impedence value.? amp to preamp.

05-05-09: Bob_reynolds
Sorry for being dense, but I don't understand what interactions there would be by adding a resistor bewteen the source and amp. Could you give some examples? Thanks.

Bob, 1stly, who is the question directed to? The forum in general OR to any particular member?
2ndly, not sure what you are asking - you mean what are the ill-effects of adding a SERIES resistor between pre & power?
You wrote "source" which I interpret as CDP/tape-deck/reel-reel/TT, computer, etc but the author was talking between pre & power. So, you mean between pre & power OR source & power amp, as you wrote?
Thanx.

First, start with the source impedance. Then add to it the value of your passive. That is now the source impedance (much higher) at low volumes. A tube amp has a high input impedance- 100K is common.

The result is that the high output impedance of the volume control, with the high input impedance of the amp, and the character of the interconnect cable itself will result in drive difficulties at low volume, because the source impedance will be primarily the value of the control. At higher volumes this effect is reduced. Thus it is to your advantage to not have a whole lot of voltage output (3 volts max) out of your source, so that you can run the volume control near the top! Midway down, and the control is already degrading the signal.

Most CD player manufacturers don't get this simple point, and so put **way** too much output from their players. I've seen them as high as 15 volts- making a passive control useless (if you want it to sound right).

To put some numbers on Ralphs comments, for example, one of those inexpensive Creeks, the OBH-12, has an output impedence of 0 to 50K, depending of course on the amount of attenuation used. Sonic effect would be sort of a crap shoot with this type of attenuator I think.

The result is that the high output impedance of the volume control, with the high input impedance of the amp, and the character of the interconnect cable itself will result in drive difficulties at low volume, because the source impedance will be primarily the value of the control.

Atmasphere - the resistor attenuator made by EVS seems to have exactly the opposite problem. I.E. a higher volumes the sound might be degraded. Take a look @ the link I provided in my prev post.
The EVS attenuator has a 1K in series & uses shunt resistors to provide the attenuation. So, for any attenuation setting, isn't the effective resistance of the attenuator the parallel combination of the 1K & whatever attenuation setting resistor?
So, for normal volume settings, I see that the shunt resistors are very small in value thereby making the effective resistance this shunt resistor value.
It appears to me that this EVS resistor attenuator is correctly made & will avoid the lack of drive levels at low listening volumes.
You agree?