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Old 13th January 2007, 08:08 PM   #1
snkby is offline snkby  United States
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Default 53v limit due to caps ?

i seem to remember reading somewhere that the reason the ucd180 was limited to 53v rails was because the output caps were rated for 53v and that substituting higher rated caps would allow higher rails voltages.

is this true ?

i have a killer unregulated psu at +/-54vdc that i would like to use but i am afraid the amps will just shutdown.

thanks.
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Old 13th January 2007, 08:19 PM   #2
BWRX is offline BWRX  United States
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The on board supply caps are 63V but the overvoltage protection is set at 52V according to the UCD180 manual.
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Old 13th January 2007, 10:22 PM   #3
rogs is offline rogs  United Kingdom
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I think you'll find that the limiting factor is the output MOSFET voltage rating, not the Caps.
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Old 13th January 2007, 10:27 PM   #4
BWRX is offline BWRX  United States
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We've been told they're listed as 100V but are actually 120V devices, so the FETs are part of the limitation. You really don't want to be close to the voltage limit of the caps or the output devices, which are very close to each other.
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Old 13th January 2007, 11:42 PM   #5
snkby is offline snkby  United States
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Default its been a while since i looked at

all the info and just saw the 52v limit again in the manual.

anyway i can mod the ucd180 for either/and/or :

1) +/-54vdc ?

2) optimized power output for 16ohm ?

thanks.
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Old 13th January 2007, 11:55 PM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
keep in mind that the PSU voltage will vary with input voltage.

+-54Vdc is just nominal and based on the input voltage at the time you took the measurement.
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Old 14th January 2007, 12:13 AM   #7
RX5 is offline RX5  Philippines
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why ucd180 rates ONLY at such :

- 120V devices (MOSFET)

- 'some' input section for ucd is rated at a max of +60V(per rail)? dunno what spec/part# for transistor..

- decoupling/filter caps 470uF/63V .. but can be changed to 100V devices...

-the shutdown circuitry shuts down at +/-75V 5-10% tol....

I guess thats only it...
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Old 14th January 2007, 12:47 AM   #8
snkby is offline snkby  United States
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Default anyone willing to give me a --go ahead--

for hooking-up the +/-54vdc ?

i know when i tried using some mismatched va rated xformers to make a ct xformer the voltage difference was enough that the amps would just shut down.

is the protection circuitry robust enough to shrug-off the +/-54vdc attempt ?

psu in use right now is runing +/-38vdc@1.2kva.

is htis close enough to the max +/-45vdc that i wouldnt notive a difference running the +/-54vdc ?

i think eventually i will end-up with the either the ucd400 or ucd700 as i am running 16ohm speakers.

thanks for all the help.
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Old 14th January 2007, 12:27 PM   #9
rogs is offline rogs  United Kingdom
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I reckon that +/- 54V will trip the over volt protection on a UcD180.

If you're currently using +/-38V, then the max. power into a 16R load is going to be about 45W. Up that to 45V, and the max power is going to be about 63W. (Those are no loss figures, so slighlty less in reality).

To increase the max SPL out by 3dB, you would have to double the power from 45 to 90W, so 45 to 63 is only going to increase by 1 -2 dB. Probably not worth the effort, IMHO.

Now changing the load to 4R...... that would be a different story!
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Old 14th January 2007, 04:11 PM   #10
snkby is offline snkby  United States
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Default trying to get the load to 4ohm is kinda

what started this whole thing about a 16ohm load.

even though 8ohm and 4ohm are delivering more power the sound is no where near as good as when the system is 16ohm.

checkout the info about the zero autoformers and try it yourself.

didnt take me very long to decide that 16ohm sounded the best even though the nominal impedance for the drivers is rated @8ohm.

hope you try it and report back.
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