Speaker ground?
Hi Jan-Peter,
I heard earlier on the forum that speaker grounds were to be taken from the module because of some looping questions, is this true?
I ask because my intended tweeter connectors have chassis ground (they're UHF coaxial connectors, yes I *know* it's weird to hook up speakers with RF connectors, but this works for me). I can run the speaker ground line from the module to these things, but at the end of the day they're still grounded to chassis, and thus to each other and everything else hooked up to chassis.
Will this be a problem?
Cheers,
Francois.
Hi Jan-Peter,
I heard earlier on the forum that speaker grounds were to be taken from the module because of some looping questions, is this true?
I ask because my intended tweeter connectors have chassis ground (they're UHF coaxial connectors, yes I *know* it's weird to hook up speakers with RF connectors, but this works for me). I can run the speaker ground line from the module to these things, but at the end of the day they're still grounded to chassis, and thus to each other and everything else hooked up to chassis.
Will this be a problem?
Cheers,
Francois.
Hi DSP_Geek,
We use a balanced feedback network, so the both speakerterminals are sensed in this way.
You don't have to use it, but for the highest sonic performance this will be ofcourse the best!
Regards,
Jan-Peter
We use a balanced feedback network, so the both speakerterminals are sensed in this way.
You don't have to use it, but for the highest sonic performance this will be ofcourse the best!
Regards,
Jan-Peter
UCD180 and electrostatics
Hello Jan-Peter
The capacitance is more than 100 pf, rather 1,200 pf...
Of course I don´t know the reactive capacitance of the transformer. I took a reading on the DC resistance, it´s
around 250 ohms.
Do these values give you an ideia about any possible
lack of compatibility?
Thanks for the feedback.
Hello Jan-Peter
The capacitance is more than 100 pf, rather 1,200 pf...
Of course I don´t know the reactive capacitance of the transformer. I took a reading on the DC resistance, it´s
around 250 ohms.
Do these values give you an ideia about any possible
lack of compatibility?
Thanks for the feedback.
Regarding ESL impedance:
The capacitance of the ESL panel is "multiplied up" by the square of the transformer turns ratio. This means that the effective capacitance seen by the power amplifier can be 3 to 12 uF or higher. This is a bit too much for most amplifiers for high quality reproduction. I recently measured my electrostatic panels. They are equivalent to and LRC series circuit with 13.4 uF capacitance, 11.6 uH inductance (leakage inductance of the transformer), and 1.324 ohms resistance (this includes 1 ohm "tuning resistor" and 0.324 ohm effective transformer resistance).
It would be of interest to measure ucd amplifier performance into the load described above using an LRC circuit, checking stability and distortion.
Martin Logan publishes the minimum impedance for their products on their web site.
The capacitance of the ESL panel is "multiplied up" by the square of the transformer turns ratio. This means that the effective capacitance seen by the power amplifier can be 3 to 12 uF or higher. This is a bit too much for most amplifiers for high quality reproduction. I recently measured my electrostatic panels. They are equivalent to and LRC series circuit with 13.4 uF capacitance, 11.6 uH inductance (leakage inductance of the transformer), and 1.324 ohms resistance (this includes 1 ohm "tuning resistor" and 0.324 ohm effective transformer resistance).
It would be of interest to measure ucd amplifier performance into the load described above using an LRC circuit, checking stability and distortion.
Martin Logan publishes the minimum impedance for their products on their web site.
ESL and class D amps
Interesting, to say the least.
I had no ideia about these numbers and it comes to me that
I had the wrong notion on the final capacitance of my Esl.
Funny because I was only thinking in terms of picofarads,
never UF.
Now I understand why my small class T Sonic impact blew
right away as soon I connected it to the Esl. This was the
reason why I started all these questions, obviously I don´t
want the same to happen to an Ucd module.
Thanks anyway for your input.
Interesting, to say the least.
I had no ideia about these numbers and it comes to me that
I had the wrong notion on the final capacitance of my Esl.
Funny because I was only thinking in terms of picofarads,
never UF.
Now I understand why my small class T Sonic impact blew
right away as soon I connected it to the Esl. This was the
reason why I started all these questions, obviously I don´t
want the same to happen to an Ucd module.
Thanks anyway for your input.
Well, my dear and old friend Mateus, some idea of what to make with your
Electrostatic speaker is passing insistently inside my mind...well, well, what to make with those electrostatic...hummmmm, too big they are my dear friend....hummmm.
I will not say here or even personally, but i never heard notices about my passed ESL friends, i am imagining if they were electrocuted or have bad digestion eating ESL with mustard at breakfast. They disappeared as a magic!
Despite sounding wonderfull, it is something alike a cover to coffin in size, and create zilion problems to match with amplifiers made in planet earth.
I am very close to discover, if the amplifiers are not adequated to ESL, or if ESL is not adequated to amplifiers.
Will burn last neuronium to discover that, but i have some idea to use your ESL...will tell ya directly...hehe
Carlos
Electrostatic speaker is passing insistently inside my mind...well, well, what to make with those electrostatic...hummmmm, too big they are my dear friend....hummmm.
I will not say here or even personally, but i never heard notices about my passed ESL friends, i am imagining if they were electrocuted or have bad digestion eating ESL with mustard at breakfast. They disappeared as a magic!
Despite sounding wonderfull, it is something alike a cover to coffin in size, and create zilion problems to match with amplifiers made in planet earth.
I am very close to discover, if the amplifiers are not adequated to ESL, or if ESL is not adequated to amplifiers.
Will burn last neuronium to discover that, but i have some idea to use your ESL...will tell ya directly...hehe
Carlos
We should await Jan-Peter's comments on this, but generally the insertion of the very large capacitive load of an ESL63 in series with the existing 680nF output filter will seriously affect the filter's effectiveness at removing the 350KHz switching noise of the UcD module. This filter is designed to work primarily with resistive loads, with a little inductance thrown in, that is, conventional electro-dynamic speakers.
This means that the ESL itself will comprise about 95% of the reactive (capacitive) load of the 'filter'. It may not damage the ESL because it will dissipate most of this power in the transformer, but it could cause nasty problems for the output stage of the UcD because it is still a feedback amplifier.
If it turns out the UcD180 cannot drive an ESL, as I suspect, then this is probably no cause for alarm. The ESL was created by Walker Inquisition Laboratories (UK) in the sixties specifically to torture amplifiers, so failure at this draconian test puts it in the company of some of the world's best amplifiers.......
Cheers,
Hugh
This means that the ESL itself will comprise about 95% of the reactive (capacitive) load of the 'filter'. It may not damage the ESL because it will dissipate most of this power in the transformer, but it could cause nasty problems for the output stage of the UcD because it is still a feedback amplifier.
If it turns out the UcD180 cannot drive an ESL, as I suspect, then this is probably no cause for alarm. The ESL was created by Walker Inquisition Laboratories (UK) in the sixties specifically to torture amplifiers, so failure at this draconian test puts it in the company of some of the world's best amplifiers.......
Cheers,
Hugh
Ahahaha!, to torture amplifiers!
Well Mateus....write on it in a good latim language:
"Revertere ad locum tum".... that means return to earth, your mother earth.
I will prepare my black jacket!
My God!..... to torture is terrible Mat!!!
Carlos
Well Mateus....write on it in a good latim language:
"Revertere ad locum tum".... that means return to earth, your mother earth.
I will prepare my black jacket!
My God!..... to torture is terrible Mat!!!
Carlos
More on ESL impedance:
The model I posted above (series RLC with 13.4 uF capacitance, 11.6 uH inductance, and 1.324 ohms resistance) implies an impedance that has a minimum of 1.324 ohms at between 10 and 15khz, but it rises to greater than 20 ohms at the switching frequency of the ucd amps (the impedance is highly inductive up there, highly capacitive below 10khz). A conjugate network (RLC network) can be used to flatten the impedance to 4 ohms in the high frequency range if this is necessary for the stability of the ucd amplifier.
Again, most amplifiers do not perform really well such such loads, but a few do OK.
In my case I am using a tube amplifier that just happens to work quite well (measuring a fraction of a dB drop in amplitude at the point of minimum impedance, despite the 0.6 ohm output impedance of the amplifier).
The model I posted above (series RLC with 13.4 uF capacitance, 11.6 uH inductance, and 1.324 ohms resistance) implies an impedance that has a minimum of 1.324 ohms at between 10 and 15khz, but it rises to greater than 20 ohms at the switching frequency of the ucd amps (the impedance is highly inductive up there, highly capacitive below 10khz). A conjugate network (RLC network) can be used to flatten the impedance to 4 ohms in the high frequency range if this is necessary for the stability of the ucd amplifier.
Again, most amplifiers do not perform really well such such loads, but a few do OK.
In my case I am using a tube amplifier that just happens to work quite well (measuring a fraction of a dB drop in amplitude at the point of minimum impedance, despite the 0.6 ohm output impedance of the amplifier).
So, as Goudey is showing us, those speaker represents to amplifiers...
represents some load that is a hell thing to power amplifiers.
Amplifier output have to be stable with enormous capacitance, this is hard to construct and design.
The amplifier have to work with something that may be very near to a short circuit, will be expensive as will have a lot of output units in parallell,
Will need special Hi voltage transistors, as this "spring effect", coil counter force will produce thousand volts that will "cook" any normal transistors.
As this is a hell speaker, needing a hell solution to work, a good place to send it, my dear friend Mateus...hehehe..... will not say...no,no,no!...you will have to conclude.... you must send it to work with some low power class A, as spikes can be reasonable, and those amplifiers can stay alive after a nuclear war...class A and some insects too.
Have some beer John, and say some names to the speaker...i will send you a list of names by direct mailing...this way you will send all demons out of the grille cloth.
My God!
Carlos
represents some load that is a hell thing to power amplifiers.
Amplifier output have to be stable with enormous capacitance, this is hard to construct and design.
The amplifier have to work with something that may be very near to a short circuit, will be expensive as will have a lot of output units in parallell,
Will need special Hi voltage transistors, as this "spring effect", coil counter force will produce thousand volts that will "cook" any normal transistors.
As this is a hell speaker, needing a hell solution to work, a good place to send it, my dear friend Mateus...hehehe..... will not say...no,no,no!...you will have to conclude.... you must send it to work with some low power class A, as spikes can be reasonable, and those amplifiers can stay alive after a nuclear war...class A and some insects too.
Have some beer John, and say some names to the speaker...i will send you a list of names by direct mailing...this way you will send all demons out of the grille cloth.
My God!
Carlos
Hi,
attached is a simulated response of UcD180 to 10kHz burst signal into proposed ESL load. UcD180 simulation model was provided by Analogspiceman here.
Traces are:
red=input voltage
green=UcD output voltage
blue=UcD filter inductor current
grey=13.4uF load capacitor voltage
It can be seen that classD amplifiers are actually capable of driving ESL. Problem with actual UcD circuit might be current limit since peak mosfet current in simulation exceeds 22A.
I also think that it would be possible to design classD amp without output filter using actual ESL speaker as a filter. It should be integrated with outpt transformer, or you would enter EMI hell. Also high voltage feedback might be a little problematic. Transformer losses from switching action of output stage might also be problematic, although my experiience shows that deltaB of less than 25mT at 80kHz is quite acceptable for standard iron cores.
Best regards,
Jaka Racman
attached is a simulated response of UcD180 to 10kHz burst signal into proposed ESL load. UcD180 simulation model was provided by Analogspiceman here.
Traces are:
red=input voltage
green=UcD output voltage
blue=UcD filter inductor current
grey=13.4uF load capacitor voltage
It can be seen that classD amplifiers are actually capable of driving ESL. Problem with actual UcD circuit might be current limit since peak mosfet current in simulation exceeds 22A.
I also think that it would be possible to design classD amp without output filter using actual ESL speaker as a filter. It should be integrated with outpt transformer, or you would enter EMI hell. Also high voltage feedback might be a little problematic. Transformer losses from switching action of output stage might also be problematic, although my experiience shows that deltaB of less than 25mT at 80kHz is quite acceptable for standard iron cores.
Best regards,
Jaka Racman
Attachments
Jaka, good work on the simulation of the ESL load.
I presume that you also included the resistor and inductor elements of the ESL model.
I have been wondering if the ucd amplifiers might be the "magic amplifiers" that work with ESLs. The ucd is strange in that its stability (or designed-in instability to ensure oscillation) depends upon oscillation where most loudspeakers present an inductive load (at > 400khz). Whether ESL or conventional, for such speakers the ucd output filter will dominate the open-loop gain at the oscillation frequency. The peak output current required is another issue.
I have thought of building a ucd-based ESL amplifier with the transformer installed inside the amplifier to form a simple second stage of RF filtering. Another approach, simpler to implement, is to move the ESL "tuning resistor" (the 1 ohm resistor I mentioned) into the amplifier case, and add an impedance compensated notch that would provide > 20 dB suppression between 400 and 500khz. The load seen by the amplifier would be about 4-6 ohms between 30khz and 1Mhz.
I presume that you also included the resistor and inductor elements of the ESL model.
I have been wondering if the ucd amplifiers might be the "magic amplifiers" that work with ESLs. The ucd is strange in that its stability (or designed-in instability to ensure oscillation) depends upon oscillation where most loudspeakers present an inductive load (at > 400khz). Whether ESL or conventional, for such speakers the ucd output filter will dominate the open-loop gain at the oscillation frequency. The peak output current required is another issue.
I have thought of building a ucd-based ESL amplifier with the transformer installed inside the amplifier to form a simple second stage of RF filtering. Another approach, simpler to implement, is to move the ESL "tuning resistor" (the 1 ohm resistor I mentioned) into the amplifier case, and add an impedance compensated notch that would provide > 20 dB suppression between 400 and 500khz. The load seen by the amplifier would be about 4-6 ohms between 30khz and 1Mhz.
This looks like a perfect application for the leapfrog method of switching amplifier design. 🙂 🙂 I noticed that with critical damping, the ESL rolls off the upper treble starting at about 12kHz or so. This could probably be extended to >20kHz closed loop BW with leapfrog.goudey said:
Actually, since the ESL is well damped, just a passive, open loop pre emphasize would probably do. -- a.s.
regarding ESLs and step-up transformers, I should mention:
The output voltage of the ESL step-up transformer can be lethal, or can lead to severe damage of vital organs. We haven't had many reports of death-by-electrocution arising from the use of electrostatic loudspeakers, but I am sure we would if the proper precautions are not taken to make accidental contact with the high voltages nearly impossible. For this reason I have discarded the idea of moving the step-up transformer into the amplifier case, though this may make sense if the amplifier case is then permanently installed and attached to the ESL loudspeaker.
regarding the leapfrog method:
I took a quick look at the writeup at the start of the leapfrog thread. It looks like the analysis of the design can be repeated using the ESL load model to determine the overall response. Such a design may offer good load independence (for ESL and conventional) and good filtering of the switching frequency.
Back to the ucd amps:
I am seriously considering acquiring some ucd400's to see how they work into an ESL. I think it will work, but I want the higher power ucd400 rather than the ucd180 simply because ESLs benefit from higher voltage and better current reserves.
The output voltage of the ESL step-up transformer can be lethal, or can lead to severe damage of vital organs. We haven't had many reports of death-by-electrocution arising from the use of electrostatic loudspeakers, but I am sure we would if the proper precautions are not taken to make accidental contact with the high voltages nearly impossible. For this reason I have discarded the idea of moving the step-up transformer into the amplifier case, though this may make sense if the amplifier case is then permanently installed and attached to the ESL loudspeaker.
regarding the leapfrog method:
I took a quick look at the writeup at the start of the leapfrog thread. It looks like the analysis of the design can be repeated using the ESL load model to determine the overall response. Such a design may offer good load independence (for ESL and conventional) and good filtering of the switching frequency.
Back to the ucd amps:
I am seriously considering acquiring some ucd400's to see how they work into an ESL. I think it will work, but I want the higher power ucd400 rather than the ucd180 simply because ESLs benefit from higher voltage and better current reserves.
UCD and ESL
Let us know, Goudey, how the result was, it would be interesting to know.
My ESL were made from scratch and the transformers were
salvaged from an old tube amplifier, they are big ones for
40 watts, but I´m not sure if they are more than 50:1 turns
ratio even though they respond quite well.
What I´m trying to say is does this have any effect on the
impedance or otherwise parameters seen by the amplifier?
Let us know, Goudey, how the result was, it would be interesting to know.
My ESL were made from scratch and the transformers were
salvaged from an old tube amplifier, they are big ones for
40 watts, but I´m not sure if they are more than 50:1 turns
ratio even though they respond quite well.
What I´m trying to say is does this have any effect on the
impedance or otherwise parameters seen by the amplifier?
jmateus:
Quick answer: Nothing so far indicates a problem with your particular ESL setup, other than the somewhat low turns ratio and the resulting loss of peak sound output. The general question of compatibility of the ucd amplifiers with and ESL is unproven but plausible. Until proven any attempt should be considered an experiment and appropriate precautions should be taken, such as starting with a high value of the tuning resistor.
You can measure the impedance of the transformer/ESL panel yourself if you have the right equipment (oscillator, voltmeters, amplifier). If not, then we can only guess the parameters of the transformer. A 50:1 ratio may be correct for a 40 watt amplifier, though it could be more or less. For a 1200pF ESL panel this gives a 3 uF net capacitance as seen by the amplifier (multiplying by 50 squared).
You will need a tuning resistor in series with the transformer winding on the amplifier side, probably between 1 and 2 ohms (determined by experiment). The transformer resistance may be approximated by the sum of:
The DC resistance of the amplifier-side winding and
The DC resistance of the ESL side winding divided by the turns ratio squared.
The leakage inductance is unknown, but probably not of concern (can't be changed).
One option to ensure compatibility with most any amplifier is to use a 4 ohm tuning resistor and then fix the resulting high frequency rolloff by using electronic equalization before the amplifier. There is of course the issue complexity and additional peak voltage required, but high peak sound levels at such high frequences would cause hearing damage anyway, so maybe its not a problem.
Quick answer: Nothing so far indicates a problem with your particular ESL setup, other than the somewhat low turns ratio and the resulting loss of peak sound output. The general question of compatibility of the ucd amplifiers with and ESL is unproven but plausible. Until proven any attempt should be considered an experiment and appropriate precautions should be taken, such as starting with a high value of the tuning resistor.
You can measure the impedance of the transformer/ESL panel yourself if you have the right equipment (oscillator, voltmeters, amplifier). If not, then we can only guess the parameters of the transformer. A 50:1 ratio may be correct for a 40 watt amplifier, though it could be more or less. For a 1200pF ESL panel this gives a 3 uF net capacitance as seen by the amplifier (multiplying by 50 squared).
You will need a tuning resistor in series with the transformer winding on the amplifier side, probably between 1 and 2 ohms (determined by experiment). The transformer resistance may be approximated by the sum of:
The DC resistance of the amplifier-side winding and
The DC resistance of the ESL side winding divided by the turns ratio squared.
The leakage inductance is unknown, but probably not of concern (can't be changed).
One option to ensure compatibility with most any amplifier is to use a 4 ohm tuning resistor and then fix the resulting high frequency rolloff by using electronic equalization before the amplifier. There is of course the issue complexity and additional peak voltage required, but high peak sound levels at such high frequences would cause hearing damage anyway, so maybe its not a problem.
HI All,
With Quad ESL speakers (yes the old radiator-like monstrosities), the way to test if the amplifier is stable enough to drive the speaker used to be to have a 1KHz square wave input to the amp, 8Ohms load, and put a 2Uf capacitor in parallel to the load.
If there was no excesive "ringing" (overshoot on the leading and falling edges) on the output of the amp, it is deemed stable enough.
This has been borne out by numerous tests I did with almost any brand of amplifier. Some amps just burned if the output was over 10% of maximum power, and some, like Quad (of course) SAE, Crown and Krell did fine.
I haven't tested this with my modules, but that I think is the way to go....
Any comment is welcome, and I'l be trying this next week and get posted some real time results.
With Quad ESL speakers (yes the old radiator-like monstrosities), the way to test if the amplifier is stable enough to drive the speaker used to be to have a 1KHz square wave input to the amp, 8Ohms load, and put a 2Uf capacitor in parallel to the load.
If there was no excesive "ringing" (overshoot on the leading and falling edges) on the output of the amp, it is deemed stable enough.
This has been borne out by numerous tests I did with almost any brand of amplifier. Some amps just burned if the output was over 10% of maximum power, and some, like Quad (of course) SAE, Crown and Krell did fine.
I haven't tested this with my modules, but that I think is the way to go....
Any comment is welcome, and I'l be trying this next week and get posted some real time results.
Arty123:
The test you are suggesting may be helpful for understanding general amplifier stability (with the help of a signal generator and an oscilloscope), but does not well represent an ESL load. The load you suggest presents an impedance of less than 0.2 ohms at 400khz, and an impedance of about 3.6 ohms at 20khz. The typical ESL impedance is very low at 20khz, and very high at 400khz. The ucd amps rely on self-oscillation at about 450khz, so the impedance < 0.2 ohms may be a problem for it.
jmateus:
When you destroyed you Sonic Impact did you have a resistor in series with the transformer winding on the amplifier side? Without one the ESL setup will very likely either cause a weak amplifier to shut down or blow up. A resistor in series is necessary.
The test you are suggesting may be helpful for understanding general amplifier stability (with the help of a signal generator and an oscilloscope), but does not well represent an ESL load. The load you suggest presents an impedance of less than 0.2 ohms at 400khz, and an impedance of about 3.6 ohms at 20khz. The typical ESL impedance is very low at 20khz, and very high at 400khz. The ucd amps rely on self-oscillation at about 450khz, so the impedance < 0.2 ohms may be a problem for it.
jmateus:
When you destroyed you Sonic Impact did you have a resistor in series with the transformer winding on the amplifier side? Without one the ESL setup will very likely either cause a weak amplifier to shut down or blow up. A resistor in series is necessary.
I suppose I should chime in on the topic of UcD and electrostatics. I didn't exactly take the time to wade through the whole discussion so bear with me if I duplicate some answers.
A friend of mine has been using a pair of pre-hypex ucd's on his electrostatics for the better part of the last three years now, and before that the old SODA's. Intuitively one tends to worry about the high frequency behaviour of the combo. The load-independency of UcD makes this a non-issue. Even if you tie a pure 1uF capacitor straight to the output of the amplifier nothing noteworthy will happen. Besides, an electrostatic speaker is not a clean capacitance. Above 20kHz the leakage inductance of the stepup transformer takes over and the impedance becomes inductive.
No, the trouble lies at DC.
At DC, the speaker's impedance equals the resistance of the transformer primary, which is quite low. As long as you don't feed it DC, no problems. Unfortunately and surprisingly, AC coupling the input signal is not sufficient to prevent DC. As you may have seen on an oscilloscope, audio signals are asymmetrical. Any musical sound that has a second harmonic (=99.53% of all musical sounds) is asymmetrical. When you clip such a signal, you will inevitably chop off more on one side of the waveform than on the other. The result is that the chopped waveform has a DC component. This DC component produces a large current through the transformer primary and the short circuit protection cuts in.
This is not only a class D problem, any amplifier will run into trouble when clipped into a transformer load.
Another minor issue with half bridge amplifiers is that with a transformer load, not much DC offset at the output is tolerable before rail pumping occurs, tripping the overvoltage protection. Not normally a problem but not to be ignored either.
A friend of mine has been using a pair of pre-hypex ucd's on his electrostatics for the better part of the last three years now, and before that the old SODA's. Intuitively one tends to worry about the high frequency behaviour of the combo. The load-independency of UcD makes this a non-issue. Even if you tie a pure 1uF capacitor straight to the output of the amplifier nothing noteworthy will happen. Besides, an electrostatic speaker is not a clean capacitance. Above 20kHz the leakage inductance of the stepup transformer takes over and the impedance becomes inductive.
No, the trouble lies at DC.
At DC, the speaker's impedance equals the resistance of the transformer primary, which is quite low. As long as you don't feed it DC, no problems. Unfortunately and surprisingly, AC coupling the input signal is not sufficient to prevent DC. As you may have seen on an oscilloscope, audio signals are asymmetrical. Any musical sound that has a second harmonic (=99.53% of all musical sounds) is asymmetrical. When you clip such a signal, you will inevitably chop off more on one side of the waveform than on the other. The result is that the chopped waveform has a DC component. This DC component produces a large current through the transformer primary and the short circuit protection cuts in.
This is not only a class D problem, any amplifier will run into trouble when clipped into a transformer load.
Another minor issue with half bridge amplifiers is that with a transformer load, not much DC offset at the output is tolerable before rail pumping occurs, tripping the overvoltage protection. Not normally a problem but not to be ignored either.
dc protection
I saw the new ucd power supply and they have a DC protection , so looks like Hypex has choosed to put the realy on the rail . If so is it before or after the big power caps?
Giorgio
I saw the new ucd power supply and they have a DC protection , so looks like Hypex has choosed to put the realy on the rail . If so is it before or after the big power caps?
Giorgio