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Old 19th October 2001, 11:15 AM   #1
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I've been reading the ESP pages on bi-amping (www.sound.au.com). Rod (the author) is obviously a huge fan of it and backs his arguments up with explicit explanations. This has got me very interested in bi-amping indeed. But, I'm after other opinions from those who've tried it. Is it really the best thing you can do for your system without spending mega dollars?

I'm currently running Leach amps into some cheap three-ways and was thinking about bi-amping using some LM3876 IC amps for the tweeters. I'm on a budget (who isn't??), hence the LM3876s (ESP also seemed to rate the LM3876s well for some cheap ICs).

I look forward to reading your replies.
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Old 19th October 2001, 12:09 PM   #2
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Just to correct myself, I mean to use the LM3876s to run the mid-ranges and tweeters.
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Old 19th October 2001, 04:14 PM   #3
paulb is offline paulb  Canada
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I am thinking along the same lines, but have deferred it for a while until I get a bigger listening room.
My thinking was that the best amplifier (probably Class A) should be used for midrange, where most of the content is. Lower power but still clean LM3876 for tweeters (I think that's what Rod is going to use). Woofers would probably be ESP project 3A.
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Old 19th October 2001, 04:38 PM   #4
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I first went biamped somewhere in the late '70s; achieved triamp status in the early '80s. In '88 my personal world turned upside down and I was lucky to listen to music at all for several years. The first time I put the system back together with the intent to leave it going, I used a single amp. I couldn't figure out where all the music had gone. Surely, my memory of how good my system had sounded wasn't that far off...was it? I played around with this and that, and finally got around to biamping again. Poof! Some of the music came back.
To make a long story short, I'm now quad-amped and loving every minute of it. It is not cheap. It is not always technically easy. It is, however, essential in getting the absolute best sound that you can get from your system.

Grey
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Old 19th October 2001, 05:39 PM   #5
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Hi,

I have been using biamping for the last 8 years. Yes, it does raise the level of performance. But to obtain the full benefit, go active, i.e. use an active crossover and eliminate the passive ones in your speakers. You will be amazed with the improvements. Tighter bass, improved transparency, cleaner treble, etc.

N.S.
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Old 19th October 2001, 06:00 PM   #6
Freddie is offline Freddie  Sweden
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GRollins,
I've been thinking of biamping my speakers for a long time now (using 24dB/octave Linkwitz-Riley active x-over) but I still haven't.
The thing is that I don't like to have opamps in the signal-path (which 99,9% of the active x-over uses), do you use mosfets or tubes instead of opamps?
One more thing, do you compensate for the so called baffel step? Or shouldn't I be worried about that at all?

/Freddie
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Old 19th October 2001, 07:02 PM   #7
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Freddie,
Once upon a time, I used LF353 opamps in a circuit similar to the one Linkwitz wrote about in one of his papers where you compensate for the rolloff of the driver (I was using KEF B139s for subs in those days) by boosting the signal in exact accordance to the slope of the rolloff. It takes a pretty healthy amplifier to do this, as you're burning power by the pound as your frequencies decrease. After a lot of R&D, I finally got flat response into the upper teens. Pretty good. But the problem was that the drivers were being driven very, very hard and were quite non-linear by the time decent listening volumes were attained. In short, it was flat, but not tight at all above a certain volume level. Pity, as it sounded so good at low volumes that you just wanted to crank it up a notch or two or three...
I have since heard several commercial offerings that use the same strategy and they all tend to have that same muddy sound when played at even moderate volumes. After noticing the pattern, and figuring out why it happened, I gave up entirely on the technique. My current subs will eventually use a feedback network (optical, if I can make my idea work out) that reads the cone motion and returns to the amp as a negative feedback signal to correct for both driver and amp distortions.
My current crossover (very much a work in progress) uses 2N5457s (FETs) and MPSA18s (bipolars) in follower configuration for the mids and highs. The original LF353 crossover boards are still in use for the subs, though, as I haven't taken the time to put together a discrete lowpass section, not that it's difficult, there just aren't enough hours in a day. Note that I've removed the board that compensates for the KEF B139 rolloff (I'm using twelve 12" Titanic drivers these days). This was simple, as I've always tried to build modular projects so as to be able to upgrade or reconfigure at a later date; I simply removed the boost board. (It's now on my video system upstairs, pushing KEFs again.)
My plan is to build a tube crossover later, at least for the mids and highs, once I've got some other things settled out. I've got a bunch of 6922s waiting to take flight--it's back to the time factor. Way too many ideas to implement in a day, or even a month, and I'm far behind on my writing, which does earn a penny or two, unlike audio, which costs money.
It's quite simple to use a gain device as a follower instead of an opamp. A follower has a very high input impedance, and low output impedance, just like an opamp. Use a Sallen-Key configuration, and you'll be just fine. Yes, there'll be some insertion loss, as followers are always less than unity gain. In practice, it's not enough loss to be a problem.
I'm not sure what you're talking about when you refer to a baffel step.

Grey
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Old 19th October 2001, 07:35 PM   #8
paulb is offline paulb  Canada
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Another advantage to bi/tri/quad-amping is you never run out of things to build: "You're building ANOTHER amplifier?" becomes easier to answer. I always have lots of long-term ideas on the go, but I get around to building very few of them. Hmmm, sounds like somebody else in this thread...
For me, the journey really is the reward.
Edit: I also meant to add:
While you may want to avoid op-amps for the crossovers, my feeling is it's probably better to tri-amp with op-amps than single-amp with tubes (or whatever your preferred active devices are).
Grey, any comments about where to place the highest-quality amps, given that you're starting with legacy equipment and slowly evolving the system?

[Edited by paulb on 10-19-2001 at 02:37 PM]
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Old 19th October 2001, 07:47 PM   #9
Super is offline Super  United States
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I think that the placement of amps is subjective. For example, if you're combining tubes with SS amps, you may want to have the SS controlling the bass. In my situation, I have two SS, one of my amps had better highs, and the other a more defined midrange, so I used them accordingly. Sounds infinitely better than when I had them reversed. If you have big power differences however, I'd put the lesser powered amps up with the tweets and work my up as I go down the audio spectrum.
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Bryan
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Old 19th October 2001, 11:44 PM   #10
paulb is offline paulb  Canada
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Yesss, know the parts about power, Rod Elliott summarizes it nicely in his article at his ESP site.

btw, I just received Linkwitz-Riley crossover PCBs from Rod; I don't plan to use them right away but I'll have them on hand for the future. They look very good, quality- and flexibility-wise. If one were to use high-quality op-amps, Rs and Cs I very much doubt it would be worthwhile to use a bunch of tubes instead. IMHO. But I'll never actually compare the two approaches anyway.
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