Fisher 500B - Listening With Headphones

Discussion in 'Fisher' started by 4everanalog, Aug 11, 2017.

  1. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    Hi all,
    If I were to use the item shown in the listing below ...
    http://www.ebay.com/itm/AIQIN-headp...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649
    to listen to my 500B through headphones,
    would I be able to leave it hooked up to the speaker outputs with the speakers or would it show up as a 4ohm load to the amplifier?
    (my apologies if some of the language is incorrect - I'm still learning)
    Long story short - I don't (obviously) want to do anything that would damage the unit.
     
  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,846
    Location:
    Ball Ground, GA
    The answer is unclear, as it doesn't state precisely what it does. But in looking at it, it appears that the device is merely a tap into the speaker lines. That is, it apparently does not control the speakers (as in being able to turn them on and off), so they would be connected all the time. If that is so, then there is no need for any internal load resistors to take the place of the speakers, since they would always be connected -- therefore, the thought that this unit is merely a "tap". As a tap then, the load it would present to your 500B is no different than if the speakers were connected directly to it without this device. All that said however, the connections on the back are a bit strange -- either it is a mono unit (it never states that it is a stereo device), or it is only handling the hot side of each channel -- i.e., two hots in, two hots out. Even this would be strange as then there would be no ground reference for the phones to operate from. It appears then to be a mono device. I'd want questions answered by the manufacturer before making a purchase.

    I hope this helps!

    Dave
     
  3. Dadbar

    Dadbar Super Member

    Messages:
    1,799
    Location:
    Waltham & Gloucester MA
    I would pass on this thing. It looks a bit sketchy.

    If you are handy, you could build your own and emulate the headphone circuit used on the 400. IIRC that unit uses 25 ohm 5 watt resistors in parallel to the headphone outputs to protect the transformers when the speakers are shut off manually by the slide switch.
     
  4. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    Thanks for the response Dave.
    Food for thought for sure.
    I guess I sort of assumed there would be some sort of resistor(s) inside just like the headphone tap on any amplifier.
    My impression is - this and the speakers would be hooked up in parallel (both at the same time) and this unit would convert what is basically a line-level output down to whatever signal is required to drive headphones at a normal listening level (via resistors inline).
    There are many aftermarket car amplifiers that do this so you can add them to a factory system, taking the signal from the speaker outputs.

    Not seeing how it would be mono - I see left/right, +/-. If the output from the Fisher is stereo why would the headphone output be mono?

    Regards,

    -Rob.
     
  5. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,846
    Location:
    Ball Ground, GA
    Ah! I see how you are looking at it. My quick read was that you connected it to the Fisher, and then the speakers to it, and that's where my comments came from. If this connects along with the speakers to the Fisher, I suppose it makes more sense then -- except that your basic question is still left unanswered (whether there are load resistors in it or not), because they don't give that kind of information.

    Dave
     
  6. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    Hey Dave - yeah, they don't tell you much in that listing.
    I've done a bit more digging around and found this:
    http://www.diyaudioblog.com/2015/06/speaker-amp-to-headphone-converter-box.html
    You reckon the guts would look something like that?
    BTW, there's that reference-to-ground you mentioned (which I still don't fully understand).
    But I do understand that you know what you're talking about! :thumbsup:
     
  7. Rockyhill

    Rockyhill 148 State Street Subscriber

    Messages:
    3,012
    Location:
    Maine
    Yes, sketchy:
    • using copper crystal input terminal,
    • you can directly speaker wire banana head.
    • 6.35mm headphone jack, offer a 3.5mm adapter
    I would not risk harm to my 500B.
     
  8. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    I hear you - but not because of some grammatical errors. I have bought some quality items directly from china (cables, interconnects and so-on). Sometimes things get lost in translation. This does not necessarily mean it's not a decent item. I have requested some pics of the guts. Look at Hifiman. They have quite the audiophile community of their own over there these days.
     
  9. Rockyhill

    Rockyhill 148 State Street Subscriber

    Messages:
    3,012
    Location:
    Maine
    I agree. I have also bought products directly from China (via their Canadian distributor) such as Musical Paradise and Grant Fidelity. The quality was solid and as advertised.
     
  10. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    :beerchug: Yup ... and boy are they pleasant to deal with.
     
  11. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Here is a very similar device. It may be the same device with a different name. The point is it looks the same on the outside as the OP's device. Something about not judging a book by its cover.

    Note the supplied adapter...

    upload_2017-8-13_17-35-36.png


    A picture of the insides...

    upload_2017-8-13_17-36-47.png

    It appears to have a 3 conductor headphone jack. It appears to have 5 resistors in parallel as a load for each channel and additional resistors to provide attenuation to the signal to the head phone jack.

    And one more picture.

    upload_2017-8-13_17-56-20.png
     
  12. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,846
    Location:
    Ball Ground, GA
    Agreed -- so if this is the same as the one the OP was questioning, then it is always placing a load on the device it is connected to. In addition, because of the common ground required between the channels for the headphone jack, this device cannot be used with any unit offering a powered center channel speaker output. It would be best to use this device with appropriate switching to select either the speakers, or this device.

    Dave
     
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  13. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    Good find!
    Thank you for that.
    This helps a LOT.
     
  14. 4everanalog

    4everanalog Active Member

    Messages:
    149
    Location:
    Burlington, Ontario, Canada
    My concerns right from the start.
    If only the dang receiver was set up to drive more than one pair of speakers ... :no:

    Another question:
    Is it really always placing a load on the amp or would it only do that with the headphones actually plugged-in, completing the circuit(s)?
     
    Last edited: Aug 13, 2017
  15. I LIKE MUSIC

    I LIKE MUSIC Super Member

    It appears that it will always place a load on the amplifier. It looks like about 10 Ohms per channel.
     

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