Impedance mismatches between pre and amp do this?

Moving equipment,IC's, spk.wires around will result in thin sound until things settle down and a certain warmth/fullness should return. How large of a room are these spks in? Most of the ss int. amps I've used w/my JM Lab spks. resulted in less than what I've been looking for. I have the Chorus 705's in a downstairs basement system which sounds superb w/an 80's based Sony int. amp./tuner/tape-deck/and a late 80's NEC CDP.(Cost of electronics less than $200.) Mid-level IC's/spkr. wires. In this set-up, in this room (12'x14') the sound is really great. I hope your new pre-amp does the trick! Keep us posted. Bill.

I tried to find some specs on you gear. I found tech specs for the Arcam A65Plus, but not the B&K ST-140. The closest I could find was the ST 125.1/2/3

For the Arcam A65+ preamplifier outputs are listed as, nominal output level 510mV and output impedance of <3 Ohms.

I found that the B&K ST 125 series has a an input impedance of 33.2kOhms. I'm not sure if this is the case with your ST-140.

Usually the ratio that is bandied around here is output impdeance of the preamp to input impedance of the amp of between 10-100:1.

Usually you run into problems if the ratio is smaller than this, such as the sonic abnormalities you described. I've had them too. However, <3 Ohms to 33,200 Ohms exceeds 10,000 to 1!

I don't know if I've arrived at the correct ratio, but this seems to be an incredibly high number. Maybe other forum members can clear up what I've offered.

There have been a few forum members that have had great success with the ST-140. The output impedance of the Arcam seems to be much lower than anything I've seen. I wonder if the problem could be with using the A65+ integrated as a preamp.

I've also experienced Kotta's example of cable movement to cause the same phenomena.

I hope this helps.

Thanks for the help guys! Im one day closer to finding out. From the specs you quoted and the sound Im getting it sounds like a mismatch. Someone on another board suggested the Arcam was running in passive mode and it sucked as a preamp. I guess the real beauty of the Arcam is the amp section but the highs in combo with the JM Labs kill it. I just received my 2nd pair of Synergistic Research Alpha X ic's (well packed but box was mangled by FEDEX!) Hopefully that will help a little. Any other ideas or suggestions on the system? Thanks again!

The preamp section of the Arcam is a passive unit? I didn't realize that. THAT could explain the whole thing.

A 33K Ohm input impedance for a power amp might be a bit too low being fed by a passive pre, especially if the output voltage on your source is less than 2V. Your amp would probably need to be in the 47K-100K Ohm range.

Good luck!

Im not sure if it is but someone else on another board said it was. Do those numbers coincide with a passives ouput? Im taking it with a grain of salt but who knows? Anyway Im anxiously awaiting my PS Audio 4.5 preamp. Ill let you guys know how everything turns out when I hook it up Saturday (knock on wood). Thanks for the help!