UcD400 Q & A

[Bruno Putzeys]

Re: ucd400/ma240

I am considering building an amp with UCD400 to drive my Quad ESL's. Does anyone see any objections? Someone tried this before?

I heard the Van Medevoort MA240 which uses a UCD chip as well although it seems to be a diffrent one. Sounded good, but the Quads could theoratically do with some more power. Maybe Bruno knows about the MA240 and the possible differences with, or advantages of, the UCD400.

Anybody in the neighbourhood of Utrecht (The Netherlands) who is willing to give his UCD400 a try on my Quad ESL's?

Several people out here are using UcD modules on electrostatic loudspeakers, with good result. Actually the UcD circuit is the only class D amp that can do this without producing response aberrations (that would otherwise be caused by uncontrolled resonances between the capacitance of the speaker and the output coil).
Technically, the difference between the MA240 and the UcD400 is mostly output power, the latter putting out over 4 times as much as the vM. There will of course be quite a few sonic differences due to implementation details, but I can't elaborate since I haven't heard the vM product yet.

Drop me a private mail. I do visit Utrecht from time to time.

 

[matjans]

hehe... tegelijkertijd een pm van mij en een reply van bruno.

populair?

 

[Bruno Putzeys]

hehe... tegelijkertijd een pm van mij en een reply van bruno. populair?

It's simpler than that. He's looking for someone with a UcD400 to try out on his Quads, I'm looking for someone with Quads to try out on my UcD400 😀

 

[jurjaan]

Bruno and Matthijs,

Thanks for your reactions. I'll first check Matthijs his UCD amp before putting my tender Quads at risk😉

Would be nice to talk to you Bruno, I'll send you an e-mail🙂

 

[nyman]

Is there any sonic difference between the standard and the ad8620 version below 200Hz? as I'm going to drive a perless xls10. I just received my 2 free samples from analog devices, and is wondering if I should save them for future projects or just do an upgrade on this one.
Is there something else I need to change when i change the op?

 

[Bruno Putzeys]

Is there any sonic difference between the standard and the ad8620 version below 200Hz?

No. Perceived differences at low frequencies are due to what happens at high frequencies. So, you can get the impression that such and such op amp sounds nicer in the bottom end in a full-range system, but the effect goes away when the signal is band-limited, as in subwoofers. In other words, save your samples for a full-range system.

 

[a007udio]

Hello.

I would like to bouild 3 channel amplifier with ucd400.

I have 800VA transformer and . Is this enough?

Thanks

 

[Bruno Putzeys]

I would like to bouild 3 channel amplifier with ucd400.
I have 800VA transformer and . Is this enough?

800VA is enough, although the power supply will not be stiff enough to guarantee 3x400W simultaneously.

 

[Yves Smolders]

Bruno, a very personal question:

Take the example above, 800VA 3 UcD. I'm looking at that solution also, but with a switch to disable the "center" channel.

* Would, in your opinion, 800VA be enough for a "stiff" PS using 2 channels? (4 ohms load, not that it matters)? Don't know how I did it but I calculated 826VA once, considering full continous power, a situation that never happens

* And THE question, how much capacitance would *you* connect to these 2 (sometimes 3) channels? 2x10.000uF slitfoils?

I know, the question is asked 1000 times already, but now I'm asking the designer 😀

 

[Bruno Putzeys]

Bruno, a very personal question

😱

* Would, in your opinion, 800VA be enough for a "stiff" PS using 2 channels? (4 ohms load, not that it matters)? Don't know how I did it but I calculated 826VA once, considering full continous power, a situation that never happens

In terms of reliability, a transformer may be overloaded by a factor 2 for short periods (5 minutes). This is already implausible in audio use. The "stiffness" (load regulation) is more a matter of the supply voltage not sagging below what the module requires to deliver its full rated power. If you intend to get 400 full watts out of two channels, this is an issue and you will need 800VA for 2 modules. Otherwise, smaller is no problem.

* And THE question, how much capacitance would *you* connect to these 2 (sometimes 3) channels? 2x10.000uF slitfoils?

For 1 channel of 4 ohms I'd probably allot a minimum of 6800uF per rail. For 2 channels this works out as 13600uF per rail. Since 10000uF is the standard value for the slit-foil caps, this rounds up to 20000uF per rail, as in the Hypex supplies.

That said, my UcD400 listening test contraption has only one pair of 10000uF caps for two modules.

 

[sx881663]

Caps

Bruno,
Do you have an ESR measuring instrument? Have you found any useful correlation between this and sound? If the bulk storage caps have a serious impact on sound I would guess replacements for the 470UF @ 100 caps also would. Anything to report on this?
Thanks,
Roger

 

[Yves Smolders]

Bruno,

Thanks for your opinion.

Is it right to believe that, if the transformers are large enough, the cap size becomes less important? Less sagging of the rail voltage -> less need for "power on tap" in the capacitors?

So the 40.000uF will do just nicely for full power (hypothetical again, music never does that) if I have 800VA transformers?

Thanks for your insights

 

[Bruno Putzeys]

Is it right to believe that, if the transformers are large enough, the cap size becomes less important? Less sagging of the rail voltage -> less need for "power on tap" in the capacitors?

Unfortunately not. The output voltage of the supply is a DC voltage with a 100Hz sawtooth ripple superimposed on it. The transformer size tells you what the variation in DC voltage will be depending on load current. The capacitor size tells you how large the 100Hz ripple will be.

(There's some interdependence but it's not very significant - the transformer size determines variation of the peak, not average DC voltage, not ripple, but there you go).

 

[Bruno Putzeys]

Re: Caps

Do you have an ESR measuring instrument? Have you found any useful correlation between this and sound?

I don't have a network analyser. I use a square wave current generator and look at the voltage on the cap.
Some results:
http://www.diyaudio.com/forums/showthread.php?postid=464097#post464097

I find little correlation between ESR and sound quality. In fact, most low ESR caps sound quite bad to me (although there are notable exceptions).

On the other hand it was quite interesting to discover that "non-audiophile caps" had little distributed resistance, while the audiophile ones (except silmic but they sound horrible anyway) behaved nearly like an "ideal" RC series network. Who knows if there's a correlation there.

 

[ghemink]

Re: Re: Caps

I don't have a network analyser. I use a square wave current generator and look at the voltage on the cap.
Some results:
http://www.diyaudio.com/forums/showthread.php?postid=464097#post464097

I find little correlation between ESR and sound quality. In fact, most low ESR caps sound quite bad to me (although there are notable exceptions).

On the other hand it was quite interesting to discover that "non-audiophile caps" had little distributed resistance, while the audiophile ones (except silmic but they sound horrible anyway) behaved nearly like an "ideal" RC series network. Who knows if there's a correlation there.

Hi Bruno,

Is there anything to say about the difference between 85C specified caps and 105C specified caps? I plan to try 105C specified caps (1000uF 100V) Nichicon KMG instead ofthe 470uF caps. As the modules still can reach relatively high temperatures, especially in these hot Japanese summers, I think lifetime of the caps can be extended by using 105C types. Are there any other benefits of using 105C types?

Best regards

Gertjan

 

[Franklin]

Bruno/Gert-Jan,

I want to build two mono-amps each using 2 bridged UCD-400 modules.

Is there a connection diagram available for the UCD-400 used in bridged configuration?

What kind of Power Supply configuration can be best used?

Anyone here build such a configuration already and what are sonic benefits/improvements?

Thanks all

 

[Bruno Putzeys]

I want to build two mono-amps each using 2 bridged UCD-400 modules.

Is there a connection diagram available for the UCD-400 used in bridged configuration?

Wire the amplifiers as a stereo amp, with the same power supply you'd use for a stereo connection. Wire the audio inputs together with +/- inputs swapped on one amplifier. Connect a 47nF capacitor in parallel with the load (=from one amplifier output to the other).

Anyone here build such a configuration already and what are sonic benefits/improvements?

Expect no sonic improvement. Bridging only serves to get more power into a higher-impedance speaker, not to improve the sound.

 

[kephaudio]

Ucd 400 impedence

Hi Bruno,

I couldn't find any reference about impedence matching of the UCD400.


I mean which is the input impedence of the module? And moreover, which range of output impedence you expect from a preamplifier to work corretley with the UCD400?

Also, what is the behaviour of the modul with speakers that go down 4Ohms with some transients?

I Thank you in advance for your answer.
KEPha

 

[kephaudio]

heatsink

Sorry,

do you have any suggestion for the heatsink? Which size, where can I buy some in Europe (UK or Italy)?

KEPha

 

[Bruno Putzeys]

Re: heatsink

I mean which is the input impedence of the module? And moreover, which range of output impedence you expect from a preamplifier to work corretley with the UCD400?

Both inputs are 100k ohms referred to ground. There are no special towards drive impedance. Anything can drive 100k.

Also, what is the behaviour of the modul with speakers that go down 4Ohms with some transients?

The current is peak-limited to around 20A. The module will "clip" the output current. This produces distortion similar to voltage clipping, but the music keeps playing.

do you have any suggestion for the heatsink? Which size, where can I buy some in Europe (UK or Italy)?

Anything around 4K/W will do nicely. Farnell sells various shapes and sizes. Probably the other mail-order suppliers as well.