An interesting experiment


I have recently been experimenting with different preamps, as I found a while ago that this seems to be the component that influences the sound of my system the most. Being an EE (and a physicist by training)I was trying to figure out the source of the different sounds that tube and SS give me. I am a firm believer that good designs with modern electronics all sound the same (at least to my ears). As tubes are new to me I studied their specs a little, and recently realized that one big difference vs. SS is their output impedance. To be clear, I am talking about minimalist tube design, where the output stage is driven directly by the tube. As it turns out, tube designs have much higher output impedance. For example a 6SN7/6922 based preamp probably has an output impedance on the order of 8K/3K ohms respectively. While a typical SS would be less than 500 ohm. So as an experiment I put together a passive preamp with a series potentiometer that allows me to change the output impedance of the source. I connected my CD output through this "preamp" directly to the power amp. At this stage after listening for awhile I believe that my new setup sounds a lot like my tube setup (which has an audible illusions M3A pre, and magnepan 20.1s). The curious thing is that I had to dial the output impedance to around 30K ohm, which I believe is significantly higher than the tube pre. I know this setup by all accounts should be bad....

Regardless, to my ears this strange setup sounds excellent. I dare even say, better than with the preamp in the loop.
oferi
to be clear, the I have a 10K POT for volume control followed by a series resistor (also a pot so I can adjust it). After thinking about it I realized that I made a mistake when saying that the amp is rated for 10K. Since each module operates in fully balanced mode there is a single ended to balanced input buffer. So likely the actual input impedance of the amp I am using is higher than 10K.

The setup with the 10K volume pot and 20K series resistor sounded a lot like the AI preamp. But I wouldn't assume it would be the same with other power amps.
Oferi,

Many SS amps designed specifically for good performance with all pre-amps, including tube pre-amps, have 60Kohm or higher input impedance to compensate for higher general output impedance of tube pre-amps. That helps keep distortion minimal and retain good dynamics with most all pre-amps out there, SS or tube.
Oferi your Ice Power amp/s with 10kohm input impedance is not a good match for any passive pre or even some tube preamps.
However your CJ MV60SE is 100kohms input impedance and this is a great match for a 10kohm passive preamp.

Cheers George
This kind of experimenting with various impedance matches is very interesting. Looking forward to whatever general findings or patterns might be detected.
Georgelofi - not a good match by traditional thinking, except it sounds good to him.