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Old 17th February 2007, 08:07 PM   #1
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Default Se KT88 with Quad ESL

Has anyone had success driving a Quad 63 electrostatic speaker with a SE KT88 amp?

I've recently built my own SE KT88 using a 6SL7, KT88 in UL and Hammond 1627. The 8 ohm output is also used as CFB. The amp is great with conventional speakers but with the ESL's the treble is reduced and the bass is excessive. Is this normal for a SE amp of this type with an ESL?

Thanks
Andrew
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Old 17th February 2007, 08:29 PM   #2
rdf is offline rdf  Canada
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My guess is the Quad's high frequency impedance is too much a challenge for a low damping factor SE.

http://www.stereophile.com/floorloud...6/index11.html

Cathode feedback isn't likely enough to make up for no global negative feedback with UL. You probably won't get enough volume but triode connecting the KT88 and/or using the 4 ohm tap should provide useful info.
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Old 17th February 2007, 10:00 PM   #3
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No great expert on this, but I do have a pair of ESLs. I have always heard that PP works better with the quads than SE amps. My own amp is PP and works beautifully with my esl (57s). A friend has some 63s and was using a croft amp, again lovely sound.

Fran
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Old 17th February 2007, 11:49 PM   #4
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the 63 is 86dB efficient - personally I would go for at least a 60W+ push pull amplifier, but mileage may vary depending on your listening space. Best I ever heard a pair of 63s sound was back in the late 80s using a heavily modified mac240 with all Lambda regulated power supplies including the plate b+
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Old 18th February 2007, 02:11 AM   #5
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just to let you know my PP amp is an audio innovations 300mk2 (pretty rare) using 12AX7 and ECL86. Gives 10WPC and is more than enough to amp these to respectable levels, but not if you want to shake the whole house. Then if you have a set of quads you won't really want to do that anyway!

I think Quad recommend anything from 10 to 80WPC as being capable.

The 63s have protection built in so you won't damage them by over amping


Fran
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Old 18th February 2007, 02:40 AM   #6
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Thanks guys, I think you're right, the impedance of the Quads is a difficult load for the KT88's. I'll try again using the 4ohm tap and perhaps triode as suggested above...

Looks like I'll need to try a different approach. Perhaps a KT88PP with cfb is the way to go!

Kind Regards
Andrew Parsons
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