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FT-891 Audio Hiss?

Discussion in 'Ham Radio Discussions' started by W1SRD, Jun 28, 2017.

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  1. W1SRD

    W1SRD XML Subscriber QRZ Page

    Have any other 891 owners noticed a lot of audio hiss when using headphones? Very noticeable to me even with band noise. Not very noticeable with the speaker and would not be an issue if mobile. I've tried various headphones with different impedance.
    For a modern rig it seems excessive to me. The 857 is almost perfectly quiet by comparison.
    Wondering if it is common to all or I have a bad unit.
    Yes, I understand the DSP settings.
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Does it hiss when the volume is turned all the way down ?
  3. W1SRD

    W1SRD XML Subscriber QRZ Page

    Yes. I suspect it is either a defect or cheap audio chips.
  4. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    What headphones at what impedance? Do they match the radio spec?
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If it hisses, I'd boo at it.
    WU8Y likes this.
  6. W1SRD

    W1SRD XML Subscriber QRZ Page

    Heil Pro Set 6 = 200 ohm
    Sony MDR-7506 = 63 ohm

    The 891 manual(s) do not specify a headphone impedance that I could find.
    The recommended Yaesu YH-77STA is 35 ohm.

    In my experience higher impedance headphones tend to minimize hiss, not the other way around.
    The SP/PH switch is set to PH.
    Last edited: Jun 29, 2017
    KA0HCP likes this.
  7. WA7PRC

    WA7PRC Ham Member QRZ Page

    If there is noise w/ the AF gain at zero, add an attenuator between the PA and headphones. In fact, because headphones require a lot less power than a speaker and to keep things simple, it's common to see series resistance feeding the headphone jack:
    In my old Kenwood TS120s, R4 & R5 not only split the monaural output to be compatible w/ stereo headphones, they also attenuate the signal. Yours is similar. In fact, the schematic in the FT891 service manual (page 81) shows R4701 & R4702 = 100Ω. If the level is too hot (and noisy) and you have plenty of overhead, just increase the value.
    WZ7U likes this.
  8. W1SRD

    W1SRD XML Subscriber QRZ Page

    Thanks WA7PRC. I'll try a series resistor.
    I googled for the Service Manual but couldn't find it. Is there a link?
    Comments from any other 891 owners?
  9. WA7PRC

    WA7PRC Ham Member QRZ Page

    Since you need to reduce the level, it's simplest to just add TWO resistors inline with the headphones. A male-female adapter or short cord w/ two resistors inside does the job (you don't have to modify the rig). My PC-rig audio interface uses short cables that have resistors inside the connector shells.
    I found both user and service manuals here:
  10. W1SRD

    W1SRD XML Subscriber QRZ Page

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