Need help with mic specs vs mixer/ preamp gain specs - makes no sense to me

[DMOD]

No mods to the 32V-2, standard mic input circuit.

OK, then see page 2 of the pdf file.

There is a "Behringer DEQ2496 EQ/RTA Mastering Processor " in the rack for use with this, but it is not on-line while I tinker with the basic signal.

Yep. DO the basics and get the input audio levels to the 32V set before putting any junk in between.

[KJ4OLL]

Cool!
Thanks very much, trip to Skycraft Surplus later in the week to find resistors.

[DMOD]

Owing to the fact that your M67's VU meter is calibrated for near 600 ohm loads, the loading resistor value on the M67 should be 680 ohms.

Phil - AC0OB

[W9ZSL]

I went through the same hassle when I attempted to use a dynamic mic with my DX-60B.  The first problem is going from balanced to unbalanced as in the mic input. The second is trying to convert a low output mic to high output as found in a crystal type and the third problem is matching impedance.  I almost went nuts because nothing seemed to work.

You can go into a mic preamp / mixer to boost the gain as with the M67 but then what?  If you feed the transmitter mic jack, it's unbalanced.  The mic output of the M67 won't match the Collins input as far as voltage is concerned. It would be too low.  By rule of thumb, it's totally possible to feed a very high input impedance like the 1 meg+ of the Collins with something lower, say 50K or more.  In my studio, I have some gear that is unbalanced and about 50K input and I actually feed it with an unbalanced 600 ohm source!  My entire studio is unbalanced and is totally functional and QUIET.  Another rule of thumb for consumer gear is use 47K ohms input as a benchmark.

Theoretically you could try taking the 600 ohm output of the mixer, take the #2 binding post as your "hot", short #3 to ground and unbalance the output...a common practice, and then feed directly to the Collins.  That eliminates the balanced-to-unbalanced problem.  Next you would have to insert a volume control or cut the master on the mixer down to nearly zero.  Driving a high impedance input with a low impedance source always works provided both are unbalanced.  That would solve the level problems.

With an input impedance on the Collins of over 1 megohm, and a crystal mic such as an Astatic D-104's impedance of only 5,000 ohms, you don't need any math to see how unbalanced, low to high works.

All you have to do is worry about levels.  Just keep in mind, there is nothing sacred about balanced audio lines unless they are really long.  You certainly can feed the output of the last device in the chain to the volume control inside the Collins, but guess what?  It would be unbalanced.  If you went that route, you wouldn't have to do anything but short out one side of the balanced output of the last device in the chain and have at it...you wouldn't need anything in between regardless of impedance.  Just don't try to drive a device with low impedance input with one with high impedance output.

[DMOD]

Next you would have to insert a volume control or cut the master on the mixer down to nearly zero.

On the M67 you have two level controls: the Mike Level (internal 50k ohm pot) for each of the four mic channels and the output level (Master control pot) to control audio output levels, plus the gain pot on the 32V; Plenty of level control available for the 32V.

With an input impedance on the Collins of over 1 megohm, and a crystal mic such as an Astatic D-104's impedance of only 5,000 ohms, you don't need any math to see how unbalanced, low to high works.

Actually, the D-104's output impedance is 1 to 3 Megohms depending on the vintage:

http://amfone.net/Amforum/index.php?topic=8975.0

Historically, most older transmitter speech amplifiers used 470k to 1Meg or greater unbalanced inputs.

K4KYV feeds his mike into a HiZ speech preamp balanced from the balanced output of his D-104. There is no rule that says you have to use an unbalanced connection for a D-104.




Phil - AC0OB

[MikeKE0ZUinkcmo]

In reference to Phil's statement;





I just use an Astatic D104, with a simple mic pre-amp driving a transformer coupled output to whatever transmitter I'm using.  FET input Emitter follower, level control, 60db gain in 20db chunks, 150 Ohm balanced/un-balanced output.   Allows me to use virtually any conventional transmitter and/or microphone combination.  

[w1vtp]

Why try and inject line level audio into the mic input on the 32V?

As Steve said, feed it into the high side of the audio gain pot or into the cathode of the second audio stage. No need to buy a matching transformer. The Shure M67s were widely used in remote service in broadcast. They are nice units.

Al VE3AJM

This is what Tim HLR did with my 32V1 and I get good audio reports.  Most cannot tell the difference between my 32V1 and my class E transmitter.  My AF system is 1) EV RE15, 2) dBx 286s and the output goes in the "line input" of the 32V1.

Al

[W9ZSL]

I stand corrected.  The 5,000 ohm impedance apparently is the output of the amplified version.

[flintstone mop]

Why try and inject line level audio into the mic input on the 32V?

As Steve said, feed it into the high side of the audio gain pot or into the cathode of the second audio stage. No need to buy a matching transformer. The Shure M67s were widely used in remote service in broadcast. They are nice units.

Al VE3AJM

This is what Tim HLR did with my 32V1 and I get good audio reports.  Most cannot tell the difference between my 32V1 and my class E transmitter.  My AF system is 1) EV RE15, 2) dBx 286s and the output goes in the "line input" of the 32V1.

Al

There's no beatin WA1HLR, Timmy. The guy has a golden ear for audio and can run circles around most of when it comes to RF.
Anybody get in any QSO with Tim lately??

Fred

[DMOD]

Anybody get in any QSO with Tim lately??

Fred

I heard him the other nite on 3.885 with K4KYV and W4BVT, but was working on the Viking II-CDC, and by the time I got over to the Ham station, the atmospheric noise made it impossible to contact anyone.