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Old 21st August 2005, 08:40 AM   #1
jj2 is offline jj2  United States
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Unhappy need help ! ucd 400 turn off and on

just finished building a stereo ucd 400 amp, every works but it will for no reason turn off and come right back on while playing music and this has happen a few times today.
Thanks for any help.
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Old 21st August 2005, 09:01 AM   #2
IVX is offline IVX  Russian Federation
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Try to check the rails voltage.
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Old 21st August 2005, 05:53 PM   #3
jj2 is offline jj2  United States
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Default all votage check ok, 56.6 VDC

voltage rail 56.6 VDC
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Old 21st August 2005, 06:57 PM   #4
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Both UcD400 turn off? or only one !
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Old 22nd August 2005, 03:09 AM   #5
jj2 is offline jj2  United States
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Default it was the tube pre amp.

it was the Aes1 tube pre amp, after switch to a 10K passive pre amp it went away.
how can i make the tube amp to work with ucd400 ?????
thanks for all the help .
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Old 22nd August 2005, 03:38 AM   #6
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Default preamp problem

What is happening is all the low frequency noise from the pre is triggering the protection circuits. You probably noticed woofer cone pumping as well. There are several ways to attack the problem but the more practical ones are to limit the input bandwidth severely in comparison to what it now is. That would be replacing the amp input caps with .047-.1UF. This might be enough to do it. The other thing would be to reduce the time constant of the preamp's power supply to so low to noise canít pass. This would require 5-10 times more DC filter capacitance being added. This is a better fix as it corrects the real problem, a preamp with low frequency stability issues.
Roger
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Old 23rd August 2005, 12:12 PM   #7
jj2 is offline jj2  United States
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Default Roger how???

The other thing would be to reduce the time constant of the preamp's power supply to so low to noise canít pass. This would require 5-10 times more DC filter capacitance being added. This is a better fix as it corrects the real problem, a preamp with low frequency stability issues.

would like to do that but how? by putting bigger cap ?
Thanks.
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Old 23rd August 2005, 05:56 PM   #8
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Default Way off topic

Please send me a circuit drawing for this unit and I will send you back what to do. Use the forums email for this.
Roger
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Old 24th August 2005, 03:06 PM   #9
ac2005 is offline ac2005  Hong Kong
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just out of curiosity. How does your UCD sound?
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Old 24th August 2005, 07:13 PM   #10
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Default UcD sonic impressions

Quote:
Originally posted by ac2005
just out of curiosity. How does your UCD sound?
I assume this was addressed to me? The stereo UcD400AD amp I put together replaced an amp of my own design. This original was an all out A/B design that had been compared favorably to the best there are! It kicked over a lot of sacred cows for sure.
The UcD based amp was implemented in exactly the same way with the same power and chassis as well as all the support stuff so a direct comparison could be made to the A/B design. This means it is a non optimum layout for the UcD as it only will deliver 110W. This appears to be no real disadvantage as it immediately became our new reference. It has all the advantages everyone talks about but the bottom line is that it is just way more enjoyable to listen to. In fact you soon forget the system and concentrate on the music. Listening sessions can now last way too long as you donít want to stop.
It is just more right and I canít give it any higher praise than that.
Roger
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