K40 Speech Processor Model K40-7

The radio can already receive below the noise floor of anywhere on planet earth. All increasing gain in the RX chain will likely do is ruin the selectivity so the rig suffers bleedover. Put the effort into the antenna system installation and if you want more receive buy an adjustable pre-amp.

W4CJB said:

Well it's rough without CBTricks but I believe the K40 is just a Uniden Pro510e with a different shirt on. The chassis looks the same. Also, no ANL switch on the K40. Thanks to anyone that at least gave me a passing glance.

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Well it's a shame you feel that way....

Because of the loss of much of the MANY Many sites that used to host CB topics such as yours. The database from those that participated is also lost in the "deletion" of such resources - with CB Tricks being one of many that could have provided your info.

But as with CB Tricks and with anything else - you did mention that the radio is a 510 in a different wrapper, so if that's is the case, can you post pics so that those whom may be able to come to your aid can provide assistance? We can only guess because, we too, have seen more of our favorite sites turn "closed" or off-the-map due to lack of interest or funding, or the loss of its' main server and the owner of it.

So to help you prove your side of the story, we need to know what your up against.

Oh heck, go get a 520e manual - or schematic - I've got a 520XL over here in SMD while a 510 in Discrete...

Not much can be done - true - but we do have your number...

That TDA1220 AM/FM on a chip was also incorporated in a lot of other radio chassis from Uniden in that era including the 538 - so even a 540 or 530 can provide some insight and upgrade values if you wish...the board layouts will be different but not impossible to decipher and use for such ideas.

What we'd like to see more of is that mic circuit...too bad the compressor isn't made (NOS). But I'm sure something is out there to replace it...

Thank you!

The 520e seemed really close . This guy came up with a cool circuit. Glad you got it figured out

http://raymerrick.freeservers.com/cgi-bin/i/RifeMods/520e_main_print.gif
http://raymerrick.freeservers.com/RifeMods/My Rife Machine.htm

Well, as long as I'm here I will try to help. Those are fun little dinky radios with not much, but are a lot of fun to just use.

Now for some stuff I do know... not sure of you have a 'Scope - because the Receive on these things is SELECTIVE and if you are talking to say, another CB'er using an Xtal synthesis radio like an early generation Midland - the Xtals it has may make it's transmitter too far off your center-band peak on the TDA chip.

You'll hear some fuzz and a lot of hiss from the carrier noise passing thru from that transmission - your carrier detector is past this - so your IF on the TDA is what makes it noisy - it's their off frequency signal getting thru the IF bandwidth the TDA uses.

Unfortunately you can't compensate for this - it's lost in noise of the passband of the channel. You can tune a Piano, but not this fish...

• OF any effort to help, there was an adjustment of VR4 - the output of the 1st IF into the TDA1220 chip - pin 2 - so locate Pin 2 of the TDA1220 and follow it back to either a set value resistor or VR4 - if your board has one (You're in luck it's SENSE by 3-pin Ceramic IF Filter it follows) and you can adjust receiver acceptance level - I say that because YOU'RE GONNA GET NOISE TOO when you adjust this pot.
• You can also look at this thread to help you understand more of the issues around the latest efforts to use Xtals versus ceramic filtering in IF strips not just for IF bandwidth but for pass band overall of IF signals.

But it's saving grace is the novel use of the ANL and Detector functions and their support circuitry.

Like most other Cobra 25's and PC-66/68 ones, they capped off the IF - tapped right off the top a signal and rectified it directly. But in light of the design, it's how the RECTIFIED it to detect as well as generate AGC control.

It never got sent thru a diode, instead the used the ANODE (positive end) only gather audio as a single ended tap then sent carrier envelope and all the information of the, now passed thru and ready to rectify, signal to the AGC chip - the AUDIO detection occurred from the Rectification, but it (the audio) never passed thru the diode and in doing this method, avoided the degradation and coloring of the audio envelope. (See Schottky) ANL became more effective because they incorporated more of that AGC effect to push down the noise and signal level and yet allow the audio to pass.

So yes, you may need a little more info to be ready for events like that. The 1220 chip was nice and had a good audio frequency response that really helped make that setup with it's own tiny speaker sound good for what little they used in the chip to make it work but had issues with passband, mixing in the IF, the captured received signal and it's own passband roll-off effects.

So glad you have a nice little radio that got away with a lot for what little it had in it to work with in the first place.

Enjoy.

Lucky I found a fairly recent thread. I have a question about a K40-8 (if anyone can answer). Since the K40-8 has the speech processor chip mounted inside the radio(Not in the Microphone). Can any noise cancelling mic be used with this radio? Did any of the other K-40 models have the speech processor chip mounted in the radio?

You may have to check the audio to ground wire pins at the mic socket to be sure - but it should be ok if it can use a Dynamic element.

Some Speech processor mike's as of late, use a Electret Confessor element - requires power from the radio to work.

So to be safe and sure, check the radios sides' mic connector - from the Audio line to Ground with a DVM set to read voltage 20V or so, to see if you get a reading, if you do, then the mic element in that K40 handset is Electret type, and so it BOOSTS audio signal to the speech processor IC inside - which may require you to change the mic element from Dynamic to Electret because he IC requires more power than a typical Dynamic element would provide.

The K40 Model 6 and later had the speech clipper board as an add-on board on the side of the radio, based on a later non TDA1220 chip Pro510 chassis (I have one of these). I can't say whether Model 5 or earlier ones did, but here is the schematics for the Model 6.

http://www.cbtricks.com/pub/secret_cb/vol_26/graphics/secret_cb_vol_26_pg63.pdf

Secret CB does not have any info after Model 6. There was an SSB radio too, I have never seen it, though.

I just looked at the schematics for Models 1-3, the add-on clipper board is not on these, so they must have used the Speech Clipper/Processor microphone with these earlier models. Schematics for Models 1, 2, 3, and 6 are in Secret CB Vol.26.

http://www.cbtricks.com/pub/secret_cb/vol_26/index.htm

Handy Andy said:

You may have to check the audio to ground wire pins at the mic socket to be sure - but it should be ok if it can use a Dynamic element.

Some Speech processor mike's as of late, use a Electret Confessor element - requires power from the radio to work.

So to be safe and sure, check the radios sides' mic connector - from the Audio line to Ground with a DVM set to read voltage 20V or so, to see if you get a reading, if you do, then the mic element in that K40 handset is Electret type, and so it BOOSTS audio signal to the speech processor IC inside - which may require you to change the mic element from Dynamic to Electret because he IC requires more power than a typical Dynamic element would provide.

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Thank you for the reply

NZ8N said:

The K40 Model 6 and later had the speech clipper board as an add-on board on the side of the radio, based on a later non TDA1220 chip Pro510 chassis (I have one of these). I can't say whether Model 5 or earlier ones did, but here is the schematics for the Model 6.

http://www.cbtricks.com/pub/secret_cb/vol_26/graphics/secret_cb_vol_26_pg63.pdf

Secret CB does not have any info after Model 6. There was an SSB radio too, I have never seen it, though.

I just looked at the schematics for Models 1-3, the add-on clipper board is not on these, so they must have used the Speech Clipper/Processor microphone with these earlier models. Schematics for Models 1, 2, 3, and 6 are in Secret CB Vol.26.

http://www.cbtricks.com/pub/secret_cb/vol_26/index.htm

Click to expand...

Thanks