Blendable Klon-type Overdrive

[BlueToad]

Based on the claim that the original tone control is "neutral in the middle", I think that the circuit uses either a BSIAB-type tone control, or an active circuit such as the baxandall. Based on my own fooling around, the latter can give a very 'transparent' sound, enabling a more or less independent boost or cut of the high frequencies. It might actually be possible to improve on the Klon by using individual bass and treble controls, rather than just a single knob TC. The baxandall would lend itself to that very well, although I suppose the more tone controls there are, the further away from the 'transparent' goal you get.

As to getting the balance of gain right between the two stages, how about putting a fixed resistor in parallel with the half of the dual gang pot responsible for adjusting the gain of the OD250 stage? That seems like it would be a pretty quick fix, without greatly effecting the frequency response of the circuit. Actually, looking at the schematic, I might raise the value of the capacitor from the inverting input of the opamp to ground, in the hopes of reducing the hi-pass effect. Not that I know what the hell I'm talking about . Well, now I know what I'm going to spend the next week fooling around with!

Kudos Mark, this is a good idea. I have been working along similar lines recently, but due to a stupid tendency to over-complicate things I haven't gotten nearly so far. Very interested to see where this ends up. Thanks!
Carl

[freddd]

I like the idea of a baxandall. I like the SWTC for it's transparency - you can trim just enough of the highs to stop your ears sizzling.

It's not the relative gain that is the problem - it's the volume of the two sections (The OD250 is quieter than the microamp due to the clipping) slacker came up with a good fix a couple of posts back I'm implementing it as we speak.

[markm]

Well, now I know what I'm going to spend the next week fooling around with!

Kudos Mark, this is a good idea. I have been working along similar lines recently, but due to a stupid tendency to over-complicate things I haven't gotten nearly so far. Very interested to see where this ends up. Thanks!
Carl

Thanks for the kind words Carl....been thinking about this now and again for some time now but, finally came up with something reasonable, I think 
The jury is still out!

I'd like to keep it simple with the SWTC, but who knows at this point.
Here's a look at it re-arranged with a Buffer at the end of the "dirt" side and a change to the resistor at the gain from 47K to 4.7K in hopes of making up for some loss from the clipping section.

[jaytee]

I think the output of the dirty side is restricted by the diodes at 0.6v pk pk. At first I thought of lowering the gain of the clean side, but then if you want to have high output maybe the buffer can be made to have some gain, maybe 2-4 times. I'm not sure how noisy it would get. I like asymetrical Ge diodes in a circuit like this. I believe the pedal in question uses Ge clipping?

[markm]

I think the output of the dirty side is restricted by the diodes at 0.6v pk pk. At first I thought of lowering the gain of the clean side, but then if you want to have high output maybe the buffer can be made to have some gain, maybe 2-4 times. I'm not sure how noisy it would get. I like asymetrical Ge diodes in a circuit like this. I believe the pedal in question uses Ge clipping?

Both good points.
Ge's in the Klon huh? Now that you mention it, I have may have heard that somewhere but, I'm not sure.

[freddd]

Hey Mark. I tried what you asked - It didn't like not having a buffer on both outputs. The Micoamp seemed to go a bit fuzzy.

the microamp sounds good at 18v, lots of headroom. I placed a simple volume control on the clean boost side (Just a 100k trim to ground) -  made it easy to balance the volumes.

I did work out a problem though - I havn't been using a dual ganged 470k rev log pot (just 2 470kB) Now if I did use a dual ganged pot wouldn't one of the tracks be working in the wrong direction (As it is a reverse log)? I've been trying to adapt the design to use 2 10kB pots, I'm sure this would be better.

[Bernardduur]

Cool!

Must build this quite soon!

[markm]

Hey Mark. I tried what you asked - It didn't like not having a buffer on both outputs. The Micoamp seemed to go a bit fuzzy.

the microamp sounds good at 18v, lots of headroom. I placed a simple volume control on the clean boost side (Just a 100k trim to ground) -  made it easy to balance the volumes.

I did work out a problem though - I havn't been using a dual ganged 470k rev log pot (just 2 470kB) Now if I did use a dual ganged pot wouldn't one of the tracks be working in the wrong direction (As it is a reverse log)? I've been trying to adapt the design to use 2 10kB pots, I'm sure this would be better.

It would be a B500K, a dual gang linear but, reverse wired like The Crank and the SparkleDrive etc.
The idea is to have the dual gang set up, like the Klon.
The trim control seems like a good temporary "fix" however, maybe you could measure the resistance set by the trimmer and replace it with a resistor of the same value?
Too bad about the buffer, perhaps the design is going to have to take another turn and become a bit more complicated?

[Bernardduur]

What about an IC buffer; one at the start to split the two signals into two individual sources and one at the end to buffer all?

[markm]

What about an IC buffer; one at the start to split the two signals into two individual sources and one at the end to buffer all?

I suppose that would work as well.
Perhaps use 2 dual op-amps, one side on each one as a buffer. 

[jaytee]

Hey Mark. I tried what you asked - It didn't like not having a buffer on both outputs. The Micoamp seemed to go a bit fuzzy.

Did you put a 10k resistor after the buffer? I think you need something like that to mix the outputs.

[markm]

Hey Mark. I tried what you asked - It didn't like not having a buffer on both outputs. The Micoamp seemed to go a bit fuzzy.

Did you put a 10k resistor after the buffer? I think you need something like that to mix the outputs.

Ummm,  I didn't put a 10K in the layout, I don't know if freddd did or not......how 'bout it freddd? 
Are you suggesting the 10K after the 10uf cap from the buffer or before it?

[jaytee]

After the cap. One end to C9 the other end to R13.

[freddd]

Nope, I didn't place any resistance after the OD250 buffer. Just had it running to the same point as the microamp output.

I tried something a little different mark. I took the splitter blend design from runoffgroove and removed the phase switching part (So it basically had two "red" lines). Between the "green" send and return points I placed the OD250 and between the "red" the microamp. The blend control can then be used to dial in just the right volume of microamp boost. You can then wire up your gain control and hey preto . . . .

The thing with linear pots is the change in gain isn't regular at all, it's all rammed down one end of the pot so when you have the gain control wired up your just going to get two extremes on either side of its rotation with nothing in between.

[markm]

Interesting.
Perhaps the gain could be a B50k or B100k dual.
The idea of the blendable gain is to model it after the Klon.....I just don't want to make it overly complicated and if I add all of the controls then TMK syndrome sets in. 

[freddd]

You don't actually have the 25k blend control as a pot. You can just replace it with two fixed resistors when you decide the balance is right. It's just a circuit "restructure". This just leaves you with the original controls you outlined - gain and volume (with "tone" if you decide to add it)

I think 50kb sounds best. I wish I had one to try it out!

[jaytee]

You could use a 1M LIN dual pot then use resistors to contour each side as in the info over at GEO to get the response and gain that you want.

[markm]

Very true.
I think what I'm going to have to do at this point is one of 2 things;

1) give it up......it's on the right track but, no cigar

     -or-

2) Build it and try and work some of the bugs out of it from there.

Any other thoughts fellas?

[Bernardduur]

2!

Else I will build it

The idea is pretty great; and fit's right into my niche of pedals I need to build quite soon; alas to say the shop I get my stuff from is closed now so I can't build that quick!

[freddd]

Build it, but like I suggested - in the loop of the splitter blend. It sound pretty cool.