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Julie KC0TMD
Julie KC0TMD Member ✭✭
edited June 2020 in Third-Party Software

I have a FLEX-6600M. I just picked up a new PreSonus TubePre V2 Single-Channel Tube Preamplifier/DI Box from Guitar Center today. I got it home with and it hooked it up, and nothing is working and it won't even drive to the VU Meter in the V2 Mic Pre Amp VU.

I notice that when I remove the PreSonus TubePre V2 Single-Channel Tube Preamplifier/DI from between the my Mic, Flex-6600M and PALSTAR LA-1K AMP, eveything is working as it should with+20db in the radio setup and Bias off.

After getting confused and putting the mic in the output and the Radio
in the Input. I then had to find the correct cables that I did have on
hand. I finely was able to get the Mic in to the Input and the Radio to the output of the Mic Pre Amp.

According to the user manual of the PreSonus TubePre V2 Single-Channel Tube Preamplifier/DI, the first thing is to hook your balanced mic up to the Mic input and adjust the Drive.

Set the input level on your audio interface or mixer, using the recommended level-setting procedure for that device.

Speak into the microphone while monitoring the TubePre V2 (again, following the monitoring instructions for your audio interface or mixer), and turn the Drive knob clockwise until the desired effect  is is achieved.

Speak into the microphone while watching the VU meter on the front panel and slowly turning the TubePre V2 Gain knob clockwise.

The entire user manual can be found at,


I notice that if I keep the drive down to 0, and toy around with the Mic Gain, I can get my LA-1K Amp to have spikes from 150 to 300 watts for a few sec, but no SSB carrier. I notice to even get it to the spikes I have to set select the the BIAS and the +20 DB.

I don't get this, but I seen photos of Flax Radios users with that same Mic Pre Amp. What I not doing or failing to do!

Once again with the  PreSonus TubePre V2 Single-Channel Tube Preamplifier/DI removed, my PR40, FLEX-6600M and PALSTAR LA-1K works with no issues.

Any Help would be greatly appreciated in this matter.

My Phone Number is 636-578-1990.

Thank You,

Julie K0CTMD.


  • Paul - K6HR
    Paul - K6HR Member ✭✭
    edited May 2020
    Hello Julie,
    Which input on the radio are you connecting the output of the preamp to?
    It should be connected to the LINE input, and LINE should be selected as the input on the "P/CW" tab. HTH.
  • Rick N0VT
    Rick N0VT Member ✭✭
    edited May 2020
    Hi Julie--Unlike FM, AM or CW, there's no power output with SSB until you have audio.   That's why you see the output spikes.  It sounds like It's working the way it should.

    Rick WR0H
  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator
    edited June 2020
    Another thing, make sure phantom power is disabled on the tube pre. The PR40 is a dynamic mic and the 48 volts can damage the mic.. What input are you using on the Flex? Mic, line, or balanced? Make sure your selection on SmartSDR matches the input you are using. If you are not seeing any audio on the level indicator on the mic pre then that is where you need to start looking. I am not familiar with that equipment so cannot offer any additional advice. Dave wo2x
  • Bob Needleman
    Bob Needleman Member ✭✭
    edited May 2020
    Dynamic mikes, like the Heil PR-40 and all Bob's  other mikes designed for amateur use, do NOT need any preamps. Mike preamps are generally reserved for use with condenser mikes, which require phantom power and amplification. So that is not the right mike to be using with a mike preamp. 

    Bob K3AC. 
  • KD0RC
    KD0RC Broomfield, COMember, Super Elmer Moderator
    edited May 2020
    Julie, what are you trying to accomplish with the preamp?  It sounds like it was working without it.
    Len, KD0RC
  • Bob Needleman
    Bob Needleman Member ✭✭
    edited May 2020
    Julie - if you're trying to do external EQ with a PR-40, I'd return the tube preamp, and pick up a mixer board (eg. Behringer Xenyx) or W2IHY EQ Plus box. That will allow you to connect your PR-40 and have external audio control over several parameters, such as parametric EQ, echo effect, background noise reduction (eg. amp blower noise), etc. I use a W2IHY EQ Plus with my RE-27 dynamic mike feeding the audio into the rear mike jack with very good results. It has a built in pre-amp circuit if you need it, but with a PR-40 you won't  need it. 
    Bob K3AC
  • Brian Denley  KB1VBF
    Brian Denley KB1VBF Member ✭✭
    edited May 2020
    But it’s the right mic for the Flex.  Keep the mic and dump the preamp
  • I just got a PR40, have it plugged into the 1/8 Mic jack and have the MIC option selected, as well as the +20db selected, and Bias off. Virtually NO audio. I can hear my voice faintly on another tranceiver, and a HAM who lives 1/4 mile from me heard nothing on transmit. Full 100w setting on Power gave me 11 watts out on sideband, and in FM mode I get the 100w carrier with no audio. So I am having same problem that Julie had, but if this is a dynamic mic, why won't it work? Bob, K3AC, and others, appreciate any feedback. I'd rather NOT get a preamp with or without mixer, if I don't need it. Thanks for any comments! 73 de W8RBD Bob
  • Mike Steventon
    Mike Steventon Member ✭✭✭

    Check your mic cable connections. I have PR 40 and it is absolutely fine with +20dB and set to about 80 gain. No need for external preamp. I use the balanced line 1/4 inch jack as we are told in the manual that it gives the best quality. You have to select Bal, as opposed to Mic. The manual gives clear instructions on the wiring of both types of microphone plug. It really sounds as if there is a faulty connection in the mic lead. Hope that helps!

    73 de Mike G4GWH

  • WX7Y
    WX7Y Member ✭✭✭

    I have my PR40 Wired for Balanced Audio with the +20 Mic amp turned on level set about 83. 

    The PR40 if VERY VERY directional MIC and you need to talk straight into the Mic and not to the side and you need to be within 2 to 3 inches away from the MIC. 

    The Audio using the PR40 set up correctly using just the settings in the Flex Radio is OUTSTANDING and far better then the Heil Gold line Mic's or about any other MIC I have tried. 

  • KD0RC
    KD0RC Broomfield, COMember, Super Elmer Moderator

    @Bob Dushkoff , what radio do you have? Are you connecting to a Maestro? The mic jack options are different on different radios. For example, the 6400 does not have the 1/4 inch jack for balanced input, it just has the 1/8 inch jack for pseudo-balanced input. That also means that Bal, is not a choice, just Mic. Let us know so that we can give you better guidance.

  • Mike Steventon
    Mike Steventon Member ✭✭✭

    Attn. WX7Y:

    “‘’’”’The Audio using the PR40 set up correctly using just the settings in the Flex Radio is OUTSTANDING and far better then the Heil Gold line Mic's or about any other MIC I have tried. ‘’’”””

    I could not agree more!!!!

    73 de Mike.

  • WX7Y
    WX7Y Member ✭✭✭

    Bob, in the title of the message he says it is a 6600M.

  • Mike VE3CKO
    Mike VE3CKO Member ✭✭✭
    edited October 2021

    Of course the PR-40 with the +20db mic preamp enable will do the job and you will get great reports using the internal EQ. The point is she is trying to use a tube preamp and the mellowness it will add to her voice. You can't get that with the suggested W2IHY EQ Plus. Keep trying Julie don't give up. In addition to what Dave said about making sure the phantom power is off on your PreSonus, be sure you DISABLE the 20db mic preamp in the FlexRadio.

    I currently have my PR-40 going direct in the balanced input of the 6700 with level at 73. I was using a Behringer tube preamp but it failed and I haven't replaced it yet, not sure I will. Hoping Flex will add some EQ enhancements to SmartSDR like a few parametrics and more bands. The 8-band is surely very useful but having more sweet spots to enhance or reduce would be very welcome.

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