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.
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.
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
An externally hosted image should be here but it was not working when we last tested it.
-chris
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
-chris
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:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=12162&highlight=dual+bridge
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?
If you have split secondary (not the center tap kind) just use the much better real split dual rectifier circuit. It's posted here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=12162&highlight=dual+bridge
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?
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