I need some amplifier help


I have an Adcom 555 and an Adcom 555II. Right now I am using them to power a pair of B & W DM640. I am using the 555 for the left ch and the 555II for the right ch. Should I keep it this way or change it to one amp for the low end and one amp for the high end? Just wondering because of the fact that the 2 amps are not exactly the same. Also, am I losing a lot of signal splitting the lefts and rights coming out of the preamp and is there any other way of doing it? I split the left to both ch of one amp and the same with the rights. Any suggestions will be appreciated.
joeseppe
First of all the two amplifiers are not identical and should not be used to drive separate channels. The 555II actually has slightly higher gain than the 555.

If I remember right the Adcom GFA-555 is rated at 200 wpc. The B&W DM 640s are rated to handle a maximum of 200 wpc. Your speakers have a sensitivity rating of 91db and will probably play as loud as you would ever want to hear them with a good 35 wpc tube amp with a bigger sound and better dynamics.
Since both amps are rated 200wpc(though the II may have a slightly higher sensitivity); you should be able to get away with it by using the II as the bottom end amp. Having more power than a speaker is rated for is never a problem, as long as you aren't actually using all that power(highly unlikely, with speakers as efficient as yours). Just don't get crazy with the volume control. If you like the result of the experiment: leave it that way. If not: disconnect. What's there to lose?
you could sell your adcoms and go with a good pair of mono blocs.also a change in preamps could be beneficial.not all preamps give you the same rate of gain.
Your speakers have a sensitivity rating of 91db and will probably play as loud as you would ever want to hear them with a good 35 wpc tube amp with a bigger sound and better dynamics

Maybe better sound? But not better dynamics. The B&W's like power and current.

I would use one for the bass the other for the top. Bi-amping this way is absolutely the best way.

Your speaker will sound better bi-amp ( all will ) the only issue you have to be aware of is the load impedance to your Pre-amp. If your pre cannot drive the combined impedance of both amps the sound could be degraded. Cables make a another big difference here because of such, but absolutely the best way to go if done right...
Could be better dynamics, depends on the tube amp. But if it is true that the B&W need current (low, and variable impedance)they may very well need an SS amp to sound their best.
Yes, definitely put one amp on top and one on bottom. Most definitely....there's no other way.

Could I ask, how did you arrive at your current setup? I mean the amp hookup....

Take care
Chas
"There's no other way?" What he's doing is called, "vertical bi-amping"( http://www.caryaudio.com/articles/bi_amping.shtml ), the other method, "horizontal bi-amping."( http://www.roydaudio.com/articles/bi-amping-royds-passively/ ) Then, of course, there is active bi-amping(which is the best method).
am I losing a lot of signal splitting the lefts and rights coming out of the preamp
You are not "losing signal," but there is a possibility that you could be introducing some degree of frequency response irregularity. There are two possible issues:

1)The GFA-555 is spec'd as having an input impedance of 22K, which is lower than ideal. Assuming the GFA-555II is also 22K, the preamp output for each channel would see a load of 11K. Preamp output impedance should be less than one-tenth of that amount at all frequencies (some would argue for a smaller fraction than that), or significant frequency response irregularity may result.

I could not find specs on the output impedance of your CT-17 tuner/preamp. Since the CT-17 is solid state, I would guess that it has an output impedance of well under 1.1K at all frequencies, but I can't say for sure.

2)The total of the capacitances of the interconnect cables to BOTH amps will affect the signals going to BOTH amps, by interacting with the preamp output impedance, resulting in some degree (probably small) of upper treble rolloff, IF the cables are long AND they have high capacitance per unit length AND if the CT-17 output impedance is high.

If your cable length is not particularly long (say ten feet or less), I wouldn't worry about this. If they are much longer than that, I would make a point of using low capacitance cables. How low is low enough depends on the length and on the preamp output impedance, but as a rough general guideline I would say aim for 30 picofarads (pf) per foot or less if your cables are long.

Regards,
-- Al
Keep in mind both amps sound different.

Yep, having more power than a speaker is rated for is never a problem, unless you are unnecessarily complicating the system and you have two different amplifiers with different input sensitivity.