Really Smooth Overdrive!  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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mictester
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Post by mictester »

This is one I've had around since the early 1970s in various versions. This is it brought (almost) up to date. As ever, it's open to many modifications. The values shown work well, but you might want to tweak some of the values to better suit your rig. You'll see that there's no traditional "Drive" control - I found that it wasn't ever necessary. I always preferred to control the levels from the guitar, and this circuit is very responsive to that.

The first stage is just a unity gain buffer. This gives buffered bypass. Some "true" bypass believers will insist that there should be a "copper" path between input and output when the effect is bypassed, but in practical terms, this way is usually much better. You're guaranteed a low output impedance regardless of mode, and you can drive long leads without loss.

The second stage is where the magic happens (for me, anyway). It's a lowpass filter. It takes all the high end off the guitar altogether. This is deliberate, and is what gives this effect its unique "voice".

The third stage is the usual sort of "diodes in the feedback loop" clipper (asymmetry can be applied here if you like), just like a zillion other pedals, but the addition of the series resistor with the diodes changes the character of the distortion somewhat. Versions have been built with series potentiometers replacing the 1k (I used 22k to get a good range), but the additional change in tone wasn't worth drilling another hole in the box for! By all means increase (or decrease) that value - I've used 4k7 on some builds.

Following the clipper, there's a passive tone control. Put your favourite version of Big Muff Tone circuit if you want, but the simpler one here works really well. The clipping stage introduces lots of harmonics, and the tone control can round them off nicely. The capacitor values can be open to experimentation, of course. If you change the 33n for 22n or even 10n, you can get some really nasty high-frequency content - I don't like it, but some might!

The final stage is another buffer. The output jack "sees" the same impedance whichever feed is selected, so that subsequent equipment doesn't get any surprises.

Overall, this is a fairly low gain pedal (certainly by modern standards), but it will give you a sound that you've heard on some very famous records!

Here's the schematic:
ReallySmoothOverdrive.png
ReallySmoothOverdrive.png (7.6 KiB) Viewed 8348 times
A couple of PCB versions will appear here later (I can't find them right now) - one uses a TL074 and the other uses a TL072 for the buffers and a 4558 for the processing. There's little difference in the sound of the two versions, and I tend to build the TL074 version for reasons of economy.

The LED switching looks complicated, but isn't. It doesn't "click" when switched, and it's pretty smooth to have a bi-colour LED change colour when you kick the effect in. I also found that the green LED needed a bit more current for equal brightness with the red one, but you may find that yours are different - you might have to change the series resistor values to suit. Generally, you should go for the highest resistor values you can in that position, and still have the LEDs visible. After all, the LEDs are just status indications, and it would be pretty stupid to have a 2mA pedal become a 30mA pedal just because of the LEDs!
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Post by SPeter »

Thanks for sharing!
:applause:
:thumbsup
:D

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Post by drijaya »

layout please

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mictester
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Post by mictester »

drijaya wrote:layout please
Can't you do your own?

I'll post one later.
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mictester
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Post by mictester »

OK folks. PCB for the Really Smooth. There is an added diode for asymmetrical clipping (D3) which can be omitted, but you have to connect the solder pads between the diodes together. You can also add a switch for symmetry if you want, but the tonal change is small.

Vero to follow!
ReallySmooth.gif
Here's the PnP!
ReallySmoothPnP.gif
ReallySmoothPnP.gif (6.83 KiB) Viewed 7662 times
"Why is it humming?" "Because it doesn't know the words!"

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Post by DrNomis »

Hmmmmmm...Cool....might build one soon... :thumbsup
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Post by phatt »

Thanks for that Mic,
Obviously you've done this before,, Wink.
I only had a short time to mess with it so of course I may have missed something,,, which is not news.

Rolloff point looks to be a little low but hey it sounds good with my tone stack in front.
Yes it works well but you may have missed a cap? :shock:

Inserting a 100n cap before u3 seemed to fix some kind of DC offset problem that made it very sputtery.
Once I worked that out it was very impressive.

Still some noise so I inserted a 10k/10k divider after the first stage which helped bring the dreaded hiss down to a respectable level.

That will of course stuff up the buffer bypass but heck I don't bother with such things.

So yeah mate a plus from me. :applause:

Cheers, Phil.

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Post by borislavgajic »

:thumbsup

thanks

Boris

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Post by roseblood11 »

phatt wrote: Inserting a 100n cap before u3 seemed to fix some kind of DC offset problem that made it very sputtery.
Once I worked that out it was very impressive.

Still some noise so I inserted a 10k/10k divider after the first stage which helped bring the dreaded hiss down to a respectable level.
Could you show that in the schematic, please?

----

I´m just trying to make a veroboard layout for two dual opamps.
Or has anybody already made one?

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Post by mictester »

roseblood11 wrote: Could you show that in the schematic, please?
I´m just trying to make a veroboard layout for two dual opamps.
Or has anybody already made one?
Amended version will be uploaded later. I've done a vero version as well, which I'll upload when I've converted it from notebook scribbles to something legible.
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Post by mictester »

Here's the corrected schematic, PnP and board layout:
ReallySmoothOverdrive.png
ReallySmoothOverdrive.png (7.72 KiB) Viewed 7425 times
ReallySmooth.GIF
ReallySmooth.GIF
I checked my own example of this, and it had that extra capacitor! My mistake!
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Post by phatt »

Hi mic,
I have had even less time today to fiddle with this but here is what is on my BB right now.
Seems to have silenced the beast somewhat with little loss in effect.
The circuit certainly does the big long Carlos Santana sustain. :thumbsup

The 10k/10k divider works better at the end of the circuit and of course will not effect your buffered bypass.
Cheers Phil.
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Post by SPeter »

Thanks mictester!
:thumbsup
:D

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Post by mictester »

phatt wrote:Hi mic,
I have had even less time today to fiddle with this but here is what is on my BB right now.
Seems to have silenced the beast somewhat with little loss in effect.
The circuit certainly does the big long Carlos Santana sustain. :thumbsup

The 10k/10k divider works better at the end of the circuit and of course will not effect your buffered bypass.
Cheers Phil.
OK. The resistor from the mid-rail to the non-inverting input of the clipper was to allow the use of ordinary bipolar op-amps. The last two op-amps on the one on my pedal board are in a 4558, and there are some with LM833 in there. If you use a pair of 072s or a single 074, you can short that resistor.

Your 10k / 10k divider is OK, but it's got a bit more grunt if you put a 4k7 in series with the output of the op-amp with the 10k to deck.

The sustain really sings, doesn't it? :)
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Post by mictester »

phatt wrote:Hi mic,
I have had even less time today to fiddle with this but here is what is on my BB right now.
Seems to have silenced the beast somewhat with little loss in effect.
The circuit certainly does the big long Carlos Santana sustain. :thumbsup

The 10k/10k divider works better at the end of the circuit and of course will not effect your buffered bypass.
Cheers Phil.
The 47p at the input was just to keep the local AM radio station out of the effect!
"Why is it humming?" "Because it doesn't know the words!"

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Post by phatt »

Hi mic,
I'm not up to speed on some of the deeper things bout opamps but I've got LM833 chips.
So I'm vauge on the reason for ground lift 4k7? seems to work the same either way for me.
Remember some of us don't have the scopes and sig gens that you guys have,, but it's all good fun. :)

Just saw something that might interest you,,, A CS2 *infront of a Bog standard TS9*
I'd like to do it With Your circuit,,, might be interesting but bum I've got to BB a CS2 first.
Oh well always next week.
Cheers Phil.

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Post by Cannibal »

hi mictester, could you please explain me how the low pass filter stage works?
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Post by mictester »

Cannibal wrote:hi mictester, could you please explain me how the low pass filter stage works?
Look up "Sallen and Key" on Google. It's a standard lowpass circuit. You can pick the frequency response by choosing the capacitors. There are online tables to save you doing the mathematics, or you can get a copy of "The Art of Electronics" by Horowitz and Hill.
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Post by earthtonesaudio »

mictester wrote:
Cannibal wrote:hi mictester, could you please explain me how the low pass filter stage works?
Look up "Sallen and Key" on Google. It's a standard lowpass circuit. You can pick the frequency response by choosing the capacitors. There are online tables to save you doing the mathematics, or you can get a copy of "The Art of Electronics" by Horowitz and Hill.
For a typical Saleen-Key lowpass with gain the 4n7 cap would normally go to the output, not the inverting input. Having it arranged as drawn will still filter, it just won't be a second order lowpass.
rocklander wrote:hairsplitting and semantics aren't exactly the same thing though.. we may need two contests for that.

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Post by gght »

I know this is an old thread, but... I am intrigued. I am wondering if a gain control would be as simple as a pot and a fixed resistor in parallel with the diodes, ala a tubescreamer? I just never have liked using the guitar volume to control pedal gain. is Mictester still around? Also, did anyone try LEDs as clippers here?

Thanks!
gght

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