SDA-1B: Possible to use bridged amps?

Schurkey

I have done some searches; but not found a definitive answer.

I just bought a pair of monoblock amps; and I expect they'll have to stay in storage until I get different main speakers. I've had my SDA1-B for 20+ years, I'm well aware that they need a common-ground amp.

Perusing this forum, I discover a DIY-project (an AI-1) using a transformer that can allow SDA users with blade/pin connecting cables to use non-common-ground amps. Problem is, the 1B doesn't use a blade/pin connecting cable. It's more of a big blade/little blade cable.

Any hope for driving these speakers with a pair of monoblock (bridged) amps?

Dennis Gardner

Some mono blocks will handle the circuitry short. I used tube monoblocks this way on my 1Cs, but most solid state monos won't allow it, esp. bridged amps.

You may ask the manufacturer if the monos can take having their negative binding posts strapped together. SDAs have seen alot of amps/speakers go up in smoke taking this risk.....so proceed with caution.

lightman1

POOF!! I believe is the operative term.

danger boy

you could probably get away with using the mono block amps on your SDA's, but WITHOUT the SDA cable would be the only way for sure that everything would be ok. and not go POOF!

lightman1

Best I can tell, The AI-1 should take care of that.

Dennis Gardner

lightman1 wrote: »

Best I can tell, The AI-1 should take care of that.

Doesn't work with blade/blade cables period, only the newer pin/blade models.

lightman1

Your right. Forgot about the reversal on blade/blade. Carry on! DON'T DO THE AI-1. Brain POOF.

F1nut

Are they bridged stereo amps or are they really mono blocks? The reason I ask is that the 1B's are 4 ohm loads and bridged amps are usually rated to drive 8 ohm loads only. That would mean you shouldn't use them with the 1B's, period. Now, if they are really mono blocks, you may be able to strap the negative outputs and strap the chassis grounds. It would be best to consult the amp manufacturer as Dennis pointed out before doing so. In any case, you can not use the AI-1.

Schurkey

F1nut wrote: »

Are they bridged stereo amps or are they really mono blocks?

Factory-bridged mono amps. True monoblocks.

F1nut wrote: »

The reason I ask is that the 1B's are 4 ohm loads and bridged amps are usually rated to drive 8 ohm loads only. That would mean you shouldn't use them with the 1B's, period. Now, if they are really mono blocks, you may be able to strap the negative outputs and strap the chassis grounds. It would be best to consult the amp manufacturer as Dennis pointed out before doing so. In any case, you can not use the AI-1.

I was reasonably certain that the 1B was/is a 6-ohm nominal load.

These amps'll laugh themselves silly at a 4-ohm nominal load. Rated for 1000 watts into a 2-ohm load, and I expect they'll drive a load under 2-ohm without damage, but perhaps at reduced wattage. (Aragon Palladium II)

I'll be in touch with the manufacturer about strapping the negative outputs and the chassis grounds. Do you mean the two negative outputs are strapped together, and then the chassis are strapped together--or--that both negative outputs and both chassis are in a 4-way tie-up?

Yeah, I kinda figured the AI-1 was out when the instructions specifically mentioned a blade/pin connector cable.

Dennis Gardner

Common ground is a term used to indicate that the negative posts are connected in common in the circuit design. Mono blocks can sometimes have their posts strapped together to simulate this circuit design without issue, some can't tolerate it, hence the question to maker.

The chassis ground isn't the ground referenced for SDA connections, (common ground) is simply strapping both channels (-) posts together.

DarqueKnight

Schurkey wrote: »

Any hope for driving these speakers with a pair of monoblock (bridged) amps?

Different manufacturers use different terminology with regard to what "bridged" means. For example, the Pass Labs X series monoblock amps and the Krell Full Power Balanced MCx series monoblock amps are high power "bridged" amps in the sense that two amplifier stages are connected together and some proprietary distortion reduction schemes are employed. For the bridged design Krell and Pass amps mentioned, both outputs are "hot" and thus the negative terminals cannot be strapped together. The Krell MCx manual even goes so far as to specifically mention that the stereo version (Cx series) amps are not common ground and that the monoblock versions cannot be used in a common ground configuration.

As others have said, it is best to contact the manufacturer to avoid unpleasant surprises.

BobMcG

If the amps can't be strapped to make them common ground, it's hard to tell. The speakers are similar and the early 1Cs might be even closer.

SDA-1B
4 ohm
92dB effic.
50Hz & 2000Hz Cross Freq
4 x 6509
Crossover not specified
B/B IC

SDA-1C
6 ohm
90dB effic.
50Hz & 2000Hz Cross Freq
2 x 6501
2 x 6511
Crossover BE1618-B (At least the later models.)
P/B IC Except for early models which were B/B IC

My point to this is that the early model or B/B 1Cs could use a special/custom B/B AI-1 IC. If it could be determined that the 1B and the early 1Cs used the same crossover, one could make a custom B/B AI-1 and use it with the amps. I think it's possible that the early B/B 1Cs could have the same crossover as the 1Bs. (Using up parts and in the process creating another in house "FrankinPolk".)

Ken?

Schurkey

Ken at Polk has e-mailed me; it's his opinion that the blade/blade interconnect cable won't work with an AI-1 sort of deal without totally new crossovers and perhaps internal wiring mods.

As the amps are genuinely bridged; there's no connecting the negative speaker terminals to make it "common ground".

I therefore come to the conclusion that the SDA-1B is simply not suitable for my new amps, and cannot be modified (easily) to become compatible.

I'm not sure what this means for me. 1Bs seem to be not worth bothering to sell; the prices are so low. On the other hand, it's not like I dislike the speakers--after twenty-plus years, we've become "good friends". At this point, I'm just gonna store the Palladiums and see what happens in the next couple o' years. Maybe I'll get adventurous and score some 1C crossovers on ebay.