Cure for nasal fuzz?

[loudthud]

I've been thinking of building some stomp box fuzz/overdrive pedals. Looking around, I haven't seen anywhere that has the in-depth kind of discussion like I've come to expect here. What I've found seems like a bunch of young guitar players trying to clone exsisting products. So here goes... sorry but these are solid state projects.

I've worked on quite a few pedal designs using CMOS inverters. Most of the other peoples' designs I've looked at run the things on 9V. What a waste. Some of them suck over 20mA. None of my designs draw over 1mA. I use a J201 to drive the output.

Anyway, there is one problem I'd like to solve. The pedals tend to sound nasal. They are just straight gain with no tone tweeks along the way. Do these thing just square up the signal too symmetrically? I never tried any kind of clipping circuit to shift the baseline.

[Steve Conner]

Have you tried one of those wee nose hair trimmers from Sharper Image?

Building a good sounding overdrive pedal is a subject in itself. I got a bag full of nuvistors the other day, and I'm hatching a plan for something that runs off about 10 9V batteries, or a 6V lead-acid one with a DC-DC converter. Either way, a "pedal" the size and weight of a house brick.

The pedal most in line with my philosophy of how a good overdrive should be is the Blackstone MOSFET one. I don't know anything about the circuit, though.

There are some interesting "tube emulating" circuits at runoffgroove.com - home of the Fetzer Valve.

[Ronsonic]

None of my designs draw over 1mA. I use a J201 to drive the output.

Yeah, but they sound nasal.

You have wandered into a very strange and subjective area of The Craft.

You can approach this technically and go for a reverse engineering of what you know sounds good to you or you can monkey-poke your circuitry until it does what you want. Mostly, we all end up doing some combination of those two, initial design based on what we know we want to do to the signal and then tweak it into submission.

Nasal, will usually be about filtering.

I can suggest getting used to life with a breadboard. I spend a fair amount of my time soldering on hot circuits plugged into an amp with a guitar on my lap.

[R.G.]

I've been thinking of building some stomp box fuzz/overdrive pedals. Looking around, I haven't seen anywhere that has the in-depth kind of discussion like I've come to expect here. What I've found seems like a bunch of young guitar players trying to clone exsisting products. So here goes... sorry but these are solid state projects.

Have you read the "Technology of..." series at GEOFEX? In particular, "The Technology of the Tube Screamer" is pretty much about what I think you're talking about.

The nasal quality is a classical complaint about the tube screamer; the article explains this and a bit of why the rolloffs that give it the "honk" are there. There are reasons.

On the other hand, there is at least one company that I know of that sells a pedal they sometimes describe as "the cure for the common tube screamer", which is specifically intended not to have those colorations. Seems like it was named "Open..." something or other.

[loudthud]

Have you read the "Technology of..." series at GEOFEX? In particular, "The Technology of the Tube Screamer" is pretty much about what I think you're talking about.

Thanks RG, I'll see if I can find that.

Yeah, but they sound nasal.

I'm a bass player. I don't own any commercially made or boutique fuzz/overdrive pedals. I have nothing to copy and I've moved past the two germanium transistor thing. I'm just trying to address peoples complaints as they come up.

The last guy that tried it said he thought all CMOS pedals had sort of a nasal/hollow sound.

I remember tweeking up an Oberheim(sp?) Synth where you adjusted a square wave for 50% duty cycle. If you didn't have a scope, the service manual said adjust for the most hollow tone. That's what made me think of the symmetrically clipped signal.

I also have a couple of ceramic capacitors in the signal path. I'll try subing those out for some film types.

[Steve Conner]

You're right about the 50% duty cycle thing. My experiments with symmetrical clippers came to a similar conclusion, they sound hollow, maybe even dull and nasal.

The reason, according to grandpa Fourier, is that when the duty cycle is 50% there are no even harmonics. They disappear with quite a sharp null. Nasal-toned instruments like the oboe and clarinet have none either, and the square wave patches on synths were originally meant to imitate these.

The best kind of clipping circuit is one that generates a DC offset and shifts its duty cycle according to how hard you drive it. You get a constantly shifting blend of harmonics that adds interest to the tone in exactly the same way that PWM on a synth does. It also busts the nasal quality, because the duty cycle is never exactly 50%.

One mod that seemed to help is to replace one of the diodes in the clipper with a Schottky: an 1N5819 or whatever, just as long as they have different VI characteristics.

[Robert M. Martinelli]

Hi all,
I've built an improved TS clone, using an NE5532A, metal film resistors and the possibility to switch between symmetrical and asymmetrical clipping, based, as Steve pointed out, on the tendency of asymmetrical clipping to somehow preserve the presence of even harmonics, so I'd recommend you to give it a shot.

I believe symmetrical clipping to yield better results when used in "distortion" pedals, especially if Germanium diodes are used, because of their lower forward voltage that results in a heavier clipping action (thus better approximating a square wave).

I use my TS clone when I play with my band (classic '60s and '70s rock) and it sounds incredibly good, at least to my ears, round, full, but definitely not nasal, with a very good definition, and the added benefit of a very low noise (noise may not be an issue if you use only one stompbox, but it definitely becomes one when you have several in your signal chain).

JM2CW

Hope this helps

Best regards

Bob

[Steve Conner]

Yes, I think as RG and Bob say, the sound of the Tube Screamer is the way it is for a reason. When you use it at gig volume with an old tube amp, the mix of tube and solid-state distortion just sounds right. You set the amp up for a good cleanish rhythm tone, and the TS is your dirty channel.

I think a bit of asymmetrical clipping by changing one of the diodes adds a nice touch to all the TS style circuits. I did it to a Marshall Shred Master.

[Ronsonic]

Yeah, just razzing you a bit with that.

You are onto something with the duty cycle. CMOS distortions do square it up and yes, the answer is likely a less symmetric distortion.

[JoeM]

Hi all,
I've built an improved TS clone, using an NE5532A, metal film resistors and the possibility to switch between symmetrical and asymmetrical clipping, based, as Steve pointed out, on the tendency of asymmetrical clipping to somehow preserve the presence of even harmonics, so I'd recommend you to give it a shot.

I believe symmetrical clipping to yield better results when used in "distortion" pedals, especially if Germanium diodes are used, because of their lower forward voltage that results in a heavier clipping action (thus better approximating a square wave).

Hope this helps

Best regards

Bob

Bob,

What are using for the clipping diodes in your TS clone? R.G.'s article mentions using different kinds, LEDs etc. Just curious.

[Regis]

Building a good sounding overdrive pedal is a subject in itself. I got a bag full of nuvistors the other day, and I'm hatching a plan for something that runs off about 10 9V batteries, or a 6V lead-acid one with a DC-DC converter. Either way, a "pedal" the size and weight of a house brick.

Awesome, I want one. Then we'll show those pussys and their tiny little ZVex pedals a thing or two!!!

[Robert M. Martinelli]

Bob,

What are using for the clipping diodes in your TS clone? R.G.'s article mentions using different kinds, LEDs etc. Just curious.

Joe,
I tried several diode arrays, and I ended up using 3 x 1N4148s in an "asymmetric/symmetric" clipping configuration (the third diode can be shorted by means of a switch, I used a DPDT, the second section of the switch changes the color of the "FX on" LED, clearly indicating which kind of clipping is currently being applied to the output signal).

Germanium diodes sound too fuzzy in a TS, at least to me, and tend to take away some of the original TS "roundness", but they're excellent if you plan to build an MXR D+ based distortion pedal; thanks to their very low forward voltage, they square the signal very heavily, and give a very nasty, fuzzy distorted sound (after all, a square wave, as good ol' Mr. Fourier tells us, is made only of "nasty" odd harmonics).

Hope this helps

Best regards

Bob

[Ashleyslidewhip]

I'm a newbie to this forum, so bear with me. I've built a Fuzzface and a Mk II Tonebender, so got a cheap Ross Distortion kit of e-bay to try next. Reading up on clipping diodes has led me to try the following ... it's not done yet, but I'd appreciate you guys thoughts on what I've got planned ... the ideas have come from GGG kits and various mod newsletters

It seems that we can try a clipping section at the output (for distortion, as the Ross or DOD250 or Distortion Plus were designed) or on the feedback resistor to the chip (for overdrive, like EHs Big Muff or the Tube Sreamer) . If I miss both of these out, I'll get "just" a boost, which may or may not be clean or dirty depending on the gain, and can see no reason not to have both

So, if I get a couple of 9 way rotary switches, I can put the following into both (output and feedback) positions:

1 - nothing (boost only)
2 - 1 x Si diode (asymmetric)
3 - 2 x Si diodes (symmetric)
4 - 1 x Ge diode (asymmetric)
5 - 2 - Ge diodes (symmetric)
6 - 3 x Si diode (asymmetric)
7 - 3 x Ge diodes (asymmetric)
8 - 2 x red LED (no one ever suggests 1 or 3?)
9 - 2 x MOSFETs (no idea what type)

So that gives me almost 50 combinations of overdrive/distortion. Couple that with 3 cap options at the input and 3 cap options on the feedback loop, I have a whole bunch of combinations

I know should really try this on the breadboard, but I'm still going to have to build something eventually and this one looks fun

I'm appreciate any thoughts you might have, and in the box of tricks somewhere. might there be a cure for nasal fuzz?

[Steve Conner]

I don't see the distinction between placing the clipper on the output and placing it on the feedback network. To me they do just about the same thing.

I would make my mind up which of the two positions to put it in once and for all, and then set up two rotary switches to select what device is used for the positive and negative clipping.

As far as MOSFETs go, I can recommend the little high voltage TO92 ones like the BS108, with drain connected to gate.

[Ashleyslidewhip]

Thanks - I've often wondered about the difference and have only played pedals with output clipping so interested to hear that there isn't much difference, as there do seem to be "two schools" of design.

Are you suggesting that I should try something like 1 x LED for positive and Si and Ge diodes for negative or LED for negative and a diode for positive? I'd not got that far in my thinking ... is there a chance it'll sound different depending on whether the distortion is on the positive or negative part of the wave? ... think this really does call for the breadboard

thanks