And the award for my smoothest overdrive to date goes to...

[Frank_NH]

...the Ibanez MT-10 Mostortion!  

http://tagboardeffects.blogspot.com/2013/02/ibanez-mt10-mostortion.html

I actually built the Quantum PCB from Aion Electronics, which has the BJT buffers at the input and output, but otherwise the circuit should be identical to the vero above.  For the IC, I found a CA3260 dual CMOS op amp online.  I also made one mod - swapped the 220 nF cap for 100 nF to tighten up the bass.  

I really like the way this thing sounds - it's definitely smoother then a tube screamer in that the note decay is very natural and it doesn't breakup or crackle as much. Maybe "less wooly" is better term.   Yet the gain range is very tube screamerish, and I would not, for that reason, call this a distortion.  

The tone controls are outstanding as well.  You can get a very mid-scooped sound rolling the Mids all the back, perfect for those mid-eighties hair-metal tones.  And the treble range is quite wide too, allowing appropriate settings for both humbuckers and single coils.

I'm thinking that the magic in this case is due to the CA3260 chip as the rest of the design doesn't deviate that much from a tube screamer (apart from the tone stack).  Anyhow, give this circuit a try (with the 3260) if you want something a little different from the average overdrive.  

[motterpaul]

Frank - I will definitely try it. It reminds of one I tried today -- the JHS Morning Glory, in the sense that it has one "rare" IC, and 4 SI diodes. The IC on the JHS is an LM833 which is a "Low Noise Audio Dual Operational Amplifier" chip (?), which I don't have, and it seems like the circuit needs it.

The recommended substitute IC (5532) oscillates.

http://3.bp.blogspot.com/-fM1xOaW41HM/UZKD7l4u42I/AAAAAAAACQM/GhMc5U1blVU/s1600/JHS-Morning-Glory.png

[Muadzin]

I've always seen the word smooth being used a lot, but I never really understood what it exactly means in this context. The impression I get is that the rough edges are shaved off, leaving a kind of...... bland end product?

[Frank_NH]

By smoothness, I mean that as you hit a note you hear the distortion bloom then die away without the "crackle" or "graininess" you sometimes hear.  I know it's pretty subjective, and everyone has their favorite tones they prefer.  But while it's pretty subtle, but I know it when I hear it!  Supposedly, CMOS op amps are "smoother" than JFET or BJT, but in reality a lot of the tone has also to do with circuit design (i.e. gain stage design and filtering).  And I still like a good old basic tube screamer, like the OD-808 I recently built, but with three diode asymmetric clipping instead of the usual two diode clipping.

[Silver Blues]

Yeah I've heard good things about that op-amp. I've been meaning to get a few to try in some circuits.

[motterpaul]

To me a smooth overdrive is one where you have a wide freq response (low lows and high highs) but it is neither boomy or biting - more clear and even. And you get a clean, solid sustain with no modulation in tone or volume - a clean decay with no sputter, crackle or hair.

If you hit a power chord and every note in the chord stays at the same volume, no change in tonality as the chord dies out - that is also smooth to me.

[Frank_NH]

Silver Blues wrote

Yeah I've heard good things about that op-amp. I've been meaning to get a few to try in some circuits.

The CA3260 is somewhat expensive on eBay (about $7.50 for one including shipping).  There may be cheaper sources (let me know if anyone finds any).

[motterpaul]

Yeah, I looked up that opamp and I was shocked at the price. You can find them much cheaper from China - but they will take a month to arrive. (Chinese New Year, I guess) - also, you have to question the quality of those.

[motterpaul]

By the way - I took a shot at this:  http://www.ebay.com/itm/131383838047

5 ICs of CA3260 AEZ for just $5.50 (+ $2 shipping).

According to the data sheet they have the same specs:
http://www.intersil.com/content/dam/Intersil/documents/ca32/ca3260.pdf

[Pavlos]

I'd agree with that completely and add that to me it also means the sort of tone is warm, sweet, syrupy, reminds you of chocolate, something along the lines of more than a feeling by Boston (Although not necessarily with so much gain) though of course we all hear things differently, and one man's warm and full is another man's flabby and dull........or is that one woman's........oh I don't know ;o)

[Frank_NH]

Here's a great thread at DIYStomboxes.com that discusses the CA3260 and the Ibanez MOStortion MT10.  This is where I got the idea to reduce the feedback network cap from 220nF to 100nF.

http://www.diystompboxes.com/smfforum/index.php?topic=45480.0

It would be interesting to pop a CA3260 into a regular TS-9 tube screamer and see what it sounds like...

[Muadzin]

motterpaul wrote

By the way - I took a shot at this:  http://www.ebay.com/itm/131383838047

5 ICs of CA3260 AEZ for just $5.50 (+ $2 shipping).

According to the data sheet they have the same specs:
http://www.intersil.com/content/dam/Intersil/documents/ca32/ca3260.pdf

I don't trust any IC's sold through Chinese Ebay sellers. At best you get reused IC's, at worst fakes.

[rocket88]

I've got to disagree with you on that one. Nearly all my IC's are from chinese sellers on eBay. You just have to use ones that are reliable. Every single IC I've got are genuine.

[Muadzin]

rocket88 wrote

I've got to disagree with you on that one. Nearly all my IC's are from chinese sellers on eBay. You just have to use ones that are reliable. Every single IC I've got are genuine.

And all the J201's I got from Chinese sellers were fakes. So excuse my weariness in regards to Chinese sellers. Better to pay more from reliable sellers elsewhere then dodgy Chinese. Because if there's a universal constant its that shitheads will always ruin it for the good ones. Which then begs the question, which are the good ones?

[motterpaul]

I have had pretty good luck when it comes to Chinese sellers - especially with ICs. Transistors are another story, I got ripped with some fake 2n5457s, they don't even look original. They work, but at about half power.

[rocket88]

Muadzin wrote

And all the J201's I got from Chinese sellers were fakes. So excuse my weariness in regards to Chinese sellers. Better to pay more from reliable sellers elsewhere then dodgy Chinese. Because if there's a universal constant its that shitheads will always ruin it for the good ones. Which then begs the question, which are the good ones?

I completely agree about a lot of the Chinese sellers being doggy, and some being even more then doggy, as in I've seen a Chinese seller selling transistors that were obviously sanded and relabeled, well attempted relabeling. And yes, the shitty ones ruin it for the many. What I find is if it's something that really is hard to find or the price has skyrocketed and they're being sold for like nothing, example I saw a Chinese seller that had 25 2n5457's for $10 when there normally $0.50 a pop, avoid that seller. For instance polida and gc_supermarket have prices that are way below value, gc has a listing up for 100 lm358's for $3.78, even ignoring their recent history with selling "counterfeit" parts, sanded and relabeled, I wouldn't even think about buying them cause the price is too low and too good to be true. With that being said, I have bought from both those sellers nj the past, like 3yrs ago, and got everything quickly and the ICs were brand new and perfect, now with the shit they've been pulling and hearing a lot of people getting sanded and relabeled parts from them or IC's that are original, but don't work, I wouldn't give them another penny.

 The problem with buying through hole fets from china now is that the demand is high since they're now obsolete, so you're more likely to encounter a fake. I only buy them from reputable sellers and online stores, I've also been fine with the ones from tayda, all in spec and new. The bottom line is you get what you pay for. If you're really cheeping out you're going to get burned, if you're trying to save a couple of bucks you'll be fine. My dad always has said pigs go free, hogs get slaughtered, if you know what I mean.

I'll gladly go through my favorited eBay sellers and find them for you if you want.