The AM Forum

Okie doke.  I got lots of advice on how to monitor my transmitted signal -- for which I am grateful.  Now I'd like to know what specific audio processing devices you're using in your audio chain.  As I mentioned, I plan to use an Electro Voice RE-20 microphone from my broadcasting days -- and an RCA 77-DX, too. 

What would you recommend to install between these mikes and my 32V-2?

Many thanks and 73,

Craig
W3CRR

"To those who asked...the audio mods to my 32V-2 were performed by Howard Mills, W3HM, during his expert and beautiful restoration of the transmitter.  They're all to the speech amp section and include -- and as been suspected -- the substitution of a large value (4.7M) resistor for R202 on the first grid of V201.  Other mods include a 220pf mica paralleled with C201, a 380 f cap from pin 2 of V201 to ground, the changing of C202 and C205 to .001uf, the addition of a 100 pf cap from pin 1 of V202 to ground,and the addition of a 50 uf/150 V electrolytic from R210 and R211 to ground. I wouldn't rely on this description, however, to institute these changes since I'm reading them from a reworked schematic whose accuracy I can't guarantee.

I don't where these mods were published originally, but I suspect they're from the Hollow State News archives.  Does anyone know?"


It won't make that much difference what mic or audio processing is used because the frequency response of the transmitter is very limited, especially on the low end. Suggest you make some mods to open up the response before traveling down the processing road.

One set of mod is found here.

http://www.amwindow.org/tech/htm/32v.htm

I use a Dorrough DAP 610 Here

Whenever I use external audio with with any of my tabletop transmitters I always feed the audio from the outboard device (processing device) to the 2nd stage of the transmitter through a high quality 600 ohm balanced to HI-Z single ended transformer. I have never had much success in trying to feed the mic input of the rig directly.

As Steve said, whenever you start using mics and audio gear that is capable of good low end, you will quickly notice the deficiency of the TX in the bottom end. The mod that was suggested is a good one and the one I mentioned to you the other day on 40. It uses some neg feedback.

As to what I use here: The main device is a Symetrics 528E. It combines the functions of Mic amp, EQ compression, limiting, de-essing and phase switching...plus a few more.

You will probably have quite a few suggestions to look into the BEHRINGER line of audio processing gear. I don't have any experience with them, but they work well and you get a lot of bang for the buck.

I use a Behringer VX2000 for all of the homebrew rigs. I don't use any procesing at this time on the "commercial" rigs.

I did the Tim tron audio mods to my 32V1 and that opened the audio up fine.... so  that it sounds great with a D104.    On the Bcast rigs I use a Behringer VX 2000, Audimax limiter, and a Behringer B1 Mic.. The home brew rigs all use tube type speech amps with tone controls (Radiotron speech amp) and an Elvis Mic

This is a great time to pick up some broadcast audio processors, because a lot of the AM stations are owned by a chain that has directed those stations to cut their high end response to 5 KC as a way of making digital sound better to consumers, at least that's one of the rationales put forth by outsiders.

So a few years ago I picked up a trio of CRL, Circuit Research Laboratories. They were marketed for the  LOUD SOUND and I have to say, they really cook.

(http://www.wa3vjb.com/pics/CRL-Trio-Sm.jpg)

Gary, INR, on the other hand, decided to match his Collins 21XS to an RCA processor that featured just the type of audio that would suit him.
(http://www.wa3vjb.com/pics/XS'.jpg)

I use a UREI model BL-40 Modulimiter.  Works great.  Keeps the average percentage up and limits overmodulation much better than my old tube type Collins peak limiter, yet seems completely transparent to the audio.

I agree with Paul. The CRL stuff is pretty good gear and extremely easy to repair, as long as they keep making the OP amps for it.

Modified Radio Shack 5-band graphic EQ mic preamp from the 80s, asymmetrical peak-limiting compressor.  Viking II with highly modified audio section.

For commercial gear, I like the idea of redesigning the speech amp so it is compatable with a D104....(After spending a couple of years trying to be happy with outboard
processing on my Globe King 400, 32V3, and the such, I gave up...on the
Home brew stuff, I use a Berhinger mixer, blending a B-1 and an D-77 mic together, then into a VX2000 with a BBE Sonic Maximizer in the side chain....this is fed into the
Speech Amp, which was gutted and rebuilt with passband from about 80 hz to 12 KHZ...
After the SA, is a variable filter, which allows me to cut the Highs or Lows as needed
before they get to the modulators....
But like I said, sometimes it is nice to simply run a mic straight into the rigs and not
worry about all the extra knobs...!
73 es gl steve 8tow

Hi Craig!!!

Great to see ya on the board!

I have many processing boxes...the best ones so far I have found are:

Optimod AM/HF (if ya can get one!)
Behringer DSP 9024 (no longer made, but available on eBay)
PR&E Miltilimiter
CRL tri set of boxes (I have the PMC300A limiter)

Others are good too.

To me the Behringer is the cheapest, but does not provide real good brick wall limiting. Some kind of preamp and EQ is needed before the box. A small Behringer mixer (UB802??, $60.00) is good. Many people use the Symetrix 528E, but I feel it is overpriced.  Some kind of pad after the processor to get into the mic or phone patch of the transmitter.

Now, the transmitter's freq response will affect the total quality...the flatter the modulator, the better the results. Pre-emphasis of the midrange and highs before the processor is key to good AM.

Look at the Audio tech area here for more info (http://amfone.net/Amforum/index.php?board=51.0).

I'l love to chat on the air with you. January is best for me as xmas is very busy...going to New Orleans after xmas for a week.

BTW, I heard WTIX, the Mighty 690, finally changed their call letters to something else. Rats! I miss the old radio of New Orleans (and a lot of other things since Katrina!).

73
Dan
W1DAN
Ex KA5DNH
Natick, MA

RE-20, Mic mixer, DSP9024 BehRINGer, EQ, rig.

I use...

One of three Mikes;

Electrovoice RE-20
Senheiser MD-421
Behringer B-1

Into a BBE Model 401 balanced input, Mike preamp / "sonic maximizer" ( modified w/ phase switch)

The output of that goes into the three devices shown below. in order from top to bottom,

Behringer DSP-9024 6 band digital compressor/limiter (the poor man's Optimod)
Behringer DSP-8024 31 band digital eq
Behringer MX-882 8 channel splitter/mixer

The MX-882 is used in "splitter mode" an audio distrubition device that feed the individual exciters and transmitters in the shack, each device having it's own level control.

I've ordered an all-in-one audio chain to feed my broadcast mikes into my Collins 32V-2 (with modified speech amp).

It's the Ashly DPX-200 - a Made-In-USA mic preamp/compressor/limiter/parametric equalizer combo.  It should arrive early next week.  I'll let you know how it works out.  In the meantime, I'm on 7.290 with a trusty old D-104.

Thanks for the many suggestions, fellas.

73,

Craig
W3CRR

RE-20 mic, Symetrix 528, [on ONLY when working west coast], EQ.   Simple, baby!

Behringer B-1 mic, Symetrix 528 and a Behringer DSP-9024 (poor mans optimod) big bang for the buck.

Brent W1IA