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unit248

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  • dave457
    Thats fine,Was just looking to mod it for wider response on AM
    for both TX and RX, right now I inject the audio thru the ACC2 port
    but I believe it can be better by direct injecting
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    unit248
    The bass response will still be a little limited if all you do is feed the audio through the ACC2 port. You will gain a bit of improvement by direct-injecting pin 1 of the AN612 modulator chip.
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    unit248
    Check the schematics: the balanced modulator chip is IC5 on the IF unit. You'll see that feeding pin 1 there's a buffer amplifier, Q44. I'm pretty sure the audio has to pass through this buffer regardless if the source is the front panel mic jack or the ACC2 port. You'll notice it has several limiting factors: coupling caps C133 and C135, and the emitter shunt cap C136.
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    unit248
    C133 is 1uF, and I *think* C135 is .1uF -- it could be 1uF too (it's a little hard to tell from the schematic I'm looking at). C136 is 47uF. The coupling caps should really be more like 4.7uF and the emitter shunt cap should be more like 220uF or 470uF, otherwise the low end will probably roll off around 80Hz.

    Treble response is limited by the filters at the IF stages, which is another matter.
    dave457
    Hi Bill, Do you work on Radios, specifically a ts-440 ?
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    unit248
    I only tinker with my own. I have a day job that keeps me busy enough. :) I know a little about the TS-440 (don't have one, but I do have a TS-430) but I've never really played with one. All I really know is to stay away from the ones with the Sonybond goop in them.
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