Max voltage for bpa200

enter · 22nd January 2006, 06:15 PM

Hi

I am planing on puting together some 3886 briged\parallel circuit BPA200 from national for a subwoofer amp and this will drive a 4ohm sub.

My problem is that i have a transformer 500VA 25-0-25 and with the psu i will have +/-38V.I know this is to much.

What can i do to reduce it to 28-30v as National recommends???

Thanks

Bazukaz · 22nd January 2006, 07:54 PM

Unwind some secondary windings of your transformer.

MikeLewis · 22nd January 2006, 10:26 PM

(25 * 1.414) - (2*0.7) = 34V

the 0.7v drops are due to the diode voltage drops.

Those numbers are actually very accurate, as I run a pair of 625VA 25-0-25 traffos that put out ~34V unloaded on each rail after rectification

enter · 22nd January 2006, 11:05 PM

I know this is a solution, searhing the forum i read it somewhere but i haven't done this befor and i'm afraid i will damage my toroidal.Is it so easy?About how many windings must i cut off?

digi01 · 22nd January 2006, 11:56 PM

Quote:

Originally posted by MikeLewis
(25 * 1.414) - (2*0.7) = 34V

the 0.7v drops are due to the diode voltage drops.

Those numbers are actually very accurate, as I run a pair of 625VA 25-0-25 traffos that put out ~34V unloaded on each rail after rectification

and as my experience,the traffos that put out VDC=1.2*VAC full loaded on each rail after rectification.

1.2*25=30V

enter · 25th January 2006, 09:06 PM

HI

Sorry about the 38V, it is 34v.I will tray it with this voltage and see it, if i manage to make it work.

I build the bpa200 basic circuit p2p exactly as it is in AN-1192 no servos and with lf412acn.The resistors are 0,1% as national recommends.
I connected a cdplayer and a 8ohm old speaker i have for the first tests and nothing is going out from the speaker. Dead silent.
I mesure the supply voltage on each IC and all is ok
I mesure the dc offset and i have 3mv with a 8ohm load!
I used some pc speakers to hear if the signal is ok at the lf412 output(because i dont have a oscilloscope) and it is.
I have overchecked all the signal paths, supply rails, grounds, all ok
The only thing i dont know if it is ok and haw to check is the lm3886's without ansoldering them. Is there a way to check them???

Can someone experienced please help me???

Thanks

jaudio · 25th January 2006, 09:51 PM

What is the value of the resistor on the mute pin?

Have you tried each 3886 separately to see if they work?

enter · 25th January 2006, 09:54 PM

I dont have any resistor there. Must i put a resistor at the mute pin???

jaudio · 25th January 2006, 10:00 PM

Yes each 3886 need a resistor from pin 8 to pin 4

Bazukaz · 25th January 2006, 10:01 PM

Hah

). So your amp is mute , and you will never hear anything from it.
resistor is usally selected ~40 kOhm and connected from -Vs to Mute pin.
There is formula how to calculate Resistor's value exactly in datasheet.

22nd January 2006, 06:15 PM	#1
enter diyAudio Member Join Date: Jun 2005 Location: Athens	Max voltage for bpa200 Hi I am planing on puting together some 3886 briged\parallel circuit BPA200 from national for a subwoofer amp and this will drive a 4ohm sub. My problem is that i have a transformer 500VA 25-0-25 and with the psu i will have +/-38V.I know this is to much. What can i do to reduce it to 28-30v as National recommends??? Thanks

25th January 2006, 09:06 PM	#6
enter diyAudio Member Join Date: Jun 2005 Location: Athens	BPA200 problem HI Sorry about the 38V, it is 34v.I will tray it with this voltage and see it, if i manage to make it work. I build the bpa200 basic circuit p2p exactly as it is in AN-1192 no servos and with lf412acn.The resistors are 0,1% as national recommends. I connected a cdplayer and a 8ohm old speaker i have for the first tests and nothing is going out from the speaker. Dead silent. I mesure the supply voltage on each IC and all is ok I mesure the dc offset and i have 3mv with a 8ohm load! I used some pc speakers to hear if the signal is ok at the lf412 output(because i dont have a oscilloscope) and it is. I have overchecked all the signal paths, supply rails, grounds, all ok The only thing i dont know if it is ok and haw to check is the lm3886's without ansoldering them. Is there a way to check them??? Can someone experienced please help me??? Thanks

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22nd January 2006, 07:54 PM	#2
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	Unwind some secondary windings of your transformer.

22nd January 2006, 10:26 PM	#3
MikeLewis diyAudio Member Join Date: Aug 2005	(25 * 1.414) - (2*0.7) = 34V the 0.7v drops are due to the diode voltage drops. Those numbers are actually very accurate, as I run a pair of 625VA 25-0-25 traffos that put out ~34V unloaded on each rail after rectification

22nd January 2006, 11:05 PM	#4
enter diyAudio Member Join Date: Jun 2005 Location: Athens	I know this is a solution, searhing the forum i read it somewhere but i haven't done this befor and i'm afraid i will damage my toroidal.Is it so easy?About how many windings must i cut off?

25th January 2006, 09:51 PM	#7
jaudio diyAudio Member Join Date: Oct 2004	What is the value of the resistor on the mute pin? Have you tried each 3886 separately to see if they work?

25th January 2006, 09:54 PM	#8
enter diyAudio Member Join Date: Jun 2005 Location: Athens	I dont have any resistor there. Must i put a resistor at the mute pin???

25th January 2006, 10:00 PM	#9
jaudio diyAudio Member Join Date: Oct 2004	Yes each 3886 need a resistor from pin 8 to pin 4

25th January 2006, 10:01 PM	#10
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	Hah ). So your amp is mute , and you will never hear anything from it. resistor is usally selected ~40 kOhm and connected from -Vs to Mute pin. There is formula how to calculate Resistor's value exactly in datasheet.

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