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Any Direct Drive ESL Amp projects someone could share?
Any Direct Drive ESL Amp projects someone could share?
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Old 22nd November 2017, 03:37 AM   #81
djmiddelkoop is offline djmiddelkoop  Netherlands
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Quote:
Originally Posted by esl 63 View Post
Why solid state? Tubes and direct drive ESL is a perfect match.
My Beveridge is playing just awsome and you can see the schematics above nr:73
The tubes are dirt cheep and there is a lot of them... so what are you waiting for guys and girls?
The schematics shown at post #73 contains some erratics :
Both bases of differential amp Q6 and Q7 are tied together, in this way they will output nothing.
Q4 and Q5 are fully shorted at all pins.
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Old 22nd November 2017, 07:34 AM   #82
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by djmiddelkoop View Post
The schematics shown at post #73 contains some erratics :
Both bases of differential amp Q6 and Q7 are tied together, in this way they will output nothing.
Q4 and Q5 are fully shorted at all pins.
There's also the large capacitance across the 'transducer'. That can't be right.

It seems this is a schematic derived from a board, and it's very hard to do that right.

Jan
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Old 22nd November 2017, 05:09 PM   #83
bolserst is offline bolserst  United States
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Quote:
Originally Posted by jan.didden View Post
There's also the large capacitance across the 'transducer'. That can't be right.
It does look odd , but actually is correct.
The transformer and direct-drive version of the Beveridge circuit topology are shown in attached pic.
This drive method enables you to get twice the voltage differential between the diaphragm and stators for a given amplifier output capability, so 2x the SPL. Essentially this is a form of amplifier bridging for ESLs. The downside is that it only works with highly conductive diaphragms.

It is very similar in concept to the Final “inverted” circuit arrangement.
More details and comparisons between the two methods posted here:
Beveridge vs Final ESL Configuration
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File Type: png Beveridge_ESL_Drive_Method.png (40.0 KB, 331 views)
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Old 20th July 2018, 08:31 AM   #84
Lampie519 is offline Lampie519  Netherlands
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You do not need a lot of power to drive an ESL. The output impedance should be reasonable low because of the capacitive nature of the panels.
I have build many DD amps for more then 10 years now and all work stable. No tube failures so far and enough power to drive 8 Acoustat panels.
I suggest you start with the Beveridge amp as these tubes are very good and can be replaced by the PL509/519.
I do not like any solid state component therefor i replaced all transistors by tubes and omitted the filtering during prototyping.

Once you have a working amp you can add all the filtering you like.

To get a low output impedance you will have to add some (DC) feedback as this also stabilizes the DC bias on the output tubes and prevents runaway of the tubes.
Attached Images
File Type: jpg 25_mei_2008_HS-amp_frank.jpg (122.3 KB, 245 views)
File Type: jpg HS-amp%20frank.jpg (155.7 KB, 246 views)

Last edited by Lampie519; 20th July 2018 at 08:42 AM. Reason: Adding images
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Old 6th August 2018, 12:00 PM   #85
Lampie519 is offline Lampie519  Netherlands
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I just started recycling my old Acoustat amps:
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File Type: jpg IMG_4032.jpg (103.1 KB, 171 views)
File Type: jpg IMG_4030.jpg (70.8 KB, 166 views)
File Type: jpg IMG_4020.jpg (103.2 KB, 66 views)
File Type: png IMG_4028.PNG (759.4 KB, 64 views)
File Type: jpg IMG_4029.jpg (107.2 KB, 66 views)
File Type: png IMG_4033.PNG (830.6 KB, 73 views)
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Old 2nd November 2018, 06:50 PM   #86
MarcelvdG is offline MarcelvdG  Netherlands
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FYI, I just learned that some of the ignition transformers for gas and for oil appliances produce voltages and currents that are of the right order of magnitude for the power supply of an amplifier that drives electrostatic loudspeakers directly. Microwave oven transformers may also be suitable. Needless to say, they are all quite dangerous.
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Old 2nd November 2018, 06:59 PM   #87
Lampie519 is offline Lampie519  Netherlands
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I tried those but they can not handle the continuous current just for a short time.
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Old 2nd November 2018, 07:01 PM   #88
MarcelvdG is offline MarcelvdG  Netherlands
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That's a pity, thanks for the warning!
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Old 2nd November 2018, 09:00 PM   #89
bentoronto is offline bentoronto  Canada
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Any Direct Drive ESL Amp projects someone could share?
Quote:
Originally Posted by MarcelvdG View Post
FYI, I just learned that some of the ignition transformers for gas and for oil appliances produce voltages and currents that are of the right order of magnitude for the power supply of an amplifier that drives electrostatic loudspeakers directly. Microwave oven transformers may also be suitable. Needless to say, they are all quite dangerous.
About 40 years ago, I ran a transformer from a fuel-oil furnace as HV supply. The interface board had fancy HV caps and big resistors (remember when TV''s had CRTs?) and insulation spray and mostly isolated from chassis ground. Possibly dangerous but I was young(er), poorer, and wilder.

An awkward way to make to HV bias today and not sure about amp power supply use.

I scrounged-up a great collection of stuff by repeat visits to the local "war surplus" stores when building my DD later 70's, an advantage of life in the big city. HV oil-filled caps, chokes of many sorts, transformers, fans,etc. often MIL-spec.

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Last edited by bentoronto; 2nd November 2018 at 09:07 PM.
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