It should be noted that the above mod is only intended to provide a line level input, but not necessarily HiFi line level input. I decided to try this mod myself and discovered this first hand. If you only replace C154, C158 and C161 as described above, you end up with a low end roll-off that's still well above that of the mic input.
This appears to be mainly due to the emitter shunt capacitor C159 on the ACC2 buffer amp formed by Q42. It's 10uF, while the equivalent cap on the mic pre-amp (Q251) is 47uF. This causes the gain of the amplifier to roll off at lower frequencies. To shift the cutoff frequency down to an acceptable level, we need to increase C159 a lot.
Thus, I humbly suggest that the above modification be amended as follows:
On the IF unit (X48-3100-00):
1) Change C154 from .1uF to 4.7uF
2) Change C158 from .1uF to 4.7uF
3) Change C161 from 1uF to 4.7uF
4) Change C159 from 10uF to 220uF
On the signal unit (X57-4130-00):
5) Change C152 from 1uF to 4.7uF
Once these hardware mods have been performed, and before you slap the bottom cover back on the rig, you should also do the 12Kc LC filter adjustment that's documented here:
http://www.voodoo-labs.com/index/sdxmod ... termod.htm
(The short story: you need to adjust L28 and/or L29 on the IF unit for loudest noise in the receiver. This should only take a minute to do.)
Note that in my case, I found some 4.7uF electrolytic caps small enough to fit under the IF unit, and I soldered them in parallel with the existing SMD chip caps. Doing it this way saves you from having to unsolder the old caps, which is difficult without proper tools.
Once the radio mods are complete, you'll need to interface your audio gear. The ACC2 port uses a 13-pin DIN connector. Several suppliers have these. I got mine here:
http://parts.digikey.com/1/parts/264899 ... d-130.html
In my case, I took a spare 1/4" unbalanced patch cable, chopped off one end, and replaced it with the 13-pin DIN connector above. The audio line (tip) goes to pin 11, and the shield goes to pin 12.
Lastly, to connect balanced output of my audio rack to the unbalanced line level ACC2 audio input, I used this:
http://www.guitarcenter.com/Radial-Engi ... 1527435.gc
This device has RCA, 1/4" and 3.5mm TRS unbalanced output jacks. I used the 1/4" one since I had the cable handy.
Note: if you're still not satisfied and want to "go deeper," then you can try the following:
1) Use 470uF for C159 on the IF unit instead of 220uF
2) Instead of the PRO ISO, use the J ISO:
http://www.guitarcenter.com/Radial-Engi ... 1527434.gc
The above unit has the same Jensen transformer that's recommended for the official TS-950SDX TX mod. The PRO ISO unit uses transformers made by Radial, which are actually quite good, but the Jensen ones are the gold standard. It's decidedly more expensive though. You can read the spec sheet for both of them here:
http://www.radialeng.com/pdfs/manual-j-iso-pro-iso.pdf
One more tip: when operating the radio using the ACC2 input, press the desired mode button twice. For example, if you want to operate in LSB mode, press the LSB button twice. On the second press, the 'DATA' indicator should light up in the display, and the mic input will be muted. I do this so that I can connect my MC-43 hand mic to the radio and use it as a hand switch without getting any pick-up from it.
In my opinion this mod results in audio response that's just as good as what you can achieve with the official TS-950SDX VooDoo TX mod, without requiring you do drill a hole in the back of the radio. The only down side is that the audio still passes through two transistor amp stages, which may offend the delicate sensibilities of those who prefer to use tubes to put the voo in their doo.
-Bill
