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Old 30th October 2004, 05:54 PM   #11
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It is ok to drive els with tubes. I have years ago build a 40W se amp. 2 parralled Svetlana 811-10 transformerdriven from 300B and 6SN7 srpp driver. The amp is driven at 1200V dc. The amp is not transformerless. The outputtubes drives a 1-2.5 centertapped transformer. To give the differentialdrive to the speakers. It works better than differential drive from the tubes. Less ringing and lower outputimpedance to get a better drive tin the high frequencies. My els is 40cm X 200cm and the capacitance is 1200pF.
There is no ringing on the drivesignal and the amp i capable to give out about 500V at 12kHz. I should be enough.
If you use tubes forget all about full output at 20 KHZ.

Before the se project i had an 6550 pp amp with 1 - 7 outputtransformer it had far to high outputimpedance. I modified it to 2-6SA7 regulator/outputtubes kl A driven at 250 V it works ok but much has much less power than the 811 amp.

I use the electrostatics to 300Hz, below that @-6dB a 10" speaker in closed boxes q= 0,5 and below 60-70 Hz @-24dB adjustable cornerhorn with 15" speakers. This systen is not rocking good at rockmusic but very good at symphonic orchestra and jazz.
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Old 31st October 2004, 11:16 AM   #12
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An ESL need a lot of current if you want to acheive 20khz.

My esl (acoustat 2+2) are 1800pf per stator. At 20Khz, that represent 4.4kohm...

Esl need around 1000Vpeak-peak per stator for an appropriate listening level.

So the current needed for chargind the capacitance=1000/4400=227mA

How can you charge the panel if you have only 6ma avaible????

So the good thing is that in music, you never find a 20khz equal level compared to the rest of the spectrum... So you can divide this number by 2 or 3.

My amplifier will use 8 845 (4 parallel single ended, one for each stator). The current will be 160mA per output section (80ma per tube).

from calculation, I can hope -2Db at 18Khz at full output (2100Vp-p)

My output impedance will be approx 1Kohm


the stage will be like that. A 100% otl!!!

417A(rc)-->EQ-->10Y(lc)--> parafeed centertaped choke for phasesplit-->vt62(LC)-->845(rc).

I curently in the stage of buying the parts
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Old 31st October 2004, 02:56 PM   #13
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Seems interesting!

Keep us posted on what the results are!!

:- )

Oh, are you going to drive the stators or the diaphragm?

:- )

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Old 1st November 2004, 10:10 AM   #14
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Quote:
An ESL need a lot of current if you want to acheive 20khz.
Quote:
So the current needed for chargind the capacitance=1000/4400=227mA
Quote:
How can you charge the panel if you have only 6ma avaible????
Martin, you are right, this is not possible.

Quote:
So the good thing is that in music, you never find a 20khz equal level compared to the rest of the spectrum... So you can divide this number by 2 or 3.
This is also true, but i'm very shure that the division number is much larger than 3. Don't know howmuch, but it must be because when listening to an Acoustat X with the OTLamp there is nothing wrong with the sound. (on the original unit swap out the opamp for a TL074, which is better than the original opamp).

And the Acoustat X is made of 3 panels in parallel !
I would suggest to listen to one before judging.

In normal music the spectrum above 12kHz is besides hardly used, also much less in amplitude.

Hence, testing with test tones will not work with the mentioned SRPP, but music is no problem.

Ofcourse the described class A amp from Martin would work and sound very well, but it's a bit overkill.

Dick.
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