Matching the sensitivity of two amps for bi-amping

Nikmilkov

I ran 20watt single ended (SET) tubes on the mids and highs of esl's and then used a 300watt transistor with input gain pots for the bass driver.
Then for the master preamp I use a passive pre to drive both amps. (In your case you'll be using you active CJ pre which is no trouble maybe even better load wise)
This was very successful, because the transistor amp was higher in sensitivity than the tubes and therefore able to be gain matched with its own input pots to the same volume of the lower sensitivity SET tube amp, and then the passive pre became the master volume control.

Cheers George

Hello Nik,

First, to be sure it's clear, "higher sensitivity" = a lower sensitivity number, assuming that sensitivity in each case is defined as the input voltage required to drive the amp to its maximum rated power.

Second, per my earlier comments you don't necessarily need higher sensitivity. What you need is higher gain (assuming the amp provides a volume control). Assuming that the low frequency amp will be considerably more powerful than your present 8W amp, having higher sensitivity (defined as the input voltage required to drive the amp to its max rated power) would also assure that the higher powered amp has higher gain. However, you would be unnecessarily limiting your choice of amplification by choosing based on sensitivity rather than gain. Perhaps severely limiting it.

Finally, I suspect that any McIntosh amp you might choose would be far more powerful than your present 8W amp. If you were to passively biamp such a combo (i.e., without a crossover "ahead" of the amps), using the Mc's volume control to gain match, as I indicated earlier you would not be able to turn the preamp's volume control up high enough to utilize most the the Mc's power capability without driving the 8W amp into clipping, resulting in severe distortion.

Although passive biamping (i.e., with no crossover ahead of the amps) relieves the high frequency amp of having to supply current and power at low frequencies, it does not relieve that amp of having to output voltages corresponding to the full frequency range of the signal, including the deep bass content. Your 8W amp would almost certainly not be capable of outputting nearly as much voltage as a much more powerful McIntosh. So you would be paying for a lot of watts in the Mc that you wouldn't be able to use, and that would not increase the overall power capability of your system as much as you might expect.

Best regards,
-- Al

"Some Mcintosh amps have gain knobs, should I try this?"

Yes this is the way to get the right balance between the amps so long as the Mac is higher in sensitivity than your AN amps, and then use your CJ preamp for the master volume.

Cheers George

Thank you fellow audiophiles for your input. I didn't reply for a couple of days for the purpose of getting more opinions. It looks like the passive bi-amping is a contradictory approach. Will try to gain some experience by using amplifiers from friends and at that point i will refrain myself from buying. The specific requirements needed for the second amplifier(s) further limit the possible choices. Yes, I do have Y-splitters - two Audioquests that I am using from my CD player for sending the signal to two different set-ups - one for a higher quality system and one for a conventional system used when I am doing fitness. I do have also balanced and unbalanced outputs from the CD player (Esoteric DV 50 S) but the preamp has only unbalanced inputs, so I am not using the XLR's. Some Mcintosh amps have gain knobs, should I try this?
Regards to all of you and happy listening.

Nikmilkov hi,

All you need to do is purchase a solid state amp that has higher sensitivity than your AN amps that also has input level controls.

Set the level controls so your bass sounds balanced in your system with the AN amps, an then your CJ preamp volume will be the master volume for both amps.

Cheers George

I've been biamping a pair of DIY speakers that are similar in design to the Legacy Focus using a pair of Peerless 12" woofers per side as well as Eton midbass, midrange, and tweeters. The bass drivers seem ever so slightly less efficient than the rest so biamping was the only way to get the sound I was looking for, otherwise the speakers seemed bass shy and 4 12" woofers shouldn't sound that way.

My sources are mostly cdp or universal players though I occasionally hook up a Revox B261 tuner. All of my sources have at least 2 outputs, the universal players having the stereo outputs as well as the full range FRONT outputs for surround. The tuner has fixed and variable outputs. I connect the stereo outputs to my main amp (presently a JAS Array 2.1 integrated using 805 and 300B tubes with a passive linestage) and the FRONT outputs to the amp I will drive the woofers with. In the past, I've used an integrated amp for this purpose, a Consonance Calaf, with great results. Presently I use pro amps, having both a Hafler and a Face Audio that see duty (only 1 at a time).

You could go from your source(s) into your preamp with 1 output and and use that to drive the Audio Note amps and into a pro amp with attenuators with another output on the same source or an integrated or get another preamp that will drive a separate amp for the woofers. If your source(s) doesn't/don't have 2 outputs, you could get the same result using a Y-cable. You don't see many high-end Y-cables out there so you may have to build your own or have someone build you such a cable. I've used soniccraft for this and their work is very good and affordable.

I've always found the bass to blend in well with rest of the range only standing out if turned up to high like any subwoofer. You should be able to get not only acceptable results but much better results than biamping with another pair of the Audio Note amps as you can use whatever solid state amp you wish. One issue with the pro amps though is that most use XLR and don't have RCA inputs. Just use XLR to RCA interconnects. If you have a pair of unbalanced interconnects that you like, you can always have XLR's installed at one end. Good luck!

I too agree with ZD. I would add, with respect to the passive biamp configuration you are proposing, that in most cases it would not be correct to match the sensitivities of the two amps. What should be matched is their gain, the relation between voltage out and voltage in.

Sensitivity is the input voltage required to drive the amp to some power level, usually its maximum rated power. Since the max power ratings of the two amps would probably be different, if sensitivities were matched the same input voltage would result in different output voltages from them, and hence different output powers for a given load impedance.

Power amp gains are often unspecified, but are commonly indicated in measurements provided in reviews, such as those in Stereophile. Also, gain can be approximately calculated from the sensitivity and max power capability specs of an amp, as I described here.

Finally, I see that your present amp is rated at 8 watts. A point to be aware of is that if you were to passively biamp that amp with a much more powerful solid state amp, that is somehow properly gain matched, you would not be able to utilize most of the power capability of the solid state amp without driving the lower powered amp into clipping.

Regards,
-- Al

I agree with Zd. Even if you get the gain to match at a certain level, both amps won't increase at the exact same rate.
If you want to see if bi-amping helps, you could use both of your amps on one speaker and see if you get more detail or punch? Then, you may end up buying 2 more Audio Notes :-)

You're just going to spend a lot of time and money on something you probably won't be happy with, for 2 reasons. First is that you'll hear the 2 different amps quite clearly. It will sound like 2 different systems patched together. Second, is you are almost certainty going to have to use an external active xover.

The only practical way to biamp is to use 2 stereo amps or 1 4 channel amp, and do it vertically.