ICOM IC-706MK2G

19 April 2007 / rev. 19 April 2007

Audio Punch overwork

by Jochen Heilemann (DG2IAQ)

[e-mail]

© 04/2007 by Jochen Heilemann. All rights reserved.

1 / 5

Regarding the “Audio Punch overwork” mod of my ham radio friend DF1ELB, Ernesto,

(published on

www.mods.dk

/ Icom / IC-706) I received this email from him:

Hi Ben,

I have done this mod for the older first version 706 series, but the MKII has a similar
version, I will contact my friend DG2IAQ he has done this mod on his newer unit. I will
get back to you if you wish !

Many greetings to you and belated happy easter !

Vy 73 de Ernesto DF1ELB

-----Ursprüngliche Nachricht-----
Betreff: Re: IC-706 Audio Punch overwork

Hi

the name here is ben nichols. I was wondering is this mod for the Icom
706 Mk II G USA version.
73's
Ben

Ben kk6as

So originally it was the other way around. I discovered the mod for my MK2G model and

we adjusted it for Ernesto’s IC-706 (first model, old version) later.

J

But the result should be nearly the same on both rigs, including the MK1 and MK2 in

between. But for those 2 versions I don’t have a PCB layout so I can’t tell you where

exactly the belonging resistor is located.

The Mainboard-PCB of Ernesto’s “non-MK” and my “MK2” model were totally different. So

I would expect this for the “MK1” and “MK2” as well, but I can’t verify it.

Now let’s do the simple modification which has so much difference on audio dynamics

and loudness and mouth-to-mic-range…

ICOM IC-706MK2G

19 April 2007 / rev. 19 April 2007

Audio Punch overwork

by Jochen Heilemann (DG2IAQ)

[e-mail]

© 04/2007 by Jochen Heilemann. All rights reserved.

2 / 5

We have to raise the value of the DC BIAS resistor (R942) of the electret capsule from

originally 1k up to 4k7.

That’s all.

The 1k is for the DC supply of the electret capsule. There’s one resistor in the RIG,

meaning on the MAIN UNIT. A second one is in the originally HM-103 handmike. The one

in the handmike can be kept like it is. We only change the internally one on the MAIN

UNIT.

Why ?

The DC is feed into the MIC IN line (knot C931), so the DC goes out of the 706 and into

the HM-103 handmike. But this is only the DC “view”.

On the AC view the electret audio goes back from the handmike into the IC-706 and the

audio goes via C931 into the MIC AMP (IC931). But on the AC view the audio also goes

back into R942 (only 1kohms) and is then “connected” via C941 (22µ) to ground. Cause

a capacitor blocks DC, but lets pass AC !!!

If you now look again on the schematic below this means, the audio goes into the MIC

AM via C931, but also (only for the audio = AC) a 1kohms resistor goes directly to

ground (via C941) and destroys a big amount of the audio level of the electret capsule.

This is the reason why you always have to speak very close to the IC-706 microphones

and audio level drops down significantly if you raise the mouth-to-mic range a little bit.

ICOM IC-706MK2G

19 April 2007 / rev. 19 April 2007

Audio Punch overwork

by Jochen Heilemann (DG2IAQ)

[e-mail]

© 04/2007 by Jochen Heilemann. All rights reserved.

3 / 5

The mod is very easy to do (if you’re used to solder SMDs) cause the resistor is located

on the easy-to-touch upper side of the mainboard.

So just open the upper case and see where we have to go now:

ICOM IC-706MK2G

19 April 2007 / rev. 19 April 2007

Audio Punch overwork

by Jochen Heilemann (DG2IAQ)

[e-mail]

© 04/2007 by Jochen Heilemann. All rights reserved.

4 / 5

Now remove R942 (1k) and solder a 4k7 there instead. You can use a SMD type as well

or a common 1/8W one. It’s on your decision and ability.

I used a SMD one and placed it vertically.

ICOM IC-706MK2G

19 April 2007 / rev. 19 April 2007

Audio Punch overwork

by Jochen Heilemann (DG2IAQ)

[e-mail]

© 04/2007 by Jochen Heilemann. All rights reserved.

5 / 5

Before:

After:

SMD type

placed vertically

to solder