Valiant audio

[W9BHI]

Hello all,
I was thinking of using the KD7YY D-104 preamp and connecting to the phone patch input on the back of the Valiant.
The phone patch input is 600 ohms and the D-104 preamp output can be set to 600 ohms.
Will this give better results than going through the 12AX7 input stage?
Thanks,
Don W9BHI

[W3GMS]

Don,
With a good D-104 you should not need an additional gain stage.  To properly match the high impedance element, the mike should see at least 5 M of input resistance.  I forget the actual circuit in the Valiant, but putting a 5 M to ground and getting rid of what they have should do it.  The audio in the Valiant can be improved greatly with some modifications.  Not sure how far you want to go with your Valiant.  Here is one set of Mod's that I got from Steve's AM Window web site.  Those mod's show a low impedance input.  You could simply put a 5M from grid to ground and use that for your D-104.  If you need some more gain, put a 20 or 30 ufd cap across the first cathode resistor to prevent de-generation.  If you want some more "highs" and you have enough gain, experiment with smaller values of caps across the first cathode resistor to give some "presence rise" 

http://www.amwindow.org/tech/htm/valiant/valiantmods.htm

Have fun!
Joe, W3GMS
     

[Todd, KA1KAQ]

Joe has pretty well covered it. A few simple mods can improve the audio noticeably, but without major surgery to replace stock iron and other mods, it will never be a broad, HiFi sounding transmitter. Not that it's a bad thing.

If you're looking to play with audio circuitry without a major redesign, the Ranger or DX-100 are much better candidates. The Valiant would be a good set to use in noisy conditions when you need that punchy audio sound. Tweak it a bit for the D-104 and you're good to go. You definitely don't need another stage of amplification with that mic.

[WQ9E]

And pay special attention to the clipper setting in the manual, MINIMUM clipping (actually zero) occurs with the clipper control fully CLOCKWISE.   

As Todd said, for a hifi transmitter start with something else.  With the clipper set to zero the Valiant sounds OK for normal use and when your signal is weak (or cutting through interference) dial in a little clipping, that is what it was designed to accomplish. 

Last summer I did some simple experiments with a station in the southwest on 75 and my unmodified Valiant with a little clipping was better copy than my Ranger/Desk KW running considerably more power.  The Ranger/Desk definitely has better audio but when conditions are rough speech processing can help.  There are many ways of accomplishing this but the Valiant (and Viking 500) come with it built in unless you modify it out.

[KC9LKE]

If it’s the same one I’m thinking of it’s not really a pre-amp but its main purpose in life is as compressor limiter that has a 6.8M ohm input and 0 dBm out into 600 ohms. I like the low Z out. Low noise.

You can add a small daughter board with two pots so you can adjust the comp ratio and the noise gating to your liking. You’ll need to power it externally. You can do this through a mic cable with an extra conductor like the HEIL cable. It really needs to “run” all of the time, not the way it comes, but I don’t remember the mod, mute?. IIRC when its first turned on, (mic keyed) you can lose the beginning of your first word.

If you would like I’ll look in to the mod maybe its not the mute.

Its not $3k of oxygen free audio processing but it fits into the mic base and keeps a vintage rig vintage. No JS needed.  It does its main job, limiting so you can pull the stock clipper tube if need be, and its also does a job of compressing.

Heck maybe it’s easier to widen the 600 ohm input of the Valiant rather than the whole audio chain and just go from there.
 
For now hook it up and see how it sounds!!

Phase the mic element properly.

Best of luck   Please post results.

Ted / KC9LKE