build report -- a Tube Screamer project w/a stacked op amp combo

[mordechai]

Not that this hasn't been discussed hundreds of times already, but I wanted to report on some nice success in a recent modified TS project.  Some folks out here have made some amazing spaceship-level tubescreamer projects with astounding tweakbility, and I applaud that, but I just wanted to make a simple variant with a specific, tailored tone instead of having tons of knobs and switches.  So I made the following changes to the circuit before implementing the stacked op-amp strategy people have been discussing out here.  Below is the general scenario of what I did leading up to the stacked op amp combo that worked best.

1. CLIPPING DIODES: for D1 I used 1n4148 and for D2 I used a red LED.  The parallel cap was 47pF.  The result was a more "open"
tone, nice complexity perhaps due to the asymmetrical clipping arrangement, and the cap offered just enough smoothing to tame harsh edges.

2. INCREASED DRIVE: I lowered the drive range resistor from 4.7K to 3.3K.  Not a huge difference but there was a notable increase in drive, without too much additional noise introduced.

3.  CAP CHANGE: I upped the cap to .068uF to maintain a focused midrange, but the pronounced "honk" of the midrange bump is decreased a bit, perhaps due to the new diode/drive resistor combination.

4. OP AMP: I've found happiness with two options that work really well with the above changes.  Option 1 is with a JRC4558DD, which seems to have higher gain characteristics than the standard JRC4558D or RC4558P.  (I must say, by the way, that I really was not taken with the RC4558P despite the many great testimonials to its performance.  Admittedly, this is probably due to the fact that I used it with the aforementioned modifications rather than with the standard TS circuit, so maybe in the standard circuit it really does sound nicer.  Anyway...)

Option 2 is with stacking a JRC4558D and a JRC4559D together.  This stacked combination REALLY sounds great.  For some reason, they just interact beautifully together, (seem to) increase the gain, provide a nice open, powerful tone and don't seem to add unwanted noise.  The 4558DD and the stacked 4558D/4559D are real winners with the above-mentioned mods.  The former has a nice, aggressive but pleasing sound and the latter does as well, but with a "deeper" more open type of tone.

I should say that I tried a variety of combos before settling on this.  I used a 4558DD stacked with a 4559D, a 4558D, a RC4558P, and a TL072, and they didn't complement each other as well.  I did the same with a 4559D as the base and tried combining it with each of the others listed above.  I also tried doing this with the Burr Brown OPA2134 as the base combined with a 4559D, a 4558DD, etc.  But the 4558D/4559D combo seemed to be in much better "dialogue" with the other mods listed above.

In the end, the version of this I've put on my board is the stacked version.  I made another pedal with the same mods but a single 4558DD and gave it to a recording/touring guitarist I worked with in the past and it is his "go-to" overdrive for regular gigs.  But for me, the stacked version does what I want from this circuit.  When I A/B it against my original TS-808, it has noticeably more drive, a deeper but clearer tone with less compression, but still has a nice tight midrange that allows it to stand out (just without quite the same honk as the original TS-808). 

One day, I will try to make a mondo-gonzo mother of all tube screamer project (when I have the time and mental fortitude).  For the time being, though -- this basic mod plan really does the trick nicely and has a simplicity that I think is eminently practical for gigging musicians who want a solid drive tone with a bit more subtlety in terms of coloration.  I highly recommend the 4558D/4559D stacked combination -- it really does the trick.