Hello,
I have a pair of Definitive Technology BP2000TLs that use 75ohm 15” subwoofer drivers and 500watt amps. The built in amps have finally died and the place I sent them too for repair said they can’t repair them. My guess is because of the 75ohm load. Anyways, I have a few question
1) I’d really like to fix the original amps. Does anyone know where I might be able to get them repaired. I’d really love to keep them as original as possible since I have always love how these speakers sound!
2) I completely understand that an amp is going to be putting out only a fraction of its rated power at 75ohms, but if I put enough power to them with they still perform. I kinda tested this theory using one of my Onkyo M-501s that are only 150w a channel. At a moderate volume and enough gain they do sound good. Anything beyond that and the amp just doesn’t have output to keep up. I was thinking of maybe using a D-class amp module, and modifying it to fix, but how big would I have to go for it to perform close to the original 500w amp?
3) if #2 is an unreasonable option, then I need to find a reasonably priced 15” 4 or 8ohm sub that will perform well in about 2.8 cft. enclosure with a port that’s 1.5” x 7”x 14”. I don’t have modeling software so any help here would be greatly appreciated!
Thank you in advance!
I have a pair of Definitive Technology BP2000TLs that use 75ohm 15” subwoofer drivers and 500watt amps. The built in amps have finally died and the place I sent them too for repair said they can’t repair them. My guess is because of the 75ohm load. Anyways, I have a few question
1) I’d really like to fix the original amps. Does anyone know where I might be able to get them repaired. I’d really love to keep them as original as possible since I have always love how these speakers sound!
2) I completely understand that an amp is going to be putting out only a fraction of its rated power at 75ohms, but if I put enough power to them with they still perform. I kinda tested this theory using one of my Onkyo M-501s that are only 150w a channel. At a moderate volume and enough gain they do sound good. Anything beyond that and the amp just doesn’t have output to keep up. I was thinking of maybe using a D-class amp module, and modifying it to fix, but how big would I have to go for it to perform close to the original 500w amp?
3) if #2 is an unreasonable option, then I need to find a reasonably priced 15” 4 or 8ohm sub that will perform well in about 2.8 cft. enclosure with a port that’s 1.5” x 7”x 14”. I don’t have modeling software so any help here would be greatly appreciated!
Thank you in advance!
Not exactly, you want an amp that has traded current for Voltage. A very high powered amp designed for 4 ohms will do the job but will be more than you need in the current department.
How sure are you that the driver has a 75R nominal impedance? That choice complicates many aspects of the design and makes little sense from an economic standpoint.
110% sure. The BP2000TLs all used 75ohm subs. It’s printed right on it and I personally measured it thinking the very same thing.
This is what I found on the manufactureres site:
BP2000TL Specifications: Dimensions: 9"W x 17"D x 50"H". Response: 15 Hz–30
kHz. Efficiency: 92 dB. Drivers: 4–61/2" cast-basket, bass/midrange drivers, 2–1" pure
aluminum dome tweeters in D’Appolito arrays, 15" sub w/500-watt RMS Infinite
Power Source amp. Connections: tri-wirable with separate five-way gold binding
posts and optional separate low level full range and LFE inputs. Rec. Amp.: 20–500
watts. Nominal Imp.: 4–8 ohms. Auto On/Off: Signal sensing. Finish: piano gloss
black or cherry. Weight: 125 lbs.
So what?
Yes, and I still don’t know what those specs have to do with what I’m talking about here? Could you please be more specific.
Yes, that’s overall impedance 4-8 ohms. Please note it has an internal amplifier that powers the subwoofer, therefore the impedance of that subwoofer would have no effect on the overall impedance. It’s not a big secret in Def Tech circles that this speaker uses a 75ohm subwoofer. Plus it’s stamped right on it and I have personally measure both. As out of the ordinary as it is, it is FACT that they are 75ohm drivers.
ok, found them now as spare part. I do not see any advantage in this proprietary impedance except protetection of sales of the brand.
I do understand your point of view, but still doesn’t help me in what I’m trying to accomplish. I’d like to keep the bass drivers if I can, just wondering if that’s possible with a “normal” amplifier.
500W/75 Ohms requires 193Vrms, i.e. +-300Vpk. In other words a full-bridge amp with 300V dc supply. This in fact could by powered directly from rectified 240V mains without transformer. Anyway there is little chance to find an adequate amp - I would try to repair the original amp.
Thank you very much, that was pretty much the answer I was looking for on using a “normal” amp. Much appreciated!!!
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There is an obligation to point out that this illegal in many places and with good reason, as it can be particularly dangerous.
How about looking at pro amps like the Extron XPA 2001-100V? They are built for >50 Ohm loads. You won't get full power, but maybe enough. Not sure if they sound any good!
Agreed. Luckily I did not design that active woofer which looks to me like some kind of madness.