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TX audio mods

Discussion in 'CB and Export Equipment and Accessories' started by Crasher, Nov 19, 2013.

  1. Crasher

    Crasher
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    Can someone tell me how to widen the tx audio bandwidth a bit on either the Galaxy 99v (old version) or an original rci-2950? I've been reading up a ton on hifi audio, but it is not something I really want to dig into right now...however I have no problem changing out caps/etc. Much appreciated!


     

  2. RatsoW8

    RatsoW8
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    :pop:
     
  3. 9C1Driver

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    Let the 2950 & Galaxy 99 be what they are. You want to do the hi fi rack gear and heil mic thing then get a ham rig and be done. Can you make a Yugo run a 12 second quarter mile......sure, why not just buy a camaro or mustang.
     
  4. Crasher

    Crasher
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    Got it. I do run a 440s and 430s Kenwood as well....just thought it was easy enough to widen the tx audio bandwidth on these radios. I'll let them be, the 2950 does sound great with the EC-2018, with little effects on.
     
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  5. Robb

    Robb
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    Goldfinger's HiFi mod for ept3600 series board

    Receive:

    C36: Change to a 2.2uF, 50 Volt (or better) mylar/polyester film
    C38: Remove for more highs
    C39. C154, C155: change to 2.2uF 50 volt (or better) Non-polarized electrolytic or mylar/polyester film
    C157: Change to a 2.2uF, 16 Volt (or better) tantalum (observe polarity)

    Transmit:

    C129: Change to a 10uF, 16 Volt (or better) tantalum (observe polarity)
    C187, C191: Change to 2.2uF, 50 volt (or better) mylar/polyester film
     
    #5 Robb, Nov 19, 2013
    Last edited: Nov 19, 2013
    Sonar and GnG8d like this.
  6. Crasher

    Crasher
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    Exactly what I was looking for. Thanks!
     
  7. 9C1Driver

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    So when you complete all that what is the end result? Will people say,"wow what did you do to your radio"? Or will it be oh sounds ok I guess?

    Reason I say this is a local did all these hi fi mods he found on the net to a Uniden Washington. When done it had a nasal monotone drone sound. He had a second stock Washington that he put a Turner plus 3 desk mic on and sounded better then the hi fi radio.

    Many years ago I heard an old orange display 2950 that had the SP-1A speech processor installed and wow, loud, crisp, and clean audio.

    Robb do the hi fi mods respond better in an Export radio? Would those mods and the SP-1A work well together or not? Just wondering.
     
  8. Robb

    Robb
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    What does it accomplish?
    Fair question.

    First, it works by minimizing any filtering in the audio circuit and allows the ~2.8khz audio TX bandwidth dictated by this filtering to be extended to about +/-4khz. As well as the receive audio. So long as the modulation level is correct and a decent mic is used, a flatter, wider audio response can be realized. Has nothing to do with being 'loud'; that is a matter of signal strength dictated by the power output and the antenna used. Using a three-way car stereo speaker/enclosure also makes receive far less hard on the ears over an extended period of time when the receive audio is made wider.

    This allows them to transmit a better audio signal that is easier to understand at the receiving end. Beats the crap out a radio that has a boxy, narrow, and tinny audio signal, especially if traffic makes it otherwise hard to understand. The idea that a radio's audio must sound crappy is just not so and it can be changed for the better - is all. Not really that big of a deal, some prefer it and others don't. Take it or leave it situation. Hams have been doing it for years, about time that CBers finally caught on.

    Never have done it to a 3600 chassis yet. I did try it on an old Uniden Grant that I got working, and I must say that I was more than pleased with that result. Took a little time and cost just a few bucks. In fact, there were more parts that had to be changed out in the Grant than the 3600 chassis requires. But it was a learning experience that paid off far better than the 2999 receive mod which doesn't work, I can tell ya that much.

    Any radio can benefit from this kind of modding.

    The SP1A is an audio compressor which tames the mic's audio amplitude, but changing out a few caps as suggested changes the audio bandwidth.
    Apples and oranges.
     
    #8 Robb, Nov 19, 2013
    Last edited: Nov 20, 2013
  9. dave457

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    After the mods you,ll need audio processing to take advantage of the increased bandwidth the mods have done

    Sent from my SGH-T599N using Tapatalk
     
  10. Robb

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    Collection of Audio Mods from 'Goldfinger':

     
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  11. Shockwave

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    The old D-104 can be modified to work quite nicely on most radios once these bandwidth mods are done on the radio. The D-104 is noted as sounded tinny for one reason, Astatic loaded the element down to an impedance that is four times too low for bass to transfer from the element.

    The preamp must be rebuilt using an FET as the first stage with a gate impedance of at least 4.7 meg. How low will it go? How about 30 cycles! That big crystal element has plenty of bass, you just have to let it out by lightening up on the loading the preamp places on the element.

    You cannot take a shortcut here and simply replace the existing base resistor with a higher value because the input to the base of a bipolar transistor is inherently going to be a lower impedance than its FET counterpart.
     
  12. Robb

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    bob85 had the best solution for the D-104. By adding a 2m pot in series with the 270K resistor, it will give it a bass control. I just take the easy way out and just clip the 270k resistor. It doesn't have the same response as bob85's mod, but it sure does boost the bass a lot just the same.

    It works, and do it to all of my D-104's.

    *EDIT*

    AS pointed out by tecnicoloco below, I was referring to the Astatic D-104/M6 handheld mic; not the lollipop/base mic version.
     
    #12 Robb, Nov 21, 2013
    Last edited: Nov 21, 2013
  13. Shockwave

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    I think you're talking about the stock 150K resistor in the mic because there is no 270K. That will increase bass response by lightening the load on the element through the transistor junction. It can also introduce distortion by offsetting the DC bias of the first transistor.

    This may be overlooked if you don't check the output of the first stage on the scope. The thing to look for is the positive peak will flat top long before the negative peak since the emitter voltage will be much higher than 50% of VCC before signal is applied.
     
  14. tecnicoloco

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    You guys are talking about 2 different mods for 2 different microphones

    Rob is talking about the D-104 MB6 Handheld Microphone

    Don/Shockwave is talking about the D104 Lollipop Desktop Microphone
     
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  15. M0GVZ

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    Nothing unless the other station has modified their transceiver to receive 4kHz.

    Really it doesn't because the frequency range that affects articulation and therefore clarity is around 2kHz to 2.4kHz.

    Oh and they also have to have modded their transceiver.

    MISGUIDED hams have been doing it for a while.

    Does Bob Heil do it? No. He actually rolls off the top and bottom end to improve articulation and intelligibility. Tells you all you need to know.
     

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