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Trc457 modulation clicking

You will have to see if the clicking is from the input, from Mic Gain TO the mic amp IC is too much for the IC to handle - an input cap of 0.1uF (C69) - make sure it's fresh.

Why I say that? There were several mods and ways to bring more signal in to the mic amp - one was to raise the capacitance of the input cap - C69 from a 0.1uF to a 1uF - which can make the Mic amp unstable and squeal - or even clip.
  • It didn't matter how much signal - just that the input capacitance level that the mic amp inputs could use, was only so much before it became unstable and unusable because of too much drive or an unbalanced input condition like XLR versus 600Ω impedance elements - the dynamics between the two affect how the signal can even be transferred - let alone amplified.
Too much of a good thing - usually is.

It's also why I mention checking the output cap of TR24 - the 8V regulator - any sags in key up will also reduce the ability to even amplify the mic signal - so if the amp draw was too much for TR24 - the mic amp starts to clip.
 
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Handy Andy said:
You will have to see if the clicking is from the input, from Mic Gain TO the mic amp IC is too much for the IC to handle - an input cap of 0.1uF (C69) - make sure it's fresh.

Why I say that? There were several mods and ways to bring more signal in to the mic amp - one was to raise the capacitance of the input cap - C69 from a 0.1uF to a 1uF - which can make the Mic amp unstable and squeal - or even clip.
  • It didn't matter how much signal - just that the input capacitance level that the mic amp inputs could use, was only so much before it became unstable and unusable because of too much drive or an unbalanced input condition like XLR versus 600Ω impedance elements - the dynamics between the two affect how the signal can even be transferred - let alone amplified.
Too much of a good thing - usually is.

It's also why I mention checking the output cap of TR24 - the 8V regulator - any sags in key up will also reduce the ability to even amplify the mic signal - so if the amp draw was too much for TR24 - the mic amp starts to clip.
Click to expand...
Ok, I pulled alc transistor out of circuit and like you thought it's worse. I checked the 8v for sag and it's solid. I do not see a diode going to the cap from pin 2 of the ic.
 
Then we have a "signal strength" problem.

Like when you play Madonnas' True Blue on CD into an Analog EQ - all kinds of headroom distortions to clicking due to lack of headroom.

So, it is good to know, in this case it was not caused by the limiter engagement.

So, the 0.1uF is stock? As in OEM?

We can work further down to see if the clipping is in the "compressor" portion of the audio chain, but the issue isn't with AM - it's with the SSB side. So, it would immediately bring me back... to here...

1644289236627.png

This is really a gain compressor, designed to limit negative spikes in the audio signal - That is the purpose of TR19 - similar to the Limiter function in a Cobra 29 - search - seek out the negative peaks and simply clip them. The IC simply EQ's the audio signal - Pin 1 is that EQ circuit - simply narrows down the bandwidth. While Pin 2 has a gain of nearly 4:1 (ratio of Pin 1 56K to Pin 2 Internal resistor R2 220K) so it does amplify some signal
  • - TR19 then trims these peaks using TR18
  • TR17 is the MON CB PA switch - sends the output to the MON-itor or PA
    • - check that too, see if the clipping occurs in the PA mode.
  • IF I can be allowed a little liberty...
1644291276474.png​
  • This is similar to the PC-122/TRC-453/465 mic amp sections.​
  • Nothing big - but the clipper circuit TR19 is - affects the level of compression IC3 can deliver - so to help, the ABOVE circuit can help explain or show, some of the parts you see as support parts to the pins of IC3. The above circuit is an example of a two stage. The IC3 has 3 - it's shown to help you put it together. In the example of something like the above might help you understand the imposition (the effort to impose) compression on an audio signal to reduce the dynamics but help keep intelligibility - the first thing that has to be worked on is the reduction of the dynamic element.​

Else with the type of caps used, note the Cap I talked about earlier - that "A" designation simply means Aluminum - you can use it for Audio - but is not the "Best" at it.

There are several of these all along the chain. So, if you are not able to hear the "clip-clippity-clip" on syllabic "s" or "CH" sounds (sharp inflections) the issue is further into the chain. What am I talking about? Read on...we will have to locate the clicking by monitoring the audio thru the chain.

IF this clip doesn't occur on PA/MON function - then the issue is further into the clipping side.

There are several cures, but most are reducing the input - but which input? That is dependent on what stage the clipping distortion you don't want, its occurring in.
 
Last edited:
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Handy Andy said:
Then we have a "signal strength" problem.

Like when you play Madonnas' True Blue on CD into an Analog EQ - all kinds of headroom distortions to clicking due to lack of headroom.

So, it is good to know, in this case it was not caused by the limiter engagement.

So, the 0.1uF is stock? As in OEM?

We can work further down to see if the clipping is in the "compressor" portion of the audio chain, but the issue isn't with AM - it's with the SSB side. So, it would immediately bring me back... to here...

View attachment 57181

This is really a gain compressor, designed to limit negative spikes in the audio signal - That is the purpose of TR19 - similar to the Limiter function in a Cobra 29 - search - seek out the negative peaks and simply clip them. The IC simply EQ's the audio signal - Pin 1 is that EQ circuit - simply narrows down the bandwidth. While Pin 2 has a gain of nearly 4:1 (ratio of Pin 1 56K to Pin 2 Internal resistor R2 220K) so it does amplify some signal
  • - TR19 then trims these peaks using TR18
  • TR17 is the MON CB PA switch - sends the output to the MON-itor or PA
    • - check that too, see if the clipping occurs in the PA mode.
  • IF I can be allowed a little liberty...
  • This is similar to the PC-122/TRC-453/465 mic amp sections.​
  • Nothing big - but the clipper circuit TR19 is - affects the level of compression IC3 can deliver - so to help, the ABOVE circuit can help explain or show, some of the parts you see as support parts to the pins of IC3. The above circuit is an example of a two stage. The IC3 has 3 - it's shown to help you put it together. In the example of something like the above might help you understand the imposition (the effort to impose) compression on an audio signal to reduce the dynamics but help keep intelligibility - the first thing that has to be worked on is the reduction of the dynamic element.​

Else with the type of caps used, note the Cap I talked about earlier - that "A" designation simply means Aluminum - you can use it for Audio - but is not the "Best" at it.

There are several of these all along the chain. So, if you are not able to hear the "clip-clippity-clip" on syllabic "s" or "CH" sounds (sharp inflections) the issue is further into the chain. What am I talking about? Read on...we will have to locate the clicking by monitoring the audio thru the chain.

IF this clip doesn't occur on PA/MON function - then the issue is further into the clipping side.

There are several cures, but most are reducing the input - but which input? That is dependent on what stage the clipping distortion you don't want, its occurring in.
Click to expand...
Later today I will check it on AM and the PA. Yes the .1 is original. This radio was a virgin when I got it. Never had a screw out. Everything is as factory.
 
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KneeBiter said:
Later today I will check it on AM and the PA. Yes the .1 is original. This radio was a virgin when I got it. Never had a screw out. Everything is as factory.
Click to expand...

Ok, you don't have to beat me up too much...:giggle:

But you need to know that as with anything that ages, it will need some TLC, including replacement of the tires, change the oil, Re-lube the bearings, wash the windshield - e&c...

Same applies to older radios - only the process is Electonic parts that will need attention.
 
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Handy Andy said:
Ok, you don't have to beat me up too much...:giggle:

But you need to know that as with anything that ages, it will need some TLC, including replacement of the tires, change the oil, Re-lube the bearings, wash the windshield - e&c...

Same applies to older radios - only the process is Electonic parts that will need attention.
Click to expand...
No beating up. I truly appreciate all the help. AM has the click. Not so pronounced like on ssb but with a whistle I hear it right at the beginning of the whistle. Where on ssb it is there with every peak clear but under the voice. PA is clear as can be with no click I could hear.
 
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nomadradio said:
Awright, so now I gotta wonder, do you hear the 'click' in a nearby radio a couple of channels or more away?

Might point to a source that's not part of the audio circuits.

73
Click to expand...
No. It is only on the channel I'm talking on. It's not like a clicker click with a dead key. It's more like the alc limiter is kicking in on high.
 
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