Question on Bi-Amping

[pvannest]

I am considering bi-amping my system.   Looks like my better half is going to get me a new Class D audio amp for Christmas to replace my older Adcom GF545.    That in and of itself is great, but it got me to thinking about using both of the amps, since there really isn't anything wrong with the Adcom..     That said, I do have a few questions.   First is that the Class D audio is capable of over two hundred watts per channel and the Adcom is capable of over 100 watts per side.    The nice thing about the Class D amp is that is has output gain controls on the back of the amp.  As a result,  I should be able to match its' output to the Adcom's.    Could be a bit tricky but I think is should not be that difficult.   Would that make sense or am I going the wrong direction with that?

The second question that I have is that I have a Beepre.   It has one set of RCA's out.    Do I just use a Y connector or cable into the different amps or is there some else that I should do to split the signal?

PS.  my speakers are already set up for bi-amping.   In fact from what I have read they do respond nicely to it.

[Grainger49]

Yes, a simple Y-connector will do.

But there are two other things you will need.  You will need a level control for one and maybe both amps.  The Adcom and Class D will not have the same gain, much less the same power.

Also, you need to play with phasing.  One might invert phase and the other not.  If this happens and you wire red to red on both sets of speaker inputs there will be a discontinuity in the sound.  Swapping one amps connections will correct it.  You will know when it is right, the sound goes together.  The highs and lows don't sound like there is a hole between them.

[pvannest]

Thanks Granger.   The Class D does have a level control on the back of the amp.  That might work by itself but if not, there is more than one way skin a cat.  The amps themselves are radically different from each other.  The Adcom's claim to fame is its ability for high current output.   I don't know enough about the Class D though.   It has received really good reviews from many different sources.   The bottom line is that I have a very good synergy with my current set up and with luck will make it even better.    Do you know or have any input on the class d?



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[RPMac]

I too have a BeePre to build and want multiple outputs...2 sets for bi-amping and a third for dual subwoofers(only need one input for a BH-DAC...if Doc will stop letting the smoke out of the prototypes )

 Would it be better to isolate two of the outputs with 1K resisters?

[Paul Birkeland]

I too have a BeePre to build and want multiple outputs...2 sets for bi-amping and a third for dual subwoofers(only need one input for a BH-DAC...if Doc will stop letting the smoke out of the prototypes )

 Would it be better to isolate two of the outputs with 1K resisters?

You can if you want, there's nothing wrong with building the BeePre with no balanced outputs and two single ended outputs. 

[xcortes]

Mine has four SE outputs (and I need more!).

[RPMac]

I don't foresee me needing balanced outputs.
Xavier, do you use resisters to isolate the outputs?

[xcortes]

Nope

[xcortes]

Here's a a pic

http://www.bottlehead.com/smf/index.php/topic,3910.msg37066.html#msg37066

[ssssly]

What speakers are you using?

Class D amps produce high frequency radio waves as a byproduct of amplification. So if the tweeters are super sensitive you can pick up the radio waves as interference.

They also have pretty limited dampening factors. So they aren't great for use with speakers that are large or have a long travel. They just can't control the cone and sound all loosey goosey.

For mid size speakers in high Q enclosures they sound pretty darn good. Have a nice little trio of 8" subs that I run off a class D amp. The high Q keeps the speakers in line and matches well with the amp for a good tight sound.

I would also suggest setting the gain properly for the wattage of the speaker and then utilizing a passive attenuator to tune volume levels. Due to the above mentioned dampening issues, class D amps are more picky about gain levels than other amplifier classes. And if you use the gain as a volume control instead of a gain control it will likely lead to poor sound.

[Paul Birkeland]

They also have pretty limited dampening factors. So they aren't great for use with speakers that are large or have a long travel. They just can't control the cone and sound all loosey goosey.

I think this really depends on the amp itself.  Something like the smaller Hypex Class D amp has a damping factor of 400 at 8 Ohms, and I think even the little Tripath amps are up pretty high as well.