Maxon OD-880 - great!

[Lee Oswald]

Just finished putting this one together. I like it a lot. It's very nice.
I don't have any LM1458 op amps on hand, so I have no idea what
it might "actually" sound like. I'm using TL072 IC's in it right now,
I'm wondering if others found other 1458 substitutes they like.

My only beef with this pedal is it's a bit dark, but of course it has
no tone control. What can I do to allow for more high end response?

I socketed the clipping diodes, as I think this circuit might benefit from
a high clipping threshold.

[Lee Oswald]

Question for |V|ark -

Can a tone control be added to this circuit? It's a little on the dark side
through my gear.

[Vince]

I've never tried it but I've heard a lot of people mention this.

http://www.muzique.com/lab/swtc.htm

Or maybe this.

http://www.beavisaudio.com/techpages/BigMuffToneControl/

This might be an idea as it has a boost for the inevitable volume drop when installing a passive tone circuit.

http://tagboardeffects.blogspot.co.uk/2013/08/bmp-tonestack-w-lpb1.html

[Lee Oswald]

Thanks for the help Vince. One more question, as I'm pretty dumb when
it comes to this stuff. How and where would one insert the SWTC into the 880
circuit?

[IvIark]

The problem with the SWTC and similar is that they're low pass filters designed to roll off top end which is how most simple tone controls work.  So if the effect is already too dark it's not going to do anything except make it darker because it won't increase top end.

But it would be a great addition if you can tweak the circuit to make it a little too bright which will then allow you to roll off that treble to get to a point more pleasing to you.  So to make it brighter I would look at lowering the value of the 47n caps.  There is a 47n input cap and coupling cap between the first and second stage and they are a high pass filter.  Increasing them allows more bass frequencies into the circuit, decreasing them allows less.  There is also a high pass filter at the inverting input of the second stage which is the 47n cap in series with a 4K7 resistor to ground.  Again, lowering the cap means more low end roll off.

So those three caps are where I would suggest experimenting.  Maybe socket them so you can try a few different values to get it right for you.  Start off by just reducing the input cap though, if the low frequencies are removed at the beginning of the circuit then you may get the results you're looking for without messing with the others.

[induction]

Actually, the SWTC version 2 (the second one on the linked page) goes from flat at minimum to treble boost at maximum. The third one on the page combines the previous two and goes from treble rolloff at minimum to treble boost at maximum. So it might work, if you're looking for versatility.

But if you just want to add treble, and are not looking for increased versatility, it's easier to just modify the caps until you get what you want.

[Lee Oswald]

I was looking for more treble, but I'll take increased versatility if
you wouldn't mind explaining how and where to install SWTC 2.

That would be killer.

[induction]

First, some caveats. Unless you breadboard it, you won't know how it's going to sound, so I can't promise it will give you as much treble as you want. You may also want to experiment with cap and pot values.

I still think IvIark's suggestions are a better way to go, but since you asked, here is my suggestion for how to add the SWTC2 to the 808 without modifying the vero. (This is for the second one on the page, with only treble boost, no cut.)

At the output for Level 3, connect instead to Tone 3 (50K B). Attach a 22nF cap between lugs 2 and 1 of the Tone pot, and attach lug 1 to Level 3. Attach the rest of the Level lugs as suggested on the layout.

I haven't tried this, so consider it unverified. Let us know if you try it and how it works out.

[Lee Oswald]

Induction, thank you.

I'll try this as soon as I get a chance. I tried
|V|ark's suggestion, and it helped, but once
I implemented these changes, it became obvious.
The 880 circuit needs greater versatility.

I'll try this and report back on it.

Also, as I said before, this circuit would probably
benefit from a greater Vf, so it's worth socketing the diodes
if you build this one.