Help with gainclone power supply

Eargasm · 25th March 2003, 10:44 PM

Hello,
After reading so much about the gainclone I decided to throw one together for myself. I went out to used electronics stores to find the parts so that my prototype doesnt cost too much money. I am using 4 transformers with dual 120V primaries and dual 12V secondaries, two for each channel. The secondaries are wired in series to produce 24V. When measured directly at the transformer output, the output is 24V. And then at the DC output of my bridge rectifiers it is 24V DC (+/-). The problem that I am having though is once the 1000uf capacitors are hooked up, I am getting 35V, and it puts that lightning bolt on my meter (it's a fluke and I think that means it's pissed off at me). I can't for the life of me figure out why it magically gets 11 extra volts when the caps are hooked up. Is this because there is no load on the unit, and some extra current is being converted to voltage in some strange way?

I am very confused, and before I hook up my amp chips I would like to find out what the deal is. The reason my caps are hooked up before the chips is because they were some extra's I had lying around that have the screw terminals on the top, which can't be soldered directly to the leads of the LM3875, and I decided to use them just for the sake of it. (Dont worry, they are very close with short runs of wire like everything has said to do) I triple checked everything and I am 99% sure I have it wired correctly, I would just like an explanation as to why I am getting this voltage increase when the caps are hooked up, and if this is going to be a problem.

My free samples are supposed to be here today, so I am going to go check the mail right now, and hopefully I can get this all straightened out so I can listen to ths thing play tonight.

zx3chris · 25th March 2003, 10:50 PM

if your tranny is 24volt secondary, that is the rms voltage. you need to divide by .7 to get the peak voltage.. 24/.7 = 34 volts. after the capacitors smoothing out the peaks, you will be near 34, possibly a bit less due to the voltage drops from the diodes. for example, in this gif from elliot sound, he uses a 25-0-25 transformer and obtains +/-35VDC.

-chris

Eargasm · 25th March 2003, 11:28 PM

thank you for the explanation about the increased voltage, but why does it make the lightning bolt appear on my meter?

zx3chris · 25th March 2003, 11:35 PM

your meter may not be able register voltages above a certain amount.. sometimes you need to change the plugs on the bottom--different ports can accept different voltages/amperes.. a fluke that cant do 30v is kinda odd---my $20 radio shack meter can do 100V...

-chris

Eargasm · 26th March 2003, 12:03 AM

lol...always helps to read the manual. Even though it's just one man's opinion. Apparantly the lightning bolt just means that it is greater than 30V and that I need to be careful.

faustian bargin · 26th March 2003, 12:59 AM

Quote:

Originally posted by zx3chris
if your tranny is 24volt secondary, that is the rms voltage. you need to divide by .7 to get the peak voltage.. 24/.7 = 34 volts. after the capacitors smoothing out the peaks, you will be near 34, possibly a bit less due to the voltage drops from the diodes. for example, in this gif from elliot sound, he uses a 25-0-25 transformer and obtains +/-35VDC.

-chris

another question, as i'm also figuring out this power supply stuff:

can i consider that a general rule of thumb for figuring out voltage after rectification? does the rectified & smoothed voltage usually approach the peak transfo output voltage?

/andrew

zx3chris · 26th March 2003, 01:29 AM

yes, although it isnt a rule of thumb---thats exactly what is happening.. when you rectify the ac wave, you have a bunch of positive waveforms (picture a sine wave, and flip all the negative---now it is just a bunch of humps --- where the top of the hump is the ac peak to peak voltage).. now to smooth out the humps, you add capacitance. you will get some voltage drops due to the diodes however it usually isnt much and i always neglect it anyways. also, if the capacitance is way too small, it wont do as well of a job as smoothing out.

-chris

faustian bargin · 26th March 2003, 02:03 AM

thanks. i learned something *useful* today!

/andrew

grataku · 26th March 2003, 03:09 AM

Eargasm from Potterdam,

If you have split secondary (not the center tap kind) just use the much better real split dual rectifier circuit. It's posted here:

2 Rectifier bridges : Why ?

Post #38 in that thread contains a great expl. of why it's better.
Only drawback is that it may take a couple of volts so you may end up with 33-0-33 instead of 35-0-35 but who cares?

25th March 2003, 10:44 PM	#1
Eargasm diyAudio Member Join Date: Mar 2002 Location: San Marcos, TX	Help with gainclone power supply Hello, After reading so much about the gainclone I decided to throw one together for myself. I went out to used electronics stores to find the parts so that my prototype doesnt cost too much money. I am using 4 transformers with dual 120V primaries and dual 12V secondaries, two for each channel. The secondaries are wired in series to produce 24V. When measured directly at the transformer output, the output is 24V. And then at the DC output of my bridge rectifiers it is 24V DC (+/-). The problem that I am having though is once the 1000uf capacitors are hooked up, I am getting 35V, and it puts that lightning bolt on my meter (it's a fluke and I think that means it's pissed off at me). I can't for the life of me figure out why it magically gets 11 extra volts when the caps are hooked up. Is this because there is no load on the unit, and some extra current is being converted to voltage in some strange way? I am very confused, and before I hook up my amp chips I would like to find out what the deal is. The reason my caps are hooked up before the chips is because they were some extra's I had lying around that have the screw terminals on the top, which can't be soldered directly to the leads of the LM3875, and I decided to use them just for the sake of it. (Dont worry, they are very close with short runs of wire like everything has said to do) I triple checked everything and I am 99% sure I have it wired correctly, I would just like an explanation as to why I am getting this voltage increase when the caps are hooked up, and if this is going to be a problem. My free samples are supposed to be here today, so I am going to go check the mail right now, and hopefully I can get this all straightened out so I can listen to ths thing play tonight.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
gainclone power supply	student	Chip Amps	49	21st July 2010 09:38 PM
Gainclone Power Supply	iandrum	Power Supplies	11	28th January 2009 02:23 PM
Power supply for bridged Gainclone	Mrpong	Chip Amps	1	1st July 2006 04:28 AM
Gainclone power supply	soundNERD	Chip Amps	10	4th February 2004 01:31 AM
Power Supply for 5 channel Gainclone	Gcollier	Chip Amps	3	25th March 2003 08:53 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

25th March 2003, 10:50 PM	#2
zx3chris diyAudio Member Join Date: Oct 2002 Location: south amboy nj	if your tranny is 24volt secondary, that is the rms voltage. you need to divide by .7 to get the peak voltage.. 24/.7 = 34 volts. after the capacitors smoothing out the peaks, you will be near 34, possibly a bit less due to the voltage drops from the diodes. for example, in this gif from elliot sound, he uses a 25-0-25 transformer and obtains +/-35VDC. -chris

25th March 2003, 11:28 PM	#3
Eargasm diyAudio Member Join Date: Mar 2002 Location: San Marcos, TX	thank you for the explanation about the increased voltage, but why does it make the lightning bolt appear on my meter?

25th March 2003, 11:35 PM	#4
zx3chris diyAudio Member Join Date: Oct 2002 Location: south amboy nj	your meter may not be able register voltages above a certain amount.. sometimes you need to change the plugs on the bottom--different ports can accept different voltages/amperes.. a fluke that cant do 30v is kinda odd---my $20 radio shack meter can do 100V... -chris

26th March 2003, 12:03 AM	#5
Eargasm diyAudio Member Join Date: Mar 2002 Location: San Marcos, TX	lol...always helps to read the manual. Even though it's just one man's opinion. Apparantly the lightning bolt just means that it is greater than 30V and that I need to be careful.

26th March 2003, 01:29 AM	#7
zx3chris diyAudio Member Join Date: Oct 2002 Location: south amboy nj	yes, although it isnt a rule of thumb---thats exactly what is happening.. when you rectify the ac wave, you have a bunch of positive waveforms (picture a sine wave, and flip all the negative---now it is just a bunch of humps --- where the top of the hump is the ac peak to peak voltage).. now to smooth out the humps, you add capacitance. you will get some voltage drops due to the diodes however it usually isnt much and i always neglect it anyways. also, if the capacitance is way too small, it wont do as well of a job as smoothing out. -chris

26th March 2003, 02:03 AM	#8
faustian bargin diyAudio Member Join Date: Jan 2003 Location: piedmont	thanks. i learned something useful today! /andrew

26th March 2003, 03:09 AM	#9
grataku diyAudio Member Join Date: Dec 2000 Location: -	Eargasm from Potterdam, If you have split secondary (not the center tap kind) just use the much better real split dual rectifier circuit. It's posted here: 2 Rectifier bridges : Why ? Post #38 in that thread contains a great expl. of why it's better. Only drawback is that it may take a couple of volts so you may end up with 33-0-33 instead of 35-0-35 but who cares?

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)