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Class D Switching Power Amplifiers and Power D/A conversion

UCD180 or UCD400?
UCD180 or UCD400?
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Old 13th July 2004, 02:01 PM   #1
ghemink is offline ghemink  Netherlands
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Join Date: Jun 2004
Location: Japan
Question UCD180 or UCD400?

Hello all,

I`m quite new on this board and this is my first post. I have been following the threads on Class D amps.

I`m interested in Class D amps because my experiences with Class D are quite good up to now. I want to use the Class D amps in an active speaker system, so I need quite a number of amps in total.

I`m using now a Tripath based 4 channel amp from Marantz for mid and high (I think that amp is only available in Japan, by the way, I`m not Japanese, I`m from Holland, just working in Japan) and I`m using the power amp section of my Accuphase E407 integrated for the woofers. Woofers and mid are dipole speakers and tweeter is a Vifa ring radiator.

With the Marantz amp directly coupled to the tweeter, I have a little bit too much noise for my taste. During silent passages, I can hear the noise of the poweramps at the listening position. With normal non-active speakers (B&W CDM9NT), the noise is far less audible. So I`m looking for a very silent amp that sounds good. Have been thinking of buying the ICEpower based Enigma from Acoustic Reality. However, that amps is quite expensive, especially if you need 3 of them. For the price of one such amp I can buy a lot of Class D modules and start experimenting which is a lot of fun in itself. I have bough a couple of ZAPpulse modules from LCaudio. These have about 33dB gain or so (don`t need that much for the tweeter) and are therefore a bit too noisy as well. I may want to try to modify the feedback loop to get less gain out of them but I`ll wait a bit with that. I`m actually thinking of adding an additional UCD like feedback loop that takes the feedback after the output filter. That way I plan to reduce the gain (more feedback), correct some of the non-linearities of the output filter and have a better high-frequency behavior that is less dependent on the load (as in the UCD concept) and has a slower 1st order like roll-off without resonance peak.

In the mean time, I discovered that Hypex makes UCD based modules. The concept sure looks very interesting and taking the feedback after the output filter has potential advantages. So I want to try a few UCD modules as well to see what they bring.

Now I`m just wondering, which one should I use, the UCD180 or wait for the UCD400. I would like to know whether the UCD400 would have advantages over the UCD180 when I use it at low power, say with a +-40V power supply and at relatively low power levels for a tweeter. Is the deadtime less for the UCD400? Less distortion for the UCD400? Is the parasitic resistance of the output coil less? Any other differences in the specification between the two amps that could have benefits for my application (tweeter and midrange amps).

I can wait for the UCD400, I have enough amps right now to play music, just want to improve things further. Since both designers, Bruno and Jan-Peter are on this board, I hope to get some feedback from them (have got some feedback from them already with private mail, however, I think this subject maybe interesting for other readers as well).

My system consists of:

Teac Esoteric DV50 universal player
DEQX digital active 3-way filter and speaker correction system
Accuphase E407 integrated amp (used as preamp before the DEQX and as poweramp for the woofers)
Marantz DA04 4 channel Class D amp.
Speakers are a DIY 3-way (under development) and a passive B&W CDM9NT set
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Old 14th July 2004, 09:01 AM   #2
IVX is offline IVX  Russian Federation
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Well, while Bruno and Jan-Peter offline both, maybe you'll tell us about ZAPpulse sound quality?
Some time's ago here Lars said that several audio magazines after listening have estimated his amplifier very highly or highest even.
Would be great to see the sound comparison UcD vs others!
Best regards,
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Old 14th July 2004, 01:09 PM   #3
ghemink is offline ghemink  Netherlands
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Join Date: Jun 2004
Location: Japan
Hello IVX,

I will sure compare the ZAPpulse with the UCD once I have the UCD modules at home.

The ZAPpulse sounds good, I have not done extensive listening with the ZAPpulse because of my system that is still being developed. I have listened to the ZAPpulse with my CDM9NT speakers. Comparing them with the Accuphase E407 power amp (using the accuphase as pre-amp in both cases), I find the ZAPpulse better sounding (also the Tripath sounds better to my ears). However, I have to say that this is based on a listening session of only 1-2 hours or so already a few weeks ago. My real application for the ZAPpulses and/or the UCD modules is for the active 3-way I`m working on. The active 3-way sounds better than the CDM9NT, so it would be better to use the 3-way system for comparison. However, that is complicated again since then I need to hook up 6 amps. You see my problem. So to make a relatively fair comparison between all those amps without too much hassle, I probably need to dust of my CDM9NTs and hook them up to the various amps for a comparison. In that case I only need to build stereo amps instead of 6 channel amps.

I will keep you updated.

Best regards

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Old 15th July 2004, 07:23 AM   #4
Bruno Putzeys is offline Bruno Putzeys  Europe
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Join Date: Apr 2004
Location: BE/NL/RW/ZA

There is no advantage in using the 400W module at reduced powers. If 180W is enough, get the 180W module. If you need 400W, wait for that one. Using the 400W module for low powers will only result in higher idling losses (idling loss is typically 2% of rated output power).

Both modules have very similar measured performance. Both use the same grade of passives and the same opamp as preamp.

The inductor resistance does not differ by a lot either. It's on the order of 20mOhms either way.

Sonically they're completely interchangeable. You can put a 400W on one channel, a 180W on the other and never notice.

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Old 15th July 2004, 01:45 PM   #5
ghemink is offline ghemink  Netherlands
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Join Date: Jun 2004
Location: Japan
Hi Bruno,

Thanks for the additional info. I have ordered 4 of the UCD180 modules. I`ll check them 1st with my passive speakers to see (hear) how they compare with my other amps. Then I plan to use them in my active 3-way system for the mids and highs.

I`ll post again if I have some results.

Best regards


p.s. if you have any tips for tweaks, would be happy to hear them. Myself I`m thinking of possibly replacing the elco`s with black gates and possibly replacing the opamp with an OPA type or so. Also may want to reduce the gain of the preamp on the module to reduce the noise level. Have not heard them yet so can not judge the current noise level.
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