Debugging a Klone - it works but has very low gain

[JoelTone]

I built a Klon using the Grind Customs Chimaera kit (buffered version), and it works but the gain is very low. I have to turn the gain all the way up and hit a chord to hear any drive at all, or boost the input with another pedal. Other than that, though, it seems to work properly. The buffered bypass works fine. And with the gain all the way down, it's totally clean (which is expected, since the Klon has the clean blend). Taking the gain from all the way down to all the way up, there's a slight volume drop and less treble, and that very small amount of drive when playing hard.

I know a lot of people only use their Klons as mostly-clean boosts, but from the demo videos I've seen it should still have a lot more gain than this (and the main gain stage should boost 30-50 dB with the gain maxed), so I'm pretty sure something's wrong.

I've checked almost all the voltage test points and they're all fine (+18 V is more like 16.25, but other than that they're all within half a Volt). I figured something is probably wrong with the main gain stage, so I've probed between the inputs on that opamp, and everything seems to be fine - with the gain all the way up, my DMM reads 434k between out & -in, 486k between out & +in, and 53k between -in & +in (that might seem low, but I've done some circuit analysis and the theoretical number I got is 51.8k). Since those numbers check out, it's probably not a problem with a bad solder joint, short, or bad component in that part of the circuit. I also don't think it's a problem with the clipping diodes, because it should be a lot louder if the gain stage works properly but isn't clipping.

Does anyone have any idea what else I should look at? There's a build doc with schematic & layout here (though the circuit should be exactly the same as the original).

Or is a Klon really supposed to have that little gain?

Thanks!

[midwayfair]

Audio probe pin 7 of U1. Does your signal volume change when you change the gain?

[HOTTUBES]

be sure that R4 is 560R , and not 560K !!
I did this once , and it acted alot like what your describing !
It's worth checking ....

[JoelTone]

I finally got around to building an audio probe today. The signal does change on the output of that opamp when I adjust the gain. With the gain all the way up, the volume is a bit lower than the bypassed pedal. With the gain all the way down, it's silent. So it's behaving about as expected, except with really low gain. I don't see how this is possible, the gain of that stage should be much higher.

And I checked R4, it's 560R.

[jaredmcohen]

Just wondering if the OP ever found a solution?  I built a Klon from |v|ark's vero layout and this sounds like the exact issue I've got.  Everything works, but I only get moderate gain if I turn the gain past 2 o'clock.  Everything before that is more like a clean boost.  I've checked that all resistors are correct (I was also afraid I'd swapped a 560R for a 560k on accident, but I haven't). Volume does increase at IC1 pin 7 as I increase the gain.  All solder joints look good.  And I've razor-bladed the hell out of the vero to make sure there are no solder bridges.

Using the audio probe at IC2 pin 2, I have no audio, and I feel like I should, but I'm no expert when it comes to interpreting schematics, so maybe I'm way off.

Many thanks to anyone who's got any advice.

[vigilante397]

I tried to build a Klon 3 times on 3 different layouts with no success before I finally bit the bullet and bought a kit (still cost me less than everything I put into the previous 3), but the last one I built seems to have had this same problem. Buffer bypass worked great, and I got decent gain until 12 o'clock then the gain went back down as I kept turning. One of these days I'll get back and troubleshoot the ones sitting in my "broken box"  

[italianguy63]

Code Select Expand

sitting in my "broken box"

Burst box.

[vigilante397]

Code Select Expand

sitting in my "broken box"

Burst box.

Good catch, thanks for that correction

[JoelTone]

Just wondering if the OP ever found a solution?

Nope, never did. I've been meaning to sit down with an oscilloscope and try and figure it out, but I've been too busy with school. Finally graduating as an EE in a month though, so hopefully I'll have time to figure out the problem then.

[vigilante397]

As a fellow EE student I have to admit I've found an audio probe significantly more helpful than an oscilloscope in troubleshooting pedals.

[JoelTone]

Yeah, I use both. I mainly want to use a scope because come September I probably won't have access to one anymore.

[jaredmcohen]

Nope, never did. I've been meaning to sit down with an oscilloscope and try and figure it out, but I've been too busy with school. Finally graduating as an EE in a month though, so hopefully I'll have time to figure out the problem then.

Congrats on graduating.  If you do ever find the cause, or a solution, please come back and post it!

[JoelTone]

Yeah thanks, and will do. It'll be nice to be have free time again - I should finally be able to start working on pedals again.

[vigilante397]

Yeah thanks, and will do. It'll be nice to be have free time again - I should finally be able to start working on pedals again.

My pedal building is helping pay for my tuition granted pedal-building time does cut out of sleep time... 

[JoelTone]

I actually considered doing that. Alas, it never ended up happening. I don't know enough people locally who would be interested (I have some connections, but they're not where I'm going to school), and I don't know if I want to attempt to get into the online game (at least, not while I'm still in school).

Plus, if I'm going to sell something, I want to make sure it's well built and not going to break within a year or two, and I'm not sure I trust my abilities well enough. For one, I have no idea how to mount a board in an enclosure in a way that's going to last a long time that doesn't involve custom designing a PCB (i.e. adding screw holes so I can JB-weld standoffs into the enclosure).