# made PCB's for LM317/LM337 and DC coupled Szekeres (100KB)



## weeghel

Hi,

 Two weeks ago I found out how incredibly easy and cheap it is to make your own PCB's. So I've decided that for everything of certain importance I will design a PCB. For my new headphone amplifier (for which I now have all the compenents, so I will finish this in max 2 weeks!!) I have designed 3 PCB's. One for a DC coupled Szekeres headphone amp (one channel, so you will need two!), and for the powersupply based on a lm317/lm337 combination.

 Since I designed these, and since I'm very new at designing pcb's, can someone with more experience and/or with a fresh eye (I have no doubt that I'm overlooking at least 5 mistakes) take a look at my designs?


 Here are the pictures:

 First the schematic of the powersupply:







 And now the LM317 section pcb:





 Componentlayout:





 The lm337 section, please note the link for connection to the lm317 board, I will explain furtheron:





 Componentlayout:





 I figured that a lm337 will mostly be used in combination with a lm317. So when you need a dual powersupplu (as the one in the schematic above) you simply connect the GND out from the transformer to the lm337 board, and fit a link to the lm317 board. The one "live"wire to the lm337 board and one to the lm317 board. The only difference to a fully integrated dual supply is that this one needs 4 extra rectifier diodes. And you can use the lm317 board for projects that only need a positive supply.

*Can someone please comment if the above statement is true?*


 And now for the szekeres schematic:






 And the pcb I designed for it:





 Componentlayout:






 Any feedback would be very welcome on the general design and layout, and also if you spot any errors.

 If you decide to take the risk, print the graphics on 300dpi and you will heve the correct size.

 A similar post will be made on HeadWize, so if you read this and think by yourself "huh, I thought I just left This site?"; this is why!


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## weeghel

I updated the images.
 The Szekeres has had a small update, in the lower right corner, there was a sharp angle. This is softened somewhat.
 The lm boards now have a protection diode, as suggested by Pbrown on Headwize. According to the datasheet, there can be a protection diode across the in and output, I chose to add one only on the output.


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## Tomo

Hey,

 I think your components are too close. Note this amp will heat up a lot and it is important that you keep the mosfet and R4 away from other components in the amp. Heat can damage components.

 It is a good idea to give some extra space for upgrading. Your design is space critical and it allows very small possibilities of upgrade once the amp is assembled. Many parts have different footprints and dimentions. Also, you will have to get to the parts to replace them (or repair them). 

 Additionally, you might want to use a constant current supply in the place of R4. The directions are posted on the addendum of Mr Szkeres' article. I can testify that that upgrade is worth it considering how cheap LM317's are.

 Tomo


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## weeghel

Small update: The powersupply boards work. (on the 337 board, the large cap is displayed incorrectly. It should be installed the other way round, I will update the image ASAP)
 I'm now starting on the Szekeres


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## weeghel

The powersupply, which works flawlessly, a nice +/-7,50V on the outputs:






 The Szekeres PCB:






 I removed the 2 diodes, for testing purposes, because this one DOESN't work!!

 It draws an incredible amount of current, heating up my 25VA transfomer within 20 seconds. Note: this is only ONE channel. 
 With my previous Szekeres both channels operated without problems from this transformer.
 So there must be something wrong, but I've checked and rechecked and I can't find anything. Maybe this is how it should be, and my previous amp was wrong, but I find that hard to believe. I'd really appreciate it if someone would take the time to check my PCB layout very carefully.


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## weeghel

Update:
 I did some measurements. And I've probably solved the problems. (still have do the final and most conclusive test: play music through it)

 There were two problems: 
 1. One busted mosfet (hate when that happens!)
 2. I wired my powersupply the wrong way. Although the powersupply put out +/- 7,5 volts at 300mA, the current drawn from the transformer was 2,5A. I messed up the rectifier diode layout. The PCB's are good, but when making a dual supply, don't install all 8 diodes, but use 4 (2 on each board) and make some wire links between the PCB's (using the holes that aren't used by the non-present diodes 
	

	
	
		
		

		
		
	


	




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