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-   -   UcD 180 or UcD 400 with +/- 48VDC supply (http://www.diyaudio.com/forums/class-d/79874-ucd-180-ucd-400-48vdc-supply.html)

Ray Weikel 20th May 2006 06:23 AM

UcD 180 or UcD 400 with +/- 48VDC supply
 
I have two Monoblcok Chassis with defunct kit power amps in them. Each has a 300VA torroidal transformer +/-33VAC secondary and deliver +/- 48 VDC, filtered with two 22,000uf caps with small bypass. My question is which UcD module would be best for this. The speaker is a triamped system Driven by a DEQX front end. The Amplifier will be used for the madrange dipole panels, which have 8 drivers 4 ohm per side and can be wired for either an 8 ohm load or a 2 ohm load. The tweeters (Heil AMTs) are driven by a Pass Aleph 30, and the dual subs are driven by plat amps.

From the specs I understand I am near the upper limit of the UcD 180, but in rather the low range of the UcD 400.
Will I be overstressing the UcD 180 with +/-48VDC ?
Will the UcD 400 not sound optimum with only +/-48 VDC ?

I don't really need the more than 100 watts, as the system is pretty effeicient. These rebuilt monoblocks will replace a Parasound A-23 which is about 120 watts/channel into 8ohms.

Thanks for any guidance

Ray Weikel

MOER 20th May 2006 07:17 AM

+/-48 voot supply
 
You will activate the over-voltage protection on the 180 and if by some chance it does not activate you WILL blow the output FETs. They are only rated at 100v and running them at 96v is dangerous. You could of course simply put in higher voltage (160v) FETs and that will solve your problem.

Ray Weikel 21st May 2006 02:10 AM

Thanks for the reply.

You will activate the over-voltage protection on the 180 and if by some chance it does not activate you WILL blow the output FETs. They are only rated at 100v and running them at 96v is dangerous.

The specs say the over-voltage protection trip point is 52V, so I was hoping 48 was safe. Is this incorrect. I don't have any specs on the FETS.

I'm typically only getting +/- 46 to 47 - not far above the recommended 45V.

I have though about added some sort of regulation or perhaps Inductors before the rectififers, which will both filter out some RFI and reduce voltage slightly.

Workhorse 21st May 2006 04:08 AM

Quote:

Originally posted by Ray Weikel
Thanks for the reply.


The specs say the over-voltage protection trip point is 52V, so I was hoping 48 was safe. Is this incorrect. I don't have any specs on the FETS.


Hi Ray,

The overvoltage on the supply rail bus could also be caused by "Bus Pumping " phenomena, rather than increasing the rails externally.....

Cheers,
K a n w a r

Ray Weikel 22nd May 2006 07:49 PM

The overvoltage on the supply rail bus could also be caused by "Bus Pumping " phenomena, rather than increasing the rails externally.

I don't know what "buss pumping" is, but my situtation is that I don't have a UcD180 yet, just a power supply that happen to put out +/- 47 VDC and an wondering if it is too much for a UcD180. I assume there is no "Bus Pumping" going on in an unused power supply - right?

Is "Bus Pumping" something that can make my +/-47VDC worse?

Thanks,

Ray

Pjotr 22nd May 2006 08:12 PM

Hi,

“Bus Pumping” or “PSU Pumping” can be caused by an inductive load delivering the stored energy in the load back to the PSU rails. An extensive discussion on the Dutch DIY forum with JP from Hypex turned out that this does not occur. Hypex tested for it with heavy woofers that are prone to this effect. But to be on the safe side I would not go higher than 42V – 45V on the rails when the amp is idling (that is, not driven by a signal) to accommodate mains variations. If your tranny is a toroid you can always remove some secondary windings if necessary.

Cheers ;)

Ray Weikel 23rd May 2006 01:59 AM

Pjotr,

Thanks for the explanation. In my case the panel drivers this amp will drive are not at all reactive, they have a nearly ruler flat impedance (they go up about 1 ohm at resonance) so this is likely not an issue. To be safe I will find some way to lower my B+, either through regulation, or removing turns.

Thanks again,

Cheers

Ray

classd4sure 29th June 2006 07:28 AM

Overvoltage is at 52Vdc for the 180's and they use 150V mosfets.

I ran mine with 47Vdc rails unloaded and drove them hard often enough, never any problems, never even got them warm.

Now running UCD400's on the same rail voltage, with excellent results. Have no fear.

PassiveO 29th June 2006 04:08 PM

I am running UCD400s at 43v and they sound fantastic. 48v will be no problem.

classd4sure 29th June 2006 06:53 PM

You can go alot higher still with the 400's, check the data sheet as always.


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