power supply for P3A

soundnovice · 29th November 2011, 05:29 AM

hi all,
i am building Rod's P3A power amps. the guidelines tell to use 300VA/25-0-025 trafo means 6A for the pair of amps. but i am already having a stock of 5A (i.e.25-0-25/250VA). will it be enough if i am ready to compromise some output power? or is it must to go for 300VA/6A trafo?

thanks
pranam

twest820 · 29th November 2011, 11:34 PM

The answer obviously varies based on listening preferences, environment, and speaker efficiency but if you do the SPL math most likely you'll find most listening occurs at levels on the order of 1mW output power.

AndrewT · 30th November 2011, 06:40 PM

ESP's P03 project is a 60W into 8r0 amplifier.
Total maximum output power of two channels is 120W.
Recommended transformer to power two channels is 120VA to 240VA.
The amps will work with a transformer outside this range.

soundnovice · 1st December 2011, 04:28 AM

thanks Andrew.
one more thing is that i am using bridge rectifier rated at 8A while Rod suggests to use 35A. what implications it will have if i use lesser rated bridge rectifiers?

mightydub · 1st December 2011, 05:27 AM

The rectifier current spec is for the average forward current. You have to look at the peak charging currents into the filter caps, these can be very high as the diode is only conducting for a very small portion of the AC cycle. Peak current will be especially high at startup when the DC voltage at the filter caps is zero.

The Non-repetitive Peak Forward Surge Current spec can be very high but it is only for a single 1/2 cycle.

Overkill on the current spec for the bridge rectifier is doesn't cost much and means you never have to worry about it.

soundnovice · 1st December 2011, 05:36 AM

i am using MR8100 diodes whose spec is given below,

Type - Ultra Fast Recovery Rectifier
Maximum Continuous Forward Current - 8A
Peak Reverse Repetitive Voltage - 1000V
Supplier Package - TO-220AC
Peak Forward Voltage - 1.8V
Peak Reverse Recovery Time - 100ns
Configuration - Single
Peak Non-Repetitive Surge Current - 100A
Peak Reverse Current - 25μA
Pin Count - 2

29th November 2011, 05:29 AM	#1
soundnovice diyAudio Member Join Date: Jan 2011	power supply for P3A hi all, i am building Rod's P3A power amps. the guidelines tell to use 300VA/25-0-025 trafo means 6A for the pair of amps. but i am already having a stock of 5A (i.e.25-0-25/250VA). will it be enough if i am ready to compromise some output power? or is it must to go for 300VA/6A trafo? thanks pranam

30th November 2011, 06:40 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	ESP's P03 project is a 60W into 8r0 amplifier. Total maximum output power of two channels is 120W. Recommended transformer to power two channels is 120VA to 240VA. The amps will work with a transformer outside this range. __________________ regards Andrew T.

1st December 2011, 05:27 AM	#5
mightydub diyAudio Member Join Date: Dec 2006 Location: Where the sky loves the sea	The rectifier current spec is for the average forward current. You have to look at the peak charging currents into the filter caps, these can be very high as the diode is only conducting for a very small portion of the AC cycle. Peak current will be especially high at startup when the DC voltage at the filter caps is zero. The Non-repetitive Peak Forward Surge Current spec can be very high but it is only for a single 1/2 cycle. Overkill on the current spec for the bridge rectifier is doesn't cost much and means you never have to worry about it. __________________ "We monitor many frequencies. We listen always. Came a voice, out of the babel of tongues, speaking to us. It played us a mighty dub… "

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29th November 2011, 11:34 PM	#2
twest820 diyAudio Member Join Date: Jun 2009 Location: Orygun	The answer obviously varies based on listening preferences, environment, and speaker efficiency but if you do the SPL math most likely you'll find most listening occurs at levels on the order of 1mW output power.

1st December 2011, 04:28 AM	#4
soundnovice diyAudio Member Join Date: Jan 2011	thanks Andrew. one more thing is that i am using bridge rectifier rated at 8A while Rod suggests to use 35A. what implications it will have if i use lesser rated bridge rectifiers?

1st December 2011, 05:36 AM	#6
soundnovice diyAudio Member Join Date: Jan 2011	i am using MR8100 diodes whose spec is given below, Type - Ultra Fast Recovery Rectifier Maximum Continuous Forward Current - 8A Peak Reverse Repetitive Voltage - 1000V Supplier Package - TO-220AC Peak Forward Voltage - 1.8V Peak Reverse Recovery Time - 100ns Configuration - Single Peak Non-Repetitive Surge Current - 100A Peak Reverse Current - 25μA Pin Count - 2

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