Any Tubescreamer clones without clipping diodes?

[Ell]

I built a Tubereamer, using Torchy's "Ultimate" layout, which has a switch going between super bright LED's, and a 1N914 and 1N4007.

The LED's don't shine with the switch in either position, so I'm assuming they don't work. When I have the pedal with the switch set to one position - the sound is loud and clear. On the second position it's a lot quieter, and has a lot more gain. I'm guessing that the second position is the 1N914 and 1N4007, and the other setting is just the circuit without any diodes connected. I much prefer the first setting. Are there any Tubescreamer clones which have left out the diodes altogether?

[earthtonesaudio]

LEDs typically have a forward voltage drop of 1.5V or higher.  Si diodes are typically 0.7V.

The gain of a typical TS clipping stage is still substantial, typically around 117 at maximum, so given an input signal of 100mV p-p, the amp will try to make an output of 11.7V p-p, which is impossible with a 9V battery.  However, the diodes will limit the output to their forward voltage (in either direction), which for Silicon means a max output voltage of 1.4V p-p.  Obviously the op-amp is trying to generate a larger voltage, so the excess is "clipped" by the diode, and you hear the result as distortion.

For LEDs, they will allow a max signal of perhaps 3V p-p, which is quite a lot more.  Many guitar signals are less than the 100mV example I gave above, so often you will hear no clipping at all.  However, the output level will be higher because a 3V signal is larger than a 1.4V signal.  You would hear this as louder but cleaner.

The gain is the same in both situations, which is a good example of how terms come to mean different things in different contexts.  In an electronics context, "gain" is independent of distortion, but in guitar effect and amp marketing, they are often synonymous. 


Also, just because your LEDs are dark doesn't mean they're broken.  It just means they're not getting enough current at a high enough voltage to cause them to give off light.  For many guitar signals you won't get enough voltage to light them up, so that's relatively normal.

[Ell]

So you mean that the LEDs are in fact affecting the sound even though they aren't lighting up?

[BAARON]

LEDs need current to light up.  The combination of a 4k7k resistor with a .047µF capacitor in the path of ground means that there's a lot of impedance there (i.e., 47k impedance on a low E), which means that the mere few volts you get out of the op-amp can't push enough current (milliamps) to light the LED up (current = voltage/impedance, and 9v/47,000 ohms is too little current to be visible).  However, that doesn't mean the LED isn't conducting.  It still conducts, because the voltage the op-amp is sending through that part of the feedback loop is higher than the LED's forward voltage.

If you don't think the LEDs are clipping, pull them out and listen to the difference.  If you're using a 4558, it'll be way louder and the distortion will be hideous.

To answer the topic's question, yes, there are some Screamers that have the option of running without clipping diodes.  The Landgraff Dynamic Overdrive has a diode lift mode (no diodes), as does the sometimes controversial Zenkudo.  Generally speaking, people don't do this because the hard clipping from a 4558 sounds pretty gross.  If you replace it with something nicer like an OPA2134, though, it's actually quite usable.


P.S. The output of the gain stage in a non-inverting opamp with diodes in the feedback loop is actually higher than combined forward voltage of the clipping diodes.  http://www.bteaudio.com/articles/TSS/TSS.html hints at this in the text surrounding diagrams 3 and 4.  It's complex and mind-boggling when you get into the math of it.

[aziltz]

P.S. The output of the gain stage in a non-inverting opamp with diodes in the feedback loop is actually higher than combined forward voltage of the clipping diodes.  http://www.bteaudio.com/articles/TSS/TSS.html hints at this in the text surrounding diagrams 3 and 4.  It's complex and mind-boggling when you get into the math of it.

I read that article quick.  It's interesting how moving from inverting to non-inverting with the same gain and clipping type introduces such a difference in the output waveform.

[vondran]

I've built a TS with switchable diodes, including no diodes.  I've gotten great sounds with them switched out just from the op-amp clipping.  Note, choice of op-amp makes a more significant difference in this case.

[Ell]

Okay. I initially was thinking that I just liked the sound of the chip, but I suppose that's not quite so. Although, I've heard bad things about LED clipping in the past, and I'm preferring it to the mix of silicon and germanium diodes. Am I weird or is the idea that one type is better than another weird?

[CynicalMan]

This isn't a tube screamer clone but it uses opamp clipping:
www.runoffgroove.com/mm2.html

[oliphaunt]

Okay. I initially was thinking that I just liked the sound of the chip, but I suppose that's not quite so. Although, I've heard bad things about LED clipping in the past, and I'm preferring it to the mix of silicon and germanium diodes. Am I weird or is the idea that one type is better than another weird?

Different clipping diodes, whether LEDs, silicon or germanium, zener, etc. have different characteristics, so it's not strange to prefer one over another in the same circuit.  I've found so far that they can all sound good except for LEDs.  I have yet to find a circuit where I like LED clipping, but I am sure I will so I always try them.

[BAARON]

LEDs can sound gross.  So can germanium or silicon.  It depends how they're used.  Personally, I really like them in *properly voiced* TS style circuits (the default voicing is a bit gross), because they allow for a very touch-sensitive response and the clipping doesn't seem as grainy as straight up silicon, sometimes.

[Processaurus]

I wonder if a TLC2262 would sound good, the sansamp pedals use them for clipping (no diodes in sight on the GT2 schematic).

[BAARON]

They sound quite nice.  In my experience, the OPA2134 is nicer yet, but the 2262 is still a major step up from the 4558.

[petemoore]

  Time for a 'where's the booster' discussion?
 Would pre-boost have a chance to light LED's in TS feedback loop ?
 

[BAARON]

 Time for a 'where's the booster' discussion?
 Would pre-boost have a chance to light LED's in TS feedback loop ?
 

Whether or not the LEDs can light up depends mostly on the value of the RC network to ground in the feedback loop, not on how large a signal is hitting the op-amp.  That RC combo basically acts like a current-limiting resistor, as far as the LED lighting up is concerned, and if it's a small cap like 47n, its reactance is so high that you probably won't ever see the LED light up, even hitting it with a large signal.

[Crazyyellowfox]

Might just be personal taste but in the Shaka 5 the only clippers I like are LEDs. They have the perfect amount of crunch. Super bright green LEDs are my favorite. different color and types of LEDs sound different. I've never tried them in a tube screamer tho, maybe I should give it a try.

[fuzzo]

Someone has tried to put a kind of blend pot to mix led/1N4148 ? that could be a cool control instead of the stwitch we often see in TS.

[BAARON]

Someone has tried to put a kind of blend pot to mix led/1N4148 ? that could be a cool control instead of the stwitch we often see in TS.

Yes, they tried.  I followed that thread.  It didn't work, due to the way diodes do their job in the feedback loop of the non-inverting opamp circuit.

[studiostud]

Personally, I really like them in *properly voiced* TS style circuits

What do you mean by "properly voiced"?  Does it involve biasing resistors?