Modifications for Icom 706 Mark 1, Version 1.1 Dirk Schray, DG3DIS 12.5.05

www.schray.de

/ [e-mail]

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Audio modification for Icom 706 (Mark I) by DG3DIS, 12.5.05

The original setup of icom´s 706 has a very poor audio quality on tx and even on rx. So i

tried to improve this a little bit.

All the parts in this rig are smd and very very small, so you should
have some experience in smd-soldering, you can easily destroy
your transceiver by doing this mods !!

Receiver modifications

• better RX-Audio on SSB (more basses and higher lowpass frequency)

• better RX-Audio on FM (more basses and higher lowpass frequency)

• better sensivity on VHF-frequencies outside 144-146 mhz

(for NOAA or airband RX)

• change agc-time (faster)

Transmitter modifications

• more basses in ssb and fm modulation

• cooling-fan adjustment

Modifications for Icom 706 Mark 1, Version 1.1 Dirk Schray, DG3DIS 12.5.05

www.schray.de

/ [e-mail]

- 2 -

1.) FM Receiver modifications (only narrow-FM)

The original FM-NF Filter has a cut-off frequency of 400-500 Hz.

All parts are on the Main-Unit, the pcb under the speaker. Remove all cables, mark all

three coax-kabels bevor removing. The

red marked

parts have the biggest effect.

Part Nr.

original value

changed value

C 184

(100 nF)

→

4,7 nF (C ist an IC12b)

C 182

(10 nF)

→

4,7- 22 nF

C 181

(10 nF)

→

10-22 nF

New FM-

Filter

:

After doing this mod you can hear some distortion on very strong signals (>9+60 dB).

Modifications for Icom 706 Mark 1, Version 1.1 Dirk Schray, DG3DIS 12.5.05

www.schray.de

/ [e-mail]

- 3 -

2.) SSB Receiver modifications

original SSB-Filter:

All parts are on the Main-Unit

Part Nr.

original value

changed value

C 162

(100 nF)

→

47 nF or 39

C 442

(22 nF)

→

4,7 nF (only small effect)

2.) FM/SSB transmitter modification

All parts are on the Main-Unit

Part Nr.

original value

changed value

C 169

(4,7 nF)

→

100 nF

C 218

(33 nF)

→

66 nF (simply solder 22nF oder 33nF over C218)

C 428

(100 nF)

→

1 μF electrolyt, - to IC 22, + to R 493

3.) Microfon modification

open microfon and remove electretmicrofon. Drill a small hole (4mm) to the outside and

mount electretmicrofon. Sounds more naturally.

4.) Cooling-Fan adjustment

after this modification the build-in fan only runs fast when tx on shortwave. The fan is

does not switch on when transmitting on 2m.

Remove big R65 (47Ω) (on PA-Unit, near fan) and replace with 100Ω

Modifications for Icom 706 Mark 1, Version 1.1 Dirk Schray, DG3DIS 12.5.05

www.schray.de

/ [e-mail]

- 4 -

5.) better rx on vhf outside 144-146 mhz. (for noaa or airband-rx)

All parts are on PA-Unit

Remove C53 (20pF) and C153 (12pF). Solder removed 12pF over C152(20pF).

This mod has no influence on 144-146 m bandfilter but now you have much more

sensivity outside the band

6.) change agc-time

. The agc-time is very slow, even on “fast” mode. This helps:

All parts are on the Main-Unit

Part Nr.

original value

changed value

C141

(10µF)

4,7µF or 3,3µF

7.) Change ssb-carrierfrequency. Makes your ssb-modulation brigther oder darker.

Change to ssb

Push [disp]-key for 2 sec. [set menü]

Push menu-key until you get to Q4 [carrier-freq]

Change frequency with vfo-knob.

Negative values make your modulation darker, -120 is a good value

After all the TX-Audio modifications you have to readjust your mic-compressor gain !!