I built my electrostatics three years ago and I've been estatic with
their sound, either driven by my tube amplifiers or a JLH class A which
got to be my pride and joy.
But class D amplifiers came up on the scene some time ago and just
for kicks I bought one of those Sonic Impact 20 some dollar jobs which
I've been playing with good dynamic speakers. Good but not out of
this world.
Yesterday came the time for an experience, to connect the SI to the ESL's. Of course now I will say to myself "you should have never done that", and in fact I shouldn't, but the fact is the little thing called Sonic
Impact blew right before my eyes, it played for 2 or 3 seconds and then
quit working.
Can anyone help me to understand why the heck did my class T SI
blew that way? I've heard about amplifiers that are not very suitable
for the ESL, including regular class AB solid state amplifiers but I never
understood why...Is that because of the internal capacitance of the
ESL? What is wrong with 1,200 pf that the ESL show to the amplifier?
Is that capacitance determinant to the amplifier?
I really would like somebody to explain to me the true reason why certain amplifiers don't live well with electrostatics.
Thanks.
their sound, either driven by my tube amplifiers or a JLH class A which
got to be my pride and joy.
But class D amplifiers came up on the scene some time ago and just
for kicks I bought one of those Sonic Impact 20 some dollar jobs which
I've been playing with good dynamic speakers. Good but not out of
this world.
Yesterday came the time for an experience, to connect the SI to the ESL's. Of course now I will say to myself "you should have never done that", and in fact I shouldn't, but the fact is the little thing called Sonic
Impact blew right before my eyes, it played for 2 or 3 seconds and then
quit working.
Can anyone help me to understand why the heck did my class T SI
blew that way? I've heard about amplifiers that are not very suitable
for the ESL, including regular class AB solid state amplifiers but I never
understood why...Is that because of the internal capacitance of the
ESL? What is wrong with 1,200 pf that the ESL show to the amplifier?
Is that capacitance determinant to the amplifier?
I really would like somebody to explain to me the true reason why certain amplifiers don't live well with electrostatics.
Thanks.
Take a look at this for a good explanation of amplifier stability (not just op-amps) and capacitive loads: Stability
You can put an Ohm or two resistor in series with your amp and it might help, but that's a less than ideal solution. The real solution is to design the amp with sufficient phase margin to prevent instability.
I used to have a Carver amp that was one of their real small, high powered things (M200t if I recall correctly). It didn't like my ESLs at all. Piece of junk... Eventually cooked the power transformer which started buzzing loudly after that (not while driving ESLs- it sounded like **** with the ESLs because it was oscillating at ultrasonic frequency). I was glad to throw it away.
I_F
You can put an Ohm or two resistor in series with your amp and it might help, but that's a less than ideal solution. The real solution is to design the amp with sufficient phase margin to prevent instability.
I used to have a Carver amp that was one of their real small, high powered things (M200t if I recall correctly). It didn't like my ESLs at all. Piece of junk... Eventually cooked the power transformer which started buzzing loudly after that (not while driving ESLs- it sounded like **** with the ESLs because it was oscillating at ultrasonic frequency). I was glad to throw it away.
I_F
Class-d amps with pre-filter NFB (like this one) are usually quite robust regarding load impedance, apart from the subsequent response deviations.
There may be the odd case when the combined impedance of the filter and the load may cause trouble (like in your case). Another danger are the very LOW impedances of ESLs at high frequencies though I doubt that this was what caused your troubles since there is not much audio power needed up there usually.
Unfortunately many speaker manufacturers don't specify the impedance vs frequency properly for their ESLs. They just make statements like x Ohms @ y Hz.
IMO a switching amp with an output filter that is dimensioned exactly for that purpose might perform very well driving an ESL.
Regards
Charles
There may be the odd case when the combined impedance of the filter and the load may cause trouble (like in your case). Another danger are the very LOW impedances of ESLs at high frequencies though I doubt that this was what caused your troubles since there is not much audio power needed up there usually.
Unfortunately many speaker manufacturers don't specify the impedance vs frequency properly for their ESLs. They just make statements like x Ohms @ y Hz.
IMO a switching amp with an output filter that is dimensioned exactly for that purpose might perform very well driving an ESL.
Regards
Charles
Thanks for your answer phase accurate.
In fact this was my first opinion, that the odd impedance of the filter
and the capacitance of my ESL would have colide somehow...
As I said before I made the ESL, they were not any brand name
ready made, I made them from scratch so It's really difficult to say
what kind of impedance they have, the only thing I know is the output capacitance which is based on the physical dimensions of the panels.
Of course we can calculate de impedance (nominal, of course) as well
by other formulas taking other factors into consideration. But I never
did that, I was very happy they could play with no problems whatsoever
with my tube amplifiers or the JLH, class A so I never bother to do it.
Now that this happens with the SI, I'm debating very hard if I should
connect the module class D I'm working on now. This one is not that
cheap and I hate to have it damaged.
Oh well, thanks for your input.
In fact this was my first opinion, that the odd impedance of the filter
and the capacitance of my ESL would have colide somehow...
As I said before I made the ESL, they were not any brand name
ready made, I made them from scratch so It's really difficult to say
what kind of impedance they have, the only thing I know is the output capacitance which is based on the physical dimensions of the panels.
Of course we can calculate de impedance (nominal, of course) as well
by other formulas taking other factors into consideration. But I never
did that, I was very happy they could play with no problems whatsoever
with my tube amplifiers or the JLH, class A so I never bother to do it.
Now that this happens with the SI, I'm debating very hard if I should
connect the module class D I'm working on now. This one is not that
cheap and I hate to have it damaged.
Oh well, thanks for your input.
It is a module that 41Hz.com sells on their web site and is based on
Tripath chipset 2350, it´s supposed to be 2x300W nominally and is
supplied by +- 45 volts.
Before I bought it I adressed the problem of the ESL and was told,
after the guy consulted Tripath, that there would be no problem in
driving the ESL.
However after this stupid experience with the SI, I don't know if
I should take that kind of risk.
Tripath chipset 2350, it´s supposed to be 2x300W nominally and is
supplied by +- 45 volts.
Before I bought it I adressed the problem of the ESL and was told,
after the guy consulted Tripath, that there would be no problem in
driving the ESL.
However after this stupid experience with the SI, I don't know if
I should take that kind of risk.
The problem with ESL is that they look like a resonable size capacitor to the amplifier, say a couple of uF depending on type and stepup transformer.
Most commonamps don't like this, because they are designed to drive resistive loads.
The better amps can take a phase shifting load without problems.
The class D amps work very different. To filter out the PWM high frequency there is a special filter at the output.
Guess what is doing this capacitive load, read ESL, to this filter ?
That is what happend with your amp and it obvious couldn't take it.
I have heard of more problems with class D and ESL, even from the better brands so be warned.
Dick.
Most commonamps don't like this, because they are designed to drive resistive loads.
The better amps can take a phase shifting load without problems.
The class D amps work very different. To filter out the PWM high frequency there is a special filter at the output.
Guess what is doing this capacitive load, read ESL, to this filter ?
That is what happend with your amp and it obvious couldn't take it.
I have heard of more problems with class D and ESL, even from the better brands so be warned.
Dick.
What you said makes a lot of sense although I already had a pretty
good ideia that the filter at the output of the amplifier would somehow
crash (for better term) with the combination ESL and transformer capacity.
Instabiity at high frequencies in regular push pull amplifiers would
have a similar efect.
Anyhow I'll be aware of that in my next endeavour...
Thanks a lot for your enlightment.
good ideia that the filter at the output of the amplifier would somehow
crash (for better term) with the combination ESL and transformer capacity.
Instabiity at high frequencies in regular push pull amplifiers would
have a similar efect.
Anyhow I'll be aware of that in my next endeavour...
Thanks a lot for your enlightment.
I'd imagine the output filter (inductor) in a d-class would cause a "tank" effect with the load capacitance.
I've been giving ESL serious consideration in my next project. I've done some searching but can't seem to find anyone who has tried direct driving ESLs from a d-class by putting a step-up transformer before the output filter.....similar to many SMPS designs. Is there something fundamentally wrong with this approach?
Sam.
I've been giving ESL serious consideration in my next project. I've done some searching but can't seem to find anyone who has tried direct driving ESLs from a d-class by putting a step-up transformer before the output filter.....similar to many SMPS designs. Is there something fundamentally wrong with this approach?
Sam.
I tried to do this.I used TDA7294 and small toroid trannie with 1:1 step ratio.
Unfortunately , it didnt work well , altrough some sound was coming out of my speaker(I used regular speaker).It seems that low frequency is still generated in transformer.One my friend suggested that output should be filered with diodes first straight after transformer , similar to switching power supplies , but he was not sure. I didnt try this.
Any suggestions ? Would be interesting to build a ESL - Sub
).
Lukas
Unfortunately , it didnt work well , altrough some sound was coming out of my speaker(I used regular speaker).It seems that low frequency is still generated in transformer.One my friend suggested that output should be filered with diodes first straight after transformer , similar to switching power supplies , but he was not sure. I didnt try this.
Any suggestions ? Would be interesting to build a ESL - Sub
).Lukas
you have to keep the pwm duty cycle under 50% to stop the transformer from saturating. Therefore, you'd probably need it to step up. dunno about diodes between the transformer and the inductor. Ideas, anyone?
having a class-d that steps up before being filtered solves a few problems like tranformed capacitance, frequency response, etc.
comments welcome.
Sam.
having a class-d that steps up before being filtered solves a few problems like tranformed capacitance, frequency response, etc.
comments welcome.
Sam.
The Force
I just picked up a set of the NuForce Ref 8 switching mono blocks. These have been running a set of modified Acoustat 0ne plus 0ne's. These produce some of the very best sound that I have ever heard an Acoustat make. Play back level is very good however the Ref 8's will not quite make the stats go as loud as I know that they can. They can be made to shut down if you try to play too loud. I would say though that most folks would be very happy with the play back level that the 8's can achieve. The limiting factor in play back level is I think power supply clipping. These amplifiers do respond very well to the use of after market power cords which can sound very much better than do the stock cords which the units are supplied with. I should think that the Hypex UcD modules would equal or better the NuForce units. I see no reason why anyone would want to bother with huge hot analog amplifiers to run thier stats anymore. I do not think that I have heard an analog amp equal the switching amps regardless of price. The switching amps never even get warm. They are small and only weigh three pounds each. Time to make the change and save a lot of money and gain a lot of sound. A Hypex UcD180 module has a factory retail of 60 euro so a full amp could be built for 6-800 dollars depending on how you want it to look and your parts preference. Regards Moray James.
I just picked up a set of the NuForce Ref 8 switching mono blocks. These have been running a set of modified Acoustat 0ne plus 0ne's. These produce some of the very best sound that I have ever heard an Acoustat make. Play back level is very good however the Ref 8's will not quite make the stats go as loud as I know that they can. They can be made to shut down if you try to play too loud. I would say though that most folks would be very happy with the play back level that the 8's can achieve. The limiting factor in play back level is I think power supply clipping. These amplifiers do respond very well to the use of after market power cords which can sound very much better than do the stock cords which the units are supplied with. I should think that the Hypex UcD modules would equal or better the NuForce units. I see no reason why anyone would want to bother with huge hot analog amplifiers to run thier stats anymore. I do not think that I have heard an analog amp equal the switching amps regardless of price. The switching amps never even get warm. They are small and only weigh three pounds each. Time to make the change and save a lot of money and gain a lot of sound. A Hypex UcD180 module has a factory retail of 60 euro so a full amp could be built for 6-800 dollars depending on how you want it to look and your parts preference. Regards Moray James.
switching amp patents
hope these are of interest. Regards Moray James.
http://www.acutechnology.com/ClassD/Pat_list.html
hope these are of interest. Regards Moray James.
http://www.acutechnology.com/ClassD/Pat_list.html
Hi,
i tried class-D amps for my ESL's and i have been very surprised about the quality. I never expected these amps to match to ESL so perfectly.
Talking to the manufacturer of the amps, he told me that they match so good, since class-D amps do not care about capacitive load.
Take a look, unfortunaltely just in german language:
www.hifiakademie.de
capaciti
i tried class-D amps for my ESL's and i have been very surprised about the quality. I never expected these amps to match to ESL so perfectly.
Talking to the manufacturer of the amps, he told me that they match so good, since class-D amps do not care about capacitive load.
Take a look, unfortunaltely just in german language:
www.hifiakademie.de
capaciti
Hi
I made a posting on this subject before:
"The output stage of a digital amp is (basically) a pair of transistors generating a square wave of (say) +/- 50V. To make this more "analog" the square wave is put through a choke and then loaded by a capacitor, before being sent to the speaker.
If we could use (some sort of) transformer instead of the choke, we could produce a high voltage squarewave loaded by the ESL panel (being a capacitor in itself).
As the transformer would work at the sampling frequency (I suppose) say 96kHz, all the problems that are frequency related, as the transformer having to cope spanning from 20Hz to 20kHz, would be gone. Also, the efficiency would be much higher, i.e. it could be made smaller and cheaper."
I think (well...) that a class-d amp made for driving an ESL could possibly be just what would solve the problem. Haven't thought a lot about this but this is a forum for ideas really. Now wereees that beer...
/U
I made a posting on this subject before:
"The output stage of a digital amp is (basically) a pair of transistors generating a square wave of (say) +/- 50V. To make this more "analog" the square wave is put through a choke and then loaded by a capacitor, before being sent to the speaker.
If we could use (some sort of) transformer instead of the choke, we could produce a high voltage squarewave loaded by the ESL panel (being a capacitor in itself).
As the transformer would work at the sampling frequency (I suppose) say 96kHz, all the problems that are frequency related, as the transformer having to cope spanning from 20Hz to 20kHz, would be gone. Also, the efficiency would be much higher, i.e. it could be made smaller and cheaper."
I think (well...) that a class-d amp made for driving an ESL could possibly be just what would solve the problem. Haven't thought a lot about this but this is a forum for ideas really. Now wereees that beer...
/U
Hi Urban,
anyway you need the low-pass filter for a class-D amp. If you establish this filter on the secondary of the step-up transformer the value of the inductor coil need to be increased significantly to some tenth of millihenry. In addition such a coil need to handle +/-2,5KV square wave. Such a coil might cost even more than the stepup + the amp itself !!
Capaciti
anyway you need the low-pass filter for a class-D amp. If you establish this filter on the secondary of the step-up transformer the value of the inductor coil need to be increased significantly to some tenth of millihenry. In addition such a coil need to handle +/-2,5KV square wave. Such a coil might cost even more than the stepup + the amp itself !!
Capaciti
Hi Capaciti
I haven't given this much thought. I kind of see it before me as: An autoformer (transformer with just one winding) with a centertap held att (say) +200VDC, with two symetric taps at say 30% being driven by two MOSFETs (much as a standard tube outputstage). The end taps driving the ESL panel. Poosibly an extra winding for feedback.
If the swing at the MOSFET drain is +/-200V the swing at the end taps would be 200/0.3 = +/-670V at +200VDC (yes, a lot less than +/-2.5kV ....)
Skipping the secondary winding is possible because we don't have to put some 2kV to the centertap, as if tube driven, but a more humane +200VDC (just killing off small children and pets...). The autoformer is a lot more efficent. Also, on top of this is the high switch frequency. How would this work in the MHz region ?
Possibly the autoformer can/needs to be small to be able to work.....
A transformer is an induktance and an ESL panel a capacitor so basically it would make sense. I'm not sure that I follow you here. Yes the current flowing trough the autoformer winding is much lower than through the 'standard' class-d coil, and you need current trough the coil to get inductance.
If you don't shield this outputstage very well, possibly men in black suits would come knocking on your door claiming you have closed down all radiotraffic south of the north pole. Hmmm. Not to play with.
/U
I haven't given this much thought. I kind of see it before me as: An autoformer (transformer with just one winding) with a centertap held att (say) +200VDC, with two symetric taps at say 30% being driven by two MOSFETs (much as a standard tube outputstage). The end taps driving the ESL panel. Poosibly an extra winding for feedback.
If the swing at the MOSFET drain is +/-200V the swing at the end taps would be 200/0.3 = +/-670V at +200VDC (yes, a lot less than +/-2.5kV ....)
Skipping the secondary winding is possible because we don't have to put some 2kV to the centertap, as if tube driven, but a more humane +200VDC (just killing off small children and pets...). The autoformer is a lot more efficent. Also, on top of this is the high switch frequency. How would this work in the MHz region ?
Possibly the autoformer can/needs to be small to be able to work.....
A transformer is an induktance and an ESL panel a capacitor so basically it would make sense. I'm not sure that I follow you here. Yes the current flowing trough the autoformer winding is much lower than through the 'standard' class-d coil, and you need current trough the coil to get inductance.
If you don't shield this outputstage very well, possibly men in black suits would come knocking on your door claiming you have closed down all radiotraffic south of the north pole. Hmmm. Not to play with.
/U
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