dc volts

mike dodd · 7th August 2009, 05:50 AM

I'm new to building amps so I hope some one can help. I'm building a LM3886 kit from chipamp.com and am getting 2mvdc from the psu. I thought it should be about 30vdc. I've rechecked the entire pcb and can't find the problem. Are there any suggestions. chipamp does not respond to my emails.
Thanks Mike

AndrewT · 7th August 2009, 12:20 PM

pull out the mains plug immediately.
You may have left a wire unconnected, can it short while you are fiddling around?
or
You may have wired the mains transformer wrongly. This could destroy the transformer if you try connecting it to the mains supply again.

Redshift187 · 7th August 2009, 01:52 PM

Are you using a light bulb tester? If not, you should make one and use it before continuing.

odysseybmx414 · 7th August 2009, 02:02 PM

a light bulb tester, and a drawing for us to look at would be great.

mike dodd · 7th August 2009, 05:37 PM

Thanks for the replies,
The transormer is wired correctly and there is the proper acv. when testing from v+ to v- there is the same acv. Is this the way it should be? I thought it should be dcv. I'll build a light bulb tester this weekend. I've been going over this psu for a week, even disassemled it and resolderd everything. Attached is a picture of the psu from chipamp.com. Mine looks the same.
Thanks Mike

PJPro · 7th August 2009, 05:56 PM

Take a look at this thread and skip to page 4 for details on how I made my deluxe light bulb tester.

odysseybmx414 · 7th August 2009, 05:57 PM

does the kit have two or one bridge rectifiers?

if one, than the secondaries hook up to that at ~ and ~ pins on the rect. the dcv is output at + and - pins of the rect. your center tap than goes to ground.

if two, than your transformer must have dual secondaries, thus each one (pair of wires) would connect to one of the rectifiers.

!!!!! if your + and - pins have acv on them, this means so do the capacitors, and they soon could explode on you.

if you could draw an mspaint diagram up real quick, showing how you connected transformer wires to the pcb.

edit i see it has diodes. still, we cannot tell what is going on until we can see how it is connected.

mike dodd · 7th August 2009, 11:49 PM

Thanks again,
there are two rectifiers. the pcb is clearly marked for the ac inputs, binding posts are soldered there as per instructions. the transformer has two pairs of secondaries. I have never used ms paint so attached is a jpeg of the boards. it is pretty straitforward as to where everything goes and polarity. The bands on the pcb for the diodes indicate metal side.

Redshift187 · 8th August 2009, 02:30 AM

Since you have already answered the question about diode polarity, what about the large capacitors?

Stuey · 8th August 2009, 08:06 AM

Hi Mike,

Can you please clarify - you say the PSU output is 2mV DC in the first post, but then that it's the same AC out across + & - as the AC input, in post #5. What is the actual output?

It'd be highly unusual for AC to get past the rectifiers if they are correctly aligned and properly functional, and as you state, it's almost foolproof on these boards because of the band markings, if the diodes are those supplied by Chipamp (MUR860?). If not, make sure the pin polarity is correct (I'm not sure if all diodes in this package are pin compatible - maybe they are?).

BTW I've built one of these kits and it's a nice, compact, good sounding unit when up and operating.

Stuey

7th August 2009, 05:50 AM	#1
mike dodd diyAudio Member Join Date: Aug 2009	dc volts I'm new to building amps so I hope some one can help. I'm building a LM3886 kit from chipamp.com and am getting 2mvdc from the psu. I thought it should be about 30vdc. I've rechecked the entire pcb and can't find the problem. Are there any suggestions. chipamp does not respond to my emails. Thanks Mike

7th August 2009, 12:20 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	pull out the mains plug immediately. You may have left a wire unconnected, can it short while you are fiddling around? or You may have wired the mains transformer wrongly. This could destroy the transformer if you try connecting it to the mains supply again. __________________ regards Andrew T.

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7th August 2009, 01:52 PM	#3
Redshift187 diyAudio Member Join Date: Aug 2008	Are you using a light bulb tester? If not, you should make one and use it before continuing.

7th August 2009, 02:02 PM	#4
odysseybmx414 diyAudio Member Join Date: Feb 2005 Location: Watertown, NY	a light bulb tester, and a drawing for us to look at would be great.

7th August 2009, 05:56 PM	#6
PJPro diyAudio Member Join Date: May 2009	Take a look at this thread and skip to page 4 for details on how I made my deluxe light bulb tester.

7th August 2009, 05:57 PM	#7
odysseybmx414 diyAudio Member Join Date: Feb 2005 Location: Watertown, NY	does the kit have two or one bridge rectifiers? if one, than the secondaries hook up to that at ~ and ~ pins on the rect. the dcv is output at + and - pins of the rect. your center tap than goes to ground. if two, than your transformer must have dual secondaries, thus each one (pair of wires) would connect to one of the rectifiers. !!!!! if your + and - pins have acv on them, this means so do the capacitors, and they soon could explode on you. if you could draw an mspaint diagram up real quick, showing how you connected transformer wires to the pcb. edit i see it has diodes. still, we cannot tell what is going on until we can see how it is connected.

8th August 2009, 02:30 AM	#9
Redshift187 diyAudio Member Join Date: Aug 2008	Since you have already answered the question about diode polarity, what about the large capacitors?

8th August 2009, 08:06 AM	#10
Stuey diyAudio Member Join Date: Mar 2006 Location: Perth, Western Australia	Hi Mike, Can you please clarify - you say the PSU output is 2mV DC in the first post, but then that it's the same AC out across + & - as the AC input, in post #5. What is the actual output? It'd be highly unusual for AC to get past the rectifiers if they are correctly aligned and properly functional, and as you state, it's almost foolproof on these boards because of the band markings, if the diodes are those supplied by Chipamp (MUR860?). If not, make sure the pin polarity is correct (I'm not sure if all diodes in this package are pin compatible - maybe they are?). BTW I've built one of these kits and it's a nice, compact, good sounding unit when up and operating. Stuey

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