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The CBC speech processor is pretty much a copy of the processor used in the 858 chassis. You can give it a try, but I don't think you'll see any improvement over the stock 858 clipper.

I've tried the Defcom mod, and the results were less than spectacular. Removing the diodes and adding/changing the resistors negates the clipping and just changes it into a standard AMC circuit.

An Op Amp after the clipper in place of TR20 is (IMO) unnecessary because TR20 recovers the losses in the clipper circuit and provides enough additional gain to drive the modulation to 100%+. I tried substituting a higher gain transistor for the stock TR20 (2SC945A-Q), but it caused the modulation transformer to be overdriven and produced distorted audio.

To me, the 858 chassis is the best mass-produced type-accepted cb ever made. I bought my TRC457 new in '78 and still run it because, for all-around performance, it can't be beat.

- "Purist" 399

<blockquote data-quote="unit_399" data-source="post: 633362" data-attributes="member: 7311">The CBC speech processor is pretty much a copy of the processor used in the 858 chassis. You can give it a try, but I don&#039;t think you&#039;ll see any improvement over the stock 858 clipper.I&#039;ve tried the Defcom&nbsp; mod, and the results were less than spectacular. Removing the diodes and adding/changing the resistors negates the clipping and just changes it into a standard AMC circuit.An Op Amp after the clipper in place of TR20 is (IMO) unnecessary because TR20 recovers the losses in the clipper circuit and provides enough additional gain to drive the modulation to 100%+. I tried substituting a higher gain transistor for the stock TR20 (2SC945A-Q), but it caused the modulation transformer to be overdriven and produced distorted audio.To me, the 858 chassis is the best mass-produced type-accepted cb ever made. I bought my TRC457 new in &#039;78 and still run it because, for all-around performance,&nbsp; it can&#039;t be beat.&nbsp; - &quot;Purist&quot; 399&nbsp; <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f606.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":LOL:" title="Laugh&nbsp; &nbsp; :LOL:"&nbsp; data-smilie="19"data-shortname=":LOL:" /></blockquote>

[QUOTE="unit_399, post: 633362, member: 7311"] The CBC speech processor is pretty much a copy of the processor used in the 858 chassis. You can give it a try, but I don't think you'll see any improvement over the stock 858 clipper. I've tried the Defcom mod, and the results were less than spectacular. Removing the diodes and adding/changing the resistors negates the clipping and just changes it into a standard AMC circuit. An Op Amp after the clipper in place of TR20 is (IMO) unnecessary because TR20 recovers the losses in the clipper circuit and provides enough additional gain to drive the modulation to 100%+. I tried substituting a higher gain transistor for the stock TR20 (2SC945A-Q), but it caused the modulation transformer to be overdriven and produced distorted audio. To me, the 858 chassis is the best mass-produced type-accepted cb ever made. I bought my TRC457 new in '78 and still run it because, for all-around performance, it can't be beat. - "Purist" 399 :LOL: [/QUOTE]

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