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Old 3rd January 2010, 02:51 AM   #1
Halook is offline Halook  Hong Kong
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Default Need help in building Ucd module based power amp for bi-amping

Hi all,

I'm a novice in DIY and know nothing in electronics. I would like to build two Ucd module based power amplifiers for bi-amping. The problem is my existing pre-amp has one set of pre-out only. How do I daisy chain two power amps from the pre-amp? Is there any trick in doing so? Would be OK by just connecting two power amp in parallel from the single pre-out of the pre-amp. Or just simply cram 4 Ucd modules into a single case? Any suggestion is welcomed.
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Old 3rd January 2010, 03:23 AM   #2
Pano is offline Pano  United States
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Unless your preamp has a high output impedance, you shouldn't have trouble with just splitting the signal as you suggest.
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Old 3rd January 2010, 03:39 AM   #3
Halook is offline Halook  Hong Kong
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Quote:
Originally Posted by panomaniac View Post
Unless your preamp has a high output impedance, you shouldn't have trouble with just splitting the signal as you suggest.
Thanks for your advice. How do I measure the output impedance of the preamp? Can it be done by a multimeter? And what range of impedance is regarded as "high"?
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Old 3rd January 2010, 03:43 AM   #4
Halook is offline Halook  Hong Kong
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Quote:
Originally Posted by panomaniac View Post
Unless your preamp has a high output impedance, you shouldn't have trouble with just splitting the signal as you suggest.
Thanks for you advice. How do I measure the high output impedance of the preamp? Would a multimeter serve the purpose? And what range of output impedance is regarded as high?
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Old 4th January 2010, 01:31 PM   #5
Bernie7 is offline Bernie7  Singapore
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Quote:
Originally Posted by Halook View Post
Thanks for your advice. How do I measure the output impedance of the preamp? Can it be done by a multimeter? And what range of impedance is regarded as "high"?
Hi

You might try checking the specifications of your preamp

The input impedance of the UcD (UcD400) is 100k, so paralled would drop to 50k.
It's good to keep the ratio of O/P and I/P impedances at more than 10.
So, if your preamp O/P impedance is less than 5k it should be alright. This is likely to be the case.

Cheers

Last edited by Bernie7; 4th January 2010 at 01:37 PM.
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Old 4th January 2010, 01:38 PM   #6
AndrewT is offline AndrewT  Scotland
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a DMM with 2000mVac scale is good enough.
You need a source of 500Hz sinewave and three resistors from 1M, 100k & 10k.

measure the output voltage with the input adjusted so that it does not clip or distort. Maybe try around half the maximum output voltage.
Add the 1M as a load and remeasure voltage.
Change to 100k and remeasure.
Change to 10k and remeasure.
Come back with the four voltages you measured.

Might be worth checking both channels.
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Old 4th January 2010, 02:47 PM   #7
Halook is offline Halook  Hong Kong
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Thanks for the advice. Actually, the "to be built" Ucd based power amps would be connected to a clone AudioNote M7 tube pre-amp that I'm going to build in the following weeks with guidance in a local workshop. I may be able to carry out your method to measure the output impedance once the pre-amp has been built.
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