UcD400 Q & A

[chrisb03]

Ahhh! What do we do?

Bruno can you enlighten us please.

[classd4sure]

lol...... yeh, like I said something so simple is not without its confusion

Ya know it would be slick to just get 40Vac secondaries and just unwind em until it hits the sweet spot, but those darn epoxy filled cores...

[ghemink]

Originally posted by mlihl
I am very interested in building an UCD400 based amp
with a decent power supply and high-end parts. However,
I need your advice now, folks. Since I'm a beginner in
amp building (I can solder well though and build a kit
from a few instructions), is this type of project really
doable for a guy without a degree in electrical engineering?
For instance, I don't know how to calculate VA ratings
of a torodial transformer etc. and I would need ready-to-use
modules (PSU etc.) that just need wiring. Would it be possible
to use modules from Schuro or LCAudio and just use them
with the UCD400s without having to be an expert? Or should
I rather buy a complete Zappulse kit instead? I am really
extremely tempted to buy UCDs but I don't want to end up
with a non-working project due to lack of knowledge.

Maybe someone who built the UCD with other "plug and play"
modules can comment on this?

Thanks for your help,

Michael

Hi MIchael,

Yes, you can use modules of other makers. In fact I have been using power supplies from LCaudio, but other makers will be fine as well.

For UcD180 modules a transformer that gives 2x33V secondary is a good choice, it will give you about 45V after rectification. For the UcD400, you may want to go for a 2x40V secondary transformer, this would give you about 55V. In both cases, the LCaudio supply is OK since the elcaps on that supply are 63V types.

I guess most other supplies for power amps will use 63V elcaps. So other supplies will be OK as well.

Best regards

Gertjan

[Tangui]

Jan-Peter,

Originally posted by Jan-Peter
We use now an OPA2134 opamp and the inputimpedance is 100K, and no coupling caps anymore. (sorry for the mods guys)

Does this mean that, in comparison with the UCD180, there are no holes anymore on the PCB to solder some coupling caps if one should want to use another (higher offset) opamp, or are they just bridged with a piece of wire?

Maybe a silly question, but the input impedance of 100k, is this measured between noninverting and inverting input, or between any input and ground? In the second case, impedance measured between + and - should be 200k then?
BUT... my source has an unbalanced output, so is it mandatory to connect UCD-ground to preamp-signal ground? If yes, the inputimpedance will indeed be 100k.

The idea behind is, that I would like to use a higher offset amp, but I'll have to combine fire and water then: high inputimpedance needed, but low offset wanted. So reducing those 100k R's but not needing GND would still keep input Z high. Or am I totally wrong ???

Yves

[classd4sure]

Hi Gertjan,

Regarding 63V PSU caps for the UCD400:

Far as I know there's usually a rule of thumb of about 30% extra headroom on the PSU caps to be safe, I suppose because mains voltage can actually vary by alot more than 10%.

So the module shuts down at ~63 volts, the supply won't. Wouldn't it be better to have some extra margin on that? I've been looking at 80V caps for that reason.

Thanks

[ghemink]

Originally posted by classd4sure
Hi Gertjan,

Regarding 63V PSU caps for the UCD400:

Far as I know there's usually a rule of thumb of about 30% extra headroom on the PSU caps to be safe, I suppose because mains voltage can actually vary by alot more than 10%.

So the module shuts down at ~63 volts, the supply won't. Wouldn't it be better to have some extra margin on that? I've been looking at 80V caps for that reason.

Thanks

Hi ClassD4sure,

Well, I think 63V caps with a nominal 55V suply should be OK, that is almost 15% margin. Where does the 30% rule of thumb come from? The caps on the UcD180 are rated at 50V, you need more than a 40V power supply to get the rated output power, so margin would be less than 20%. Maybe the caps have some margin built in as well? I`m nor an expert on stuff like that, maybe Bruno can tell you more.

Best regards

Gertjan

[classd4sure]

Hi,

I wish I could remember but.... that's probably the wrong way of doing it anyway.

Possibly a better way is, starting with the unloaded condition at 10% mains overvoltage worse case scenario, allow for the capacitors tolerance. if that's -10% +50%, then 10% extra would be required, if it's +-20%, then 20% would be required. I think that would be the minimalist approach, basically that leaves 63V rated caps out of the question if the transformer is selected to give 63Vdc worst case.

From what I've seen so far caps have a "surge" rating for which it can handle some extra voltage, for so many cycles of a certain period.

I'm not an expert either, I'm sure someone will correct me if I'm wrong.

For instance does the rated tolerances of the caps lend to the capacitance value of them or to the DC rating?

Ah, there's a lot of articles on them out there for me to find.... few coffee's and an afternoon required I've only begun researching them.

Thanks

[mlihl]

Hi folks,

I was browsing the Internet for a part list of items I need
to build an audiophile grade no-compromise UCD400
stereo amplifier with approx. 150-200W/8Ohms.

I live in a 230V country...

Can you comment on my list of items? Did I make any
mistakes? (I'm not an expert)

1.) Amp: 2 x UCD400 modules

2.) PSU (1 piece):

I would either go with LCAudio's (expensive) Virtual
4-pole 100.000uF supply at 315 Euro - is this overkill?

Alternatively, I would get this PSU from Schuro:
http://www.schuro.de/preisl-nte10-63tnet.htm
(supports max. 2x35V transformers, 4x10.000uF Caps...)
Which one would you take? I want to have enough
reserves, quality comes first.

3.) Transformers: First question - do I need 1 or 2
transfomers for a stereo amp?

For LCAudio I am thinking of this transformer:
2 x 40 V, 600VA (http://www.schuro.de/preisl-v-rkt-ms-sw.htm)

For the Schuro supply, I would take this type:
2 x 35 V, 600VA (http://www.schuro.de/preisl-v-rkt-ms-sw.htm)

Did I make any mistakes in this setup or would you suggest
any changes? I plan to order my UCDs this week.

Thanks for your help, guys!

Michael

[DSP_Geek]

Originally posted by classd4sure


Should I play the odds here and go with the 38 or go with the safer more conservative 35's? Decisions decisions..

Thanks

FYI, my transformer gives 37.5 v unloaded which, after rectification and filtering, yields 50.9 v unloaded.

You should be able to find the no-load voltage on the spec sheets someplace, or failing that, ring up the vendor.


Francois.

[Jan-Peter]

Origanlly posted by Francois;

So if I merely jumped the 22 uF caps the 5532 would have too much offset even if the inputs were AC coupled?
By the way, do you have a timeline for the UcD700?

Please when you use the NE5532, don't remove the coupling caps.

Originally posted by Jam;
Yes! The UCD700........what some of us have been waiting for.

Jan-Peter will the UCD 700 be a bridged amp?

To tell you the truth, I don't know yet. We have currently two designs on the workbench, one bridged version and a single ended. Not yet decided what will be the UcD700 or even UcD1000

Originally posted by Calimero
is that enough to drive a speaker with authority?
Don't misunderstand me, I find it quite remarkeble to have such spec for an amp of the size of the UcD400.

I was looking for an amp with at least the following specs:
- 300Wat RMS
- 60 Amps peak current
- 400 ns rise time, settling in 1,5 us -40db and a slew rate of 600V/us

That's what I have now and I would like to improve.

.....hm, am I impressed?

The proof of the pudding is the eating, I would see try to compaire the amps acoustically

Originally posted by Tangui
Jan-Peter,

Does this mean that, in comparison with the UCD180, there are no holes anymore on the PCB to solder some coupling caps if one should want to use another (higher offset) opamp, or are they just bridged with a piece of wire?

Maybe a silly question, but the input impedance of 100k, is this measured between noninverting and inverting input, or between any input and ground? In the second case, impedance measured between + and - should be 200k then?
BUT... my source has an unbalanced output, so is it mandatory to connect UCD-ground to preamp-signal ground? If yes, the inputimpedance will indeed be 100k.

The idea behind is, that I would like to use a higher offset amp, but I'll have to combine fire and water then: high inputimpedance needed, but low offset wanted. So reducing those 100k R's but not needing GND would still keep input Z high. Or am I totally wrong ???

Indeed there are no holes anymore, it's just removed. The 100K is measured between input or none-inverting to ground, indeed impedance between + and - is 200K. No when you correctly hooke it up, asymetrically, you will have 200K inputimpedance. The cinch has an hot output and ground. Connect the +input of the UcD to the hot cinch output, connect the -input of the UcD to the ground of the cinch. Connect also the ground of the Ucd to this ground at the side of the cinch.

When you wants to use a higher offset opamp, you can cut the coppertraces and add a coupling cap. Or create a DC-offset adjustment to inject several DC mV at the input just as you do to correct the DC adjustment with a normal analog amplifier.

Powersupply;
Our recommondation will be 63VDC-10%. When you order a transformer ask if the voltage of the transformer is in unloaded or loaded setup. This two voltage can have a difference of 10% (or even more)

Regards,

Jan-Peter

www.hypex.nl

PS. we have a 500VA transformer what gives 57VDC, pefect for the UcD400. And a set of BCC 10.000uF / 63V capacitors together with a 35A bridge rectifier. (KBPC3502) Please mail us for prices.