Anyone use a 251 amp to bi-amp a 122/147 cabinet?

[tpappano]

I just watched, with some sadness, part of a video of a guy stripping a 251 amp to turn it into a 122 amp. I would think a 251 amp is just begging to bi-amp a Leslie! Add an active crossover and you're in business 8) My partner and I are doing some bi-amping work, and our test setup with just a pair of 6BQ5s on the horns is super loud. It takes about 300 watts on the 15" to blend nicely with the horn!

[andyg]

Interesting thought. Do you think the 15W at the top would work against the 40W at the bottom?

But is this still not removing a 251 from the 'pool' that owners of M100's, A100's etc could use on their instruments?

[tpappano]

Should work pretty well. 15 watts on the top can be plenty loud. The bass should be stronger too because the bass channel is not having to deal with the treble bandwidth.

[David Anderson]

The secondary channel OPT is wound for an 8Ω driver, not 16Ω, but I guess you could use an 8Ω horn driver.

But I'm sure you know as well as I do that power vs. loudness is not a linear function. To achieve twice the SPL you get at 40W, you need 400W. The Jensen V-21 is not as sensitive as some other horn drivers. If you use a different horn driver that's then too loud, relative to the woofer, and you have to pad it down to blend, what was the point of the whole exercise?

My late brother ran a mobile DJ business, so I have some experience with bi-amped systems. The reason his large system was bi-amped was because, past a certain point, you could burn up a passive crossover if it wasn't built with very rugged and expensive parts. And then he might have HF drivers in different boxes from the LF drivers. It made sense in that situation to use an electronic crossover and have separate amp channels for HF and LF.

[tiredoldgeezer]

I just watched, with some sadness, part of a video of a guy stripping a 251 amp to turn it into a 122 amp. I would think a 251 amp is just begging to bi-amp a Leslie! Add an active crossover and you're in business 8) My partner and I are doing some bi-amping work, and our test setup with just a pair of 6BQ5s on the horns is super loud. It takes about 300 watts on the 15" to blend nicely with the horn!

This "active crossover" is the key.
Because an active crossover has to be added prior to the power amp, not after. So if the 251 has separate inputs for the amp channels, then you're golden.
Bi-amp setup is for dialing in. Matching components, sure. But matching venues, also. Simple turn of a knob.
Bi-amping a Leslie is time-honored and many hundreds have been done, often with external amps, though I've seen them with various configs and mounts on the cabinet.
In venues where a Leslie has to be LOUD, it's the only way to go because the internal amp will never keep up. Luckily, that's been somewhat replaced. And if you're into the "Memphis Sound", it's also almost an imperative because of both power and balance requirements.
To get low end, it takes a lot of power to move the air. So a 3X or 4X difference in amp wattage between low and high is not uncommon at all.

[Papus]

Does anyone know what the single most powerful Leslie ever created is?
I'm thinking probably a frankenleslie for the likes of Keith Emerson or Jon Lord

[tpappano]

We just tested a prototype yesterday with a live performance, sounded really great easily keeping up with a pretty loud group. A nice portable "120" size cabinet with a modest bi-amped 760 clean watts on tap. No need to mike this one 8)

[tiredoldgeezer]

Does anyone know what the single most powerful Leslie ever created is?
I'm thinking probably a frankenleslie for the likes of Keith Emerson or Jon Lord

A once-popular combination was a Crown D300 running the bottom end (300W bridged) and a Crown D75 running the treble driver.
Emerson removed the Leslie amp and used Hiwatt amps cabled straight out of the heads.
"Single most powerful" i don't know because you're limited by the physical size/shape of the box. People like Emerson would just add another pair. There comes a point where bigger amps, different drivers and speakers, don't do any good because the horn and box simply won't do any more than they do.
I think on Brain Salad Surgery, they were running 12 Leslies (of the Hiwatt variety) - but maybe just 8 on stage at any given time. PLUS they had one all mic'ed up in an iso-case beneath the stage.

Find an old 147 and re-gut the thing with JBL 15, 1" throat adapter, and bi-amped Crowns and you'll first marvel at the sound, but then wonder why anyone would want any LOUDER than that. Of course, before doing that, you might just build a plywood box that resembles a 147. The only thing "Leslie" you'll have left is the drum and horns. Those can mount on anything.

[David Anderson]

Most venues nowadays (not that many are open these days) have PA systems and mics. I remember 30 years ago playing with two Leslies and trying to compete with Fender Twin Reverbs. All we had were vocal mics. It seems to me like bi-amping to get a louder Leslie is a solution to a problem that mostly doesn't exist anymore. The best I've heard a Leslie sound live was one of my own at a venue where they put four mics on it, two above and two below. They set them panned left and right in the system, which was new and which they wanted to show off. Stock 40W amp, stock Jensen drivers.

[tiredoldgeezer]

This is all quite true, which is why I said "once-popular".
We forget that 30+ years ago, a 16 channel mixer was a BIG mixer and having available channels for everyone beyond vocals was fierce competition.
So instruments often had to make do on their own.
Then came the Mackie and others where it was no big deal. Sub-mixers, even.
Today, of course, 32-48 channels is remarkably cheap, as are lots and lots of mics, so naturally a mic setup is the way to go.

Still, having a Leslie that's louder-than-stock has come in handy a few times.

[David Anderson]

I think we're in agreement. There's so much used/working PA gear around that it's hard even to sell it. I use a Crown Macrotech 2400 as my workshop test amp. It's built like a battleship, but the new stuff is lighter, so people don't want to mess with it.