Improving the Fisher 400

Discussion in 'Fisher' started by dcgillespie, Mar 29, 2013.

  1. dannyr

    dannyr Active Member

    Messages:
    259
    Hi Dave, the input impedance is 47k. Output is 300ohm. The unit seems to have no real effect on output voltage
     

     

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  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    As I thought. That 47K input impedance will definitely load down the tuner and the phono output, and monkey with the RIAA response of the phono preamps as well. If you install the buffer stage to enable the Preamp output jacks, it will have no trouble driving your EQ unit.

    Dave
     
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  3. eduarsan1

    eduarsan1 Luis Eduardo Sanchez Subscriber

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    Location:
    Bogotá, Colombia
    Danny Let us know how it sounds with EQ the fishie!

    Luis
     
  4. dannyr

    dannyr Active Member

    Messages:
    259
    Will do. This will finally motivate me to fix the riaa curve while I have everything flipped over.
     
  5. streetwise

    streetwise Active Member

    Messages:
    114
    A few questions revisiting my 400 rebuild.
    1. I noticed that my input channels are reversed, The balance control works correctly so it must be before there, any idea where to look?
    2. Is it necessary to have shielded wire going to and from the ss buffer or does normal solid core separate wires twisted work the same?
    3. I never did sony6060's mods but im curious what Daves opinions on that one are, Always seemed pretty questionable from what I had read earlier in the forum.
    Thanks
     
  6. eduarsan1

    eduarsan1 Luis Eduardo Sanchez Subscriber

    Messages:
    503
    Location:
    Bogotá, Colombia
    Hello

    If you made the Dave's improvements in your amp probably the issue would be in the op amp, BTW how did you discovered that the channels are reversed? Using headphones? Please be aware that in the fisher amps all headphones sockets are reversed, due to in that time no standars was available about what pin was L or R in the Jack.

    Regard the PS designed by Sony6060 I did this mod in my amp where for performance I decided to do it. Has passed almost 3 years and no issues on it where my amplifier is used DAILY more than 6 hours per day.

    I hope this info helps.

    Regards

    Luis
     

     

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  7. streetwise

    streetwise Active Member

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    114
    I found the channels are reversed plugging in a dac while the receiver was on. left popped in the right channel and vise versa same with phono and tape. I don't even own a pair of headphones anymore!

    Im curious about the PS mod and whether it is just measureable or audible? I have also been curious about his Vitamin Q, russian PIO deal, never really saw anybody reliable approving or disproving that mod as opposed to just using film caps like Mcshane provides
     
  8. eduarsan1

    eduarsan1 Luis Eduardo Sanchez Subscriber

    Messages:
    503
    Location:
    Bogotá, Colombia
    Is sure that the pinout in the unity gain buffer op amp are twisted.

    On the other hand a capacitor is a capacitor period, as electronic engineer that I am the only thing that can improve a cap is the precision in reading accuracy and the ESR(equivalent series resistance) that is the responsible that a cap fails in AC circiuits and coupling designs. So if you want to waste your money in fancy stuff is up to you!
     
  9. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    380
    Location:
    New Albany, OH

    Dave,
    Do you happen to have current parts list to build your EFB board? Some of the parts you have used are obsolete and I'm not comfortable substituting to current numbers.
    Large resistor you have listed is 4 watt. I can get 5 watt but not sure it will fit. FET is no longer available. I'm not sure if I have your latest circuit either.
    Thanks for your help.
    Dmitriy
     
  10. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
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    I never provided a parts/build list -- just a schematic, although other members may have developed one. A 5W resistor will work just fine, since the size of modern components much smaller than the old style component I used. As for availability of the FET, google Component Search, which shows that nearly 4700 pieces are still available. There were no updates for the schematics posted after the original designs were published.

    Dave
     
  11. grindfix

    grindfix Full time hobby Subscriber

    Messages:
    380
    Location:
    New Albany, OH
    Dave,
    Would you please take a look at the Mouser parts list attached for building EFB board. I already have built and installed IBAM board and was able to get current to go up to 35ma with original Fisher tubes. I intend to go through all modifications that you have posted. Please let me know if any of selected components are not optimal choice for the circuit.
    Also, My 400 serial # 62053 W.
    Thanks
     

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  12. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
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    Grind -- Your list looks good, although it looks like you doubled up on the order for the parts listed in and including item 8 through and including item 13. Did you mean to do that?

    Dave
     
  13. kward

    kward Super Member

    Messages:
    3,157
    Location:
    Utah
    Considering cost, you might want to consider an alternate to the WIMA 0.47 uF/1KV cap. Look at Mouser part number 667-ECW-FA2J474J (Panasonic 0.47 uF/630VDC radial). It's about 10x less expensive.
     
    Last edited: Jul 9, 2017
  14. thornev

    thornev Active Member

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    293
    Location:
    Mid Hudson Valley, NY
    I'm a vinyl junkie and I've read a few threads where Dave talks about improving the frequency response of the phono stage in the 400-C. I have the 500-C and did find his and others' suggestions for the 500-C. Do you guys still suggest making these changes for we vinyl junkies wanting to use the 500-C?
     
  15. sberger

    sberger Hard Core Geezer Subscriber

    I haven’t tried the mod, but I use the phono in my 500C, and find it competes quite closely to my fairly expensive Avid Pulsus phono.
     
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  16. thornev

    thornev Active Member

    Messages:
    293
    Location:
    Mid Hudson Valley, NY
    sberger - I tried it too. The sound was phenomenal except for the hum (I think when I used the HIGH input). The LOW input worked fine (I forget if I had hum), but then I have to increase the volume rather high. And this is a turntable that normally is hooked up to a phono preamp which is not needed with the 500-C. I am interested in some of Dave's posts about improving the phono stage and improving the frequency response. Thorne

    PS - I forgot a rather important point... I didn't have the turntable grounded to the Fisher which could very well be the cause of the hum !
     

     

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  17. sberger

    sberger Hard Core Geezer Subscriber

    A typical modern moving magnet/high output moving coil cart will usually have enough gain to use with the low input(which is the one you want to use it on), but like you said you might have to turn the volume up higher because the Fisher will typically have less gain then a modern phono. No big deal. There are still some pretty good carts (the Shure M44-7 comes to mind) that you can use that have very high gain (9.5mV compared to modern carts that are in the 3-5mV range) which was the norm back when the Fisher receivers were new.
     
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  18. thornev

    thornev Active Member

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    293
    Location:
    Mid Hudson Valley, NY
    Thanks, sberger. My cart is the Ortofon 2M Blue. I'm sticking with it because it sounds great. Thorne
     
  19. sberger

    sberger Hard Core Geezer Subscriber

    That has an output of 5.5mV so sufficient gain for the Fisher.
     
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  20. thornev

    thornev Active Member

    Messages:
    293
    Location:
    Mid Hudson Valley, NY
    Figured out my problem. post deleted.
     

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