Can audio be feed out of the R-4A bypassing the onboard amplifier?
Yes, you can bypass the internal AF amp stages for headphone/speaker audio,
but they must remain active (see below). I do this with a Marantz 1030C.
The following mod is easily reversible without leaving no permanent
"residue" in the event of a future sale.
1) Add a 1.0 uF cap, positive end to the AF GAIN wiper arm;
2) Connect a length of shielded audio cable to the other end of the new cap,
shield to the chassis;
3) Disconnect the existing wiring to the RCA SPKR jack (dress it so that it
can be easily restored); and
4) Connect the other end of the new shielded audio cable to the RCA SPKR
jack, shield to the chassis.
With this change, the R-4A's AF GAIN control will still remain active to the
external audio amp. Headphone and speaker audio comes from the new external
amp. Tube V7 must remain in its socket for ANTI-VOX operation. The new cap
can be either a low ESR electrolytic or tantalum type. If you're an
audiophile, you'll use the former. Myself, I have no issues using
inter-stage tantalum coupling caps for "communications audio."
Paul, W9AC
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