ICOM IC-706MK2G
19 April 2007 / rev. 19 April 2007
Audio Punch overwork
by Jochen Heilemann (DG2IAQ)
dg2iaqmods@freenet.de
© 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)
dg2iaqmods@freenet.de
© 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)
dg2iaqmods@freenet.de
© 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)
dg2iaqmods@freenet.de
© 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)
dg2iaqmods@freenet.de
© 04/2007 by Jochen Heilemann. All rights reserved.
5 / 5
Before:
After:
SMD type
placed vertically
to solder