fattening stock tx/rx audio bandwidth on IC-735

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479tx
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fattening stock tx/rx audio bandwidth on IC-735

Post by 479tx »

GF/Smiley,

Any of you guys ever worked up a cap list to fatten up the stock tx/rx audio bandwidth on an older HF rig? I've seen cap mods for a Kenwood TS-440S.

I've tried feeding ACC1 (definitely improves fidelity) but I can't get the same "level" before it distorts that I can via the front mic jack, dunno why.

I was thinking of fattening up the caps, I found a guy on qrz who claims to have done this but does not have the instructions he followed anymore but said it smoothed out the receive and transmit nicely.

http://www.ko4bb.com/Manuals/ICOM/IC-735.pdf
479tx
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Post by 479tx »

The radio has a pot on the back that says "mic tone" all the way clockwise makes it rather tinny, all the way counterclockwise takes the highs out and adds lows/mids. I've tried adjusting while listening to another radio with a Heil ICM going into the front of the radio and can get an "ok" middle of the road sound, but nothing to write home about.
479tx
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Post by 479tx »

In the service manual is says AM TX does not go through any particular filter if I'm reading this correctly. So changing bypass and coupling caps could yield good results?

http://www.radiomanual.info/schemi/IC735_serv.pdf
479tx
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Post by 479tx »

What if I just took the tone control pot out of the circuitry of the radio?

It seems to roll off highs one way or roll off lows the other way, the lows and highs give in either direction sound good, but I'd like to have them both at the extremes combined.

Any thoughts on the above idea?
479tx
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Post by 479tx »

Here's a better copy of the schematic for anyone interested in helping me take a stab at this

It's in this directory, for some reason it doesn't work when I post a direct link to it http://www.w0btu.com/files/misc/Icom/IC ... ce%20Info/
479tx
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Post by 479tx »

Is this forum this slow or is it just that my thread is this uninteresting?

:P
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Goldfinger
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Post by Goldfinger »

I just can't stand the layout of Icom schematics. Lumping 50 circuit paths through one line on the schematic is idiotic at best. (maybe because I am old school and like complete schematics) Looking at the PL board, the only cap I see that might limit TX lows is C232. C234 could be made smaller for more highs.
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479tx
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Post by 479tx »

Hey Thanks GoldFinger,

What do you think about the "tone control" pot - would eliminating it increase usable bandwidth or do the opposite? As stock, it's always inline and turning it all the way clockwise rolls the lows off and turns the highs up, turning it counter clockwise does the opposite. I was thinking removing it would give me better highs + lows together.

The two caps you mentioned, are they on the "main" or "pl" section? (they re-use resistor and cap #'s on both boards! what the heck) what are their stock value and what would you suggest bumping them to?

Is it apparent to you or not if the SSB filter is inline during AM TX? I can't tell one way or the other.

Thanks again for your help! You are tha man! :p
479tx
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Post by 479tx »

From the service manual:

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So if the above means what I think it means (that no filter is in place during AM TX) then just a few caps (perhaps the ones you suggested) plus removing the "mic tone" pot on the back of the radio would really open it up?
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