Troubleshooting DIP16AMP X1 build

[ryangs]

I just finished building my first amp, a DIP16AMP X1. It kind of looks like a mess, because my soldering skills are less than perfect, but a thorough visual inspection shows that everything appears to be making contact, and nothing is jumping that shouldn't be.

When I turn the amp on, I hear nothing until I turn the volume pot all the way up. Then I hear a very quiet, scratchy version of the input.

Unfortunately, I don't have a meter with me here at school. I might be able to borrow one from somebody, or I might just go out and buy one, but before I do either, I thought I would post here to see if this is a common problem with a simple solution. Sooo... any ideas? Thanks in advance!

 

[Jazper]

post some pictures for us...

 

[ryangs]

Only if you promise not to laugh...

I ended up building it on a protoboard from Radio Shack because the dip socket was just too small to work with.

(taking pictures now...)

 

[ericj]

dip16amp is kind of a fiddly build so it's sorta normal for it to look a little scary the first few times you build one.

Stupid questions: you did put the input caps after the volume pot rather than before it, and you did ground the volume pot, right?

Also, it's very dangerous (for your headphones) to experiment with headphone amps without a fairly sensitive meter. That means either a real good analog meter or the cheapest crappiest dmm you can find.

If you have a big dc offset in the output, you seriously run the risk of damaging your headphones. But even the cheezyest centech dmm sold at Harbor Freight or similar craptacular stores for $6 or so can tell you if you have more than a few mv of DC on the output.

 

[ryangs]

Don't worry, I've been testing it with some old headphones. As for your other questions... I dunno. I just followed the diagram as close as I could.

One thing I just noticed is that one of the far outside pins of the pot is grounding against the metal body of the pot (a little too much solder). Could this be the problem?

Pictures are coming.

 

[ryangs]

Pictures. Don't laugh. Seriously.

Warning: the pictures are massive (~1 mb each).

http://webpages.charter.net/ryangs/dip16.jpg
http://webpages.charter.net/ryangs/dip16-2.jpg

Can you tell that I didn't plan my PCB layout at all? Ha!

The brown wire in the middle of the board that looks like it's shorting against the adjacent pin really isn't. It's sitting above it.

The blue wire on the far left of the volume pot in the second picture is the one that's shorting against the metal body of the pot. Haven't had any luck taking care of that one with my desoldering bulb yet...

BTW, I was too lazy to install the switch for testing purposes, so I just soldered together the connections that the switch would make. This wouldn't cause the problem, would it?

 

[Jazper]

a pic of the top of the board would be good too

 

[ryangs]

Well, sure.

http://webpages.charter.net/ryangs/dip16-3.jpg
http://webpages.charter.net/ryangs/dip16-4.jpg

Threw in another pic of the infuriatingly tiny volume pot for good measure.

 

[dip16amp]

The wire that should go from pin 3 to pin 15 looks like it is incorrectly going to pin 16 instead.

 

[ryangs]

Oh, wow. You're right. Don't know how I missed that!

I'll fix that and see what happens.

 

[ryangs]

I fixed that improper connection, but the problem persists.

 

[dip16amp]

The wire for out 2 should be connected to pin 10 but it looks like it is on pin 9.

 

[ryangs]

Indeed it was. I had mixed that up with the ground wire, and realized that I had forgotten to actually connect the grounds of the inputs to the ground on the circuit. I did that, and fixed the location of out 2. Still no sound, but the opamp is getting REALLY hot now, and I hear pops/clicks when I plug in the test headphones.

I think I've got voltage going somewhere that it shouldn't!

That, or I fried my opamp by getting it too hot while soldering. Should've used a socket...

Thanks for all your help so far!

 

[ryangs]

HA! I got it to work!

There was a really tiny bit of excess solder that was jumping two of the pins.

I can't believe how good it sounds for $15 in parts! (and lots of labor...)

Thanks so much for catching my stupid mistakes! And thanks for sharing the design, dip16amp!

Edit: Hey, so, next question if anyone is still reading this thread.

I now want to replace the mini output jack that I have installed now with a 1/4" one. I need to figure out which pin is which on the 1/4" jack that I have. Am I correct about this pinout for the mini jack?

A top-down view:
Code:

[left] | \ | | /[/left]

From left to right: out 1, out 2, ground, the jack.

So, now I need to correlate that to the 1/4" Switchcraft jack that I have. I can easily see which pins on the jack connect to which parts of the 1/4" plug. Of the tip, ring, and sleeve of the 1/4" plug, which are out 1, 2 and ground?

 

[dip16amp]

I think the out 2 is tip, out 1 is ring, and ground is sleeve.