Mic Pre-Amp

[Ian Maude]

Hi all,
I am currently using my K2 with a Heil HC-5 insert to good effect on
DX.  I was wondering though if I should build a little pre-amp for the
mic?  I notice there is a circuit on the website and I wondered if I
would gain anything from building it?  I don't want to put too much into
the K2 from the mic, I would just like to up the audio a little.

Your thoughts appreciated.

72/73

Ian
--
Ian Maude G0VGS Morecambe Lancs UK | [hidden email]
Sysop of GB7MBC, the Morecambe Bay Cluster
Running Linux and DXSpider | K2 #4044
 
Find out about Summits on the Air!  
Visit the SOTA web site at http://www.sota.org.uk

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[Gilbert J Cross]

         Hi, Ian. I too have the HC-5 element from Heil. A short time ago
I built the mic amp shown on the Elecraft site. I haywired it together
and put it inside the mic housing. It has been a very good addition for
me. I have not experienced any problems and now things work well. Now on
to build the anti- vox circuit by G3RXQ.

                        Gil  K8EAG


On Thu, 21 Oct 2004 11:20:51 +0100 Ian J Maude <[hidden email]> writes:
> Hi all,
> I am currently using my K2 with a Heil HC-5 insert to good effect
> on
> DX.  I was wondering though if I should build a little pre-amp for
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Hello Ian,

I have used a Heil HC-5 element from the very beginning with my K2, and
have always found that I needed to shout into it in order for it to work
satisfactorily. However, that same microphone, a Heil HM-10, worked very
well with my '746PRO.

In my case, I found that the levels were such that in order to overcome
the 'knee' of the built-in noise-gate of the K2's compressor chip, I had
to speak too loudly for comfort. If I spoke in a more normal manner,
only the peaks would make it over the threshold.

I built the single transistor circuit of N0MF, Mike on a 1/2" x 1/2"
circuit board, and just kind of stuffed it inside the HM-10 housing, and
it made a big difference. I can even run the K2 with the compressor off,
and while speaking at a normal level I still have plenty of drive, and
have received quite a few unsolicited positive comments about the audio.

I'd highly recommend you try out the circuit. I think you'll be very
pleased with the results.

73, Dale WA8SRA

Ian J Maude wrote:

>Hi all,
>I am currently using my K2 with a Heil HC-5 insert to good effect on
>DX.  I was wondering though if I should build a little pre-amp for the
>mic?  I notice there is a circuit on the website and I wondered if I
>would gain anything from building it?  I don't want to put too much into
>the K2 from the mic, I would just like to up the audio a little.
>
>Your thoughts appreciated.
>
>72/73
>
>Ian
>  
>

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[Joe-aa4nn]

Hi Ian,

Check http://www.qsl.net/la3za/K2/modAny.html where all official and
unofficial K2 mods are listed.

The Heil mic elements do not offer enough drive and you´re about 6-10 db
down without a modification.  Several solutions are described, yet there is
a simple mod you can make for using Heil mics.  We made these mods on the
K2s we used during the Banaba DXpedition, T33C, as suggested by Frank,
DL4KQ.

If on the mic connector you soldered a 5.6k resistor, remove it.  This is
only needed for electret mics.  You also must jumper the K2 for the Kenwood
mic.

Improving the sensitivity of the input needs to be done on the KSB2 board.
Simply replace R14 with a 5.6 k resistor.

Originally the mic gain settings were:
SSBA 1 = - 6db, SSBA 2 = 0 db, SSBA 3 = + 6db
Now they are (roughly):
SSBA 1 =  0 db, SSBA 2 = + db, SSBA 3 = + 6-10db

Using the SSBA 3 setting you will now have enough level to work with the
insensitive Heil element.  But remember when using other elements you have
to go down in setting to avoid distortions.

73, Joe, aa4nn
----------------------------------
Hi all,

> I am currently using my K2 with a Heil HC-5 insert to good effect on
> DX.  I was wondering though if I should build a little pre-amp for the
> mic?  I notice there is a circuit on the website and I wondered if I
> would gain anything from building it?  I don't want to put too much into
> the K2 from the mic, I would just like to up the audio a little.
>
> Your thoughts appreciated.
>
> 72/73
>
> Ian

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Ian,
 
The mic-preamp works very well.  I built one for my IC-765 which needed some extra help using the HC-5.  I do not use SSB very much with the K2, but I did notice you have to yell pretty loud using the HC-5 with the K2.  The mods do work also, but the little amp works great too.  
 
Lee Buller
SN 1056
 
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