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I was not interested in copying your modification, for I am happy with the results I already have. I was interested in a comparison. You made the claim that you can achieve hi fidelity with $10 in radio shack parts, implying that it would be comparable to to the Mauldulator. I am merely saying I would be interested in seeing the actual test in reality that you were discussing in words.

I have been modifying radios for years. I know my way around the coupling and bypass caps. We use the same concepts on the receiver end to improve their response, and I agree it is not rocket science. I am not critical of your work or your results, I am just responding to your comparison and I would like to see it happen. You mentioned having a flat response over a wider range than broadcast. I have no problem with that at all. The first night we got the Mauldulator functioning, we put in 30 KHz and saw the sidebands at the proper amplitudes on the spectrum analyzer. We can go as low as you like also. If you want to take out some filtering we intentionally put in, we can go to DC and you can use the audio in jack as a carrier control. You are not going to be able to do that very easily on most CBs by merely changing capacitors. Most of the audio stages are capacitively coupled and if you tried DC coupling, you would mess up the bias of the transistors something fierce.

I think it would be a fun test to compare the performance side by side. It looks like we are on opposite ends of the country, but if it could be worked out, I think it would be enjoyable.

Regards

Tink

I figured our locations would make it impractical to do your side by side testing and that's why I offered to get on 3.885. Even that probably will not work since east coast to west coast contacts their are rather difficult. Just like you I've had to add filtering after the modification because the response was from 1 cycle to nearly 100 KHz. This is no problem to do with stages that are capacitively coupled. Perhaps I can't get DC but getting the watt meter to go up and down at one cycle per second is not hard. You agree that is just as good as DC right?

The TA7222AP in the 148 GTL was designed as a stereo output chip. Surely you know it's able to reproduce Hi-Fi and the feedback loop from pin 9 (output) to pins 5 (gain adjust) and 6 (feedback) are what kills the high end. Test circuits given in the data sheet for this chip will show you how to easily configure it as an amp with flat response. Quite different from the stock circuit used in the Cobra. I'm interested in knowing what you think is going to prevent Hi-Fi modification here?

One main thing you seem to overlook is that there has never been a CB radio receiver manufactured that can reproduce lower then 200 cycles and higher then 4 KHz. Typical receiver response is 300 Hz to 3 KHz. At least on 75 meters there are receivers that can reproduce Hi-Fi. It's not very practical to think that everyone is going to modify their CB receivers to pass this bandwidth that essentially gets wasted on 11 meters.

I am not overlooking it, I am painfully aware of it. I don't use this on CB, other folks do. I have helped modify some receivers so that they can benefit from hearing the higher fidelity, but obviously the bigger crowd is going to miss out on the higher fidelity. This is a topic that I have discussed with MMM frequently.

Maybe I'll bump into you on a cold winter night on 3885. I hear those folks sometimes late on Saturday nights. We are mostly on 3870 on the west coast.

73 Tink

hello tink/shockwave,

theres no doubt most cb's without restrictive modulation transformers can do hifiwide audio on both tx and rx,
i demonstrated it to prime and mmm by direct injecting audio into the am modulator of an old cb from my wifes cd player headphone output and recording the audio received on my jrc receiver in wide am,
i did it because a bunch of superbowl guys were on paltalk claiming plastic cb's always sound plastic, i used primes song "no excuses on the bowl" which i thought was a fitting source material for superbowl naysayers,

i had been asking them for months if anybody had swapped filters and broadbanded the audio stages, i was amazed that in the land of AM cb none of them had changed any caps or fit wider filters in their plastic fantastic swingading radios,
though to myself i can make any plastic export do 10hz-20khz tx easy,
it took me all of 10 minutes to find an old ar144 and hook it up wideboy style,
even with the bandwidth restriction of the jrc's receiver and no tx eq it still made bass and trebble way beyond any stock cb transmitter as you would expect,
primes reaction was "gtfooh, that aint no plastic cb"
yes it was a plastic cb, it was just how i described it, prime called it a 4lbs globeking,
i had no eq at the time so it did not sound good to my ears but it did sound wide and not at all plastic,

next i swapped the stock 4kc am/ssb lattice filter in a second ar144 to a 15kc filter then rather than changing caps in the audio stages to broadband the rx audio i took a shortcut to hifi tapping audio straight from the am detector buffer and amplified it through a single ended tube hifi amp to get what most would describe as hifi am audio from a plastic cb,
first thing i noticed was that without audio tone shaping it sounds very wide but as flat as a kipper, needs some tx eq,

i played with it for a hour or so trying to figure out how to do asymetrical modulation which i knew tink and mmm were working on with the yet to be named prototype mauldulator then got bored and put it back in the garrage untill we get some good usa skip,
nobody in my area uses AM cb, even less want to listen to superwide AM cb transmissions, i am the AM lone ranger with nobody to bounce ideas off or listen to what im doing for some feedback,

having a deficit of power and a surplus of enthusiasm i have decided its easier and more efficient to inject audio from my datong asp,
i will slice through the wideboys like the grim reaper with my narrow intelligible rf processor

__________________
the blind lead the blind but the enlightened will lead you to the sigma4

I heard Motor Mouth on 6 today and all I can say is Ive never heard a better sounding station. If his stuff he sells sounds half as good I would be impressed.

what you hear is what you get, It's just that simple