What's a Transparent Overdrive for Bluesy Grit?

[turbolx5oh]

Tube Screamer types have too much of a mid hump. I'm playing a Suhr strat through a Crate Palomino V32. I love the clean sound of this amp but I just need a bit of grit added to that clean when I need it. I've got a few home brew Tube Screamers that serve their purpose well and I also have a modified Boss DS-1 and MT-2 for the more aggressive stuff. I was thinking about something like a Keeley modded Boss BD-2 or something similar. Anyone have any other ideas?

[Suburbanite]

Boss sd1 imho would serve that up, and the keely 5*mod gives it a little more gain. I also quite like snarling dogs blue doo which is a tube screamer clone without the mid hump and has a hell of a lot of gain on tap but still cleans up nicely

[cjlectronics]

I just repaired a TC electronics BLD and I haven't found a musician yet that doesn't like the sound of this pedal. It has a very wide tone range and you can dial in a little grind up to a mucho caliente roar (practicing my Spanish for my vacation in Playa de Carmen in 4 hours).
My client stated that he contacted TC Electronics to see if they would fix it but they said they don't work on the originals. Then they offered to buy it from him, he said.

I play an '86 vintage reissue strat through a Fender Brown Vibroverb. I can clean up the grit with a dial down of my volume on the strat and take a bite when I need it. The BLD is real and one of my favorite booster(overdrive)/distortion pedals!

CJL

[Mark Hammer]

The (by now) standard topology used in the SD1 and the TS9, as well as all their clones, assumes the goal of some reasonable degree of distortion. The mid-hump is the result of trimming back on the bass content of the input signal (in order to extract roughly as much clipping from the always-louder bass notes as from the always softer upper notes), complemented by trimming back on the treble content of the boosted/clipped signal to provide the sought-after balanced harmonic content.

So, the hump is the result of designing for more clipping potential while avoiding the disadvantages of that goal. If you raise the clipping threshold for the entire signal by using a pair of red LEDs, instead of a pair (or trio) of silicon diodes as is normally used, then you can forego the bass-trimming at the input, and lighten up on the treble filtering post-clip, resulting in a tone that is only mildly gritty with much less of a mid-hump.

[Shea]

The (by now) standard topology used in the SD1 and the TS9, as well as all their clones, assumes the goal of some reasonable degree of distortion. The mid-hump is the result of trimming back on the bass content of the input signal (in order to extract roughly as much clipping from the always-louder bass notes as from the always softer upper notes), complemented by trimming back on the treble content of the boosted/clipped signal to provide the sought-after balanced harmonic content.

So, the hump is the result of designing for more clipping potential while avoiding the disadvantages of that goal. If you raise the clipping threshold for the entire signal by using a pair of red LEDs, instead of a pair (or trio) of silicon diodes as is normally used, then you can forego the bass-trimming at the input, and lighten up on the treble filtering post-clip, resulting in a tone that is only mildly gritty with much less of a mid-hump.

I've found that the mid hump is largely caused by the symmetrical clipping that results from having two back-to-back diodes of the same forward voltage in the feedback loop of the first opamp.

If you take out one of the diodes, the tone really opens up. But then distortion sounds pretty hairy.

Insert a diode across the feedback loop of the second opamp stage, i.e, the tone circuit, oriented so as to clip the half of the waveform that isn't clipped by the first stage. Then the distortion will be a little closer to symmetrical, but still wider and more open sounding than stock. Put the missing diode back in the first stage, and it'll sound all midrangey and boxey again.

To really isolate the effect that perfectly symmetrical clipping has on midrangeyness, do this:

Breadboard a circuit that starts out with the gain stage from a tubescreamer, including the high-pass filter in the feedback circuit. Then follow it with two unity-gain, inverting opamp stages, with a coupling cap between them, big enough to pass all the bass you want to hear. Then the tube screamer's low pass filter. Then a tone control circuit (if you want it) and an output level pot.

Put two back-to-back diodes across the feedback loop of the first inverting, unity gain stage. You'll get a midrangey, Tubescreamer-like tone. Take one out. You'll get that wide-open tone with hairy distortion. Now put that diode in the feedback loop of the second inverting, unity gain stage, pointed in the same direction as the other diode, so that it clips the half of the waveform that was not clipped by the first diode. You'll get distortion that is close to symmetrical, but not perfectly symmetrical because of the effect of the blocking cap charging up -- and the tone will still be much more wide-ranging and open-sounding than stock Tubescreamer tone. Now take a third diode and put it in the feedback loop of the first unity gain, inverting stage, in the opposite orientation from the one that is already there -- you'll get narrow, midrangey tone again. The cap doesn't charge up because you've already clipped the signal symmetrically.

Also, once I made a little amp that had a pentode input stage, and I rigged up a switch that, when closed, put two back-to-back LEDs in a feedback loop from the top of the volume pot to the grid of the tube. Once again, I got that midrange hump, but only when the switch was closed, so it wasn't because of any tone-shaping caps in the circuit.

So, it appears to me that perfectly symmetrical clipping, particularly when it's in a negative feedback loop, is the cause of that midrangey tone.

Also, I don't think Maxon's intent in putting those filters in the Tubescreamer was to make the tone midrangey, although they may contribute to it. Notice that the rolloff frequency of them is about the same. I once read an article about limiting circuits which said that one simple approach to soft limiting is to boost high frequencies before the signal is limited, then cut highs by the same amount after the limiting. That way you remove higher-order harmonics generated by clipping the signal, but you don't affect the tone of the clean signal, at least in theory. It looks to me like that was what they were trying to do.

Shea

[R.G.]

"Transparent" and "overdrive" are mutually exclusive descriptions.

[R.G.]

A big third harmonic has a 'reedy' or hollow character that implies midrangey, but isn't actually the same. It's psychoacoustic. 8-)

[CitizenCain]

I was real pleased with the sound of my Blackstone MOSFET OD. It's perfect for what you're looking for. It is very dynamic, it really responds well to the guitar's vol control and your picking. If there is such a thing as a transparent OD, this is it.

[Sweetfinger]

Here's my nutty left-field approach: Try a vintage fuzzface circuit w/germanium transistors. It can't be the current offering from Dunlop, which has a buffer
To test out a FF circuit, I plug in a strat, usually neck pickup with the vol and tone all the way up. Set the FF gain up to where it has that big thick Jimi sustain(usually between 3 o'clock and 5 o' clock on the knob). If it isn't a big thick tone, I already don't like that pedal. They're all different, check several.
Then roll back the volume on the strat slightly. You should hear the FF really clean up to a clean, but gritty, partially distorted tone that is not quite like anything that an MXR/Boss/TS-9 will give you. If it doesn't clean up, move to a different pedal. You must plug your guitar DIRECTLY into the Fuzz for this to work. When you roll off the volume, the impedance change affects the gain of the Fuzzface quite a bit. Whenever I demonstrate a good, well tuned Fuzz face for someone, they're invariably amazed. Some FF clones have a pot on the input which mimics that very function and allows that clean but gritty tone to be dialed in specifically.
For more of a 'coloration' distortion, a modified Rangemaster circuit might provide just a bit of grit in a way that would work for you.

[Shea]

A big third harmonic has a 'reedy' or hollow character that implies midrangey, but isn't actually the same. It's psychoacoustic. 8-)

Thanks for the info - that must be the explanation for what I'm hearing.

[turbolx5oh]

Well rather than make one, I ended up buying the new Danoelectro Transparent Overdrive box from Guitar center. For $39 I figured I give it a try. Very nice pedal. Not too much gain and pinch harmonics seem to fly off the keyboard with this thing. I'd recommend it. I also bought their Distortion pedal as well but I don't like it nearly as much.

[abakerdabra]

OCD.

[turbolx5oh]

OCD.

Had one and sold it. I'm one of the few people that just didn't care for that pedal too much.

I've got a modded DS1 that I really like to. Turn the gain down a bit and it's nice. It's not what I would call transparent as it scoops the mids but it is still a nice pedal.