UcD400 Q & A

[maxlorenz]

I'm so pleased with my four channel UCD180 amp that I plan to build a pair of UCD400 monoblocks (HiEnd I hope) soon.

Just to clarify:
About DC offset, you said:
>>The new modules are AC coupled so you don't have to worry about DC<<. So there's no need for speaker relée protection...(?)

Somewhere I read that DC coupled amps had better low frequency response. Does this means that the new UCD400 is weaker in this aspect? I hope not.

The modules sound is dependant on the input buffer opamp but I didn't find any comparison between OPA2134 and AD8620 soundwise (that is what matters anyway).
Can anybody tell his experience with the above mentioned opamps?

What type of wire has the UCD400 signal cable?

Thanks
Mauricio

[Yves Smolders]

Just to clarify: >>The new modules are AC coupled so you don't have to worry about DC<<. So there's no need for speaker relay protection...(?)

IMHO this is about the input. Feeding DC in the input wont result in speakers on fire, this gets corrected. However, it won't help if your FETs have a problem and juice 40V DC into your beautiful speakers.

I'm not sure about this though, maybe Jan-Peter can comment on the danger of this happening?

[classd4sure]

Hi,

I think I can help somewhat here.

Yves I think you're mostly right, but the DC seen on the input will be amplified, not corrected, it's just a half bridge, and so it will also pump up the rails, the module has overvoltage protection which will kick in at 67Volts in this case.

If you have very low DC offset from your source (I think 10mV or less was said before) you can get away with no AC coupling, and so some have removed it so they wouldn't have to deal with the sound of the coupling caps. Changing from an opa2134 to an AD8620 might not have much of a difference if the sound is swamped by the coupling cap, most making that modification have likely removed them.

So something like relay protection is likely to help your speaker if you remove the coupling caps and have too much DC at the input, depending on your rail voltage, but you dont' want it tripping all the time, ideally it would only be (and is only reliably)used for a critical failure of the output stage, for which AC coupling at the input will be of no help whatsoever.


Mauricio, your'e ucd180's have AC coupling as well, it's only the first version of the 400 that didn't have it. I'm sure the 3db point of the AC coupling would be lower than 10Hz, probably something like 4 or 6Hz. It's only poorer in the effects.... coloration etc, that the cap itself has, not in frequency response. So you can experiment with adding better coupling caps (black gates or whatever) or paralleling a high quality bypass cap with the existing ones, or if your source has very very low DC offset possibly removing it altogether, that's an educated gamble for you to take. If you gamble poorly, the module will be well protected before any harms come to it or your power supply (if you chose those parts wisely) but it doesn't mean your speaker will make it.

Regards

[maxlorenz]

I'll have to re-read your answer with a textbook by my side
But I think I catch your points.

Currently a feed the UCD amp with a TVC (transformer based volume control). It will prevent DC arriving from the source to the input, I think.

I thought of building a "passive-integrated UCD amp": I mean installing the attenuating transformer in the amp box and connecting the secondaries directly to UCD's signal input connectors, saving one interconnect pair ($$). I'm affraid bypassing opamp is out of my skills ( appart the impedance issue )
What do you think?

Thanks
Mauricio

[classd4sure]

Currently a feed the UCD amp with a TVC (transformer based volume control). It will prevent DC arriving from the source to the input, I think.

I think so too, which means you can remove or just shunt the coupling caps with little worry.

I'd save that as a possible tweak option after you've listened to it for awhile though of course.

I thought of building a "passive-integrated UCD amp": I mean installing the attenuating transformer in the amp box and connecting the secondaries directly to UCD's signal input connectors, saving one interconnect pair ($$).

Sure why not, electrically it's all the same right? Nice idea, worth a shot I think.

[maxlorenz]

Hey! This fellow's hammer is for you or for me? ( )

M

[BOB LEWIS]

Hi All,
Anyone any ideas about the best way to null the DCoffset on the UCD400AD modules as I intend to actively drive APOGEE ribbon speakers with these? The MRT ribbons are very sensitive to DC,suffering displacement in the magnet structure plus premature aging and stretching.

Bob Lewis

[Yves Smolders]

Slightly off-topic question:

When ordering modules from Hypex, after they recieve payment, do your get an e-mail that confirms shipping?

I haven't seen a thing, and didn't get replies on 2 mails asking about this.

Thanks

[Jan-Peter]

Yves,

When you order something in our webshop you automatically get a confirmation of your order. When we have received the payment we ship the goods, at the day we ship the goods we will send you an email.

Regards,

Jan-Peter

[Yves Smolders]

Jan-Peter,

Thanks for the reply! We did the (international) payment, but our accountant was worried because there is no "reference" on the transfer.

It'll probably take a few days to get processed I guess, I'll just wait a bit longer, thanks