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I have a Expert 1.3K-FA Amp and and a Flex 6400. What could be the problem with my audio distorting

I have the amp connected to a inverted V that was used with another amp with no problem.


  • David Decoons, wo2xDavid Decoons, wo2x Member ✭✭✭

    Hi Dennis,

    There could be several causes. More details would help. What microphone? How is it connected to the radio? Are you using the internal EQ and how is it set? How high is your TX mic gain?

    With the mic gain it is important to understand the meter. There is a peak indicator to the right of the level meter bar graph. When adjusting the level you want to ensure the level peak indicator does not exceed zero. If using the internal EQ then do not exceed between -10 and -5. See picture below for the peak indicator I am referring to.

    When adjusting the TX EQ, start with all sliders at zero and make small adjustments. I find sliders set higher than +5 tend to start distorting, especially if mic gain is peaking close to zero.

    Last, it may be RF getting into your mic or TX audio path. Try with someone who can receive you nice and strong. Set the amp to standby and try adjusting power down. If the problem goes away then it is RF getting in the TX audio.


    Dave wo2x

  • [{"insert":"Thank you David for the help. I am using a PR 781 connected directly to the Flex locally. On a remote computer I am using a PR 40 connected to the computer using a USB input. Both are giving me the distortion. I have been using internal EQ. With the Amp in standby with the Flex at 100 watts It does not seem to be any distortion that I can hear. I have used two different tuners with the same result. I have used a dummy load to test both with the radio and the amp in operate mode with the same results. I have changed the EQ settings and turning it off with the same distortion with 8 watts input to the Amp in low operate mode about 500 watts output from the amp. \nI have had a Ameritron Al 811H used the Flex with no problems.\nI have another antenna to try but will have change the cables to connect it to the amp. the transmission cable to the DX-CC inverted V is only a year old. I might try to replace it again I have 100 Ft cable but will have to route it in, that will take some time. At this point it looks to me that amp has a issue. It does have output of watts as it should for low- mid-max settings on the amp. \n"}]
  • David Decoons, wo2xDavid Decoons, wo2x Member ✭✭✭

    Ok, with the amp straight into the dummy load and listening where? How are you monitoring your signal? Different radio or monitor on Flex?

    If on a different receiver and only with the SPE amp then there it sounds like it may be a problem with the amp. Especially if an 811 amp does not exhibit the problem.

    You might want to send an email describing the problem to SPE support. Maybe the amp bias circuit has an issue or bad LDMOS device? SPE support would be better to answer that question. But from what you describe it only happens when the SPE is in operate.

    One last question, are you using a custom cable from the amp to Flex for band/frequency control?

    Dave wo2x

  • Thanks Dave for taking the time to help. I listened with the amp into the dummy load on my Icom 7300 and Kenwood 590 with no antenna connected. I have not ran the 811 into a dummy load as yet. However I was able to have a nice QSO that confirmed that the expert amp was distorted. Later I re-connect the 811 and got a good report regarding the Audio. I am going to try the 7300 into the expert amp. First with a dummy load then into the antenna. It will take a while to get setup. I think it is the Amp as well. Yes I am using the cat cable from Dan Tassell K5PCB.
  • Larry _ W8LLLLarry _ W8LLL Member ✭✭✭

    Your not using ALC with the expert are you?

  • David Decoons, wo2xDavid Decoons, wo2x Member ✭✭✭

    If you have an RCA male to male cable try connecting that from TX1 on Flex and connect to PTT in on amp. Disconnect Don Tassels cable then test again.

    Test with amp on High power but lower drive from Flex (about 300 to 400 watts out) and see if distortion is still there. I have seen on rare occasions where a partial failure of the LDMOS device or bias circuit in amp can cause poor I.MD and distortion. Running the amp on high power will use a higher VDD voltage.

    Since so far things point towards the amp being the suspect open a support ticket with SPE. They may have other tests you can do to pinpoint the problems.

    Good luck!

    Dave wo2x

  • Thanks again David. I was going to try disconnect the cat cable that I got from Dan Tassell. connected a RCA from TX1 and the Amp. After some tests listing on 7300 it seemed to be ok. I have a Heil PR 781 mic connected direct to the Flex. Changing the Low setting output 500 watts (amp in operate mode) and off to compare the audio signals. I also have a remote computer that to connect to the Flex using a PR 40 to the computer I had used preamp. possible the preamp was still causing issues when using this remote computer with the audio. Removed the preamp connected to the mic and used a XLR to USB cable I had purchased some time ago. . I got a good report this morning from on station in Roseville CA of 20 over S9 and a good clean signal. I will have to do have to have some more contacts to make sure I have it fixed. I have yet to try the High power test as well. I will get a chance tomorrow to work on that. I not sure if the cat cable has an issue but for now I will not use it. It also has a connection to the USB port and TX1. Something possible not right with it.

    Thanks again Dave for taking the time to help. All of your ideas for testing was spot on and helped a lot.
  • David Decoons, wo2xDavid Decoons, wo2x Member ✭✭✭

    Glad to help!

    73 & good DX

    Dave wo2x

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