1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Edgy Highs

Discussion in 'Fisher' started by ReggieD, Oct 13, 2018.

  1. ReggieD

    ReggieD New Member

    Messages:
    19
    Hello fisher fans! I’m proud to own an SA-300 amplifier. But I’m having sharp highs and I’m trying to adjust. Here is my setup. Fisher SA-300 amp, Pioneer sx-850 receiver acting as pre-amp and the only adjustment that seems to help is I have the treble set to -3. I like to listen to all styles of music. The speakers are Zenith 49cz852 in basic open baffles. This may be too general a question as there are many factors. But suggestions are appreciated. Maybe I need a nice fisher 400cx to alleviate this sharp brightness.:)
     

    Attached Files:

    Last edited: Oct 13, 2018

     

    Please register to disable this ad.

  2. ReggieD

    ReggieD New Member

    Messages:
    19
    I'd been meaning to try the Peachtree decco 65 as preamp with the SA-300. I set that up and I have a four way switch box so I can still get the FM radio from the pioneer. Seem like a definite improvement but highs stilll seem sharper than I'd like. Maybe the old zenith speakers just aren't good with high pitch rock guitar. Or I can change up the tubes on the fisher to try to take more edge off. :biggrin:
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,678
    Location:
    Ball Ground, GA
    Two things you might look at:

    1. Your speakers are not connected correctly: The negative lead of your speaker should connect to the GND terminal -- not the COM terminal. The COM terminal is only for use when the damping factor of the amplifier is being adjusted in conjunction with the adjacent X terminal. Move your negative speaker lead over to the GND terminal which then results in your speaker being connected directly to the OPT secondary winding.

    2. From you pics, I can't tell which inputs you are using, but if you use the Filter IN input jack, that provides a HF cut (and LF cut as well in the early models) -- originally intended for use when the amplifier was driving electrostatic speakers. The Filter OUT jack bypasses the filter for full range amplification.

    I hope this helps!

    Dave
     
  4. ReggieD

    ReggieD New Member

    Messages:
    19
    Hi Dave,
    Thanks for your help!
    I changed the negitive lead speaker cables to ground from common. And I was using the Filter IN jack so I changed it to Filter OUT. Any thoughts on these speaker terminals, the right side has white paint mark should this be the negitive terminal for the negitive speaker wire? Here is a photo.
     
    Last edited: Oct 13, 2018
  5. ReggieD

    ReggieD New Member

    Messages:
    19
     

    Attached Files:

  6. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,678
    Location:
    Ball Ground, GA
    Normally, a marked terminal on a speaker indicates the positive terminal, but yours is white, so it's unclear. You can determine it yourself by disconnecting the amplifier from the speaker, and connecting a common 1.5 volt AA, C, or D battery across the speaker terminals. Connected one way, the cone will move in, the other way, out. When the battery is connected so that the cone moves out from it's basket, whichever speaker terminal the positive terminal of the battery is connected to in that scenario is the positive terminal of the speaker.

    If you were already using the Filter IN terminals, then it's a sure bet that if there is any real accentuation of HF signals in your system over flat performance (i.e., not just a personal preference for HF roll-off on your part), then it's coming from some other element in your system than the Fisher.

    Dave
     
    Last edited: Oct 13, 2018

     

    Please register to disable this ad.

  7. ReggieD

    ReggieD New Member

    Messages:
    19
    Hey Dave,
    I just did the battery test and the white marked terminal is the positive I’ve had them switched a couple different times, it’s good to know the correct way. I’ve got a lot to learn especially owning this type of equipment. Just listened to Pink Floyd “Money” lots of squealing saxophone and screaming guitar. It sounded good but I’ll be doing more listening to see if I still think high frequency is accentuated. Thank you sharing your knowledge and experience.
    Best,
    Brian
     
  8. heyraz

    heyraz AK Subscriber Subscriber

    Messages:
    1,881
    Location:
    Long Branch, NJ
    What is your tube complement?
    Some tubes seem "brighter" than others in my amp.
    Also, have you checked the bias, AC and DC balance levels? Are you hearing bright or distortion?
     
  9. ReggieD

    ReggieD New Member

    Messages:
    19
    hi heyraz,
    I'm looking into what brand the EL34 tubes are, as they are NOS and the lettering has worn off. But in the mean time your idea that I might be hearing distortion I think was spot on. Because I dialed back the A and B level adj the brightness seems to be gone. Really enjoyed the music last night. I think I'm finally on track in terms of setup. The amp was purchased from Classic Tube Audio and the bias was already set so I will have to learn to do some of those things myself. I'm a total rookie in terms of electronics and valve amplifier knowledge. When I read some of the threads I get lost early on. If still want less brightness what tubes do you recommend for a warmer less bright sound? If tubes are changed does the amp have to be re-biased? Is there some online info or thread that walks through the basics of biasing an amp.
    Thanks :beerchug:,
    Brian
     
    Last edited: Oct 19, 2018 at 9:48 PM
  10. heyraz

    heyraz AK Subscriber Subscriber

    Messages:
    1,881
    Location:
    Long Branch, NJ
    Here's what I use in my SA300B. People may squawk "a tube is a tube" but I feel otherwise. I'm listening to it as I type, it is clear and full bodied, not bright or brash at all.
    Mullard 5AR4's. 4 notches on the plates, F31 or F32 etched on the glass.
    Mullard EL34's. Welded plates, Fx2 etched on the glass.
    Amperex 7025 in the 12ax7 position. 7025 is a low noise version of 12ax7 usually found in phono stages.
    Raytheon CK5814 in the 12au7 postion. 5814 is a Military version of 12au7. Surprisingly, the Raytheon CK5814's seemed to "bring it on home" for my amp. Like "the secret ingredient".

    It's a complicated amp to set up, Dave did a nice write up.

    If you had to dial back the A and B input sensitivity, your amp might have simply been overdriven into distortion by the preamp. Those potentiometers only affect the input sensitivity, not the bias, AC, DC balance or hum. That stuff gets complicated.
     
  11. ReggieD

    ReggieD New Member

    Messages:
    19
    Ok great thanks for sharing the tubes you like! Dialing down the input sensitivity really did the trick, I can’t wait to turn it back on as it was really sounding excellent last night. I think adjusting bias might be something I can try to learn down the road.
     

     

    Please register to disable this ad.

Share This Page