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TX audio mods

Crasher

Member
Apr 25, 2012
49
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Norwalk, OH
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!
 

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.
 
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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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
 
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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


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.
 
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.
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.
 
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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
 
Collection of Audio Mods from 'Goldfinger':

Cobra 148/2000/Grant XL

TX

C46 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C101 Change to 1.5uf tantalum 16 to 50 volt
C102 Change to a 910pf ceramic disc
C104 Change to 2.2uf tantalum 16 to 50 volt
C108 Change to 1uf to 2.2 uf tantalum 16 to 50 volt
I found that if you have a very deep voice start with 1uf on C108
and work up if need be.
If you need more highs on tx Change C 105 to .001 to .0001uf mylar/polyester film The smaller you go the more highs you get.

RX

C71 Change to 1uf mylar/polyester film or non-polarized electrolytic
C75 Change to .001 to .0001uf this will give you more highs on rx
optional
C76 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C182 Change to .001 to .0001 for more highs on rx and tx
optional
C183 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
C187 Change to 2.2uf mylar/polyester film or non-polarized electrolytic
With C75 and C182 you can start with no Change to them, then if you feel you want more highs then change them out


Goldfinger's cobra 29 hi fi mod

Cobra 29LTD with the TA7222AP audio chip

Receive:
Change C33 and C40 to 2.2uF non-polarized electrolytic
More highs?: remove C204 (some year ranges don't have this cap)

Transmit:
Change C69 to a .001uF disc
Change C68 to a 1uF Tantalum (some radio's already have a 1uF in them)
Change C37 to a .068uF mylar (or parallel a second .033uF mylar with the existing one)


New 2010/2011 Cobra 29LTD (TDA2003 audio chip)

Receive:
Remove C170
Change C33 and C40 to 2.2uF non-polarized electrolytics

Transmit:
Change C68 to a 1.5uF tantalum with the + side towards the right side of the radio.
Change C69 and C125 to .001uF disc
Change C37 and C43 to .1uF mylar

I did this mod on my 29lx and the receive is awesome. Crystal clear with less static sound. If you can't find non polarized electrolytics you can do what I did which is take two 4.7uf and tie the neg leads togeather and use the pos leads for through hole. Two 4.7uf caps in this fashion gives you 2.4uf give or take. The only part I didnt do was remove c170 which I can not find in the lx. But transmit has gotten great reports compared to the stock setup. I also did the irf 520 mosfet mod which gives the lx roughly 30 watts pep. Hell of a nice radio.


Cobra 25LTD Classic (TA7222AP)

Receive:

Change C32 (front center of PC board) to a 2.2uF mylar or NP electrolytic
Change C54 and C56 to 2.2uF NP electrolytic
Change C67 to a 1000uF 25 volt electrolytic
more highs? Change C151 to a .001uF disc or mylar

Transmit:

Change C90 to a 1.5uF 16-50 volt tantalum observe polarity.
Change C96 to a .001uF disc or mylar
Change C89 to a .033uF (333) green mylar

From Goldfinger:
I almost always use a mylar or polypropylene for C32. The signal levels are low there so using a high fidelity cap is a noticeable upgrade.
C54 and C56 are in a higher level area of the chain so the small/handy radial lead non-polar's are fine.
All mylar's is also fine if you can squeeze them in!


Hi Fi 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


Hi Fi mod for ept6900 series board
Galaxy 900 series radios 919 through 979

Receive

Remove C39
Change C78, C40 and C185 to 2.2uF non-polarized electrolytic
To add more highs change C184 to a .001uF ceramic disc

Transmit

Need more gain for running a stock mic or noise cancelling mic?
Change R-176 from a 270K stock, to a 470K.

Want more Bass?
Change C-154, a .22uF 16V tantalum, to a 3.3uF 16V tantalum.
Change C-171 and C-235 to .47uF 50-100 volt Mylar.

For even more Bass:.
Change C-154, a .22uF 16V tantalum, to a 10uF 16V tantalum.
Change C-171 and C-235 to 2.2uF, 50-100 volt Mylar.
(the 2.2uF non-polarized and the 10uF tantalum available at Radio Shack)


Hi Fi mod for Magnum S series

Receive:

C36 - change to a 1uf non-polarized electrolytic (radio shack) Need a little more bass? Use a 2.2uF non-polarized
C39 - change to a 2.2uF non-polarized electrolytic
C57 - change to a 2.2uF 16-25 volt regular electrolytic (observe polarity)
C155 - change to a 2.2uF non-polarized electrolytic
C159 - change to a 2.2uF non-polarized electrolytic
more highs:
Remove C38, or if you only want a little more highs, change to a .001uF disc or green mylar.

NOTE: C57 is actually C157
C159 is actually C154
The schematic does NOT match the Board.

Transmit:

C128 - change to a 4.7-10uF (depending on how low you wanna go) 16-25 volt tantalum. (observe polarity)
C187 - change to a 2.2uF mylar or non-polarized electrolytic
C191 - change to a 2.2uF mylar or non-polarized electrolytic
 
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.
 
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.
 
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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.
 
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.

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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What does it accomplish?
Fair question.

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

This allows them to transmit a better audio signal that is easier to understand at the receiving end.

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.

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.

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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