How to do a volume control for UCD400 Module?

CptanPanic · 6th July 2009, 03:08 PM

Since I will be using this module sometimes connected to a speaker that cannot take 400 watts, I would like to make a volume control. How can I do this? And if I turn it to 50% does that mean it will put out 200W?
Thanks,
CP

pieter t · 6th July 2009, 07:15 PM

CP,

No, it does not work like that.
Your UCD400 puts out 400 watts at 4 ohm (loudspeaker impedance).
In voltage terms that is 40 V RMS (40 squared divided by 4 = 400).
Let's presume you have a logarithmic potentiometer as volume control (which is normal).
At 50% the volume control might be at minus 30dB (realistic).
Minus 30 dB is 0,013 times full output (40V) which is 0,52 V.
0,52 V RMS is 0,07 wats at 4 ohm.
Now you understand that at normal listening levels power amplifiers usually deliver less than 1 watt. 400 watts are peak powers which seldom occur.
When you want your UCD400 to put out no more than for instance 100 watts at 4 ohms you must reduce the output voltage to 20 V RMS by reducing the power supply voltages to + and - 30 volts. UCD400 runs well on lower power supply voltage AFAIK.

Pieter

6th July 2009, 03:08 PM	#1
CptanPanic diyAudio Member Join Date: Nov 2003 Location: WPB, Florida	How to do a volume control for UCD400 Module? Since I will be using this module sometimes connected to a speaker that cannot take 400 watts, I would like to make a volume control. How can I do this? And if I turn it to 50% does that mean it will put out 200W? Thanks, CP

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6th July 2009, 07:15 PM	#2
pieter t diyAudio Member Join Date: Apr 2009	CP, No, it does not work like that. Your UCD400 puts out 400 watts at 4 ohm (loudspeaker impedance). In voltage terms that is 40 V RMS (40 squared divided by 4 = 400). Let's presume you have a logarithmic potentiometer as volume control (which is normal). At 50% the volume control might be at minus 30dB (realistic). Minus 30 dB is 0,013 times full output (40V) which is 0,52 V. 0,52 V RMS is 0,07 wats at 4 ohm. Now you understand that at normal listening levels power amplifiers usually deliver less than 1 watt. 400 watts are peak powers which seldom occur. When you want your UCD400 to put out no more than for instance 100 watts at 4 ohms you must reduce the output voltage to 20 V RMS by reducing the power supply voltages to + and - 30 volts. UCD400 runs well on lower power supply voltage AFAIK. Pieter

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