Cheap preamps

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  • #26720
    Thomas LevineThomas Levine
    Participant

    I think I need a pre-amp for the microphone that I want to plug in to the
    LR-16. Is this right? If so, where can I buy a cheap (and low-quality)
    pre-amp? Or, maybe the thing I need is called something else.
    I don’t know much about audio equipment, as you may guess.

    Do I need a pre-amp?
    I arrived at the idea that I need a pre-amp by reading the LR-16 manual
    and by conducting the following experiment.

    I have an LR-16, a personal computer (PC), and a microphone. The personal
    computer has a microphone port and a headphones port.

    Micropone output PC output
    LR-16 input Can’t hear Can hear
    PC input (low mic boost) Can’t hear Can hear
    PC input (high mic boost) Can hear Can hear (loudly!)

    I plugged these things into each other in the various combinations above and
    heard or didn’t hear the results above.

    In addition to using the built-in PC sound card, I also tried
    a cheap USB sound card,
    and the results were the same as with the built-in card.
    I bought this on eBay and have the link to the item in case anyone is curious,
    but I’m not including it because the forum restricts the posting of links.

    This makes me think that my sound cards have pre-amps or the sound system
    software does something equivalent.

    Adding to my belief that I need a pre-amp, I see that you can lower the volume
    on individual channels within the LR-16 but can’t increase their volumes; the
    default gain level is 0 decibels, and the only other options are negative
    numbers.

    Cheap pre-amps
    I want to buy a small, cheap pre-amp for this microphone. I want it to be small
    and cheap because bad quality is fine for what I’m doing and because I want
    the pre-amp to be easy to carry.
    I’m going to have several similar inputs and thus several pre-amps.

    I found a bunch of things marketed as pre-amps, but I don’t really know what
    I’m doing. Search for something like “pre-amp board”, “amplifier board”, or
    “build a pre-amp”.

    But I’m concerned by my inability to find small a cheap thing that takes.
    On one hand, this could be a strange thing that few people need and that there
    thus is little market for. On the other hand, it could indicate that I’m doing
    something more strangely than I need to. The FiiO E3 is an example of an
    off-the-shelf thingy that does what I want. The forum limits how many links
    I can post, so you can search for information about the FiiO E3.

    Anyway, I arrived finally at the following cheap board that I think does what
    I want. If I connect this board to power, connect the input to the microphone,
    and connect the output to the LR-16, should the microphone play loudly enough?
    https://www.ebay.com/itm/The-New-Low-Power-TDA8932-35W-Digital-Amplifier-Board-Module-Mono-Power-/252115649725?hash=item3ab34384bd:g:7g8AAOSwDFNWFBtH

    #26722
    Laszlo .Laszlo
    Keymaster

    Hi tlevine,

    Yes you are right you cannot connect microphone directly into the LR-16.
    There are couple of cheap preamp on the market, what can be enough for you in this situation.
    There are couple of preamp from the cheap one to more expensive one:
    https://www.thomann.de/gb/behringer_mic100_tube_ultragain_micpreamp.htm
    https://www.thomann.de/gb/art_tube_mp.htm
    https://www.thomann.de/gb/presonus_tubepre_v2.htm
    Multi channel preamps also available if needed.
    You also need to take care with the LR-16 input connection, because the inputs designed for the insert syle connection where the TRS (jack) inputs following this pinout:
    T (tip) input signal from your source to LR-16
    R (ring) return signal from the LR-16 to the insert connector
    S : Common ground

    If you want to use the device without insert connection (I think that’s your case) you need to leave the R (ring) pin disconnected.

    The ebay link in your post are a speaker amplifier. That’s not solution for your problem.

    #26725
    Thomas LevineThomas Levine
    Participant

    Thanks!

    You are correct about how I need to leave the ring disconnected.

    It would be nice if I could use a smaller pre-amp, so I looked for some.

    I think this listing looks appropriate. (I have mono input.)

    I had trouble finding a listing that discussed the electrical characteristics of the pre-amp, but I see that this other (stereo) board uses the PAM8403 chip, of which I found the datasheet. The attached table, from the datasheet, lists output voltages that look okay to me.

    Maybe I’ll get both.

    Does that sound right?

    #26728
    Laszlo .Laszlo
    Keymaster

    Hi Tlevine,

    The easiest way for the proper connection when you take a standard “Y” insert cable then connect the TRS connector to the LR-16 input, and connect the Send connector to the MIC peramp output, and leave the Return connector disconnected.

    If I understand correctly you want to connect your Mic preamp to the LR-16, and you also want to drive some speaker with the PAM8403 speaker amplifier?

    #26729
    Thomas LevineThomas Levine
    Participant

    Your suggestion on the Y cable sounds like a good idea.

    Your understanding of my plans is incorrect. I don’t want to drive a speaker with the PAM8403; I’m recording only, not playing, and I want to use the PAM8403 board or the FK647 (the other thing I linked) as the pre-amplifier, not as the amplifier.

    #26730
    Laszlo .Laszlo
    Keymaster

    If you need a preamp I suggest to search some solution from more reliable source eg: https://sound.westhost.com/project122.htm

    #26731
    Tom SailorTom Sailor
    Participant
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