ground screw to see if they make a difference.
    The only other ones i could use are the Vishay mkp1822, but right now i have no P/P's in that size but i may have some Cog ceramics:idea:

    What are your thoughts on this? I played a lot with decoupling capacitors and bypassing them, but i haven't experimented with bypasses to ground for high frequencies in the line/rail.

    I am not so far into it to not be able to back up. I will most likely revive the thread after figuring this "best"bypass cap mystery to use. Pulling ground screws is quick, but if i am not in the ball park here with my choices, i am wasting good music. Thanks for your thoughts on this. , JK
     
    Last edited: Jul 13, 2016
  7. Salbreth1

    Salbreth1 AK Subscriber Subscriber

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    I

    I would probably still spring for the poly caps. Bypass the rectifiers then the filters using the original values, .01uf. I posted a case study a while back about noise and harmonics of different film caps, polyester was a no go. Listen and choose what you think sounds best. I don't think you can go wrong with the additional filtering of high frequency noise. Keep in mind there is a .1uf cap for each rail to ground on the amp boards.
     
    Last edited: Jul 14, 2016
  8. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

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    Thank you for the advice. For a 12,000 filter, What would you use for values of staging bypass filtering. Somewere i had read a web page from a credible source,( Amp Builder or famous name, bugs me that i forgot) saying to layer the Bypasses according to .1 .01 .001 .001 % of the filters uf value, but in the case of the amp used, they had three consecutive bypass stages added in.

    Does the % of the stages have to be a factor of 10/100/1000 etc, to keep the time factor of discharge in line with one another?? or another words keeping the phase accurate?
     
  9. Salbreth1

    Salbreth1 AK Subscriber Subscriber

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    I think it's easy to get carried away with bypassing methods. subjectively, I believe the best way to go is to buy good filter caps and bypass the rails at the pcb to get rid of wire inductance and any high frequency noise. You might drive yourself crazy convincing yourself of an audible difference, if any. o_O
     
  10. KutzlerTrans

    KutzlerTrans Jennie & I with Buddy and Barney. Subscriber

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  11. tarior

    tarior Dirty pool, old man?

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    Nice clean looking work.
     
  12. Love Vintage

    Love Vintage AK Subscriber Subscriber

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    I know this is an old thread but I am having trouble finding replacement trimmers. If any of you that replaced them would be willing to share which ones you used it would be greatly appreciated.
    Terry
     
  13. Salbreth1

    Salbreth1 AK Subscriber Subscriber

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  14. Love Vintage

    Love Vintage AK Subscriber Subscriber

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    Perfect, I spent several hours looking at Bourns spec sheets until my eyes went crossed. I was more confused after I looked at that information, I really appreciate the information you have provided. I will place an order tomorrow. I have a couple of other ouestions on the 300dc that I am working on, maybe I should start a new thread with specifics.
    Terry
     
  15. Salbreth1

    Salbreth1 AK Subscriber Subscriber

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    No problem, and sure post a thread. This is a great amp that should be done right. I have built several of them and they never disappoint. Good Luck!

    Sal
     

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