Mic for use with 32v2

[WG9P]

32v2 users: What microphone do you feel is a good choice for the 32v2. The manual does not really say what impedance mic is suggested for best performance. I have used the rig on CW for years but would like to put it on AM now.

Are the EV-638 or the D-104 good choices?

What sounds best over the air with an unmodifed rig?

thanks

[K3YA]

 A D104 does a fine job on my V1 and V3.  However to sound best it requires changing the grid resistor on the first audio stage to 5 M ohm, or larger.  Now this isn't that big of a mod and can be done by sliding the transmitter about 3 inches forward in the cabinet to access the audio stage from the side. 

For a stock radio, I don't know.

[WG9P]

Thanks, I beleive that is a 1Meg resistor now.

[W3RSW]

I put an 8 meg in my 32v2' but then used a mpf 102 source follower anyway in front of that.  The FET follower placed into the base of the mike where the two stage stock transistor amp resided before.   Used all the same switching and 9 v batt., but left pot in not connected.

Several older threads about all this on amfone including variations on the FET follower.

[KM1H]

If the D-104 has a good crystal element the last thing needed is another amp stage.

A 4.7M input resistor load is fine and altho mo is often mo betta it can lead to stage instability. The V Line can also benefit from other audio changes unless you prefer the factory restricted passband.

I got so-so reports with my V2/D-104 and 4.7M before turning it upside down for changes which havent been completed yet.

Carl

[ke7trp]

I like the EV638 with the collins rig.  One tip I learned here was to put heat shrink over the 5 meg resistor, then cover that up with some RG58 coax braid to shield that resistor.  It will pick up hum.  Works like a charm.

C

[WG9P]

what a great simple method of shielding the input resistor. THank you, I will try that.

[W3RSW]

Carl,  re: "last thing needed is another amp. stage."

The MPF102 follower does not have gain.  It is simply a very high impedance transformation to a typically lower impedance, say the 1 meg. input on common tube transmitters of 50's era.

 If you've been raised on transistors then 1 meg. sounds extremely high but from a crystal mike element it is low....   believe it or not, heh, heh.   I asssumed you knew that the D104 had lots of presence at mid to high audio freqs. but very llittle bass into a one megohm load.  Bass is much enhanced at loads of 5 to 10 megs. so that it approaches low end response of a typical dynamic mike.

The circuits described in this board or "The AM window" show phase switching, bass or treble enhancement, etc. along with simple impedance matching -- and all with one simple FET. 

[KX5JT]

Carl,  re: "last thing needed is another amp. stage."

The MPF102 follower does not have gain.  It is simply a very high impedance transformation to a typically lower impedance, say the 1 meg. input on common tube transmitters of 50's era.

 If you've been raised on transistors then 1 meg. sounds extremely high but from a crystal mike element it is low....   believe it or not, heh, heh.   I asssumed you knew that the D104 had lots of presence at mid to high audio freqs. but very llittle bass into a one megohm load.  Bass is much enhanced at loads of 5 to 10 megs. so that it approaches low end response of a typical dynamic mike.

The circuits described in this board or "The AM window" show phase switching, bass or treble enhancement, etc. along with simple impedance matching -- and all with one simple FET. 

Wouldn't changing the grid resister be a lot less trouble than building an active and extra stage? Hmmmm

[KM1H]

Thats what I thought when I read all that stuff quite awhile ago....seems a lot of work. Ive nothing against SS when it makes things work better or its easier to implement.

If and its a BIG IF, the driver and mod xfmrs have enough iron to handle the lows then the 4.7M resistor is step one with a D-104, thats basics from the 50's. If the stage is stable then 10M is fine....triodes are usually OK.

After that its the usual component value changes to actually boost the bass as well as reduce stage gain if necessary when using a D-104.

Since the 32V is notorious for poor audio and power transformer insulation its not a rig that needs much in the way of enhancements. Run the 4D32 on the Low tap and dont try for any fancy audio processing.

Carl

[Steve - K4HX]

Don’t mix apples and milk bottles. The source follower circuit is intended to be built into the TU base of the D-104 mic. This will allow use of the D-104 on any transmitter regardless the input impedance. It is not a mod specific to the 32V but one allowing greater versatility for the D-104.

Sure, you can use it on your 32V and any other transmitter. It doesn’t matter if it’s more work than changing the grid resistor, it results in more utility, so it’s worth it, in general.  It's probably easier just to change out the grid resistor, but not much when you consider the weight of the 32V!     That said, if the focus is solely the 32V than anything external is irrelevant.

The stock 32V produces audio quality equal or superior to the Viking I and II. The DX-100 might be marginally better (of the modulation is kept to about 90%) and the stock Apache usually worse (depending on the setting of the clipper). The driver and modulation transformers in the 32V are larger than those in the Viking I & II (especially the driver tranny which is very PW in the Vikings).

[KM1H]

The source follower circuit is intended to be built into the TU base of the D-104 mic. This will allow use of the D-104 on transmitters with any input impedance. It is not a mod specific to the 32V but one allowing greater versatility for the D-104.

Agree when you only have one mike

With respect to the 32V, it's probably easier just to change out the grid resistor, but not much when you consider the weight of the 32V!

Unless the owner bought a restoed one rather than work on it himself. In the latter case it needs to come out of the cabinet anyway. Its not a rig to be doing a lot of lifting with.

The stock 32V produces audio quality equal or superior to the Viking I and II. The DX-100 might be marginally better and the stock Apache usually worse (depending on the setting of the clipper). The driver and modulation transformers in the 32V are larger than those in the Viking I & II (especially the driver tranny which is very PW in the Vikings).

But the others dont short out from just normal use as do the 32V's, just ask the rewinders. The Vikings are OK in stock form if you dont run beyond about an 80W carrier and audio to match; otherwise the driver iron folds up.
I didnt notice much difference otherwise in bandwidth and distortion between them....both need TLC.

[K3YA]

The advantage of the D104 over most dynamic microphones is the pronounced rising high frequency response characteristics.  It naturally equalizes the voice in a favorably.  Many dynamic mikes lack this built in EQ, or  have it to a lesser degree.  The extended bass of a D104 when presented with a hi impedance load is a bonus.

Sounds like the source follower is a great idea if the owner doesn't want to modify the radio.

I always liked the sound of a stock 32V.  I think the Ranger is the only common vintage radio that sounds better.  I am looking for a HV transformer for one of 32V1's coincidentally.

[W2NBC]

The stock iron in the 32-V is more than capable, especially the driver. Rob, W1AEX recorded me on my modified 32V-1 late one winter afternoon last year.. The modifications followed most (with some changes) of the published ones on The AM Window..

Mods-

http://www.amwindow.org/tech/htm/32v.htm

32V-1 with an RE-20 into a a mic-pre (no processing) into a Shure mixer using the mic output transformer coupled.
Been running the high tap for 14 years, no crap outs , all original iron..

Recording-

http://dl.dropbox.com/u/17340243/32V-1%20Stock%20Iron.mp3

I agree with Charlie and Steve that the stock 32V sounds clean in stock form, and with SIMPLE mods starts to shine..

[W3GMS]

Recording-

http://dl.dropbox.com/u/17340243/32V-1%20Stock%20Iron.mp3

Hey, that recording stopped just when you were talking about your 1967 Firebird!  I want to hear the rest!!!  The audio with the mod's did sound nice.

Joe, W3GMS

[KM1H]

I agree with Charlie and Steve that the stock 32V sounds clean in stock form, and with SIMPLE mods starts to shine..

By that I take you mean it doesnt have objectionable distortion....to which I agree.

But it still has the ARRL mandated restricted bandpass in stock form as does every other make and model from the mid 40's onward. The only postwar ham TX Im aware of that is unrestricted is the HT-9 which didnt stick around long and was replaced by the even scarcer HT-20

[Steve - K4HX]

The 32V distortion specification: Audio distortion is less than 8% at 90% modulation with a 1000 cps input frequency.

We could argue endlessly as to whether that number is objectionable or not. Also, remember that that many receivers of that era produce that much distortion. To my ears, almost every stock 32V I've ever heard sounded better than any stock Viking I/II. It's usually not even close. YMMV.

[KM1H]

So 8% at 90% is considered good? What about at 95 or 99%?

The Vikers are OK at 80W as Ive already stated, at 100-120W they sound like hell without several mods.

If you want a good low distortion receiver read Jays list

http://www.w1vd.com/BAreceivertest.html

Even some of the poor ones can be helped with minimal work.

Something as simple as a 1M resistor from P to P of audio driver and output tubes and a 47uF cap at the cathode of the driver can make a noticable improvement in distortion; Ive used a 100uF in the driver in a HQ-150 to get a better balance from lows to highs using BCB music (a local Hispanic station which has excellent variety) and talk shows. Also changed the two 1000pf high end rolloff caps to 270pf.

See Jays HRO-60 review for links to more audio improvements.

And surprisingly even the 1939 HQ-120 has excellent audio as built and its easily improved too.

[W2VW]

No worries. If your distortion is higher than 8 percent just tell everyone it's your friend's transmitter.

[Steve - K4HX]

Let's take a look at Jay's list. How about the venerable SX-28, a supposedly "good" sounding receiver. Here are the distortion specs.

Mod%  100 Hz  200 Hz  400 Hz  600 Hz  800 Hz  1 kHz  2 kHz 
90%     18%    18%     16%     14%     14%     14%    14% 


A transmitter with 8% distortion is more than acceptable with such a receiver.

[KM1H]

Not everyone considers the 28 a good working receiver, its main claim to fame is its looks.

OTOH its another that can be much improved with some work.

[KZ5A]

I used a EV-638 with a HT-37, which has a similar input Z, and it sounded very clean and was well balanced.

My B&W 5100 sounds great with an non amplified D104, due to the 10M input-Z.  Also, much to my surprise, it sounds great driven directly from my Symetrix 421's unbalanced line out.   I had expected to have to do some sort of matching to make them play together well, but didn't.

If you are not hung up on Collins and just want a great sounding desktop 100W AM rig, trade it in for a 5100, which sounds better, is much more reliable, and is considerably easier to work on.

73 Jack KZ5A

BTW the EV-638 sounded like bovine flop on the 5100.

[Steve - K4HX]

they all can be improved with some work. We're talking about stock radios here.

Not everyone considers the 28 a good working receiver, its main claim to fame is its looks.

OTOH its another that can be much improved with some work.

[Todd, KA1KAQ]

We're talking about stock radios here.

Old tube radios, at that. And casual 'amateur' use, not contesting or professional lab grade operation.

I always liked the sound of a stock 32V.  I think the Ranger is the only common vintage radio that sounds better.

Exactly what I was thinking, Charlie. The Ranger is hard to top for good sound without modifications. The 32V is a close second. Collins tended to move more toward communications audio as time progressed, to get through the noise. Yet even on SSB in the 80s I would get positive audio reports using a KWM-2A, compared with the more prevalent Yaecomwood gear. I even had OTs comment something like 'you must be running a Collins rig'. Go figure!

But the others dont short out from just normal use as do the 32V's, just ask the rewinders.

That's a bit misleading. You're assuming today's conditions as 'normal' and applying them to a 60 yr old transmitter. This leaves out the obvious problems involved with aging components, aging insulation, and elevated line voltages. The low voltage transformer is the biggest issue with the 32V series today, having the sizzling 5Z4 and regulator sitting half an inch away with today's elevated line voltage doesn't help. And as you mentioned, Vikings and others have similar problems. Using a different mic or tailoring the audio won't roll back the years. And pounding the snot out of a stock old rig is more likely to cause failure.

But it still has the ARRL mandated restricted bandpass in stock form as does every other make and model from the mid 40's onward.

Huh? What power did the ARRL have to mandate anything beyond their offices and membership? Numerous transmitters from that time frame seem to prove otherwise. Sounds like a UFO sighting to me. Show us some proof, big guy. 

To the original question - a D-104 with a known-good crystal element, as discussed on here numerous times, is tough to beat for an off-the-shelf, good sounding mic. It mates up nicely with many old tube transmitters with zero mods including the 32V, and can sound even better with some simple changes to resistors and caps. There's a reason it's been around so long and used by so many. Max results with minimal effort. You can always go nuts if audio is your thing.

[w9ac]

Carl,  re: "last thing needed is another amp. stage."

The MPF102 follower does not have gain.  It is simply a very high impedance transformation to a typically lower impedance, say the 1 meg. input on common tube transmitters of 50's era.
...

The circuits described in this board or "The AM window" show phase switching, bass or treble enhancement, etc. along with simple impedance matching -- and all with one simple FET. 

One can certinly run a crystal element directly into an unbalanced mic cable and into the super hi-Z of an input grid circuit, but then you've got a hi-Z source terminated by a hi-Z destination.  On paper, all is well.  But that hi-Z mic line can then be prone to noise and buzz.  Ever connect a hi-Z crystal mic into a hi-Z input of a tube-based PA system?  Just kick the mic cord and see what happens. 

One benefit of the FET as a source-follower is that it's output is low-Z, generally set by the value of the source resistor.  This can help reduce noise on the mic cable.  For long unbalanced mic cables, take the extra step and treat the cable as a quasi-transmission line and terminate the destination into the same Z as the source Z. 

Paul, W9AC