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Old 10th October 2002, 09:05 AM   #11
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Default direct drive ESL amps

845 PP direct drive amp
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Old 10th October 2002, 11:21 AM   #12
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Quote:
Originally posted by vbd
Hi all, I will not enter the debate about transformer vs direct drive, I just give a link to a DIY amplifier for ESL:
http://www.audiocircuit.com/9041-esl...041IMAI-DI.htm
This design has MOSFETS outputs, feedback, and opamps... I found it quite interesting...
If you are ready to cope with high voltages...
MOSFETS and OPAMPS are certainly not my favourite parts.
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Old 10th October 2002, 11:45 AM   #13
vbd is offline vbd
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Quote:
Originally posted by Denis


MOSFETS and OPAMPS are certainly not my favourite parts.
Hi Denis, this is Denis !
The 845PP tube design from ultranalog is for you, then... I must admit I' m from the solid state age and I' m reluctant to design with tubes... But I also think that a good design will sound good, whatever is the technology...
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Denis
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Old 10th October 2002, 11:56 AM   #14
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Quote:
Originally posted by vbd

Hi Denis, this is Denis !
The 845PP tube design from ultranalog is for you, then... I must admit I' m from the solid state age and I' m reluctant to design with tubes... But I also think that a good design will sound good, whatever is the technology...
I equally design with tubes and solid state and I trust in transformers.

Denis.
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Old 10th October 2002, 12:22 PM   #15
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Default Off-beat transformer

Quote:
Originally posted by analog_sa
I am not a transformer guru but some of the specs of the step-up are clear. You need a step-up ratio in the region of 1:100-150 and insulation between primary and secondary capable of coping with a few kV. Dunno if all valve outputs can cope with this. Frequency response requirements otoh seem to be more easily achieved than with normal loudspeaker loads as the load is almost entirely capacitive and there is very little resistive component so very little real power transfer. I've found that even low quality non-interleaved transformers can sound quite good if they're not expected to drive directly huge areas of the panels.
You want low cost, good insulation and 1:100 stepup ratio? (=1:10,000 impedance ratio). Try a car ignition coil, it's just a transformer in disguise. It will have relatively loose primary to secondary coupling so it may be a complete flop, but you never know... Also they come in two flavours - the high voltage end with a single outlet, and the other type where both ends of the HV side are avaiable. This type has the secondary and primary separated, the former is only an autotransformer. You already have one so give it a go.

GP.
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Old 10th October 2002, 01:40 PM   #16
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Woah, so if I need say 6kV from a 60V output, I'd need an 80000Ohm <-> 8Ohm transformer? Yikes! I'm only getting a 1:35 turn ratio, then, using a 10000Ohm <-> 8Ohm one? Does that mean I need HV tube/mosfet outputs anyway, if not the full 6kV? 180V, anyway.
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Old 10th October 2002, 02:54 PM   #17
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Default Re: Off-beat transformer

Quote:
Originally posted by Circlotron


You want low cost, good insulation and 1:100 stepup ratio? (=1:10,000 impedance ratio). Try a car ignition coil, it's just a transformer in disguise. It will have relatively loose primary to secondary coupling so it may be a complete flop, but you never know... Also they come in two flavours - the high voltage end with a single outlet, and the other type where both ends of the HV side are avaiable. This type has the secondary and primary separated, the former is only an autotransformer. You already have one so give it a go.

GP.
I can not think of a way to use either one or two autotransformers to drive an ESL that would not result in applying the high voltage ESL bias directly to the amplifier output. It may not hurt a tube amp, but it is very likely to destroy a solid state amplifier. I recommend that you do NOT try this.

MR
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Old 10th October 2002, 03:09 PM   #18
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Quote:
Originally posted by Altaic
BTW, my ESLs are 18"x36" and are costing me ~$50 each without the transformer. I haven't planned for an aditional sub per channel or anything. Also, do you think it would be prudent to not make one dimension divisible by the other? It seems like I might get peaking, beaming, resonating, etc.
In theory the rectangular shape will have two major resonances- one related to the long dimension, one to the short. In practice, you're unlikely to ever hear them. If you are really concerned, build the thing so that no two sides are of equal length. That will spread the resonances out. Putting a support strip into the middle (or slightly off-middle) of the diaphragm will help, too, and allow you to bias the speaker at higher voltage (increasing the sensitivity) without the diaphragm hitting the stators.

The best thing anyone can do for their ESLs is make the diaphragm TIGHT and bias it with as high a voltage as you can muster. I like to crank it up until they hiss and whimper a bit , then turn it back down until they're quiet , but you may find your own technique that is less sadistic than mine...
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Old 10th October 2002, 04:00 PM   #19
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[frusterated rant]
So it still stands that the cost of making the panels is nothing compared to the damn transformer or special amp.

If I want to get more than 2.1kV, I can't use one of the el-cheap-o transformers, rather I either have to use one usually reserved for mains, which will have crappy freq response and kill my bass even more than it already is, or I have to spend $300 on a bloody transformer. So 70V from the 3A is okay either way in this case.

If I want to make a direct-drive amp, I have to get very high voltage parts, and a rare design. BTW, ultranalog, your pdfs are encrypted. I'm not sure how much it would cost for these parts, but I'm guessing upwards of a couple hundred dollars.
[/frusterated rant]

I don't think I need to coat my stators, because I'm making sealed ESLs, so it shouldn't arc until I get upwards of 10kV. Because the stators are uninsulated, shouldn't the voltage not need to be so high? Or is voltage a function of distance between stators? I initially thought to space the stators farther apart because I can have much higher voltage with no problem, and then the diaphram would have more travel, but now I'm thinking it would be better to shorten that distance. Does travel affect frequency response, or does it affect max volume? I'm less concerned with volume and more with frequency response.
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Old 10th October 2002, 06:36 PM   #20
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Quote:
Originally posted by Altaic
[frusterated rant]

I don't think I need to coat my stators, because I'm making sealed ESLs, so it shouldn't arc until I get upwards of 10kV. Because the stators are uninsulated, shouldn't the voltage not need to be so high? Or is voltage a function of distance between stators? I initially thought to space the stators farther apart because I can have much higher voltage with no problem, and then the diaphram would have more travel, but now I'm thinking it would be better to shorten that distance. Does travel affect frequency response, or does it affect max volume? I'm less concerned with volume and more with frequency response.
Don't worry about the transformers so much. One or two 8-10k primary side transformers per speaker will be more than adequate. Many people have built speakers using these and they work fine, even with relatively low powered amps to drive them.

Coating the stators is not done to prevent arcing. It is done to prevent corona discharge (a faint blue spark that continuously streams ions). Corona discharge makes a whining or hissing sound that is NOT high-fidelity at its finest. You do not have to coat the stators if you use a relatively low bias voltage (<=2kV or so).

Stator to diaphragm spacing has little effect on frequency response at low volume levels. At high volume, low bass will really slam the diaphragm back and forth, possibly hitting the stators. This is why full range ESLs have a reputation for not being able to play loudly.

Most people solve the problem by using conventional bass drivers in a box. Then you have to deal with crossovers...

Isn't engineering wonderful? It isn't about making things cheaper. Its about making trade-offs.

MR
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