2. amps-preamps
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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
brianmgrarcom
1,317 posts
 
You raise an interesting question that I hope some of those with greater knowledge can answer.

Many times we argue, one says a product is great, another disagrees; I wonder if some of this is due a mismatch, such as impedance mismatches as you mention.

I have read comments before on the importance of this, yet I have know idea what to look for to try and match.
kotta's avatar
kotta
649 posts
 
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.
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.
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