Impedance mismatches between pre and amp do this?

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!

I received my PS Audio 4.5 pre yesterday and hooked it up to my B&K ST-140. All connections were made with Synergistic Alpha X ics and speaker cable. The sound in Straightwirde mode is very clean and smooth with good presence. The bass is tight and full and the highs although slightly rolled off are very clean. Soundstage width isnt incredible but acceptable, while depth is better. Instruments are all equally represented with the only emphasis being on vocals. They are firmly centered and clear, giving the music a more "you are there" feeling.

This brings up an interesting dillemma for me. Is music supposed to sound like a live performance or a good studio recording. With my Arcam the music sounded like a great recording (with the exception of harsh highs, prompting the switch). With my new setup the music sounds more natural. Both are enjoyable but different.

I dont use the active high level mode because the bass sounds gritty and loose. Thank God everything seems to have worked out with this new preamp (knock on wood). Now to buy more music. Thanks for all the help guys.