Which chip and whatever happened to Mueta and UCD?

[David M]

Hello!

I've been planning to change over my old stereo equipment and would like to play with ESLs. I've got a pretty good handle on that part but know that my little NAD receiver isn't going to drive a full-range ESL (I tried driving a small test speaker...the electronics all worked but the NAD could barely move the membrane).

I've been reading this site for quite awhile as well as Randy Sloane's various books and Nelson Pass' terrific site. There are so many options that it is hard for me to assess them all. What I would like is a SS amp that can drive at least 300W into 1 ohm and still sound better than good. I'd prefer to stay away from class A--heat issues and expensive heat sinks don't appeal much.

I have modest experience with electronics and know how to make a (simple) PCB. I don't mind being pushed pretty hard--education is a major motive for me and I'm not in a rush. I also don't mind failures if I can learn something from them.

So I've looked at various chip amps and transistors, read the specs, and still don't know what is durable enough and--preferably--has excellent sound. I've drooled over the Mueta claims, discussion of the Philips SODA and UCB but can't find enough hard information to fill a post-it note. I know that the non-switching amps like the LM3875 are very popular and are likely a good place to start. However, my impression is that switching amps are on the verge of large gains in the industry and I'd like to be much more familiar with them.

Why I'm pestering folks here:

--Can we expect Mueta/SODA/UCB to see the light of day any time soon? Does anyone have more than the marketing material on these devices? More than classd.org?

--Should I run away from switching amps while the going is still good?

--Of all the chip amps, transistors, and switching thingies which one do you feel performs best?

[subwo1]

Many folks like PWM amps for subwoofer applications for several reasons. They are efficient, enabling more output power from the electrical service with less wasted heat to make the listening environment hot. Subwoofers tend to have higher distortion so any higher amount from class D amps is less likely to be a problem. They are smaller, capable of as much driver damping as a larger completely linear amp, depending on topology--self-oscillating types like UCD tend to be better at load damping than pre-oscillated types.

[David M]

Thanks for the response. Ideally, anything I made/messed-up would be targeted at a full range speaker--and then preferably an ESL. Such a project would undoubtedly put me in over my head but that tends to be where I learn the most (what I'm intending is more educational than functional).

I know that many switching amps wouldn't like an ESL load but Mueta claims that their chip can. Other than what is discussed at classd.org I've found it very hard to find any solid info on UCD etc. Does anyone know a source/site/forum where I could learn more about these new up-and-coming amp chips?

[Pabo]

Muetas technology is a very complicated way around ICEpowers patents. ICEpower uses a technique where the modulation is performed at the frequency where the loop has exactly 180 degrees phase shift. The control signal is taken from the output voltage ripple. Mueta uses the same type of modulation but measure the current through the capacitor in the output filter instead. They thereby obtain the same advantages but they have to transform this signal into something that corresponds to a voltage since the current through a capacitor becomes higher and higher as the frequency increases. You can see that the topology becomes very complicated if you visit their homepage. Five OPAMPs and a signal transformer adds a large amount of cost.

You can find a lot of information about philips ucd technique if you search on patent number WO03090343 by Bruno Putzeys. The thing is that this technique very much reminds me about the ICEpower technique so I would not be surprised if ICEpower sends Bruno a letter some day. The fact that Bruno has also been granted a patent does not actually mean anything

[soren]

Originally posted by Pabo
ICEpower uses a technique where the modulation is performed at the frequency where the loop has exactly 180 degrees phase shift.

You can find a lot of information about philips ucd technique if you search on patent number WO03090343 by Bruno Putzeys.

The thing is that this technique very much reminds me about the ICEpower technique so I would not be surprised if ICEpower sends Bruno a letter some day. The fact that Bruno has also been granted a patent does not actually mean anything [/B]

Try check the ELEKTOR reference in Bruno's patent. 180 degrees of phaseshift in a closed modulator loop is not a new idea, since it is published here, dated 1979 . However, there are tonnes of diferent ways of achieving this, ICEpower has taken out a patent on one of them.

Basically the same modulator circuit is shown here:
http://www.reed-electronics.com/ednm...=0&rme=0&cfd=1

(figure 1)

[Pabo]

Interesting.

Do you know how to find a copy of that article?

[Pabo]

The article from EDN actually describes a voltage hysteresis amplifier based on a 90 degree phase shift topology. It is self oscillating but not in the sme way as ICEpower and ucd. Actually it is the same principle as ZapPulse uses.

[soren]

Originally posted by Pabo
The article from EDN actually describes a voltage hysteresis amplifier based on a 90 degree phase shift topology. It is self oscillating but not in the sme way as ICEpower and ucd. Actually it is the same principle as ZapPulse uses.

Correct, the figure shows a hysteresis based modulator. The hysteresis adds a time delay to the loop, giving an additional phase shift, increasing linearily with frequency. Automatically the delay will adjust to 180 degrees when the gain is 0dB, and voila... oscillation!

Other types of voltage mode hysteresis controllers are well known, e.g. german patent DE198 38 765 A1 and the class d audiototurial at IR.
This type has quite a bit better linearity thah the one from ELEKTOR.
BTW. I can send you a .pdf copy of the ELEKTOR article.

[Jaka Racman]

The thing is that this technique very much reminds me about the ICEpower technique so I would not be surprised if ICEpower sends Bruno a letter some day.

Hi,

if I recall correctly, ICEpower does not include output filter in feedback loop, but instead they use low pass filtered output from switching stage to achieve phase shift for oscillation. Not very similar design besides that both are self oscillating class D designs. Correct me if I am wrong.

Best regards,

Jaka Racman

BTW, UCD modules are now comercially available. Link.

[Pabo]

Jaka Racman

Sorry, you are mistaken.

ICEpower very much includes the output filter in their design.

You can read all about it on their homepage.