The SW200 LPAM, Part #15, Amateur Radio AM, Audio Processor.

[ThaDood]

Boomer told me about this AM processor,    https://www.schlockwood.com/products    At $430.00USD's, it would cost as much, or more than many Part #15 transmitters out there, so this would be an investment. But, to get that sound that can actually be better than most commercial stations out there, (And that's not hard to do today.), it may be well worth it.

[redhat]

For that kind of money, you could buy a license to stereotool and build a powerful enough machine to run it.

...just say'in

+-RH

[Josh]

Iono, with a pc and some (probably free) audio software you could probably approximate anything that thing can do.

[ThaDood]

Sure. And, I know stations that use a PC for part of that purpose. But, if you want a stand-alone unit, where you don't have to worry about software upgrades, hard drive crashes, or even dedicating a computer with yet another task, then this could be another alternative to go. Me??? I like computer aided, but totally computer dependent, on a station. Manual override is nice.

[redhat]

I've played with various AM processors over the years, every thing from Optimod 9100B's to Innovonics, CRL, etc.  I don't like the idea of relying on a computer to process or handle audio, but the reality is we all do now.  Open up the latest Omnia or Optimod and you'll find they are largely a PC inside.

The nice thing about software processors is you can twiddle to your hearts content.  I was never real happy with the hardware boxes, there was always something about the sound I didn't like.  The Optimod had no balls (bass) due to Bob's notion that there was no musically relevant spectral content below 50hz (B.S...).  The CRL's had unfiltered clippers and if you hit them too hard they would get grungy.  Same thing with the Innovonics.

I suspect that this box on the inside is very similar to a 3 band innovonics processor from the 80's, made with surface mount parts to shrink the whole thing down. (I looked inside, it's all through hole...) Throw in a switched capacitor Caucer filter and you now have an NRSC processor.  I like the idea of a hardware box, but with the downturn in props, you gotta do what you have to, to be heard.  For a part 15, an old inno or CRL box would be just fine.  I have two in my stack for backup

+-RH

[Josh]

If I ever became a privateer of the airwaves, I'd sure be looking into prerecording the cast with whatever processing desired and saving it to an mp3 player, then skeedaddle to the tx site, violate the ionosphere with glorious audio, and then escape and evade. The guys with balls so large they need a wheelbarrow to carry them are the ones that do live shows and respond to hfunderpants logs in real time.

[Kage]

Here is more information about it and the overall internal layout and flowchart...
https://aa7ee.wordpress.com/2018/03/13/the-sw200-a-budget-am-broadcast-processor-for-lpam-and-hams-too/

I am actually building my own AM audio processor that is similar in layout but uses FET compressors instead of PWM compressors for simplicity and is loosely designed after the Dorrough DAP 310 from 1973 which is yet another popular 3 band compressor/clipper of its time (some say the first of its kind that started the loudness wars). Luckily the Dorrough schematics and manual are available online so it's not too hard to clone your own similar box if you have a lot of time and electronics skills. It's actually pretty simple under the hood, tons of op amps though. The SW200 looks to be similar while utilizing modern parts.

Software processors rival even the best analog processors except when it comes to the audible latency. I really love Stereo Tool and have an excellent AM preset I found a while back for it and tweaked. It gives *loud* punchy audio that is equal to the major market radio stations in my area and can really drive a modulator hot. The problem is that there is the need of a fast dedicated computer with a quality sound card and ASIO4ALL really needs to be running to make the latency the least noticeable. The OS needs to be stripped to bare bones so the computer can dedicate all its processing to the software and not other useless junk.
Even with the fastest computer I have it had delay that was enough to drive me crazy for live programming and really screws with my head if I listen to myself talk over the live feed.
Of course this can be fixed by only listening to the program feed output rather than the live OTA feed, but I like hearing the transmitted audio through my modulation monitor.

So in that respect I still prefer analog audio processors where suitable and if setup properly can still sound pretty damn good. If all you are broadcasting is prerecorded shows or only listening to the studio audio then digital processing is fine.
Comes down to personal preference but digital processing will give the edge, and possible listener fatigue if overused.

On a funny side note, I have heard of stations using their retired analog processors just for the studio talent since it's real-time and let them hear that "radio sound" in their headphones while using the new digital processor at the transmit end so to trick the DJs and not anger them with the delayed live processed audio

[redhat]

On a funny side note, I have heard of stations using their retired analog processors just for the studio talent since it's real-time and let them hear that "radio sound" in their headphones while using the new digital processor at the transmit end so to trick the DJs and not anger them with the delayed live processed audio

In the industry this is known as a 'talent processor' and became more common when HD arrived 15 or so years ago.  Even the analog portion of an HD signal is delayed by 8 seconds or so to match the coding and buffering delays present in the HD chain.  I've worked around the processor latency problem by monitoring off air for the control room speakers, but whenever a mic is turned on, a macro sets the monitor feed to program.  Dirty but it gets the job done.

+-RH

[Kage]

Sorry to raise an old thread but that audio processor I was working on is now complete. It has all of the features of the SW200 but with some differences under the hood including a much steeper NRSC compatible filter reaching out to 9.5kHz instead of 6kHz. Included is the ability for asymmetrical modulation, optional VU and clip/AGC LED lights and other features.
Full schematics and R&D from the beginning to the end can be found here... Page 2 of the thread gets more in depth with progress snapshots.
http://darkliferadio.proboards.com/thread/1029/diy-audio-broadcast-processor-scratch

I designed this for the pirate and part 15 community for those willing to take the effort to roll their own but trust me it's no easy undertaking. In time we will have PCB files online to simplify a lot of it for hobbyists who don't want to solder the insane protoboard work I did which took many months and instead slim it down to a few days worth of soldering onto a prefab board. This is simply my "thank you" back to the pirate community for all the incredible schematics and information you have all shared that helped me with my interests in broadcast audio and RF.
Not here to take the steam out of the SW200, I'm sure it's a fine audio processor too and is offered as a complete unit, however I wanted to design something similar *from scratch* and release the full design as open source for those wanting to build their own.

Video of my complete AM broadcast processor here..
https://www.youtube.com/watch?v=utZTQc_K0j0

Components like the Schlockwood SW200 are all generic for easy to source parts. Only exception is the VCA chip I used but that's still available from a few part sources. Tried to keep simplicity in mind and was inspired by the Dorrough DAP 310 and Texar Audio Prism circuits and sound from the 70s and 80s.

[ION Radio]

The SW200 is interesting. Seems like it would be OK for higher power also, as read in the 5th paragraph here:

https://www.mydigitalpublication.com/publication/?i=532050&article_id=3209662&view=articleBrowser&ver=html5#

I'm getting a little tired of having to pre-record and pre-process all of my audio. I may give this thing a try.

[chanito]

Best bang for your buck using hardware, if in fact you want it to sound loud and clean, is the Aphex Compellor/Dominator combo. Best $200 (or maybe less if you get lucky) you'll spend on your station. If you are feeding the transmitter with unbalanced audio, you'll need something like a Henry Matchbox II or other converter for best sound. These are on eBay all the time. Usually about $90 each for the Aphex boxes, $45 for the Henry.


This is not going to give you a heavily. noticeably processed sound, but it will be quite, again, LOUD, but still pleasing compared to the typical flatlined mid/highs and overbearing bass commercial station.


A lot of it has to do with your source material.

[Josh]

I've long been fond of US Weather Service quality audio.

[chanito]

We don't scrimp on processing here at Chanito's Holiday Station

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[KaySeeks]

I've long been fond of US Weather Service quality audio.

BEST AUDIO EVAH: https://www.youtube.com/watch?v=-wPeH0aQWTg

[Pigmeat]

We don't scrimp on processing here at Chanito's Holiday Station

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Ive got an older version of that box on top of that Orban. Walked into a pawn shop and there it was. They said it used to belong to guy just outside of town who had a recording studio who was taking that final long nap. I knew they were talking about my pal Frank. Frank was a nut and great guy to boot. He'd have probably given it to me if I'd asked. I'm proud I knew him.

Mine will do mono and stereo and has an excellent desser. For 35 bucks it was like stealing.