UcD400 Q & A

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P

pburke

Member
Joined 2003
didnt.doit.wisc.edu/audio/
kuribo said:
Curious as to why you would add all the bypass caps after Bruno said they were unnecessary????
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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
 
D

DSP_Geek

Member
Joined 2003
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.
 
A

analogspiceman

Member
Joined 2004
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.
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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)
 
C

chrisb03

Member
Joined 2004
members.optusnet.com.au/myamp/
analogspiceman said:

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)
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Is this what your talking about.

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

Bruno Putzeys

Member
Joined 2004
hypex.nl
DSP_Geek said:
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?
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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)


DSP_Geek said:
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).
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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.
 
H

hansen

Member
Joined 2004
More for the FAQ

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.
 
J

jkeny

Banned
Joined 2007
Sonic Rating of UCD400 Vs UCD180

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
 
B

Bruno Putzeys

Member
Joined 2004
hypex.nl
Re: Sonic Rating of UCD400 Vs UCD180

jkeny said:
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
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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.
 
T

Tangui

Member
Joined 2004
Re: Re: Sonic Rating of UCD400 Vs UCD180

Bruno Putzeys said:

In practice, the 400W uses a different op amp and no coupling caps, which could give it an edge over the stock 180W.
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So when you upgrade the UCD180 with a suitable opamp and bypass the caps, no need anymore for an UCD400 if 100W/8 Ohm is enough... :p

Jan-Peter, what voltage does the standard UCD180 opamp get, 12V or 15V???

Yves
 
F

FransDHT

Member
Joined 2004
5-channel amp

Hi,

I am quite new here. But I have enjoyed the discussions for a few weeks now.

I am going to build a 5 channel amp to drive my home theatre. I will pick up 5 UcD400's and 2 500VA-tranformers, rectifiers and 10.000uV BCC-caps at Hypex tomorrow.

I think I will use this to put it all in:

http://www.etnshops.com/supermoduul/listings/264.html

I might need some help with this. I will let you know how things proceed.

Frans
 
F

FransDHT

Member
Joined 2004
Hi,

As I said, I am going to build a 5-channel amplifier.

Should I connect the front channels to one power supply an de the center and rears to the other? Or should I put front and rear left to the one and front and rear right to the other and the center to either?

Frans
 
N

nickywicky

Member
Joined 2004
sarian.co.nz
FransDHT said:
Hi,

As I said, I am going to build a 5-channel amplifier.

Should I connect the front channels to one power supply an de the center and rears to the other? Or should I put front and rear left to the one and front and rear right to the other and the center to either?

Frans
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I don't know the answer but are interested in other replies on this; but the other alternative is one power supply to do one rail, the other power supply to do the other rail, and all 5 channels to share the total power available.
 
B

Bruno Putzeys

Member
Joined 2004
hypex.nl
Tangui said:
I've noticed a first commercial (OEM) UCD amplifier: the MA240 from the Dutch (!) company Van Medevoort.
See http://www.vanmedevoort.com/nl/products/ma240.html . No English page available yet... :xeye:
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The Van Medevoort amplifier uses a "sister" device of the TDA8939, namely the TDA8938 which has low-noise bipolar comparator inputs better suited for UcD operation.
 
B

Bruno Putzeys

Member
Joined 2004
hypex.nl
FransDHT said:
Hi,

As I said, I am going to build a 5-channel amplifier.

Should I connect the front channels to one power supply an de the center and rears to the other? Or should I put front and rear left to the one and front and rear right to the other and the center to either?

Frans
Click to expand...
It would be helpful to make drawings of the arrangement you are thinking of. The simple act of making such a drawing is often enlightening. If not, post it. I don't think I'm reading your description in the same way as what you wanted to say.
 
F

FransDHT

Member
Joined 2004
OK, how about this:

This is when I connect the front channels to one supply and the rest to the other
 

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