John Curl's Blowtorch preamplifier part II - Page 2841 - diyAudio
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Old 24th October 2012, 12:11 AM   #28401
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Thank you George; I've been there, done that. Mixed concrete with Poly-Vinyl-Acetate as well, it rings like a bell, compared to concrete with gravel of very random sizes, but I have to admit it flows well, and looks nice after curing.
For structural integrity I prefer rusted nails and screws. And iron wire.
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Old 24th October 2012, 01:22 AM   #28402
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Originally Posted by gpapag View Post
There were some German table radios... It was to be seen inside good speakers (AR and maybe ADVENT) in the past. A variation of this was a diagonally hanged, twisted damping foil.
Thanks a lot for all your precious comments. Any link to this German stuff ? Any idea about their foam ?

About the last quoted part, hard to find something new, in the audio world. And even if you believe it was a personal idea, how can be sure that it was not hidden somewhere in your reptilian brain ;-). The pleasure is in testing something different and find it improves something.

About A.R., those i knew at the time, where "Aerial suspension", damped in the entire volume to be adiabatic.( If i remember well ). I'm a little crossed against them, because they introduced the fashion of low efficiency closed boxes for decades...
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Last edited by Esperado; 24th October 2012 at 01:36 AM.
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Old 24th October 2012, 01:26 AM   #28403
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Respect, mr.Wurcer, you can recognize your nice babies at first sight, even in very low resolution avatars. I'm impressed.
As i was with so many good sounding current feedback op amps from A.D. (They are many in my system)
Sad to see many of them disappear one after the other from catalogs with this mention :"Obsolete".
Those input FET's are a dead giveaway, I notice not recommended for new designs, oh well.
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Old 24th October 2012, 02:05 AM   #28404
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Those input FET's are a dead giveaway, I notice not recommended for new designs, oh well.
What are they recommending instead?
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Old 24th October 2012, 02:07 AM   #28405
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To remove suspension ring, then reduces fractioning forces...
Alas, you cannot do that. The suspension ring has a more important function which is to keep the coil centred in the magnet gap. While the fibreglass can provide back/front stiffness, it cannot provide enough radial stiffness.

In most cases, you want less front/back stiffness rather than more. Stuffing the cavity with fibreglass can provide adiabatic conditions. The decrease in acoustic stiffness is limited to about 20% while true adiabatic conditions would give you 40%.

Density of fibreglass required is quite high. About that of a firm pillow or cushion. This is always good for sealed boxes.

It can also be designed into Reflex enclosures if you can allow a bit more volume but the parameters must be carefully chosen. The requirements for a big magnet are slightly relaxed though.
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Old 24th October 2012, 02:10 AM   #28406
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Mr Wurser, i'm very curious about those mysterious places, where all those integrated circuits where designed.
May i bore-you with few questions ?
Did-you build discrete prototypes before the IC ?
Did-you have good audio equipment to listen to your prototypes and first samples ?
If yes, what was the part of the listening and the measurements ?
Last question, did final Op Amps sounded very different from the original discrete prototype, if some ?
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Old 24th October 2012, 02:13 AM   #28407
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Alas, you cannot do that. The suspension ring has a more important function which is to keep the coil centred in the magnet gap. While the fibreglass can provide back/front stiffness, it cannot provide enough radial stiffness.
It was not about electromagnetic cones, but electrostatic compression drivers for horns.
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Old 24th October 2012, 02:28 AM   #28408
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Originally Posted by Esperado View Post
Mr Wurser, i'm very curious about those mysterious places, where all those integrated circuits where designed.
May i bore-you with few questions ?
Did-you build discrete prototypes before the IC ?
Did-you have good audio equipment to listen to your prototypes and first samples ?
If yes, what was the part of the listening and the measurements ?
Last question, did final Op Amps sounded very different from the original discrete prototype, if some ?
No, sorry to disappoint all sim only no audio listening. This part was done for spy sonar and CAT scanners.

Here is an interesting picture comparing it to 4 2SK170's.
Attached Images
File Type: jpg 743.jpg (64.4 KB, 139 views)
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Old 24th October 2012, 02:31 AM   #28409
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It was not about electromagnetic cones, but electrostatic compression drivers for horns.
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There were some German table radios from 1955-1965 that had small round (~30-50mm Dia) electrostatics, the construction of which fits exactly to your description. They worked fine (and the foam does not rust-disintegrate-after all these years)
The constant charge electrostatic speaker (the only one which has advantages over Rice & Kellog's invention in certain applications) doesn't really benefit from this. It's low impedance is already a good match to air. Moving coils are high impedance so gain from the transformer action of a good horn.

But a more recent application of the principle you describe is piezo film units sold by Pioneer in the late 70s, early 80s. These were very different from the Motorola units used by Dalquist etc which were just piezo bimorphs driving a cone.

I have to say, these are IMHO, just toys. I've looked at a lot of ways of making a noise and done a lot of theoretical work on some too. Only 2 methods have the potential for 'good sound'. Moving coil direct radiator speakers and constant charge electrostatics. There are good reasons why R&K is dominant from tiny transistor radios to High End. It is the only principle that allows a single unit to cover 20-20kHz and more importantly, sound like it does so and sound good too ... not that such a unit is easy

Last edited by kgrlee; 24th October 2012 at 02:46 AM.
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Old 24th October 2012, 03:17 AM   #28410
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Only 2 methods have the potential for 'good sound'. Moving coil direct radiator speakers and constant charge electrostatics
I used to work on two other designs in the 70s: Orthophase, ( http://img43.xooimage.com/files/4/5/...w4-205f678.jpg) and film with a similar magnetic circuit (a magnetic version of electrostatic. Both are better for less fractioning than cone, both suffered from low efficiency, and no way to go down to 30Hz with orthophase ...
I agree with you for cones at low frequencies, not much at medium and hight (It need further nuances). reason why i am interested, on a pure intellectual point of view, to imagine a 2" compression driver with decreased distortion and increased bandwidth to high frequencies. let say from 500 to 20 000.

Mr Wurcer, yes, i'm disappointed, in a way.
Was-it the same @ Maxims and Harris ? No listening ?
I still have those big PMI,& AD databooks... Christmas...
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