UcD400 Q & A

[pburke]

Originally posted by kuribo
Curious as to why you would add all the bypass caps after Bruno said they were unnecessary????

because that's how I do things - I overbuild them. They work for me in all other applications.

I'll also use transformers about 50% to 100% larger than he recommends. Why? Well, it won't have a negative impact, and I can't imagine how an amp can deliver high current for more than a moment if the transformer can't feed those dinky little caps with fresh juice in a hurry.

Heck, i'll double up on the capacitance as well.

But, hey, feel free not to do this. I'm sure it'll work just fine in the generic config.

Peter

[kuribo]

I understand; just wondered if there was some specific reason. Interested to hear how your amp turns out!

best of luck....

[DSP_Geek]

Hey Bruno,

Could you look at this and tell me whether I Get It:

Power supply pumping in class-D amplifiers occurs when the output delivers DC or very low frequencies, nicht wahr? In the case of woofers with 2 voice coils, and assuming 2 UcDs per woofer (as I have), does it make sense to drive the VCs with UcDs wired in antiphase?

Another question: is potential supply pumping reduced if the signal is high-pass filtered at 120 Hz? I ask because I can get my hands on parts for a 63 volt supply, which is about 20% below the 75 volt rating on the UcD400 output devices (although I might need to disable the OVP since it might kick in).


Thanks in advance,
Francois.

[analogspiceman]

Originally posted by classd4sure
AnalogSpiceman, may I be so bold as to request you post a quick diagram of your recommended bypass method? I'd appreciate it.

Just solder the caps directly across the bridge terminals. With only two caps they should go "-" to (first) "ac" and "-" to (second) "ac". With all four caps add two more from "+" to (first) "ac" and "+" to (second) "ac". This should be easy enough to do that you could try both configurations and see if either makes a noticeable difference in audible system noise.

Regards -- analog(spiceman)

[chrisb03]

Originally posted by analogspiceman

Just solder the caps directly across the bridge terminals. With only two caps they should go "-" to (first) "ac" and "-" to (second) "ac". With all four caps add two more from "+" to (first) "ac" and "+" to (second) "ac". This should be easy enough to do that you could try both configurations and see if either makes a noticeable difference in audible system noise.

Regards -- analog(spiceman)

Is this what your talking about.

http://www.lcaudio.dk/com/predpsu.gif

[Bruno Putzeys]

Originally posted by DSP_Geek
Power supply pumping in class-D amplifiers occurs when the output delivers DC or very low frequencies, nicht wahr? In the case of woofers with 2 voice coils, and assuming 2 UcDs per woofer (as I have), does it make sense to drive the VCs with UcDs wired in antiphase?

It does, and it is essentially the same as bridging. Full bridge class D amplifiers do not suffer from pumping in the same manner.
(Pumping does exist in full-bridge amps, but only momentarily when delivering power into strongly reactive loads)

Originally posted by DSP_Geek
Another question: is potential supply pumping reduced if the signal is high-pass filtered at 120 Hz? I ask because I can get my hands on parts for a 63 volt supply, which is about 20% below the 75 volt rating on the UcD400 output devices (although I might need to disable the OVP since it might kick in).

For a given power supply capacitance, the lower the audio frequency, the greater the effect gets. Likewise, for a given amount of "supply tolerance", the bigger you make the supply caps, the lower you can go in frequency before you trigger something.

I've never seen the pumping effect do anything noticeable on real music. You need quite specific test signals and test loads before anything dramatic happens.
For realistic (unfiltered) music signals and normal speakers, normally sized caps (2x4700u for 8 ohm, 2x10000u for 4 ohm) is enough to keep your amplifier happy.

[hansen]

Thanks to Bruno and Jan-Peter for answering all questions so far. This is really excellent "pre-sales support" :-)

Another question:

The UcD400 will give about 400W in 4 Ohm and 210W in 8 Ohm. How are they behaving into lower impedances? My speakers dip to 2.3 Ohm at about 55Hz.

[Jan-Peter]

Hanse,

Tis is no problem, when you ask to much current the protection starts to work. With normaly musicsignal this will not be a problem.

The UcD400 has a piek current protection, when the current comes above 15A piek, the amps is shut down for 1-2 sec.

Regards,

Jan-Peter

www.hypex.nl

[jkeny]

Bruno, Jan Peter,

Great support you are giving here. In order to get a comparison of the two modules - Could you rate them sonically on a scale 1-100 (where 100 is the impossible nirvana). If you can give a rating for Highs,Mids & Lows - this would allow decisions to be made on the correct module for driving tweeters, woofers, subs etc in an active speaker setup.

I don't believe I need the power of the 400 as I will be driving the classic BBC LS3/5A speakers (Nominal 15 ohm and no severe dips although low sensitivity 82dB). But if the 400 is sonically better than 180, I would use it anyway.

John

[Bruno Putzeys]

Originally posted by jkeny
Bruno, Jan Peter,

Great support you are giving here. In order to get a comparison of the two modules - Could you rate them sonically on a scale 1-100 (where 100 is the impossible nirvana). If you can give a rating for Highs,Mids & Lows - this would allow decisions to be made on the correct module for driving tweeters, woofers, subs etc in an active speaker setup.

I don't believe I need the power of the 400 as I will be driving the classic BBC LS3/5A speakers (Nominal 15 ohm and no severe dips although low sensitivity 82dB). But if the 400 is sonically better than 180, I would use it anyway.

John

Basically the 400W and 180W amps sound very much the same. You should choose either depending on your power requirements.

In practice, the 400W uses a different op amp and no coupling caps, which could give it an edge over the stock 180W.