Blendable Klon-type Overdrive

[markm]

Hi ya fellas,
I've been thinking, and that is dangerous sometimes for all of us, 
But, I came up with this Blendable type OD based on the OD250 type circuit that for the most part, incorporates the standard OD250 circuit along with a "Clean" version with no clipping diodes and a TL071 op amp.
The idea is to have the Gain control set-up similar to the Klon or The Crank  using a Dual Gang pot where when one side is max, the other is minimum and so on.
I'm a bit confused as to whether this here would work as I have the 2 circuits sharing the same input cap and also they share the same output to the volume control.
Any opinions as to whether they would work together when set up like this or, should I just call it a day on this one?!
Please have a look at the layout.
I have no schem as it's just 2 OD250's put together.

[Dragonfly]

just a quick thought, and i dont know if this will help, but i would look at using one input that splits into 2 input sections, so you can raise the impedance of the "boost" OD250.

[markm]

Well, the only shared part on the input is the input cap......is that going to really screw up the impedance?

[freddd]

Hey mark, quick work!

If you used a couple of dual op amps (as it is "rumoured" the real deal does!) you could place an input and ouput buffer around the two circuits. ~Or you could place a buffer in front of either circuit so that both sections have equal input impedance.

[Dragonfly]

Well, the only shared part on the input is the input cap......is that going to really screw up the impedance?

im not saying "screwed up"...i'm saying that it would be preferable, IMO, to have your gain circuit at a low input impedance, and your clean boost circuit at a higher impedance. 

Just my opinion

[markm]

Well, the only shared part on the input is the input cap......is that going to really screw up the impedance?

im not saying "screwed up"...i'm saying that it would be preferable, IMO, to have your gain circuit at a low input impedance, and your clean boost circuit at a higher impedance. 

Just my opinion

Ahhh.
Okay, I see what yer getting at here AC.

Hey mark, quick work!

If you used a couple of dual op amps (as it is "rumoured" the real deal does!) you could place an input and ouput buffer around the two circuits. ~Or you could place a buffer in front of either circuit so that both sections have equal input impedance.

That's a good idea.
Yeah, I have "heard" the original has duals, I can't confirm it but, that's the word on the street.
I guess I was attempting to keep it "simple" so to speak.
My other concern is, since the "clean" side has no diodes in the ouput, it will be much louder than the "clipping" side so, that's something to work out as well. 

[markm]

Wait a minute though.....
Won't the TL071 provide a higher impedance than the 741 or, am I sadly mistaken.
(Don't worry about it, I used to being wrong!) 

[Dragonfly]

Wait a minute though.....
Won't the TL071 provide a higher impedance than the 741 or, am I sadly mistaken.
(Don't worry about it, I used to being wrong!) 

you know what...i didnt even notice that you were using 2 different op amps.

the tl071 has a jfet input stage that has a high input impedance. 

so youre safe

[markm]

That's kinda what I was thinking when I did that but, hey.....I'm no designer, and I'm no EE.
I'm just a "circuit-hack"!!
That's what makes me so dangerous! 

[freddd]

Build it, build it, build it! And tell us what it sounds like!

[markm]

Build it, build it, build it! And tell us what it sounds like!

Well, I thinks that's what I'm going to have to do and then work some of the bugs out from there.
I think I'm going to have to lower the gain on the 071 side a bit 'cause I know it's not going be close to the 741 side.
That's when I'll screw it up!

[slacker]

Should work Ok, the input impedance of both sides is high enough that even though they're in parallel to each other they shouldn't load the signal down or anything.
Like you said you'll probably want to lower the gain of "channel B" because it will be much louder than "channel A" and if you crank the gain high enough you'll get distortion from the opamp even without any clippers.
I'd probably add a resistor between the top of C5 and lug 3 of the volume pot instead of having a straight connection. That way this resistor and R13 could be adjusted to balance the outputs from both sides. You could even use a trimmer with the middle lug going to lug 3 of the volume pot and the outside lugs going to either channel. Hope that makes sense

[slacker]

Actually, thinking about it you need a buffer after the clipping diodes on "channel A", otherwise the clipping diodes are attached to the outputs of both channels. This means your clean channel is going to get clipped as well as the dirty channel.

[markm]

Actually, thinking about it you need a buffer after the clipping diodes on "channel A", otherwise the clipping diodes are attached to the outputs of both channels. This means your clean channel is going to get clipped as well as the dirty channel.

Yes, I see.
Very true. Simple Jfet buffer would probably suit it well or, I suppose I could get "fancy" and use the TS type.
As I sit here and stare at it I do realize that oversight.....the diodes are in the signal path no matter what.

[slacker]

The other thing you could do is stick the clipping diodes in the feedback loop of the opamp TS style. That way you wouldn't need the buffer.
It's a cool idea, be interested in hearing how it turns out

[freddd]

I just breadboarded one up now. Sounds pretty good. I stuck a buffer on the end of each section though. And also one on the input. Buffer central really 

I'll have a fiddle some more - need to get the overall volumes of both side equal, I think this is going to be the key issue here.

[markm]

The other thing you could do is stick the clipping diodes in the feedback loop of the opamp TS style. That way you wouldn't need the buffer.
It's a cool idea, be interested in hearing how it turns out

I really want to stay away from that TS type soft-clipping if possible, I'm an OD250 guy!! 
My thoughts are, the buffer to help isolate the clipping diodes will not be hard to add.
Perhaps even the front-end could be buffered as well which may help any possible impedance issues.
At this point, I going to try and get the basics working on it for now then, possibly the charge-pump on the "clean" side for 18V and a tone control such as the SWTC maybe.

I just breadboarded one up now. Sounds pretty good. I stuck a buffer on the end of each section though. And also one on the input. Buffer central really 

I'll have a fiddle some more - need to get the overall volumes of both side equal, I think this is going to be the key issue here.

Can you try just buffering the clipping side and tell me if it works or not??
I agree, balance is gonna make or break this thing! 

[freddd]

Yeah, I'll give it a pop. I'll try running the microamp side at 18v too, just using two 9v batteries in series.

I think the SWTC would be a good choice - I'll try that too. The tone control of the original operates as a high cut I believe.

[markm]

Yeah, I'll give it a pop. I'll try running the microamp side at 18v too, just using two 9v batteries in series.

I think the SWTC would be a good choice - I'll try that too. The tone control of the original operates as a high cut I believe.

That would be great!
I'm not trying to clone the Klon, just make something similiar......hey, ya know.......
We could all team up and enter this thing into the FX-X as a group and kick everybody's butt!! 

[freddd]

  gotcha. heh. It's 10PM here though so I'll probably do that tomorrow. I'm sure with a bit of work it'll be great. With the gain in the middle you get a cool fizz over the clean sound - very pleasing!