Question about Bi Amping Requests

My system consists of

ML Requests, new panels new woofers and lots of internal MIT caps Cardas wiring etc, Krell KSA 250, Alchemist UK Tim Di Paravicini pre amp separate power supply, Huyuan CD player. I am amassing a vinyl collection as I save up for a table/arm/cartridge.

I am considering bi amping the Requests.

I understand the "every amplifier requires a certain voltage in for maximum output, and that all amps are different in the regards" equation.

Simple solution, find another KSA 250 in which case the volume level balance between the panels and the woofers will be as it is now. Perfect.

Not so simple solution, use maybe a tube amp to drive the panels and the KSA 250 for the woofers. In which case there most likely will be a volume level balance change between the panels and the woofers. Chances are slim to none that (for example) the tube amp will be identical to the Krell with voltage in for maximum out. In which case i need to find a tube amp with gain control.

Are my assumptions correct?

Any suggestions or ideas will be greatly appreciated.

Hola. You could match your Request with no problem with different amplifiers. What you have to be careful, is to have almost the same input sensitivity or find an amplifier with volume controls for each channel. Some amplifiers with an input of 0.775v you have maximum power output, others with 1.4V you get maximum output. So, if you have different input sensitivity, the panel will not sing and you will get too many bass info, or opposite. You need the volume knobs to control this difference in level. Trust your ears and judge the amount of bass energy you want or vice- Also, with the aid of an electronic crossover you can have this solved. Happy listening!

I am against biamping with different amplifiers, but if you do, make sure borh amplifiers have the same gain.....
With a Krell 250 I wouldnt biamp at all.

roberto said:

Hola. You could match your Request with no problem with different amplifiers. What you have to be careful, is to have almost the same input sensitivity or find an amplifier with volume controls for each channel. Some amplifiers with an input of 0.775v you have maximum power output, others with 1.4V you get maximum output. So, if you have different input sensitivity, the panel will not sing and you will get too many bass info, or opposite. You need the volume knobs to control this difference in level. Trust your ears and judge the amount of bass energy you want or vice- Also, with the aid of an electronic crossover you can have this solved. Happy listening!

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With different amps you have to also know whether they are inverting or not. If one is inverting but the other is not, you have to compensate by flipping the speaker leads.

Yup... another possibility. Thanks Bernard. Happy listening!

Thanks Roberto, I do understand about active crossovers, but if I go that way, and go pre amp to xover, then to two amplifiers, does the existing ML xover still not get in the way of the signal?

Hi Nielsen, I am somewhat on the same page so far, as far as same using the amp goes, and i take your comment, "With a Krell 250 I wouldnt biamp at all." as a vote of confidence in the Krell, but might it not be sonically beneficial if one KSA 250 only had to deal with the woofer, 180HZ and down, and the other only had to deal with the panels 180HZ and up?

I am often amazed how well the Krell does keeping the bottom end fast tight and detailed while still dealing with high transient snare drum snaps and guitar twangs and out front vocal passages all going on at once.

Maybe your point is, for the cost of finding another KSA 250 in mint shape inside and out the audible improvement would be minimal.

Thanks for your comment.

Thanks Bernard, whatever decision I make I will keep your suggestion in mind.

I do understand about active crossovers, but if I go that way, and go pre amp to xover, then to two amplifiers, does the existing ML xover still not get in the way of the signal?

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Short answer is YES, the existing ML crossover will get in the way. Solution: Follow this thread to remove the crossover if you're handy with soldering iron.
Passive Crossover bypass Quest/reQuest

...but might it not be sonically beneficial if one KSA 250 only had to deal with the woofer, 180HZ and down, and the other only had to deal with the panels 180HZ and up?

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Given 2 KSA-250, I would have each KSA-250 driving one reQuest speaker in a vertical bi-amp configuration. For example, left channel of KSA-250 drives the panel, right channel drives the woofer. In this scenario, you'll have complete separation for left and right channel.

I think you got it wrong Spike. Vertical biamp is when one amplifier drives one speaker, and the other amp drives the other one. Vertical is superior to Horizontal.
This way the amp also pumps out more power since the power supply only does one channel. Stereophile tested, a long time ago, for instance the Parasound HCA1000, and I believe it gave 125 watts in 8 ohms with both channels driven, but 150 with only one channel in use.
You might also look at Emotiva if you want some value for money. (dont know what the Krell goes for these days)

This is what I mean. I think it fits the description for vertically bi-amping, according to this audiokarma link: Bi-Wiring & Bi-Amping. Did I miss something?

No Spike, apologies, I read you post wrong, my bad...

But, I wouldnt do that personally, I would use one channel to drive the whole speaker and leave the other channel with nothing to do.

Thanks to everyone who took the time to help me understand the issue of biamping.

If my following assumptions based on everything everyone has said here and what I have read elsewhere are correct I/we can move on to my bigger question that I will post soon.

Scenario 1

(Making the assumption that each Krell KSA 250 is essentially two amplifiers in one chassis.)

I find another KSA 250, and use one amp to drive only the panels in stereo and the other amp to drive only the woofers in stereo, maybe this is called horizontal biamping.

Or use one amp per speaker,one channel for left panel, the other channel for the left woofer and then do the same for the other speaker with the other amplifier.

In either the scenario whatever amplifier channel is driving a panel, it does not also have the burden of driving and controlling and starting and stopping a woofer. Vise versa whatever amplifier channel is driving a woofer it does not also have the added burden of driving a panel.

Scenario 2

I buy a different amp, (maybe a tube amp for the panels) making sure this new amp has gain controls to balance the volume between the woofers and panels. And in this case the ONLY option is to use one amp to drive only the panels in stereo and the other amp to drive only the woofers in stereo.

Is what I said correct?

Thanks again Roberto, Nielsen, Bernard, and Spike

retiredelectrician,
Yes, I think you have a grasp of the different bi-amp configurations. FYI, my system falls into the your scenario 2 (horizontal bi-amp with tubes on the panels). For attenuation, I am using a fixed value 6db RCA modules from Harrison Labs.

Spike, I'm surprised that a fixed attenuator works fine. It would be interesting to measure the outputs of both amps to see how close a match you get.

Wow Spike... that must be a very nice sounding system! Congratulations. I love the bass of the Classé. Big power amp you have, robust and very dynamic, and tubes to the panels, very clever. Your diagrams are very easy to understand. Thanks for your patience to make them for us. Happy listening!

Hi Bernard,
According to specs, the Classe' CA-300 has 29.5db gain. Talking to Dennis Had, the SixPacs hovers around 22-23db gain. So, a 6db attenuator works just fine for this combination.

thanks for the additional info

I will now determine how I will proceed

Spike, those are great drawings of horizontal & vertical Bi Amping!

Spike said:

retiredelectrician,
Yes, I think you have a grasp of the different bi-amp configurations. FYI, my system falls into the your scenario 2 (horizontal bi-amp with tubes on the panels). For attenuation, I am using a fixed value 6db RCA modules from Harrison Labs.


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Spike - do you have some kind of splitter that is attached to the left and right channels (I am guessing two splitters - one each for the left and right channels) of the pre-amp?