audio processing tips needed, please

[W3CRR]

I'd like to use my Electro-Voice RE-20 broadcast mike with my Collins 32V-2 transmitter to best advantage.  My "audio chain" now consists of a Whirlwind "Little Imp" LO-Z to Hi-Z impedance matching transformer.  That's it.
Obviously, more is needed to take full advantage of the studio microphone and transmitter combination's sonic potential.  What do you recommend?

Many thanks and 73,

Craig
W3CRR

[W2INR]

Hi Craig,

You can start here, http://amfone.net/Amforum/index.php?board=51.0 and then go to the East Coast Sound http://amfone.net/ECSound for more material that may help .

I am sure you will get additional help here also.

My advice is simple. You need these two items before you start, 1. Oscilloscope, 2. Off the air monitor. You want to see your signal and hear your signal when transmitting. Without these two pieces of gear you are shooting in the dark.

Good luck

[W3NP]

Hi Craig
Nice working you today on 40. Your 32V sounded FB with the Heil, but I would like to hear it with the D104. Since the audio section in that TX has been reworked, it probably has a large value resistor in the 1st stage grid. It would be good to do an A/B comparison.
As to the RE20...I still think it might be a bit dull without some EQ to brighten it up a bit....BUT, it wouldn't hurt to give it a try.

What Gary said.....it's pointless to start fine tuning your audio without a scope AND an off-the air monitor. Even if your audio doesn't sound the same as it does coming through various station receivers, you will have a baseline idea of what it sound like TO YOU when your on the air reports are favorable...or NOT!!
I just use a simple diode monitor similar to the ones described in the East Coast sound section. As I was recently re-working that DX-100 that you heard me on today, I was able to listen to my progress.

Maybe you already have the scope and monitor.

73, Dave

[Steve - WB3HUZ]

What audio modification have been done on the 32V?

[K1JJ]

My advice is simple. You need these two items before you start, 1. Oscilloscope, 2. Off the air monitor. You want to see your signal and hear your signal when transmitting. Without these two pieces of gear you are shooting in the dark.
Good luck

Well said, G!  You want to hear and see your signal... I like it!

I will add: 

1) First sweep the transmitter with a tone to be sure it's clean to start with - and study the sine wave for subtle problems.

2) Tape yourself from the off-air monitor to remove the headphone voice bone conduction illusion for a true idea of your results.

3) Finally, get opinions on the air from guys who know your voice and have hi-fi RX systems. Tell them what you are looking for. [EXPECT not to please everyone] 

T

[Steve - WB3HUZ]

2) Tape yourself from the off-air monitor to remove the headphone voice bone conduction illusion for a true idea of your results.

And then record yourself off a receiver using both a wide and narrow bandwidth. This will much more closely approximate how you will sound to the guy on the distant end. Diode monitors are nice for absolute monitoring but you will usually tend to use less high frequency audio boost than you really need when setting the EQ curve. This happens because the diode monitor provides WAY more high frequency response than just about any receiver. Further the SNR is much higher than it will be on the distant end.

[K1JJ]

2) Tape yourself from the off-air monitor to remove the headphone voice bone conduction illusion for a true idea of your results.

And then record yourself off a receiver using both a wide and narrow bandwidth. This will much more closely approximate how you will sound to the guy on the distant end. Diode monitors are nice for absolute monitoring but you will usually tend to use less high frequency audio boost than you really need when setting the EQ curve. This happens because the diode monitor provides WAY more high frequency response than just about any receiver. Further the SNR is much higher than it will be on the distant end.

Ain't that the truth.  How many times have we EQed ourselves off the monitor and get told on the air we need more highs? We jack up the highs and in our monitor and it sounds like too much, but perfect on the air..

The solution is to have someone with a transparent receiver, recorder and transmitter to play it back to you.  Or send you an audio file. There's only a small handful of guys on the air who have that capability.  And, sometimes even these systems vary in quality, with problems over time.

It took me over a month to get my SP-600/minidisc and Class E rig to do an acceptable job. Even then, occassionally someone will say it's not quite right.

T

[wn5t]

1) First sweep the transmitter with a tone to be sure it's clean to start with - and study the sine wave for subtle problems.

Okay...'nuther dumb question...[seems to be the only way I learn ]  Can someone point me to a resource on "sweeping" a TX?  I have the scope (200MHz)...though the probes may need replaced....    Anywho...what kind of audio generator do I need?  Will the old Knight kit rig do the job?

TIA,
Michael
WN5T

[W2INR]

Hi Mike,

There are no stupid questions.

Tom K1JJ has an article on East Coast Sound which can be found in the Contents also.

http://amfone.net/ECSound/K1JJ1.htm

[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?

73,

Craig
W3CRR

[w3jn]

To answer your questions on the audio generator, any cheapo audio generator will do fine so long as it has a nice low distortion sine wave.  Take it easy when you're sweeping, I'd keep it below 50% modulation as observed on the scope as the modulator is being asked to crank out full CW power with a continuous tone.

As far as the scope goes, you don't need a probe.  A FB RF tap can be made from one of those 3-way TEE PL-259 adapters (available at Radio Shack).  Make a cable with a BNC on one end and a PL-259 male on the other, then cut off the center pin of the PL-259 male.  MAKE SURE that when you put this together the center pin of the PL-259 male does not make electrical contact with the TEE - what youre looking for is very loose capacitive coupling NOT DC coupling to the scope.  In a pinch you can wrap several turns of wire around the coax coming from the xmitter and clip your scope probe at each end of the wire.

Hope this helps.  73 John

[VE7 Kilohertz]

And then record yourself off a receiver using both a wide and narrow bandwidth. This will much more closely approximate how you will sound to the guy on the distant end. Diode monitors are nice for absolute monitoring but you will usually tend to use less high frequency audio boost than you really need when setting the EQ curve. This happens because the diode monitor provides WAY more high frequency response than just about any receiver. Further the SNR is much higher than it will be on the distant end.

Hey Steve,

That's exactly what I have been doing for quite a while now. It works great. And if you want to go one step further a process I use here is to record myself, using the unprocessed mic of choice onto tape (I use DAT) and THEN play THAT back thru whatever processor/TX you are tuning and listen to that in the station monitor. This way you can hear the differences between raw audio, and any processor tweaks you make, in real time without any bone conduction or other interference. You are also able to compare how you sound in the same RX and monitor system that you hear everyone else on. The only thing missing is the SSB crap,  selective fades and people tuning up.

Cheers

Paul
VE7KHz

[wn5t]

Gary,

Thanks for pointing me to the article.   I've already built an RF pickup out of an old watt-meter.  Now, to learn what the wave-forms should look like and what to do if ther're not right...

Gosh, I love this hobby.  There's always something to learn.

BTW, your pic of the AM position on QRZ.com made me drool.  I guess I've been hanging out with the dog too long! HIHI  I wonder when I'll start to get those dark patches over my eyes?

73,
Michael
WN5T
Toobs, toobs, they glow in the dark...