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The Fisher Phono Preamp, and RIAA

Discussion in 'Fisher' started by dcgillespie, Jun 25, 2014.

  1. dannyr

    dannyr Active Member

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    Awesome. That should make sourcing components a bit easier. Thanks.
     

     

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  2. ferninando

    ferninando Lunatic Member

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    A question for Mr. Gillespie.
    How would you implement your phono eq. improvement in a unit where the phono and tape eq are in the same PEC?
    I am not against eliminating all tape functions in MY unit but others may have objections.
    What say you sir?
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    You would leave terminals 1& 2 of the Fisher PEC connected, which will allow the PEC's EQ network for the Tape Head function still work, and disconnect terminal #3. The new phono network would have to be built from discrete components of course, with the end of the network including the 270K resistor connected to where terminal #3 of the PEC used to connect to, and the other end of the new network connected to where terminal #1 connects to. And that's it.

    Good luck with it!

    Dave
     
  4. ferninando

    ferninando Lunatic Member

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    So the new discrete RIAA consists of your 4 parts ''Including" another 270kR, not the one in the PEC.
    If thats correct, I got it.
    OK to make it on a little perf bd and wire it to the selector sw? Or better to hardwire directly to the sw.?
     
  5. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    Yes, you are using all new components to make up the new RIAA EQ network.

    A perf board is fine, as is hard wiring, but you will want to keep all leads as short as possible. Use the smallest components you can to help achieve that end -- this to help minimize any noise and interaction with other components.

    Dave
     
  6. ferninando

    ferninando Lunatic Member

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    got it. thanks Dave
     

     

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  7. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    That tape input isn't going to do you much good unless your tape deck has amplifier bypass outputs, or is just a transport. That's why I converted the Tape Head input to line-level on the Super Stock HF-85 schematic...that way it will work with modern tape equipment. And by "modern," I mean 1961.
     
  8. ferninando

    ferninando Lunatic Member

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    my tape is a pioneer CT-F1000 cassette recorder/player. Line level output I assume. Dont know if it needs eq or not. guess I better get the mnl. Only will use it for playback.
     
    Last edited: Aug 31, 2014
  9. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    By definition, any device that has a line level output does not need preamplification, nor equalization. All of the high level inputs on commercial stereo equipment are considered line level inputs. It is a virtually certainty that your cassette recorder would use a high level input rather than the Tape Head inputs. If you connect the Recording Outputs of your Fisher to the recording line level inputs of your cassette deck, you will also want to be certain that the input impedance of the cassette deck does not load down the Recording Output signal of your Fisher. To prevent signal degradation, any tape recorder used with a vacuum tube Fisher should have an input impedance of at least 250K ohms.

    Dave
     
  10. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    From the CTF1000 Owners manual. Looks like 50Kohms output impedance.
    .

    [​IMG]



    I just ran thru the CTF4242, 6262 and CT-F650 and they all use 50Kohm. So PIONEER pretty much used the same output impedance across the whole line
     
  11. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    If you plug that into the Fisher Recording Output jack, you will likely notice a loss of LF information as a result.

    Dave
     

     

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  12. gadget73

    gadget73 junk junkie Subscriber

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    Bumping this back to the top since I re-discovered it while looking for something else. Looks like the TA-600's phono PEC is the same as used in many other models, so I believe these mods would also apply there?
     
  13. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

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    They absolutely would Gadget. The basic Fisher phono preamp as used in their stereo pieces dates to the original 400C preamplifier, and followed through with little modification to just about anything they sold that included a phono preamp for magnetic phono pickups.

    Dave
     
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    I got this drawing somewhere years ago, but added the original values. It's correct for that. So just change the values, and build on a perf board. Pin 1 and 3 are the phono section, with pin 1 and 2 being the Tape section. Use it as you see fit. If you use a 2"x2" board, you have enough room to put both pecs on the same board (provided the originals are next to each other. ) If they are on opposite ends of the chassis, use separate boards cut down.

    Even tho it says for 400-500c-800c, it will work on any unit that has the 50187-3 PEC for RIAA EQ.

    FISHER PHONO-TAPE PEC.jpg
     
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  15. Sam Cogley

    Sam Cogley Last of the Time Lords Subscriber

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    I'm planning on adding my own design of that board to my inventory of PEC replacements.
     
  16. gadget73

    gadget73 junk junkie Subscriber

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    I should have the room to whack one together on a single piece. I can ditch the tape stuff too, since I've got it unhooked and re-wired to give me two phono inputs anyway. Might have to break down and buy some smaller parts though. All I stock are 1/2w resistors and 500v mica caps. That gets a bit bulky at times.

    Thanks for the confirmation that this would indeed apply to the 600. Its really my only piece of proper Fisher gear so I lack experience in their particulars.
     

     

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  17. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Here's a mouser list I did for PEC's. Obviously you won't need 50 of some parts, or 10 of another, FISHER PECs parts.jpg (unless you are needing these for spares)
     
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  18. CORYK

    CORYK AK Subscriber Subscriber

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    Dave, Would it be ok to use two 1 Meg ohm resistors in series for the 2.2 Meg ohm? Or should I use a 2.2 1 percent and call it good? 2.13 Meg seems non-existent. Do the 350 and 680pf caps have to be silver micas? Alternatives? Thanks, Cory.
     
    Last edited: Dec 4, 2015
  19. gadget73

    gadget73 junk junkie Subscriber

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    I think he got that 2.13M out of a low-value 2.2M resistor. You could do a 2M and a 130k in series.
     
  20. CORYK

    CORYK AK Subscriber Subscriber

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    Thank you Gadget!
     

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