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Flexradio 6600 Mic amp circuit

Hi all,

I have been using my Flexradio 6600 about year by now and in general I have been very pleased with it. However, still learning how to get all benefit out from all of its functionality. One of my recent interest has been around mic audio. Related to this, I am very interested how its build up to be used in optimum way.

I am interested if any one knows if it is possible to get partial circuit diagram which shows mic amp design up to the level meter, maybe showing also EQ part of the circuit design.

All related information is very welcome.

73 de Jukka OH2MA


  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator

    Flex does not publish the schematic for the radio so I am not sure if the internal 20 dB boost is done in software or hardware. The EQ is done in TX DSP chain and EQ is after the level meter.

    I found if using a mic such as a PR40 or RE27ND it is better to use an external preamp and not use the internal 20 dB boost.

    Dave wo2x

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Since almost all of the flex internal operation is software, there is not really a “circuit diagram” that would be helpful.

    When you say optimum, what situation is the focus since rag chew not the same as dxing or contesting? For example when chasing dx (or parks), I use a narrow transmit frequency bandwidth with a low frequency limit above 300 Hz, dx+, a lot of compression and flat tx eq. For other ops, other adjustments may be more appropriate.

    One caution, as noted above, the eq is after the level meter, so any boost won’t be captured by the meter, could cause an overdrive situation.

  • Jukka
    Jukka Member
    edited March 2022
    Hi David and John,

    Thanks for your comments. My main interest has born with the fact that I have not been able to get rid of some distortion on my SSB TX audio. I have tried almost all adjustments (all levels, EQ, proc etc), including several different mics. I can get quite feasible audio for DXing and rag chew, but still there is always the distortion which causing comments time to time. I have used SSDR with Mac, Win PC and iPad. Operating almost 100% via remote over the net.

    73 de Jukka OH2MA
  • VE7ATJ_Don
    VE7ATJ_Don Member ✭✭✭

    Hi Jukka... almost all of the time, when distortion shows up in the TX audio, it is due to setting the mike gain too high. There are numerous Youtube videos on this, but it's important to ensure that you adjust your mike gain with NO processing on (PROC button grey in colour) and the meter should never go into the red, even on peaks. It's best to adjust mike gain so that the meter peaks around -10 to -5db.

    Depending upon your mike, you may also not need the +20db boost, so you might try turning that off in the settings.

    It's also possible that you are overdriving the mike itself. It would depend on the mike technology and how close you are speaking to the element. Possibly a windsock or other mike cover may help with this.

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