"Jim Lesurf" wrote in message



I'm not sure if things have changed. However the normal assumption for
domestic audio sources in the 1970's and 1980's was that the source
(CD player, Tuner, etc) should work as per spec into loads down to
10kOhm in parallel with 1000 pF. The assumption being that any preamp
input would have an impedance that was this, or higher.

Agreed. AFAIK 10K and 1000 pF was the standard IHFM testing load for
line-level outputs. 1000 pF represents about 30 feet of standard shielded
cable.

So far as I know, 600 Ohm input impedance would be unusual in domestic
equipment.

600 ohm input impedance is unusual even in pro audio gear. Most pro audio
gear has an input impedance that is 2,000 ohms or above.

Although I think some items may use it with balanced inputs.

I know of no cases where pro audio gear has an input impedance that low.
Even mic inputs bottom out around 2K.

If so, I'd assume the source would then be expected to use a matching
output.

Most pro audio gear has an output impedance of 75-150 ohms, and can deliver
an undistorted +4 (abouit 1.25 volts) or greater into a 600 ohm load. Into
more typical loads, pro gear can delover 2 - 10 volts. Most pro gear can be
driven to full rated output with +4.

Hence in domestic practice. I would assume that having a 600 Ohm load
on a normal single-ended output would be unusual and not recommended.

Totally agreed.