Non clocked (e.g. free running, self oscillating) class d

[analogspiceman]

Originally posted by Bruno Putzeys

Never had this problem. I'm afraid the quality of my board layouts is getting in the way of me getting hard knock education

Good for you, Bruno. My hat's off to you. <tip>

[Bruno Putzeys]

Originally posted by Bruno Putzeys
For a class D amp, it's much more efficient to perform current mode control on the output cap instead of the coil.
(...)
Yes, I am saying this is a better method than leapfrog.

I just realised that the LF schematics show current sense points before and after the caps, which means that capacitor current is sensed as well.
This means as much as that cap current control methods (Mueta, UcD) can be mapped onto the LF topology.
I was a bit too quick there.

[dmfraser]

Go to this site and download the papers describing how the ICE Power people do it.

http://www.powerhouse.bang-olufsen.com/sw1061.asp

I am most happy with their sound quality. Some other features no, but their sound quality and reliability have been most satisfactory.

[Bruno Putzeys]

How have the listening tests on UcD worked out for you?

[dmfraser]

Unfortunately I had to go on a service call to Portugal for my employer so my listening tests were cut short. Got to see some really great architecture though. Charles De Gaulle Airport makes LAX look like something from the 50s designed by a not very imaginative engineer.

All I have ben able to do is a direct comparison to my Leach amplifier, which I built some years ago. However, the two are essentially the same power and I found that the UcD180, while different in a few subtle ways was every bit as good as the Leach Class AB amplifier and in some ways is superior. Even where the UcD was different than the Leach I have to say it was merely different and not inferior.

My preliminary opinion is that this is an amplifier worthy of inclusion in the category of "good amplifier" from someone for whom a Leach amplifier is a decent mid range amplifier. And in measurement, I find it the sonic equal of the ICE 250A.

[ghemink]

Originally posted by dmfraser
Unfortunately I had to go on a service call to Portugal for my employer so my listening tests were cut short. Got to see some really great architecture though. Charles De Gaulle Airport makes LAX look like something from the 50s designed by a not very imaginative engineer.

All I have ben able to do is a direct comparison to my Leach amplifier, which I built some years ago. However, the two are essentially the same power and I found that the UcD180, while different in a few subtle ways was every bit as good as the Leach Class AB amplifier and in some ways is superior. Even where the UcD was different than the Leach I have to say it was merely different and not inferior.

My preliminary opinion is that this is an amplifier worthy of inclusion in the category of "good amplifier" from someone for whom a Leach amplifier is a decent mid range amplifier. And in measurement, I find it the sonic equal of the ICE 250A.

Then the leach amp must be a very good amp (better than my Accuphase) since no doubt, in my setup the UcD180 clearly outperforms my Accuphase (E407). It maybe that things like power supply and cabling have a significant influence, I did not check that, I used quite expensive ELNA Cerafines in the power supply for the UcD180 and I used very short wires from ELNA caps to the UcD180 (few cm). Maybe Bruno can comment on the influence of the power supply caps on the sound quality?

Best regards

Gertjan

[Dibley]

I dont understand how a capacitor can offer anything more than a parallel capacitance, resistance, inductance/ impedance circuit? A storage device with a time constant which charges, discharges continuously.
Not my question but it is a good idea to use low ESR caps, rubycon offer some excellent options with ultra low impedance, also using smaller values in parallel will reduce this ESR factor.

[Bruno Putzeys]

Originally posted by Dibley
I dont understand how a capacitor can offer anything more than a parallel capacitance, resistance, inductance/ impedance circuit? A storage device with a time constant which charges, discharges continuously.
Not my question but it is a good idea to use low ESR caps, rubycon offer some excellent options with ultra low impedance, also using smaller values in parallel will reduce this ESR factor.

I've yet to hear a low esr cap sound good. Especially the rubicons you're suggesting make for a crappy sound.
Part of the problem is that their ESR is so low that their ESL gets to have an excessive Q, which shows up when other capacitors are placed in parallel.
Another part is that in "optimised esr caps" half of the esr is electrolytic, the other half is winding resistance. This produces a second, short time constant which is more than you signed up for.
Both effects are very easy to see on an oscilloscope when applying a pulsed signal to the cap in circuit.
You don't need to turn on your "golden ears", although it often helps to do so. It provides the necessary incentive to go looking for problems which otherwise would have gone unnoticed.

[Dibley]

Hello Bruno, thanks for the interesting reply. Do you mean to say that the tuned RCL circuit gets to have an excessive Q? Isn't this Q in the region required for switching around 500KHz to 1MHz where we will require instant
discharge of current (allied to DC for half( 95-5% cycle) and ultimately low resistance?
I will do some bench tests as I have a range of Low ESR caps and some ELNA 10000uF caps and take some measurements on a digital scope discharging them into 2 ohm/0ohm loads just for curiosity. It will be good to see the step in the LESR caps and the lack of step in the regular caps - perhaps they will both have a step ; - ).

[Bruno Putzeys]

A classic situation is a 1000uF cap with a 100nF cap in parallel. If you feed this combo a square wave current, the ringing will be fairly obvious.

Even with normal-esr electrolytics the effect is already marked, a problem I solve by adding a smaller electrolytic across the two. The esr of the smaller cap will serve to absorb the ringing (damp the lc circuit).

You'd only use low esr caps when there is no other way round a maximum ripple current problem (ie when lesser types blow up due to internal overheating) and when space is a serious concern.