KLON clone, even with Gain knob at 10 it never breaks up. Why?

[half_smith]

Antonis, can you tell me where to add a cap? I am beyond confused.

I've taken the whole board apart and am rebuilding it.

Do you think the Klon schematic is generally improved by adding more anti-DC caps?
Or is there a common failure that leads to this remedy being required?

[idy]

Is Antonio saying put a cap between the wiper of the gain pot and VB?
That would mean no path to "ground" (in this case VB) for DC. Since the DC is not being "divided", you will get unity gain for DC.

Klon doesn't have that cap, Tube screamer does, Distortion +, Rat, it's a normal thing in an OpAmp gain stage. Weird. Lacking that cap we might expect scratchy gain control because DC on a pot is....frowned upon....

[half_smith]

Makes sense Idy, thanks.

I just found that I had a .027uf Cap at C12 instead of .0027uf
Does having a 10x too high Cap at C12 seem like the culprit?

[idy]

27n is .027uf. That is what the schematic shows for C12. .0027uf would be 2.7n.

making it bigger means more treble cut for the clipped signal. Smaller means only high treble cut. This is after clipping, not your issue.

[half_smith]

crap, you're right, I was right the first time. Thought I'd found something. Back to nowhere... :/

[idy]

On the other hand, the fact that this confused you (and even after a few go-arounds it is easy to be confused by pico/nano/micro, all those zeros, and the funny way values are written on components)...points out...
that you may have missed one single value somewhere,
and one single cap
or resistor
off by a factor of 10
(or 100)
would produce exactly the problem you describe.

[half_smith]

Idy, you're not wrong. I've been triple checking each component, thing is I had swapped C12 (.027uf) for a "Tropical Fish" I had. The Tropical Fish is not labelled so I deduced that may be the problem. I looked up the invoice from when I bought it and it said .027uf, but at that moment I misread the schematic, wishful thinking blurred my vision.

At this point I'm rebuilding/rewiring the whole pedal and will hopefully resolve the problem even if I never know what caused it...
but if I still don't get sufficient clipping across the diodes I will be back to request further guidance...

[idy]

Tropical fish are color code. Same numbers as resistors.

I once bought a baggy of R's from down under. Baggy said 47k. Didn't read the color code. Found out by going through the board one R at a time.... Meter said 470k.

[half_smith]

Tropical fish are color code. Same numbers as resistors

whoa.

[antonis]

whoa.

[half_smith]

Thanks Idy and Antonis, yeah I figured out the color code, I thought it was just a cute paint job lol.

Anyway, I've totally rebuilt the board and wiring and it is exactly the same. fml. back to Square 1.

The Treble and Level knobs work perfectly as expected, Gain knob actually loses volume and no "clipping" as I crank it.

Is it correct of me to think of this circuit as three paths that merge into one at the 2nd OpAmp?
I was thinking of a way to direct more of the signal through the  "clipping" circuit?

Antonis' idea about DC still confounds me, but would that be causing the whole path to be weak? The pots aren't scratchy...

[idy]

We've never seen a picture of this board you've rebuilt. Some boards are more confusing than others. Off board pots= nearly inevitable mistakes.

[half_smith]

Idy, it's the General Guitar Gadgets KIT pcb. The schematic is true to other Klons I've seen, the pcb traces are a little jumbly.

• I lifted a leg on R7 and disconnected pin2 on the GAIN pot-a - so the signal can only go over the Diodes, and yes it sounds like germanium clipping.


• R7 lifted, p2 GAIN pot-a reconnected, some clipping is there.
  If I use my Xotic Compressor to seriously boost the signal into the KLON, with this configuration I get noticeable "clipping"


• With R7 modded to 10k (from 1k5), there is some barely clipping, especially with the boosted signal from my XP Comp. This seems closer to what the circuit is supposed to do, but clearly not right. As I move the GAIN pot there's kind of a phasing swoosh

Maybe the "clean" Feedforward R7 path is taking too much of the signal?

Maybe my input impedance is wonky, or, first Op Amp gain stage is weak?

If time is money I could've built five from scratch by now.

[half_smith]

I went ahead and swapped out C9

The pad was worn there and I had run a jumper to R12 - basically something funny going on right at the crucial Diodiest part of the circuit.

I put in a new 1uf Electrolytic and used the leg to jumper to R12.

Preliminary test very hopeful! I think this was the main culprit. I'll be back if not 

[DIY Bass]

, Gain knob actually loses volume and no "clipping" as I crank it.

This is very suggestive.  The gain knob in the Klon basically increases the gain in the distorted part of the circuit, but it also pans from the distorted signal to the clean signal.  As you turn up the gain you get more dirt in the dirt side, but also less clean blended in.  If you are getting little to no dirt and the volume drops as you turn up the gain almost certain you are only getting the clean signal - the dirt isn't getting through at all.

I went ahead and swapped out C9

The pad was worn there and I had run a jumper to R12 - basically something funny going on right at the crucial Diodiest part of the circuit.

I put in a new 1uf Electrolytic and used the leg to jumper to R12.

Preliminary test very hopeful! I think this was the main culprit. I'll be back if not 

and it sounds as if you found the culprit.  Nice sleuthing

[half_smith]

thanks DIY Bass. I found a thing or two that improved my pedal, but it's still not able to crank like it should, eventhough I will mostly never use that setting!
I agree with your analysis except the signal is getting through some, just not enough.

Anyone able to explain what's going on with these outboard resistors?
I don't see them on any schematics or in pictures of a real Klon


snippet taken from (http://www.generalguitargadgets.com/pdf/ggg_kc_lo.pdf)

[antonis]

Antonis' idea about DC still confounds me, but would that be causing the whole path to be weak?

Any DC gain higfher than unity "upsets" op-amp output from sitting on Vref, according to superposition theorem..
This results into asymmetrically reduced headroom, hence gain availiable..
(imagine a +9V single supply amp of any gain equal to or higher than unity biased at +9V - no responce for signal positive waveform..)

[idy]

Those off-board resistors are on your schematic.
They are part of the designer's unusual bypass scheme. By having both sides always connected through a 68k to the output, switching is quieter. To keep the effect from bleeding through, the effect is muted through grounding right at the diodes; the footswitch either grounds the LED or the signal right in the middle of the circuit.

[idy]

Testing Antonis' idea is super easy, amigo.
Just snip the wire to the gain pot wiper, (the side of the gain pot that controls the OD gain, the one attached to R6 and R10, labeled "b" in your schematic/layout)
and put a cap, maybe 47n, maybe 1uf, between the ends of the cut wire.

Viola, you will have stopped DC from being "voltage divided" and you will no longer be pushing the bias voltage of the Opamp to the ceiling when you turn the gain knob up.

This is weird, the design. Other Klons work with this detail, but the experiment is easy. And you have spent so long on this, maybe it's worthwhile trying out ideas from the knowledgeable people here.

And still no pictures of your project. Very likely things like lifted or broken traces, tiny solder bridge, the basics. It usually is. The basics. That cause us to pull our hair out and tear innocent components from their places.

Other options include animal sacrifice.  There may be a forum explaining trouble-shooting electronics through the examination of entrails, but those conversations are frowned upon here.

[idy]

Also, we are not sure if you switched the wires to the gain pot.
The side marked "b".
The terminals are correctly marked on the layout:

When the pot is turned CCW (wiper to terminal 1), the signal at R6 is being sent to VB and the Opamp non-inverting input is getting nada. Nada in, nada out.

When the pot is turned CW, the signal at R10 is going to VB, which means the inverting input is "seeing" a weak signal, and the opamp does its "magic" to amplify and bring it back up.