Audio 101

[N8ECR]

Has anybody read the recent ER mag. artical by K2DK... In the end of the artical he mentions that after all your efforts the end result of all them audio adjustments, and $4000 worth of equiptment, you get about the same results form the old reliable D-104 :-\Mike/N8ECR

[flintstone mop]

I'll look closer at the article.
Remember the D104 is a very peculiar mic. It has to see a very high impedance on the input stage of an audio circuit. If not the high megohm impedance, then the frequency response of the D104 suffers.
Dave's articles have been dealing with broadcast transmitters. They require very high audio levels to be fully modulated. You cannot plug a D104 into a B'cast rig and you get 100% modulation. I'm thinking Dave is saying you can make that B'cast rig sound like a WKBW or you can amplify a D104 and you  will have telephone quality audio.
I believe that Dave W3NP has a separate station void of all processing and a nicely matched D104 connected to his DX100 and it is a perfectly readable, pleasent, sound.
The final player in this AM sound is the characteristics of our voice. Not all of us have those golden tones like Paul, WA3VJB.
There will be other responses I'm sure.

Fred

[W2VW]

A good D-104 is the best ham radio mic to use without processing but it ain't THAT good.

[KL7OF]

A fair number of hams in the pacific NW are using a solid state voice processor designred by K7DYY that fits in the base of a D-104 and reproduces the full range of audio freqs. and sounds very good..A great mix of old and new technology ..

[Gary - WA4IAM]

Any link to a schematic for that D104 voice processor?

[N8ECR]

I must admit that I was making comments of something i heard over the air  in the last couple weeks, it may have been a wise crack comment, and however the way it really reads in Dave artical in this months ER differs.  But I; after reading it ;I see how and why it originated the way it did. Hi HI  N8ECR...

[K6JEK]

Any link to a schematic for that D104 voice processor?

Bruce's D-104 pre-amp, limiter is an SSM 2166 design with a JFET and an OP amp added for good measure. The SSM 2166 has a lot of stuff in it -- pre-amp, compressor/limiter, downward expander all in a teeny tiny little chip.  Steve, WA1QIX, did a design with just the 2166, no JFET, no OP amp that had all that and a two band equalizer.  I used to amaze my friends with that design and a three dollar Radio Shack electret.

I'm not sure you need any of this with a D-104, just a big resistor between the microphone element and the amp that's in an amplified D-104 gets you most of the distance you're going to get with a D-104.

Anyway, here is Bruce's design:

http://www.k7dyy.com/images/schemproc.jpg

Bruce will sell you  a board for that design (you supply the parts) that will fit in the base of a D104.  It wants +8V or so coming over the microphone cable.

And here is Steve's design:

http://www.classeradio.com/ssm2166_compressor.gif

Two more little tidbits.  The 2166 takes a half second or so to settle down so powering on and off with PTT like the traditional D104 amp is not a great idea.  However, it does have a quiet mode in which it draws almost no current.  I used that.  See the datasheet on the Analog Devices website.  The other tidbit.  I used a surface mount 2166 but I understand somewhere in this great universe of ours the DIP version is still available.

Jon

[K6IC]

Hi Jon,

Very informative post.
Thanks a lot for the detailed info.  73   Vic  KF6RIP

[Roy K8VWX]

          I have been using this for years commonly called the k8tv agc limiter. Have five of them running right now and have sent boards (PC) out to others but few have built them and that’s OK. (They don’t know what they are missing), SEEING THE RESULTS ON A SCOPE IS WORTH A THOUSAND WORDS. My thanks to Ken k8tv.Also put all the high end audio processing with a voice like mine and you will hear very little difference. HI  HI

[Roy K8VWX]

    After taking another look it is not the same as the k8tv limiter.Two things I have to have to run AM is a scope and the limiter.

[K6JEK]

Roy,

What is the k8tv design?

Jon

[N8ECR]

There used to be a N8JRJ/KJ8CQ version kicking around too.. A simplifiied design with a MPF102 device  Wasns't there?

[WA3VJB]

Fred's too kind.  Most of what I squeeze through transmitters like a T-368 comes from good technique with the microphone. Not too close, get rid of the background noise, blow the "P" pops above or below to avoid blasting the microphone. I use the same methods on a damn cell phone and it helps a lot, but when you're on the radio  it's something you have to keep in mind as you move around the room, looking at the scope, frequency counter, etc.