Is 100VA per LM3875 good enough?

leadbelly · 20th February 2004, 09:01 PM

I just wanted to check if the much vaunted 150VA supply per chip figure is still the consensus. I have a couple of 20-0-20 5A transformers that I would like to make a pair of bridged IGCs using LM3875's from, but only if some have experienced good results with 100VA/chip.

officeboy · 20th February 2004, 09:33 PM

Well since the LM3875 is limited to 5amps... I doubt you would have a problem.

I think the 150Va thing is more when using a 25-30V transformer. At least that’s what I’ve come to think from reading threads here. (I’ve only built one of these things, but it sounds pretty good with only a 85VA 18V transformer per chip.)

matjans · 20th February 2004, 11:52 PM

i'm using a 125VA 2x18V toroid per channel. Works like a charm.

Pjotr · 21st February 2004, 12:12 AM

i'm using a 50VA 2x18V toroid per channel. Works like a charm.

Circlotron · 21st February 2004, 02:54 AM

i'm using a 120VA 2x25V EI for 2 channels. Works like a charm.

thylantyr · 21st February 2004, 03:10 AM

I don't have a LM3875 but I hear people say it works like a charm

matjans · 21st February 2004, 03:21 AM

pjotr, you win

!

Pedja · 21st February 2004, 04:33 AM

No, Circlotron wins, 1.2A per channel’s rail.

uvodee · 21st February 2004, 04:56 AM

for testing I use item # 1013 from B.G. Micro (they still have them)
2 Basler transformers (each 20 V AC and 1.2 A) per chip
this set up sounds extremely well at low volume!!! extremely well!

By the way any cheaper?? they cost $2.49 each and are the best I have ever bought.

I also used them (with the D1213) for a cheap dc power supply!
and for $30 (including components and small enclosure) kit I have a adjustable power supply that gives 2A and aprox 28 volts DC.
yes the 2 panel meters (voltage and Amp.) are included!

J-P

intotubes · 21st February 2004, 05:03 AM

How are you guys having success with such small transformers? I tried 2 channels of LM3875's with a single 160VA @22-0-22 and it clipped bad when I tried to crank it up. I installed a second 160VA transformer, one for each channel, problem solved. I can get full power out of it with no distortion.

I must be missing something.

Mark

20th February 2004, 09:01 PM	#1
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Is 100VA per LM3875 good enough? I just wanted to check if the much vaunted 150VA supply per chip figure is still the consensus. I have a couple of 20-0-20 5A transformers that I would like to make a pair of bridged IGCs using LM3875's from, but only if some have experienced good results with 100VA/chip. __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

21st February 2004, 04:56 AM	#9
uvodee diyAudio Member Join Date: Aug 2002 Location: Washington	any one lower?? for testing I use item # 1013 from B.G. Micro (they still have them) 2 Basler transformers (each 20 V AC and 1.2 A) per chip this set up sounds extremely well at low volume!!! extremely well! By the way any cheaper?? they cost $2.49 each and are the best I have ever bought. I also used them (with the D1213) for a cheap dc power supply! and for $30 (including components and small enclosure) kit I have a adjustable power supply that gives 2A and aprox 28 volts DC. yes the 2 panel meters (voltage and Amp.) are included! J-P

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20th February 2004, 09:33 PM	#2
officeboy diyAudio Member Join Date: Nov 2003 Location: NW Washington	Well since the LM3875 is limited to 5amps... I doubt you would have a problem. I think the 150Va thing is more when using a 25-30V transformer. At least that’s what I’ve come to think from reading threads here. (I’ve only built one of these things, but it sounds pretty good with only a 85VA 18V transformer per chip.)

20th February 2004, 11:52 PM	#3
matjans diyAudio Member Join Date: Aug 2003 Location: Utrecht, NL	i'm using a 125VA 2x18V toroid per channel. Works like a charm.

21st February 2004, 12:12 AM	#4
Pjotr diyAudio Member Join Date: Nov 2002 Location: Netherlands	i'm using a 50VA 2x18V toroid per channel. Works like a charm.

21st February 2004, 02:54 AM	#5
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	i'm using a 120VA 2x25V EI for 2 channels. Works like a charm.

21st February 2004, 03:10 AM	#6
thylantyr diyAudio Member Join Date: Feb 2001 Location: Mars	I don't have a LM3875 but I hear people say it works like a charm

21st February 2004, 03:21 AM	#7
matjans diyAudio Member Join Date: Aug 2003 Location: Utrecht, NL	pjotr, you win !

21st February 2004, 04:33 AM	#8
Pedja diyAudio Member Join Date: Jun 2002 Location: Serbia	No, Circlotron wins, 1.2A per channel’s rail.

21st February 2004, 05:03 AM	#10
intotubes diyAudio Member Join Date: Jan 2004 Location: Colorado	How are you guys having success with such small transformers? I tried 2 channels of LM3875's with a single 160VA @22-0-22 and it clipped bad when I tried to crank it up. I installed a second 160VA transformer, one for each channel, problem solved. I can get full power out of it with no distortion. I must be missing something. Mark

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