Advice on Compressor / Limiter ??

[K6IC]

OK,  SssOoo am getting ready to step up my power level.   Need a Compressor / Limiter.

What recommendations do you guys have ?  Thinking of something right at the transmitter's audio input.

Could be something venerable or very modern.  Would rather NOT spend megabux for the latest Orban  .

Thanks,   Vic  KF6RIP

[John K5PRO]

If you grab a pro audio piece, it will probably have balanced outputs capable of working into 600 ohms. This can be accomidated with most BA transmitters by adding a small quality audio transformer 1:1, into a 600 ohm cathode resistor on the (first) mike preamp stage in the transmitter. Or if the transformer has taps, like so many do for 150/600 line input, then you can also have a 150 ohm load on it, if your cathode requires less.

Boxes like the old CBS Max brothers, a DAP, Texar box, CRL, Orban, etc will work. Some find the low price of the Behringer or Alesis products appealing. Also, you can do what I did and find a used mic preamp/compressor (sometimes called a microphone processor or vocal processor). This can be used to tailor the mic response, via EQ settings as well as having things like noise gates, compressor/limiter, etc.

For Dynamic mikes, you need the preamp. If you use broadcast grear with balanced input (XLR connector for example) it may handle stray RF in the shack a lot better.

Finally, you might consider a peak limiter as the last thing before the transmitter, to prevent >negative 99% modulation excursions and the splatter that they produce.

There are as many audio setups as their are boatanchor preferences, so be prepared to do a little research for what you need. Simple is good. Multiband processing, while excellent for high density broadcast audio with music, may be great but overdone for amateur applications with one microphone.

[K6IC]

Hi John,

Thanks for the meaty reply.

Have wondered about the newer boxes in the Pro audio or semi Pro audio lines.

Think that on the original W2INR php AM board there was some detailed info on some of the newer inexpensive processors,  and how AMers were steeing them up,  but I did not save it,  or memorize it.

Would like a limiter at the transmitter audio input to protect it and the band.

Prob would like some generalized processor ahead of that.

73  Thanks again.     Vic  KF6RIP

[K6JEK]

Vic, I'm glad to hear you've got the 50 KW rig almost ready to go.  I've been tempted to try something cheap for a change.  Blaine, N1GTU, likes his Alesis Nanocompressor.  At least at one time he did:

http://classe.monkeypuppet.com/viewtopic.php?t=235

He uses it as a limiter.  You find these things on eBay for not much at all.  

Jon

[K6IC]

Hey Jon,

Thanks for the info ... will study that some more.

Yep,  and that 50 KW rig runs on batteries ... can U hear me now ?

73  Thanks      Vic  KF6RIP

[W1IA]

Hi Vic,

For about $250 you can find a Bheringer Ultra-Dyne Pro (DSP9024)
these boxs are 6 band compressor limiter gates with extensive programming control. Very sweet box for the money and has been impervious to RF. I call it the poor mans Orban.

Brent W1IA

[W2VW]

Hi Vic,

For about $250 you can find a Bheringer Ultra-Dyne Pro (DSP9024)
these boxs are 6 band compressor limiter gates with extensive programming control. Very sweet box for the money and has been impervious to RF. I call it the poor mans Orban.

Brent W1IA

Stalk this box on Ebay and it will cost half that amount. Great box for the money.

[K6IC]

Thanks Brent and Dave,

Will be stalkin' and searchin'  for the DSP 9024.

Thanks all for the advice.   73        Vic      KF6RIP

[wavebourn]

Hi Vic,
what if to consider a simple idea to save a lot of money?

A FET may be used as a good voltage controlled resistor with signals of microphone level.
Just make a voltage divider of one resistor and a FET, and connect common point to input of a non-inverting amp made with a single OpAmp. Output signal rectify using a "voltage doubler" made of a cap, couple of diodes and a filtering cap with a bleeding resistor, and put this rectified voltage to the gate of your FET. You may add a mic transformer before a voltage divider to get symmetrical input.
I'll draw you a draft if you want, but I have no time for prototyping.

[KA7WOC]

Google up W7JHS and follow his links to the audio processor which will fit into the base of a D104.  Several are using them here in the pacific northwest.  The results are on par which much more elaborate (read expensive) gear.  Simple to install, easy to set up.  Bruce, the designer, installed several this past weekend at Mac's Winterfest. 

[VE7 Kilohertz]

Hi VIc,

What is the TX you are driving? What is the input Z and level required to modulate it 100%? That will determine what will work "out of the box" and what may have to be built or modified to work with it? Also, is it capable of modulating positive peaks greater than 100%?

I'll await your reply then give you my opinions.

Cheers

Paul
VE7KHz

[K6IC]

Hi Tolly and Paul,

Have been out of town ..  sri f or the delay.

1.   Tolly  (sp?) ,  am working on a new QTH out in the stix,  so do not have any time for designing and building radio stuff.  Thanks for the suggestion,  but am looking for a packaged general purpose solution -- appliance.

2.  Paul;  will be driving several rigs.  One is a broadcast rig -- 600 ohm,  transformer balanced input,  capable of 125%  +  modulation ... std BC levels,  with adjustable pad at the audio inputs.  Also need compressor/limiter for  T-368,  and  DX-100/Valient (would be nice).   .   Would like to use outboard Mic pre and processing,  so all rigs will be some form of line-level input,  each with separate pad.   Goal is to raise average modulation,  but limit neg peaks to close to cutoff,  but not quite. 

In the past,  have used the passive negetive clamp -- reverse-biased diode  with an R  equal to the RF final plate  Z,  just to protect the Mod Trans.  Some say that the C of this reverse-biased junciton limits the freq. response of the rig,  but I am not looking for that much hi freq energy anyway.  Just want to protect the Mod Iron and the neighbors above and below on the bands.  This should protect the Iron,  but still need  both the compressor / limiter function.

73,  thanks for your thoughts.   Vic   KF6RIP

[VE7 Kilohertz]

Hi Vic,

Okay, this is easy. For an out of the box solution i.e. no construction project, I am going to recommend any one of the following broadcast boxes. They all need line level (+4dBm) so you will need a mic preamp which will give 2 or 3 volts into 600 ohms. Any of these will protect the mod iron and allow +125% or more modulation. You can find them for $100 - $250 depending on condx etc.

Gates Solid Statesman AM version
CRL PMC-300A or PMC-400
CBS Volumax (any of them 400, 4000 etc)
Dorrough DAP-310 or 610 (AM version)
PRE Multilimiter
UREI BL-40 Modulimiter

There are others which are more modern but will cost a whole lot more. These are all good solid performers and will do the job. Watch out for "studio" boxes like Berhringer etc. as they don't allow assymetrical modulation and rarely have peak clippers, which is what is needed for your application.

You can drive your broadcast tx directly with these and pad it down and drive the phone patch on your ham rigs.

Good luck.

Paul
VE7KHz

[K6IC]

OK,  Paul,  and all,

Thank you very much for all the info.

Will focus my search.

73,  and C U on AM.    Vic   KF6RIP

[W1RKW]

Anyone know what the difference between a CBS Labs 411 and a 400 is? The 411 I guess is for FM and the 400 is for AM but are they really different besides pre-emphasis/de-emphasis circuits?

[K6JEK]

Vic,

I'm trying to reconcile the broadcast transmitter with off the grid battery operated which I think is what you've been the last couple of times we've talked.  Are we talking about some really big batteries and really big solar cells?  How grand.

[K6IC]

Hey John,

Well,  I am going off-grid,  and think that the BC rig will wind up there..  The batteries are about 4000 lbs -- 100 KWHr.  Now abt 10 KW hr of solar input on a sunny Winter day.  The 48 volt inverters put out 240 VC  @  11 KW continuous.  So the BC rig is doable  about 600-700 Watts standby,  and 20 % talk time or so.   A generator stands by for the hi-tap old buzzard transmissions.

Really,  a Class E rig like yours is the best solution ... much more efficient and very low stand-by power ... hope to bulid one this fall.   Hope springs eternal.

73  Jon,  C U on  AM,  soon.  Your Class E rig sounds teriffic -- right there with the very best of the Heavy Metal rigs!       Vic   KF6RIP

[K6JEK]

Wow

[VE7 Kilohertz]

Anyone know what the difference between a CBS Labs 411 and a 400 is? The 411 I guess is for FM and the 400 is for AM but are they really different besides pre-emphasis/de-emphasis circuits?

Hi Bob,

I think the 411 is the stereo version i.e. 2 channel version of the 400. Not sure about pre-emphasis.

Cheers
Paul
VE7KHz