Bass Boost CMoy Problems

I built a CMoy with Bass Boost based on this layout:



I wired up the I/O jacks with no pot, no switch for bass boost, OPA2132, .047uF for C7, 100K for R7, and a gain of 2. Last night I wired it up with one 9V and after about 30 seconds of being hooked up the C1 cap for the left channel was very hot. I unhooked the battery and tried fixing any suspect soldering. I hooked the battery back up and it didn't get hot (I didn't think), and then tried listening to some music. There was sound out of both channels but it was VERY scratchy and not very loud.

I gave up on it for the night and this morning I decided to try hooking up two 9V's in series, because I thought it sounded kind of like when my batteries were dying in my other CMoy's. I did this and within a few seconds of having the batteries hooked up the C1 cap for the left channel made a popping noise and it looked like something was bubbling out of the end of it.

I should be getting a digital multimeter soon, and then hopefully I can try to figure out what the problem is myself, but until then I was wondering if there was anything obviously wrong that anyone could notice.

Thanks.

More Info

I also removed one emty line on the protoboard you can see it marked in this pic:



I just shifted everything up. Could this cause a problem? I never knew why that open line was there, or if it needed to be there.

Here's some actual pics of my work:



In the first pic I marked a couple of jumpers that I put underneath. I didn't do a very good job soldering them, and I thought that was my problem last night, but I'm not really sure.

OK, now here's what I've done:

- Flux on whole board and reflowed all joints
- Added in switch as shown in diagram
- Removed damaged C1 capacitor (left channel)

Then I hooked up one 9V and tested it out. (Is it bad to test this amp when it doesn't have any C1 capacitor installed?) With the bass boost swithc 'off' I get what I would think is normal amped sound out of the right channel. The left channel is slightly quieter than the right, but I assumed this was due to the missing C1. When I switch the bass boost on everything gets all scratchy again.

I thought that maybe this was due to my choice of R7 (100K -> 20dB) being too much bass boost for my headphones to handle so I switched the R7 (in the right channel) to a 10K resistor for 6dB of boost. This still causes similar amounts of distortion.

For my C7 I am using Polyester-Film Capacitors. Is this OK or should I switch to Metalized-Film? Would that be enough to cause my distortion?

I'm going to get some 0.1uF Metalized-Film Capacitors to use as C7 and also a replacement C1. I'm hoping the noise in the bass boost circuit is due to the fact that the caps I used were Polyester-Film, and that the Metalized-Film caps will fix my problem.

OK, that was a stupid mistake. I switched the caps to right direction and hoped that would fix my amp, but it didn't.

Right now I have one working side (right) and one side that works, but is quieter (left). When I switch on the bass boost both sides are mostly static.

Thanks for all the suggestions!

I think you're onto something with the vision thing. I decided to turn on my desk lamp as well as my ceiling lamp and it seems I can't tell the difference between red/orange/brown on a resistor!

For R4 (which should be 10K) I had a 1K (right channel) and a 100K (left channel). I think I must have just zoned out when picking my resistors. If I had a multimeter I would have matched my resistors and this never would have happened.

Anyways, after a lot of desoldering and resoldering now I have a working CMoy with a gain of 2 and OPA2132. I am using two 9V's in series (I haven't even gotten to trying to put in my DC jack).

For the bass boost circuit I have a 0.1uF cap (lowest, Hz, bass boost) and a 15K resistor. I'm a little unclear as to whether 10K or 100K does more bass boosting. I was assuming that 10K would give less bass, but now that I think about it, does 100K give the least bass boost?

With the 15K resistor in place I get A LOT of distortion. Right now I'm running the amp out of my iPod's headphone out so I can control the volume. With the 15K resistor I hear distortion unless the iPod is at about 25% or less. With 100K resistors I don't hear the distortion until about 50%. But with either I don't hear any bass boost even when the volume is low enough that there is no distortion.

So, my question is what do I do next?

- Change the bass boost cap to 0.047uF?
- Change the bass boost resistor to 100K?
- Add in the pot and see if that will help?

Using these cap/resistor values what configuration would give me the least bass boost (I just want it to work!):

- 0.1uF/0.047uF cap
- 10Kohm/100Kohm resistor

Thank you

Just want to make sure that I'm having problems with the bass boost off, so here's a quick drawing of how I have my switch hooked up:



That drawing shows the direction of the switch in what I assume is bass boost off (this is how the switch is when my amp works). It is a DPDT Micromini Toggle Switch from Radioshack, and the A,B,C,D labels are shown on the picture in the original post of this thread.

Bump

I'm getting really tired of de-soldering and soldering different cap/resistor combinations, and I'm out of ideas with what I currently have. I think my new enclosure should arrive in a week or so, and I'd like to figure this out before then.

Is there something wrong with my layout? Or with the components I'm using?

Thanks for any help!

From my original post (http://www6.head-fi.org/forums/showthread.php?t=151722) I thought that putting the bass boost circuit in place of the R5 would be correct. Now that I look at the schematic for a PPA it seems that the bass boost circuit should be in series with R4 which is in parallel with R5. I think that may be my problem.

Once I realized I may have set up my bass boost circuit incorrectly I thought that cutting one of the pads of the proto board to make the bass boost circuit in series with R4 would fix my problem. I cut it with my new Dremel only to plug in my headphones and get no sound at all. I then realized that this also cut one pin (from each channel) of the op-amp out of the circuit, thus causing my to get no sound.

I think I may be able to just add a jumper and get bass boost to work, but I'm gonna have to think about it a little bit more. Hopefully I can figure it out before my enclosure gets here. If I can get it to work I think I'll just re-do the layout (using a little bit more space) and make sure to get it right.