It is often considered ideal to use identical amps; balanced against this is that requirements for different parts of the frequency range can be very different. The bass will benefit from SS while you can use tubes for midrange and highs. The only thing you have to do is balance the system initially. Since I assume your crossover has a level control that should be no problem; the specs do not mean a lot as they were derived from driving a full range load and you will not be doing this, the sensitivity is the one to pay attention to. The only problem you could run into is if the sensitivity is wildly different and beyond the range of your volume control to correct. This is unlikely and could be dealt with by using attenuators on the more sensitive amp. From reading the forums it appears that many of the members use dissimilar amps, I do not think you will run into any problems and using dissimilar amps in itself will not damage your system.
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Thanks for the input. The Marchand active XO does have attenuation for each Hz section. My concern is different input sensitivity of the amps. The VK-60 is 1.0V. The SS BAT amps are rated at 1.5V. Does this mean when adjusting the volume on the pre-amp the gain on the two amps change at different rates. That is, do I need to re-adjust the level controls on the Active XO to balance the gain on the woofer and mid-tweeter sections with each diffent pre-amp volume settting.
No, all you need to do is to set the relative level once and since both will receive a signal that varies in the same way from the preamp they will stay in balance. If one were coming from a fixed output like tape out then you would have to rebalance them. I often use subs powered by amps different from my main amps with no problem, you just have to set the level relatively higher on the less sensitive amp. For example my Meridian 605s [main amps] have a ,5 volt sensitivity and my Tandberg 3026A is [I think] 2 volts but I have had no trouble using them together using the crossover level control. Once you have it set they will stay in balance.
My concern is different input sensitivity of the amps. The VK-60 is 1.0V. The SS BAT amps are rated at 1.5V. Does this mean when adjusting the volume on the pre-amp the gain on the two amps change at different rates. That is, do I need to re-adjust the level controls on the Active XO to balance the gain on the woofer and mid-tweeter sections with each diffent pre-amp volume settting.No, once levels are matched between the woofers and mid/hi drivers, they will stay matched as you change the volume control setting.
BTW, what you are matching is amplifier gains, not sensitivities. The sensitivity of each amp is the input voltage it requires to reach its particular maximum rated output power. For instance, if all of the speaker's internal crossover elements were in place, and you were to drive the woofers with a 200W amp having 1.0 volt sensitivity, and you were to drive the mid/hi's with a 100W amp also having 1.0 volt sensitivity, the input to the 200W amp would have to be attenuated by 3db for a proper match.
The fact that you have the speakers' mid/hi crossover elements in place, with the woofers' crossover elements removed, complicates things a bit further, because the crossover will introduce some loss at mid/hi frequencies but not at low frequencies. But once you obtain a satisfactory volume match, it will not have to be readjusted as you change the volume control.
I'm wondering, though, about crossover slopes. I note in Figure 3 of Stereophile's measurements that the crossover slopes of the mid/hi section appear to be asymmetrical with respect to those of the woofer section (approximately 24db/octave for the woofer section, and close to 12db/octave for the mid/hi's), although that figure presumably represents the combined rolloffs of both the crossover network and the drivers. If you are saying that in your setup only the active xo is rolling off the woofers, while both the active xo and the internal xo of the speaker are in the path to the mid/hi drivers (with all of the crossover points being about 550Hz), it seems to me that (depending on what the active xo slopes are) you may be making the overall crossover characteristic significantly different than what was provided in the original design.
Very astute of you to notice the slopes are indeed not symmetrical on the Hales as noted on the Stereophile’s measurements. I did experiment with different slopes (i.e. 12 db slopes and did not like how it sounded) but ended up using LR 24 db slope on both the woofer and mid-tweeter section. However, I never tried to duplicate the off-setting slopes of the original design. I will give that a try.
Would you please elaborate further on your 3rd paragraph (“complicates things a bit further, because the crossover will introduce some loss at mid/hi frequencies but not at low frequencies”), didn’t get what you mean. Thanks.
Would you please elaborate further on your 3rd paragraph (“complicates things a bit further, because the crossover will introduce some loss at mid/hi frequencies but not at low frequencies”), didn’t get what you mean. Thanks.Hi Norm,
I'm envisioning that resistors which may be present in the speaker's crossover, and/or to a much lesser degree the dc resistances of its inductors, may be significant contributors to the relative balance of lows and mid/hi's.
Since you have bypassed the low frequency section of the speaker's crossover, but not the mid/hi section, you may therefore be raising the sensitivity of the speaker to low frequencies relative to its sensitivity to mid/hi frequencies. If so, the level matching you would have to accomplish with the active crossover would have to reflect that difference, in addition to the difference in amplifier gains.
Looks like you're getting covered technically. I can add is the quality of the level controls affects the amount of fiddling. When I first tried biamping with pots to control the more sensitive amp, I was constantly going back and forth. Upgraded to an attenuator and it was set and forget. Wouldn't worry about the Marchand.
Different amps is my favorite method. More complex to set up but it allows selecting the right amp for the specific job. Whether it's SS/tube or NFB/no NFB, or whatever criteria, there are different demands through the frequency/driver spectrum.
My two cents: I've bi-amped using a 170 wpc ss power amp (with volume control; but an attenuator would work as well) on the bass cabinets, and a pair Dynaco 60 wpc monoblocs on the mids and highs. They're run through a Juicy music peach ii preamp, which has a setting for "low" impedence. Anyway, with the pots on the ss amp turned back to about 4, the set up sounds great from low volume to high. Best of both worlds, with the possibility of adjusting the bass/mid-treble ratio to taste with particular kinds of music.
I've not tried active crossovers, so you may be right. My speaks are Von Schweikert vr4 gen iiis (with separate posts for bass and mids/tweets) and Albert himself suggested to me that that crossovers in the speakers were all that's needed. I've never been clear on why bi-amping suddenly requires active crossovers; it's not as if, say, the bass drivers know that they're being bi-amped, right? Or maybe they do.