
The fronts have the single driver.
It really does sound better.

A company in Halifax bought the original fabrication equipment, and the original tweeters can be shipped there for remanufacturing, at a cost of over $300/pair. Some insist it makes a huge difference, others swear that their untouched 22s still sound great. I haven't had a chance to hear for myself. I do know that these speakers, with their 22 woofers sound more like the 22s I owned than not, and avoid performance anxiety.
I can tell you after an hour of listening that these are not junk, and deserve serious attention and evaluation. My original (series 1) 901s are very well built, with excellent plywood cabinet construction. They pass the knuckle test solidly. All 18 drivers are good, with no deterioration in the original treated cloth surrounds, and are well sealed with putty. Eight 5 inch drivers per side generate a lot of internal air pressure, and the cabinets are up to the stress. There are no crossover caps to deteriorate, because there are no crossovers!
The speakers are not intended to be used without a purpose built equalizer box, which I do not have. I obtained frequency response curves for the series 1 equalizer easily on the internet (including the curve from the BOSE Corporation's patent), and set the curve and saved it as a custom equalization setting in itunes for my initial listening. The curve is extreme, up 12 db at 30 hz, so a powerful amp is a necessity, and the Adcom GFA-1, at 200 watts/channel, fills the bill nicely.
The many different ways that so many talented engineering minds have attacked speaker design (planar, dynamic, full range, transmission line, sealed, ported, infinite baffle and numerous hybrids to name some), are what make this obsession of ours so much fun. Never mind the overpriced crap the the Bose Corporation has produced. This was a ear opening design when it was introduced in 1968, and it still is.
I don't have them yet, but I will tomorrow. I bought them sight unseen. They're original series ones, so I won't have to refoam 18 drivers. I'm sure I'll have lots to say in the very near future. And I haven't forgotten this. I've had fakes before. I'm an adult & I know what I'm dealing with.
Studer Revox AX 4-3s. It's been a hell of a day. The crass screen grab is the original list price. CHF is Swiss francs.
The Pioneer HPM-100s have left. A pair of JBL L36s have arrived (yes, I like to trade). A beautiful little Sansui set has arrived, an AU-2900 integrated amp and a TU-3900 tune. The amp is rated at a modest 15 watts/channel, but like every Sansui I've had, sounds much more powerful, and stunningly musical.
I am loving this turntable. The automatic functions work very well, including the cool motorized cueing/cut selecting (raise the arm and advance the cartridge with > and < buttons). The only inconvenient thing is that the platter will not rotate with the cover up, so record cleaning must be done before putting a record on the platter, or by spinning the platter by hand.The way this thing sounds, I can live with that.



Check out Whetstone Audio. The owner wrote me this morning...he'd just found this blog. I checked his out, and the store and the blog look very cool. He even sells great equipment from the present!
The GFA-1 was the product that put Adcom on the map. I can't tell you exactly when it was introduced, but I believe it was the late seventies. I think I'm write because the manual has a section titled 'If You Disco', that suggests contacting the factory for information about a modification (probably to the cooling fan) for disco spund reinforcement applications. The amp employs what Adcom calls a balanced bridge design. Each channel uses two 50 watt/channel amps (one for the positive side of the waveform, one for the negative) bridged to deliver 200 watts/channel into 8 ohms, 350 into 4 ohms. Apparently the fan is noisy, so the previous owner added a crudely installed, outside the case light dimmer pot to vary the fan speed. With help from an excellent technician, who's a good friend of the blog, the fan has been disconnected. It ran for over 4 hours last night, and went to sleep listening to John Coltrane. This morning, the power LED was off, and the amp felt warm. The thermal protection circuit did it's job, and it's all fine, but I may look into replacing the fan with a newer one that will run silently. The design is compact, but very heavy (I'd guess 25-30 lbs). I've been using it to drive the DCM Timewidows and Pioneer HPM-100s, and it sounds great. I'll tell you more soon.