2. amps-preamps
  3. 1069295489

Impedance mismatches between pre and amp do this?

I think thats whats happening to my Arcam A65plus (used as a pre) and B&K st-140. Will this harm or damage any of the components in any way?

My system sounds good in the mids but the highs are grainy and sound forced while the bass is completely missing. The upper bass is tight and the detail is still there but there are huge gaps in the sound. Im waiting on a used PS Audio 4.5 preamp which should arrive Friday or Saturday along with some Synergistic Research Alpha Sterling X interconnects. Hopefully all this with my B&K ST-140 amp, Music Hall cdp and JM Labs speakers will bring me the satisfying sound Ive been searching for. Any help or opinions on coming system or causes of crap sound?
bundee1

Showing 3 responses by gunbei

gunbei
2,327 posts
 
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.
gunbei
2,327 posts
 
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!
gunbei
2,327 posts
 
Awesome Bundee! Glad to hear it worked out.

Whether your music should sound live or studio recorded is totally up to you. Many people try to build a system that reveals the "true" nature of the performance. I on the other hand like my music flavored in a distinct way, so I've picked gear that puts me front row, center whether it's a concert hall or a small, smokey nightclub.

In my book there is no proper way except the one that pleases you.

Enjoy!
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