[CQ-Contest] Dynamic Mic. Pre-Amp?

Sat Aug 1 10:18:30 EDT 2020

Thanks Jim for the info on the Behringer possible Issues.

BUT.. I am looking for ideas of a Mic. pre-amp.

Now some here may have seen the BAD Can-O-Worms that happened on a 
certain contest club E-Mail list. I do NOT want that to happen here. 
Please....

But the reply you made below about being not needed is not 100% true. 
This is where all the fighting and arguing started.

This has to do with specific items. Mainly these three.

1- A Heil HC-4 Mic.  NOT a HC-5 or any other Mic but a HC-4 and ONLY 
talking about a HC-4.

2- An Icom IC-7300.  NOT a 7000, or a 9100 ONLY talking about an IC-7300.

3- A typical DELL Windows 10 Desktop computer, with a soundblaster 
soundcard.

The story goes, I bought one of the last headsets that Heil made that 
still had the HC-4 element in it. I love the sound, it is very similar 
to the old school Astatic D-104 or the Shure 444. Awesome!

And on my Old Kenwood TS-430S It works great with just the simple 1mf 
phantom power blocking cap that Heil recommends. But that old Kenwood 
was designed to work with low level output mic's.

When we wanted to do a Multi op effort in Phone SS we wanted to for sure 
use that headset and mic.

But when we tried to use it on the stations IC-7300 the modulation was 
extremely Low. Doing research we learned like on many web sites, and on 
the Facebook 7300 owners page this is extremely common.

It is sooo common, that even Bob Heil right on his website even 
specifically covers the subject and says.

Max the Mic Gain, and use the compressor as a secondary mic gain to get 
enough drive! HEIL EVEN SAYS THIS!
right from their site......

  All Things iCOM

      Microphone Basics

      DSP and Mic Gain Settings

When using a dynamic element on rigs like iCOMs, which were designed for 
electret microphone elements, one must not be afraid to do two things: 
_*(1) utilize the full range of Mic Gain available*_, and *_(2) turn on 
the Compression, using the Compression Level control as a secondary Mic 
Gain control if necessary._*

I was told and I abbreviate here, this statement is pure "BS" Even tho 
it is copied from Heils own site.

I tried to explain That maybe for those that it works for are yellers. 
Guys that always talk very loudly into their mic's. I see it when doing 
multi op's all the time. And they don't even know or think they are 
talking loudly. Like this guy, he doesn't seem loud yet he is talking so 
loud you can hear his voice bouncing off the walls. And as his 
excitement grows he gets even louder!

https://youtu.be/THXCA-6S_Fc

There under 99% circumstances in my 45 years of being a Ham, I have 
never had to talk that loud EVER!
We always talk at a level that is clear and pronounce as well as 
possible yet at a volume level that as long as we are wearing headphones 
our speech is low enough that the others in the multi op effort can 
actually sleep in the same room!

There never should be a need to have to speak this loudly as in that 
video. NEVER should it be needed.

Plus, when we wanted to record wav files for CQ's etc. the HC-4 with the 
blocking cap of course, even with every gain maxed out on the computer, 
there was not enough audio.

So the station owner hooked up that Behringer,
now the Behringer XENYX 802 has a switchable Phantom power option, which 
is good because you can't apply any power to a dynamic mic. It may or 
may not hurt the mic. At best it makes it not work at all. At worst 
could smoke the thing.  And the Behringer XENYX 802 unit if it put power 
into the dynamic mic, to the Behringer XENYX 802 unit the HC-4 looks 
like a dead short, and it could even smoke The Behringer itself.

SO to play it safe Steve put between the Mic, and the Behringer XENYX 
802, an Isolation transformer. Heil says to just use a 1Mf cap. anyway 
this seemed better anyway it provided the isolation from any Phantom 
power if it should by accident get turned on.

PLUS this unit looks like it is also an Impedance Transformer unit also.

First impedances

The Mic. states it is a 600 Ohm unit.

The Behringer XENYX 802  says it likes a Minimum of 15K ohms and Optimal 
is around 100K ohms.

Quite a bit of mismatch. Now this isolator/transformer I can not find a 
LOT of data on. like ratios of transforming or how it even works because 
the labeling is somewhat confusing.
Make & Model, Radio Shack, 2740017

I know this group won't pass images, but I have the schematic for it, 
and it shows it and how it can be made to transform high or low.  but 
it's somewhat confusing.

Anyway the Behringer and this isolator/transformer worked and worked 
great. We saved a lot of voices from not having to talk LOUDLY. I mean 
the guy operating could be soo quiet that people still in the room gould 
be like 6 feet away, and not understand what he is saying because it is 
too faint.

It is just that it the Behringer is way overkill and large.

A recent QST article describes this exact problem and how to make a 
simple pre-amp to fix this.

A mic preamp for using a dynamic mic with radios designed for electrets 
in the Hints and Kinks column of the Dec 18 QST I think it was 2018 year?

He made it very simple, but when we tried we had RF issues getting into 
it that we just could not fix.

Just looking for ideas of alternatives, and even withwhat is happening 
with the Behringer and that transformer thing.  being 600 ohm mic and 
way high impedance on the amp.

Joe WB9SBD

On 8/1/2020 2:03 AM, Jim Brown wrote:
> On 7/31/2020 8:51 AM, Joe wrote:
>> Has anyone here used a Behringer XENYX 802 as a pre amp for a low 
>> level output Dynamic type of Mic?
>
> A preamp is un-necessary for dynamic mics in nearly all modern ham 
> rigs (i.e., within the last 50 years). All that is needed is to wire 
> it correctly.
>
> In the pro audio world, Behringer long ago earned a reputation for low 
> build quality, lousy support, and poor business practices. There are 
> plenty of good alternatives.
>
> 73, Jim K9YC
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