ok, teach me some things about broadcash transmitter audio chains.

[N3DRB The Derb]

I'm buying the Raytheon RA-250 that used to belong to 3WWL. Most of you know I have been a D-104 into the speech amp type guy.  Obviously not going to happen with the Raytheon. Can ya'll educate me on suitable mics, low cost COMPACT mixers, anything that would be helpful to a broad cash transmitter noob? don't have room for any type of console, at least not now. basically I'm not familiar with the sequence of gear needed from mic to TX and in what order they go.

TNX 

[W1GFH]

A small mixing board and a dynamic mike could get you started. The built-in EQ and gain on the board is enough to do what's needed. Mike Dorrough, KO6NM and a few others I knew used such a simple arrangement with their broadcash xmtrs, followed by a peak limiter.

[WA3VJB]

Cool !

That RA-250 needs a pretty good poke in the audio input to wake it up.  Jay had been using a Harris "AM Limiter" that took his line level feed, added maybe 5-10db of compression and peak limiting, and thus drove the Raytheon quite nicely.

I wouldn't worry much about getting a peak limiter. I seem to remember you use a scope so you are accustomed to watching your baseline (except maybe during BJB excursions, eh ?)

A number of manufacturers have VERY small desktop mixers that I highly recommend as a function of taking your mic up to the level the Harris or other processor wants to see.

This one is on clearance price for $45, and has an EQ built in.


http://pro-audio.musiciansfriend.com/product/Behringer-Eurorack-UB802-Mixer?sku=631238

As for the mic itself, look for yer basic dynamic cardioid for $30 or whatever. For a while Shady O'Rack sold a high-quality Shure with a store label and an on/off switch.

BJB will never have sounded better once you get that beast up and running.

How you set for grunting it into place ?  Holler if you need some hep.

[K5WLF]

This unit has a lot of capability in one box --

http://www.dbxpro.com/286A/index.php

I've used them and they work really well. The compression is very smooth (i.e. no artifacts) and natural sounding. They have both mic and line inputs, so you can eliminate the mixer and go out through the insert to an EQ, or follow the mixer and its EQ with the 286A. dbx EQs are also excellent.

Mackie makes some great small mixers (with magnificent EQ) and some even smaller ones (under the TAPCO brand name).

As you get into the whole audio thing, you'll probably eventually find a mic that's the perfect match for your voice. But to start off with, it's hard to go wrong for the price with either a Shure 57 or Shure 58. E-V makes some good mics with broadcast heritage too. If you're looking to spend a bit, the Shure SM-7 has a lot of followers, especially in the voice-over part of the business.

My favorite vendors for audio gear are: www.markertek.com and www.sweetwater.com

HTH,
ldb

[KD6VXI]

Derb,

You can get an MAudio sound card / mixer for less than a hundred bucks.  Plugs into the USB port.

Run Reaper, Pro Tools, Audition, etc. with associated plugins, and you can do all your processing on the PC.  Cheap to change things, add or delete items from the chain, etc.

I'm VERY happy with Reaper and Audition with my direct injected station.  Others have had VERY good luck with Pro Tools.

FYI, just something to look at.  I believe a buddy picked up a 4 channel mixer / card for about 80 dollars at guitar center on closeout.  He played with it for a couple months, then sold it to his kids "garage band".

--Shane

[N3DRB The Derb]

I'm a 100% Mac guy. I happen to have a spare 733 Mhz G4 that would be perfect for such a task. I was just going to use it to play my iTunes library in the shack.

I'm thinking rack only stuff cause I'm so cramped for horizontal space.

[N3DRB The Derb]

This will be me :

[K9ACT]

Don't know from nothin about bcst xmtrs but I have a basic audio chain question.

My chain components consist of, in no special order:

Shure 5 channel mixer
Behringer digitial processor (EQ)
CBS Audimax
CBS Volumax
CBS Dynamic EQ which is not used at the present.

It is not intuitive to me just where the EQ should be.

It is presently in front of the CBS stuff but could just as easily follow or be in between them.

I believe the CBS EQ is intended to follow the Vmax but I am not positive and if so, seems like the Behringer should also if used.

What is the reasoning behind the proper secuence?

js

[k4kyv]

You don't need an entire rack full of audio gear.  Even a D-104 mic will do if it has a good cartridge and you work it into a 10 megohm load. (Not talking here about one of those POS CB versions with the crappy amplifier built into the base of the mic stand) The transmitter undoubtedly takes a 500/600 balanced line audio input, about +16 to 24 dBm.  If you have the manual it will tell you exactly what the input level should be.  Best to have about 10 extra dB, and use a variable attenuator to get the level just right.

I would sorely miss it if I didn't have a peak limiter.  It allows me to back off from the mic, swallow the mic, shout or whisper without having to keep an eye on the  scope at every moment and constantly ride the gain to make sure the modulation level is correct.

I have found that a rising frequency response in the mic pre-amp, starting at about 800~, adds articulation and prevents a muddy inside-a-barrel sound. The D-104 has its own built-in presence rise, but I still add more, whether or not I am mixing in the dynamic mic. Everybody tells me that with my Sony dynamic, which is a medium quality mic, running with a flat response to the transmitter doesn't sound good and doesn't punch through the band crud.

[W2VW]

Keep the D-104.

Stay away from do-it-all consumer grade boxes. Most of them suck.

At my station at work there's a D-104 with a built-in MPF-102, Shure M367 mixer and a symmetrix 525. All cheap stuff sounds good.

Later you might want to dedicate a computer to performing audio shaping. Keep the original audio chain. Imagine not being able to play radio because of a computer problem

[N3DRB The Derb]

+5db 500~600Ω balanced is what the manual says.

Don, you'll like the fact that it uses 4 6B4G's to drive the 810's. not trying to squeeze 15 watts out of a pair. Thing is massively over built in every way.

[KD6VXI]

I'm a 100% Mac guy. I happen to have a spare 733 Mhz G4 that would be perfect for such a task. I was just going to use it to play my iTunes library in the shack.

I'm thinking rack only stuff cause I'm so cramped for horizontal space.

I had my station and my tech bench all on a standard "desk" before....  I had to, I couldn't walk..  BUT, that's when I found out that the Dell Inspiron has an AWESOME sound card in it for audio processing.

When I wanted it, I could bring the laptop over and have fully processed audio.  Then go back and watch movies, etc. on the bed.  My setup kills the front panel mic jack when it detects audio in the RCA in the back (direct input)....  So, I just pulled the 1/8 plug out of the lappy, and the station would operate as normal.

I see where someone else said "what about a computer problem"...  I agree.  It blows when one fails....  Especially if you've modified your stuff to the point where the front jacks don't work anymore...

Reaper is made for the Macintosh as well, IIRC.  If you decide to go that route, I have a PLETHORA of plugins for transmitting, etc.  There is also a gentleman in Italy that has cloned a BUNCH of the Omnia, DBX, etc. processors in software...  I'm happy enough with my "rack chain" so I didn't play with them, but they are there.

Congrats on the broadcash rig...

--Shane

[k4kyv]

It is not intuitive to me just where the EQ should be.

It should go somewhere between the mic preamp and any limiting or compression devices or stages.  Mine is built right into the mic pre-amp. You want the compressor/limiter to be the final processing device to handle the audio from the program source, and not mess with it any more after the final processing stage.  Sometimes, EQ will alter the peak-to-average ratio and/or the symmetry of the voice waveform, and that would defeat the whole purpose of the compressor/peak limiter.

And Derb, that 5 dB is probably based on the old 6 milliwatt reference.  Off the top of my head that should be the same as +13 dBm.

That Raytheon 6B4 quad class B driver transformer is excellent.

[N3DRB The Derb]

Macs dont have a lot of problems in general. 

with the exception of RF riding in on stuff , which will happen no matter what I'm sure at times, the Mac wont be the weak link.

I'll check out Reaper.

[KC4VWU]

Derb,
         I first bought a Behringer Xnyx and it's too balky on getting it adjusted. The gain adjustments get to a point where the unit adds way too much white noise into the audio signal. I wanted to try a Eurorack, even though they seem to be basically the same, but GuitarCenter didn't have the small model I wanted. I tried everything, but I just couldn't coax any good signal out of it; maybe I was just doing somthing wrong? There was still the issue that the plastic case would be problematic with RF feedback. Seems to do OK up to 100w power levels, but above that, it gets squirrelly.

I then found a used ART Tube MP and it works pretty good. There's no EQ, but that should be easily resolved as soon as I can get back down to the music store to smoke over the selection of EQ's. The Tube MP has a 12AX7 stage in it, XLR and !/4' inputs, phase reverse switch, 20dB boost, and analog vU meter. The only problem is it stands upright, but that is good for limited space. I bought it for 19.99 + tax in the box. They are pretty inexpensive when purchased new; well under $50. The Presonus Tube Pre is another good preamp, although they are usually about 4 times that amount used.

Phil   

[K5UJ]

Let's see..a few points in no particular order:

Derb, how much money do you have to spend?  That determines advice as you can blow a ton of money on audio gear if you want to.

Jack,  an eq should go ahead of all your leveling type processing (compression, limiting) in my opinion.  the boxes that variously deal with audio limiting should be the last things in the chain.   Don't know a thing about the CBS dynamic eq but the dyn. eq I have used let you program a boost or cut over a certain frequency range and it would kick in when your audio level reached a certain threshold (hence the "dynamic" part of the deal) that you could also program.  So you could for example use it to act like a limiter over a narrow range of frequencies.  Let's say you sweep ur rig and find it is not flat and inherently increases an audio level at say, 3 KHz and it is a problem for someone if they have a speech component that is loud there.  Such a person could use a dyn. eq to compensate for that by kicking in an attenuation at 3 KHz when the audio input reaches some amplitude.  Just one example of a way to use it.

The RS mic was a rebranded SM58 or some kind of Shure one or two notches down but I don't think RS sells them now.   Avoid condenser mics unless you have zero background noise, want to fool with pop screens, and have no extremely low freq. rumble noise--motors and stuff because condensers pick up everything.   The old Astatic mics like the D104 are great but if you need a low Z dynamic and want the most for the money get a used SM58.  

If you go with one of those you need a preamp or some kind of amp to get the mic up to line level, a 31 band mono graphic eq. is nice to have--you can find them at hamfests--here's an example:  http://www.bswusa.com/proditem.asp?item=131DBX
You can use the eq to vary your audio bandwidth and set up a flat audio level between your low and high cutoff so hams you work will copy your audio regardless of their rx passband.  You can use it to roll off your voice below say 80 Hz, so you don't waste sideband power on frequencies that convey no information.  


and some kind of final level control and isolation xformer just before the rig can be convenient and help avoid some pitfalls like RF and hum on the audio.  Something like a W2IHY iBox:  http://w2ihy.com/pdfs/iBoxOperatingManual.pdf (you can also homebrew your own with a Jensen transformer and a pot and some cable jacks in a project box).

Aside from all of that if you can get some kind of compressor (this is a good example of one:  

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160398232364 and this one but getting pricey:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190366604288

and a very fast acting tight negative peak limiter (Modulimiter, Inovonics 222, CRL Amigo AM, CRL PMC-400A, Optimod, DAP-310 or DAP-610 to name a few) that would be great.  Some of these show up on eBay and are useful with all AM rigs.

Go with balanced XLR jack and plug audio cables.   This all sounds like a lot and a real pain but it is not so bad once you get it figured out.

Rob

[Steve - WB3HUZ]

Before you worry about equipment, get the basics here.

http://amfone.net/ECSound/processing101-1.htm

[N3DRB The Derb]

thanks for the knowledge guys. This TX will be a birthday present to myself so the timetable is for it to be relocated here and on the air by April 25th. The wx is too rough up in western PA to worry about getting it here much sooner than that.

Glo is donating $100 bux to the TX project money jar from her job earnings to start it off!    I keep telling you guys, I got the bestest with the mostest wifey evar.  

[KB2WIG]

D,
Is Glo from Stepford, Connecticut ?

klc

[N3DRB The Derb]

naw, Johnstown, PA.

[KB2WIG]

D,

 You are a lucky man.

klc

[k4kyv]

Before you worry about equipment, get the basics here.

http://amfone.net/ECSound/processing101-1.htm

A concise, well-thought-out article.

One thing I would add is in regards to the 0 dB level, which might be confusing to those working with or  restoring vintage equipment.  The standard zero dB reference used to be 6 milliwatts, and the standard line impedance was 500 ohms.  Sometime, in the late 50's I think, the standard was changed to 1 milliwatt and standard line impedance was changed to 600 ohms.  Usually, the 1 milliwatt standard is represented as dBm.  If, for example, you have a transformer and the power level stamped on the name plate is xx dB, most likely the manufacturer used the 6 mw reference.

To convert dB (0= 6 mw) to dBm, just add 8. Six milliwatts is actually 7.8 dB above 1 mw, but a nice round figure of 8 is usually good enough.  So a transformer rated at +16 dB would be the same as +24 dBm.

500 ohms is so close to 600 ohms, that the two figures can normally be interchanged and the error will be inconsequential. UTC used to rate the line input and output windings of their broadcast quality transformers (LS, HA, A and O series) as 500/600 ohms. I use balanced lines to interconnect most of my audio stuff, and I have never had a problem from intermixing 500 and 600 ohm inputs and outputs.

This is something to keep in mind, since much if not most of the tube type audio gear we see at flea markets, hamfests and on ePay is likely to be rated at the older standard.

I recall a message on this board a few years ago in which someone had picked up a modulation transformer that weighed about 100 pounds but he thought the rating was ridiculously low, something like 100 watts.  Actually, the rating was closer to 800 watts.  Confusion over this issue can lead to serious errors, perhaps passing up a good deal.

[ke7trp]

Derb, I use the 802 Behringer mixer. I think its $59 at Guitar center. I needed this unit because I needed phantom power for the mic. 

I also use the 166 XL DBX compressor. Dont get the other model. It has no peak limiter. This 166 has a smooth limiter and I really like that. I can scream in the mic and it will never flat top. 

For a mic,  Look into the MXL line of mics.  I have the large diaphram condensor mic from MXL.  I will put it up against just about anything and its about $99. 

Look for the post about my Mic boom I found.

1. Decent mic
2. Mic preamp/mixer
3. Compressor/limiter.

Thats about it.   You can use the computer if you want. Shane has a good point. For me, I dont have to have to rely on a computer for my Radio to work.  It is fun though!



Clark

[flintstone mop]

Hi All,
OK FB on almost everything mentioned. I can get the spec for the amount of audio needed to drive the Raytheon, prolly the usual +4 to +10dBm. Nothing was stressed here to drive the TX.
An eq is important, as the TX is a bass monster and you want to preserve that part BUT you need the usual boost in the mids and mid-highs to get the speech clarity over a noisy radio path.
If you do not have a separate EQ, then maybe your Symmetrix mic processor or whatever you use for a "mixer" might give some eq. options to get a little boost in the upper audio freqs.

Phred

[N3DRB The Derb]

I found the entire manual online and D'Led it .