UcD400 Q & A

[classd4sure]

Originally posted by chrisb03



35 Vrms secondaries? Are u buying the UcD400's? If so you should have 40VAC secondaries. That is 40*1.41= 56VDC. That is, with a 10% variance will take it to 62VDC (which is below 63V limit).

I'm going to add some 47VAC taps (if I'm not too late) as well just in case it's required. Based on Bruno's and Lars discussion on another thread. May be able to run the UcD400 at higher voltage with some modes.

Hi,

Yep, UCD400s.

This is why I asked as I want to make sure I can get the most out of it, of course, but at same time I don't want it to go up in smoke. Of course, something seemingly so simple is not without its confusion either. For one thing you'll get different values for calculations starting from the secondary Vac ratings, than if you start with your end goal and calculate your way down. They're very close but there is a notable difference there, likely to be the percentage between the two.

More importantly, you didn't take into account a few other important factors.

Namely, load regulation of the transformer, and also in my unusual case, the difference of the given primary rating (rated at 115Vac, mains voltage here is 120). That's almost an extra 10%.

So we know that overvoltage protection kicks in around 63 volts DC right? I wasn't sure if it would be a good idea to aim for 63 volts worst case, so I was a wimp and used a conservative 60.

Let's be brave and use 62 No.... 62.5
Mains voltage here is 120Vac, the transformer ratings are given at 115Volts primary 50/60Hz. I'm guessing it's likely manditory for this variation to be accounted for, as a 4% increase on the primary equals a 4% increase on the secondary ratings which they provide.

Another issue I'm not sure about is while mains here are supposed to be 120, each time I measure them I read it at 122. So let's use that, which is a 6% variation from the given primary Vac rating, and therefore on the secondary as well. Plus the 10% margin of safety factor, plus another 4% representing the transformer's load regulation rating.
So that's a total error of 20% to account for! That is, if I'm doing this right.

To the 62.5 volts end goal, I add a 1.4Vdc drop to account for the loss caused by the bridge rectifier, assuming there's no others.

I then have 63.9*(1-.2)=51.12Vdc
And Vac would be 51.12*sqrt(0.5)=36.1
Which tells me 35Vac secondaries (as rated for the 115Vac primary) are the right choice.

I have a choice between 35Vac, 38Vac and 40Vac secondaries.

For 35Vac:
35*SQRT(2)=49.5, now we add that 20% to bring us to worst possible case 49.5*(1+.2)=59.4Vdc - the bridge rectifier drop of 1.4V =58Vdc. Not exactly the 62.5..

For 38Vac
38 * sqrt(2) * 1.2 = 64.4881384
less the bridge rectifier: 63.1Vdc

Conclusion?

38Vac secondaries might be pushing my luck a bit?
35Vac secondaries might be too conservative?
40Vac is out of the question.

Opinions?

PS:

I also read that other post and it's making me wonder.. will that be the UCD700? Hopefully we'll get the info to make those mods. I don't think I want to have a custom transformer made but it's a good idea you had for the extra taps with that in mind.

[Zodiac]

Originally posted by ghemink



If I were you, I would try the UcD modules also for mid and high. If you think UcD400 is overkill for mid and high, you could use the UcD180 for mid and high. I`m using UcD180 in an active dipole system, sounds great. UcD400 maybe better however since the coupling caps are gone, I`ll order some UcD400 modules later this year to try them out for mid and high as well. If those woofers are 4 Ohm each, you may want to spend one UcD module per woofer, you may not get maximum power at 2 Ohm because of output current limitations. And I guess those woofers need quite a bit of power, what do you use now to drive them?

Best regards

Gertjan

Thanks for your response, I am using a Pass Aleph 3 (30W) for the mids and highs and a Nakamichi PA7 (200W) for the bass, but the Nak is HUGE and I could do with freeing up some living space! I guess I could use one UCD180 per woofer, but that would work out slightly more expensive

[DSP_Geek]

Originally posted by Jan-Peter


Francois,

The 1,8K inputimpedance is in the modulator, the small 90o potted PCB. When you like to use no coupling cap, you must use an other opamp as the NE5532, please go for an OPA2134. And you have to be VERY shure you source is DC free.

www.hypex.nl

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?


Francois.

[jam]

Yes! The UCD700........what some of us have been waiting for.

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

Regards,
Jam

[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.

Henk

[nickywicky]

Originally posted by classd4sure



For 35Vac:
35*SQRT(2)=49.5, now we add that 20% to bring us to worst possible case 49.5*(1+.2)=59.4Vdc - the bridge rectifier drop of 1.4V =58Vdc. Not exactly the 62.5..

For 38Vac
38 * sqrt(2) * 1.2 = 64.4881384
less the bridge rectifier: 63.1Vdc

Conclusion?

38Vac secondaries might be pushing my luck a bit?
35Vac secondaries might be too conservative?
40Vac is out of the question.

Opinions?

Well I can say that I went through all these kind of calcs when
deciding what transformer to get and also decided on one with
35Vac outputs too.

We are rated at 230vac here but it always sits at 240 so I needed
to take that into account like you have.

Also I wouldn't take off 1.4v for the bridge; that's 1.4V total so its
only 0.7 for each rail.

[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

[classd4sure]

Originally posted by nickywicky



Well I can say that I went through all these kind of calcs when
deciding what transformer to get and also decided on one with
35Vac outputs too.

We are rated at 230vac here but it always sits at 240 so I needed
to take that into account like you have.

Also I wouldn't take off 1.4v for the bridge; that's 1.4V total so its
only 0.7 for each rail.

Hi,

Thanks for chiming in there. I guess I was on the right path then, hopefully I'll see ~60Volts DC out of it. Anyway I look at the problem the answer always seems 35Vac.


Hmmm, interesting note about the drop for the bridge, we're both right. It's good you pointed that out though, I guess it depends how it's wired. I'm tempted to use two bridge rectifiers, one per secondary. I've heard good and bad things about doing that but it seems the general consensus is it's a better way of going about it.

Luckily should I change my mind it won't be enough to throw the results off by a large margin

The main thing is I dont' want to have to continually rely upon the modules overvoltage protection under normal operating conditions, but it will be there for the odd time the mains voltage spikes to >20% or maybe supply pumping pushes a rail a bit high.

Thanks

[chrisb03]

Originally posted by classd4sure

Namely, load regulation of the transformer, and also in my unusual case, the difference of the given primary rating (rated at 115Vac, mains voltage here is 120). That's almost an extra 10%.

So we know that overvoltage protection kicks in around 63 volts DC right? I wasn't sure if it would be a good idea to aim for 63 volts worst case, so I was a wimp and used a conservative 60.

Let's be brave and use 62 No.... 62.5
Mains voltage here is 120Vac, the transformer ratings are given at 115Volts primary 50/60Hz. I'm guessing it's likely manditory for this variation to be accounted for, as a 4% increase on the primary equals a 4% increase on the secondary ratings which they provide.

Another issue I'm not sure about is while mains here are supposed to be 120, each time I measure them I read it at 122. So let's use that, which is a 6% variation from the given primary Vac rating, and therefore on the secondary as well. Plus the 10% margin of safety factor, plus another 4% representing the transformer's load regulation rating.
So that's a total error of 20% to account for! That is, if I'm doing this right.

Sound's ok. I think you may have doubled up on some of the percentages. The point of the initial 10% safety margin already includes the transformer regulation and voltage regulation at the mains (which is the main reason for the 10% margin). All you needed to do was take the difference between the mains rating and the primary rating.

Having said that, you got me thinking in regard to my selection. We have mains at 240VAC, I have requested 240VAC primary. Therefore, 40V*1.41*1.1=62V. Voltage drop of diodes may vary between different diodes and load so I didn't take this into account.

Hmmmm, should I go down a couple of volts?

[classd4sure]

Originally posted by chrisb03


Sound's ok. I think you may have doubled up on some of the percentages. The point of the initial 10% safety margin already includes the transformer regulation and voltage regulation at the mains (which is the main reason for the 10% margin). All you needed to do was take the difference between the mains rating and the primary rating.

Having said that, you got me thinking in regard to my selection. We have mains at 240VAC, I have requested 240VAC primary. Therefore, 40V*1.41*1.1=62V. Voltage drop of diodes may vary between different diodes and load so I didn't take this into account.

Hmmmm, should I go down a couple of volts?

Hmmm... I'm not sure about that. What if say you're working out the value for a puny little 100VA transformer for which the regulation factor is 10% on its own? Then you have no safety margin for the mains left?

This way I've accounted for both a 10% mains overvoltage which I understand is rather common place (if not more at times), and at idle condition (unloaded), worst case scenario, it still shouldn't be tripping the overvoltage protection circuit.

Oh, newsflash, and I quote Jan-Peter from a recent post in the ucd180 thread:

An unloaded voltage of 63VDC - 10% will be our advise

From this we see it does not include the transformer's regulation factor. So 63VDC+(whatever diode/rectifier drops will be in place)*(1-(10%safety margin + transformers regulation factor for the "unloaded" or "idle" condition+any other abnormalities such as I have in my case)).

By doing it this way we should be able to listen to it at a low volume (light load) while under the influence of a 10% mains overvoltage condition and not have the protection circuitry kick in, which I might add, doesn't just limit the voltage, but actually shuts the amp down for a few seconds. So it's important that we make a selection which won't regularly utilize the protection circuitry or it could be most annoying at every day listening levels.

It is good to second guess a few things at this stage of the game, I think, like you said a few posts ago it's not every day we buy transformers

So in my case now that it's on my mind again, if I want to play the odds of just how common a 10% mains overvoltage condition actually is, IF I use dual rectifiers (I per secondary) I might just be able to get away with using the 38Vac secondaries. Then again, how tight is the tolerance level for the overvoltage protection circuit, I could bite myself in the rump doing that. siiigh.

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

Thanks