Easiest way to achieve hi fi?

[StrangeBrew]

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The higher percentage of modulation the higher the distortion will be, that's just the nature of the beast.
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I notice in your pics that the kink in the shape appears at the same grid line that the carrier is set to in the first pic, am I correct in assuming that this is a case of the "compressed" negative side of the wave not matching up with the unmodified positive side and it's the transition between these mismatched halves of the wave that causes the problems?

Just trying to wrap my head around this.

 

[LeapFrog]

Pretty much all CB radios do that. That is what is called high level modulation. Basically the solid state equivalent of tube plate modulation. It is done for simplicity and efficiency.

10-4, price points, & price points.

So you could just adjust the transmit stages to reach an AB bias configuration on AM in a 2000 or other ssb Cobra, without swapping/hacking parts?

I understand the AM only Cobra 25/29 are class C transformer modulated rigs, the 2000/148 run AB for SSB and AM (I was under the impression this was true, as changing the bias between modes would complicate the radio more?)

Maybe that's what the Linear-Final ("Volted Final") part of the NPC does, changes the class of operation to AB for AM, instead of class C.

Thinking of audio amplifiers I rather have the cleanest chance in hell to reproduce the audio coming from my mic, a class C audio amp would be trashy compared to an AB1 biased audio amp imo.

My ears are open, and look forward to learning more on the subject.

This pertains to the thread, If someone wanted to really reproduce audio, in a true linear fashion this topic suddenly becomes relevant..
-LeapFrog

 

[Captain Kilowatt]

Nothing wrong with class C RF amplifiers being modulated. AM commercial broadcasters did it for decades with tubes. They use class C RF amps with usually class B audio amp modulators.The only problem comes when trying to pass already modulated RF thru a cass C amp.

 

[543_Dallas]

I was also under the impression that the 148/2000 operated in class B on AM. I believe the spec sheet in the owners manual says that. You can download instructions for those asymod things that actually show you how to convert a few different ssb rigs to class C for more efficiency.

I did notice alot less heat from the modulator when I switched to a cobra 29 from a 148. Both radios completely stock except for RX mods and running at the same power output That would lead me to believe the stock 148 is not running class C on AM. On a long transmission the heatsink would run at 170 degrees with the 148 and is barely warm to the touch with the 29.

 

[LeapFrog]

Nothing wrong with class C RF amplifiers being modulated. AM commercial broadcasters did it for decades with tubes. They use class C RF amps with usually class B audio amp modulators.The only problem comes when trying to pass already modulated RF thru a cass C amp.

I wonder if any commercial am broadcast stations are permitted to run with such configuration in this modern era?

So a class C "driver box" going into a bigger class c box is a big no-no? Is it a case of distortion created by the first box then amplified, plus more distortion introduced by the bigger class c box, that's what I'm getting out of what I've read.

Thanks

 

[543_Dallas]

He's saying class C is OK when it's a high level transmitter like a cobra 29. Audio is mixed at the finals.

Class C amplifiers suck on SSB. The class of operation will shift with RF drive and they are usable on AM. If you can find the sweet spot and not pinch the carrier they can work fine.

I prefer AB biased but if you have half of a brain you can use the class C amplifier and the experts will never know. It has to be built and tuned right or all bets are off....unfortunately those can be hard to come by.

Just consider a 2879 a 60 watt device or look at the spec sheet for the transistors you have to see where the IMD is lowest. Someone always brings up the lack of filtering but that can be purchased separately.

 

[Captain Kilowatt]

I wonder if any commercial am broadcast stations are permitted to run with such configuration in this modern era?

So a class C "driver box" going into a bigger class c box is a big no-no? Is it a case of distortion created by the first box then amplified, plus more distortion introduced by the bigger class c box, that's what I'm getting out of what I've read.

Thanks

Most AM broadcasters have gone solid state so that means even higher class amplifiers. Back jn tge 80s we were running MOSFETS in class D pulse width modulation. Now you have class E and some more exotic classes like class H. Nothing wrong today with running a class C RF amp and a class B audio amp to modulate it. Many stations have a tube back-up transmitter. What I am saying is that as long as the RF is NOT already modulated class C is 100%fine. As soon as you try and pass an already modulated signal thru a ckass C amp crap starts. This is why you can operate a class C amp and THEN modulate it as in plate modulation and still come out withess than 1%THD.

 

[Onelasttime]

The easiest HiFi setup is, get a Galaxy (or equivalent), Direct inject, buy a Lexicon Alpha, Buy cheap dynamic XLR mic, Buy a couple patch cords and last download free VST plugins and host!

Someone was asking about trapezoid scope pics of the Mauldulator, trapezoid is not only for testing the linearity of an amp it can test the linearity of any radio.

DISCLAIMER: Motormouth Maul "NEVER" said that his Mauldulator doesn't produce distortion, fact is it does. The higher percentage of modulation the higher the distortion will be, that's just the nature of the beast. These scope pictures were done using my "birds nest" Cobra 2000. The Mauldulator modulates the finals in a high level configuration, the Cobra 2000 is factory aligned. Factory aligned also means in AM the finals operate in class C. So there should be some distortion regardless.

Thank You very much on the Lexicon Alpha info that looks intersting. I was considering somethign else but that looks very interesting especially with the VST software included and a hi-z input and audio monitoring.

 

[Onelasttime]

I wanted to add that the mic I referenced the Bearcat 465 I think it is as a published freq response of 150-4000. I did not go to it to get more range rather to get a flat response and more natural sound at $12 adn $0.99 shipping I think they do that very well. Condensers need some power but small ones need very little and it is not hard to get them some on the cheap with out tieing directly to a source in a radio. This site has covered that before. So just keep the limits of the mic in mind. The 1000 ohm rating also means it will work with a variety of gear decently. I have some mic's that are low Z around 150ohms, some that are hi-Z around 50,000 ohms and some that are 500. I have some that are dynamic and some that are condenser. I used to own large diaphragm condensers and powered dynamics for use in recording vocals and instruments but do not own any of them any more. All of the above are great mic's depending on what it is you want to do with them. A $500-$1000 powered tube large condenser would be a waste of money on a CB radio a $25-$99 condenser would more than get the job done. Something like an NTE1000 or even an Audiotecnia 4047/4050/4057 would be a waste of money even for hifi on CB or Ham radios!

Joedirt I have watched you Youtube video's and found them very interesting. Thanks on the heads up about the Lexicon Alpha. I wanted to add that it does not have 48V phantom power so it will only work with mic's with their own built in power source or that are un-powered. Just wanted to make sure people know this. The fact that it has software based audio studio interface for your computer more than makes up for this.

 

[Onelasttime]

Google Flywheel affect as it relates to rf bias and some groovy images and a well thought out explanation will help it all make sense. You change the bias voltage on the transistors to change the class of operation from A,AB, AB1(tubes), B, C, D and E biasing. So any sound transistor circuit can be changed just by changing the bias voltage. Tubes can be a bit more complicated depending on if it is grounded grid or not and if the tubes have been properly neutralized and what type of tube it is.

On a tube setup you can get away with running in class C and using it for SSB but on transistors they make their power differently than a tube circuit does. This is also why we will sometimes us a mode with matched pairs of transistors grouped in two's and then group those into another matched push-pull group of two etc.....Some modern LDMOS transistors are really two on one die in an internal push-pull configuration.

If one transistor is only on for half of the duty cycle and the other one turns of for the other half of the cycle you get a situation that is much like a heavy flywheel compared to a light one that can power around and through he power cycle on off with out slowing down, getting stuck etc....It works really smoothly. You also generate less heat that way since the parts are cooling when not on. Durability goes up and depending on the design the quality of the output signal can be much cleaner. Taken to the extreme well beyond push-pull the smoother you can break up the signal pulse groups of transistors on and off recombine the signals into a coherent package the more average power you can get out of the parts with less heat and wear and tear. Modern broadcast gear even when the output signal is analog do this not just digital broad casts the control side and method of output is digital regardless of the type of output. You never see this in CB or ham.

If you are not using SSB than class C is just fine for AM even with transistor based amplification. Class C is prone to producing more harmonics than AB but that is only if it is operated poorly and not filtered well. On class C using SSB even with a delay producing a really bad signal and you can easily destroy the amp in short order. Harmonics on AM or SSB do not just sound bad they generate a lot of heat that has to be cleared fromt he unit just like the heat from noprmaly operation. Since the parts are not designed to effectiently get that extra and wasteful energy out of the unit more of the harmonics stay int he unit where they turn into heat. Heat destroys the ouput of electronics, shortens the life of all the parts. So the more harmonics a unit produces the more heat it has to dea with, the less power it makes because efficiency goes down as heat goes up. So the longer you operate int hat condition the more heat you make the less power you make the more you shorten the life of all of the parts. As you go past 100% modulation you make more distortion than you should which drives up heat. As you over drive the transistors with too much input power you drive up distortion which drives up heat. As you increase the voltage to the parts you make more power but distortion goes up even more than clean power does as you increase input voltage which increases distortion and thus heat even more. As you approach thermal runaway due to heat soaking the parts you add more distortion and less stability to your signal. As you go past the max input voltage rating guess what happens you guessed it more distortion and you start to break down the junction of all the tiny part on that die. That does not do you any favors in the short run or long-run.

Now over drive the radio's finals or over modulate it or suppress the carrier more than 4:1 than pump that into a class C modulator(name only) amp than into a driver amp than into the final amplifer all of which are class C and all of them being volted and over driven......

The volting of of the finals makes no sense on a SSB radio or one that came from the factory with a 1969 final because they where already operating at 12V or higher. The units that came with smaller transistors and using audio transformers even if not doing suppressed carrier, or the like could benefit from installing a 1969 and volting the final. That is not the only reason to do it but was common.

You can end with a radio that does not have the power being properly biased and not tracking properly with temp. or modulation when you volt the final. It depends on how sophisticated the "volting" is done. The term Volting or Straping the final is not always accurate because the red-necks discussing it on the air seldom performed the operation themselves.

 

[JoeDirt]

I notice in your pics that the kink in the shape appears at the same grid line that the carrier is set to in the first pic, am I correct in assuming that this is a case of the "compressed" negative side of the wave not matching up with the unmodified positive side and it's the transition between these mismatched halves of the wave that causes the problems?

Just trying to wrap my head around this.

The negative (not really negative) negative below the carrier reference line is the untouched waveform, nothing is compressed. The positive peaks are amplified, since any alteration of the waveform is distortion you will see the differnt conducting angles.

 

[JoeDirt]

Used/owned some expensive Lexicon gear in the recording studio. This Alpha is something I'd never seen before, so it must be relatively new. But they make some fine gear, and this Alpha looks like a high-end/low cost CB audio solution. i'll have to look into one of these in the near future. Thanks for that tip, JoeD.

I own a few of the Lexicon cheaper USB Interfaces, all have worked great. I do however use the ASIO4ALL driver. If you buy new Lexicon it also comes with Cubase software that supports the free VST plugin's. The Cubase software is similar to ProTools. I bought my Alpha for under $50 My Omega (discontinued) was $50 used off Craigslist. I also have many versions of ProTools and Mbox's All my ProTools stuff has been a pain in the A** I would advise against it. Cubase and LiveProffesor with the ASIO4ALL drivers have preformed flawlessly. (and there free)

 

[Onelasttime]

Have you used Adobe's audio software? If so what do you think of it?

 

[222DBFL]

I just saw that there are more people jumping on the HI-FI stuff or trying to, a seller on eBay named my-spin is installing ASYMOD boards and also selling radios with HiFi mods done and ASYMOD board added and some other things done. Receive and transit work for hifi stuff.. He had cobra 29's, strkyer 955's, some galaxy radios and some others for sale on eBay. I was looking at some other stuff and happened upon it. Also says he can install them in most any radio for you. CB's, export radios, HF radios, you name it. Let me see if I can get the link to the Stryker 955HP ad.
Here is the ad for the Stryker 955, and it should show some more of his stuff as well. I am not sure if this guy is new or what or if he is doing the work. Guess he has been around as it says he has an ASYMOD board rev. 2 that is no longer in production and this is the rev. 3 or version 3 of the board. He also adds some stuff to back of radio for external mic, key up, and for plugging into computer as well. Again not seen this guy. Anyone dealt with him?? Just curious.
Here is the link to the radio and his other stuff.
https://www.ebay.com/itm/122161841698
Don't flame me, I know this may not even be real hifi stuff, but that is just what the ad says LOL!! Like I said I stumbled upon it clicking something here on the site that was listed on eBay LOL!! Hope everyone has a great day. It's finally cooling down here in FL. Don't know for how long but I am sure glad it did!! Makes doing yard work much easier

 

[Robb]

Just the unit w/o radio - too:

http://www.ebay.com/itm/ASYMOD-IIIs-ASYMMETRICAL-Hi-Fi-AM-MODULATOR-FOR-CB-HAM-RADIO-NEW-RELEASE/122147472199?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=39861&meid=df32aabd123443eda3870d4fdb714a4a&pid=100005&rk=5&rkt=6&sd=122161841698