Spectra 2200, Hard time driving these..

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Brian Tighe2004-02-23 22:21

Hi Andy, I am having a hard time driving the Spectra 2200\'s I am using a Conrad Johnson MF 2300 amp. at 240 watts per channel and have blown fuses on the right hand panel and amp as well. What amp would you recommend to drive these panels the best, I was told they need \"horse power\" and I thought the MF 2300 should do the trick. Regards, Brian Tighe.

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Andy Szabo2004-02-23 22:21

The Conrad-Johnson MF2300, at 240 watts per channel, should be enough power to get the best out of the Spectra 2200’s. I don’t think an underpowered amplifier is causing your fuse-blowing problem.

You didn’t mention the fuse value that is in the speaker. It should be rated at 5-amperes, with a Slow-Blow characteristic. This fuse value was chosen to prevent “nuisance” blowing under normal conditions, but still blow when there is a real problem.

My initial guess is that you have a high-voltage arc occurring in one of the audio transformers. This is essentially a short circuit that occurs only when the voltage rises above a certain point. Try swapping the interfaces from one speaker to the other. I suspect you will find that the fuse-blowing problem moves to the other channel.

If the fuse continues to blow in the same channel, I would suspect something is wrong with the amplifier. The Acoustat panels are extremely reliable, and it is virtually impossible for any type of panel malfunction to cause fuse blowing. The only problem you might have within the speaker frame is a pinched or damaged wire. If this is the case, you will probably see a prominent black mark somewhere on the wires, which is evidence of an arc. (Don’t confuse this with the normal black “dust” that collects on the wires.)

If the fuse blowing problem does move to the other channel, then you have isolated the problem to the interface. There’s not much that you can do yourself at this point. I suggest contacting Sounds Like New (listed under “Refurbishing”). They are qualified, and have the parts necessary to repair the interface.

Andy Szabo2004-02-23 22:21

There are a number of factors that may be involved here:

Like all ESL’s, the Spectra 2200’s are much less efficient than conventional speakers, meaning that considerable power is required to make them play loud. Even with plenty of power, they may not play as loud as your accustomed speakers. Nevertheless, in a moderate-sized room, they can produce a sound pressure level that will satisfy all but the most hard-core rock ‘n roll fans.

Are you still blowing fuses in one channel only? If so, refer again to my previous reply. If you are blowing fuses in both channels, there may be a problem with both speakers, or, this may simply be a case of your expecting more from the speakers than they can deliver.

I assume that you have the speakers plugged into AC power. If the wall transformers you received with the speakers are not Acoustat brand, make sure they are rated for 15 volts AC (not DC), with an output current of at least 150 milliamps (mA).

If your Spectra 2200 is an early model, you may be experiencing a problem with the bias power supply, which can be easily remedied. See my Technical Bulletin “Ultrasonic Bias Power Supply – Update Acoustat Spectra Series”. To determine if this update is needed for your speaker, look at the diagram included with the article. If you see item #9 (a wire wrapped around another) then your speaker is already the improved version, and does not require the update.

Another possible problem is that the bias power supply may have been tampered with, requiring a re-adjustment of the bias supply. The playing volume is proportional to the bias voltage, so if the voltage is too low, it could cause the problem you describe.

That’s about all I can think of for now. Do write again if you are still having problems. The Spectra 2200’s are a wonderful speaker, and I’m sure you will be very happy with them once we get this problem solved.

Brian Tighe2004-02-23 22:21

Hi Andy, Thanks for your feedback, I still am having concerns. I have been using the Conrad Johnson MF 2300 with a pair of Rogers LS 3/5A\'s and Satterberg Subwoofers and everything is great, good sound and lots of volume. When I hook up the Acoustat Spectra 2200\'s I dont have a lot of volume before the amp LED peak indicator lights up and if pushed will blow the fuse. I dont understand why the amp would reach clipping and before producing enough volume. Regards, Brian Tighe.

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