Red Llama questions

[Redvers]

Hi guys, I just breadboarded a Red Llama (second time I've built one) and I can't seem to hear much of a difference when changing the power supply resistor. I swapped out the 1k for a 100 ohms on my last llama but doing it quickly on the breadboard I can't hear much of a difference other than a bit more fizz the higher the value. As it happens I won't be using a battery with this one so could I just omit that resistor? Also I use a 500k gain pot because I prefer this as an edge of breakup effect. Could I also change the 1 meg resistor in the second inverting stage for a 500k to lower the gain a bit more?

Grateful for any advice.

[Mark Hammer]

I use 100k feedback resistors.  Works fine.  I also use a 100R current-limiting resistor for the V+.

You're in good shape.

[Redvers]

The man has spoken! Cheers.

[Mark Hammer]

I'm certainly not "the man", but can simply vouch that your build won't blow up.  Will it sound the way you want?  Maybe, maybe not.

The Red Llama uses a 1k current-limiting resistor.  However, it is based on the original Craig Anderton Tube Sound Fuzz from the EPFM book, and that uses 100R.  I've never really A/B'd the two circuits to compare, and would be interested in any such comparisons.  If you, or anyone else, have the interest, it might be illuminating to stick a switch between V+ and the V+ pin/s on the 4049 and flip back and forth between the lower and higher-value current limiting resistor.

[Redvers]

I actually added a 2k trimpot where the power resistor would be. There's definitely some extra high end sizzle as you turn it up but not more gain really. To be honest I really only use this as a very light od, which is why I want to dial it right back. I'm sick of putting the gain pot at 9 o clock.

[anotherjim]

You might find another approach - If you change the output volume pot to a 2k or 2.2k and fit an 8.2k resistor in series from the output cap to the top (3) pot lug - then you have a partly fixed attenuator and you'll have a more useful range with the volume pot. Changing the components in the inverter amp circuit is going change the flavour of distortion/tone some, not only the output level.

[Redvers]

Yeah the volume pot isn't an issue for me EXCEPT that the pedal sounds best when the volume is at least 12 o clock. Which is quite loud for home playing but a lot of fun on stage.Ive heard that it affects the gain to some extent and it's definitely what I've experienced in practice. So to be honest I wouldn't want to attenuate it. For such a simple circuit it's so tweakable.

[digi2t]

I like to add an additional 470uF cap, right between the resistor and pin 1.

[Redvers]

I've built it now. To be honest the more I modded and tinkered the less difference I was hearing. I guess the main thing I learned is that the red llama can clip easily and getting it to not clip as much is the challenge. Also I swear the breadboard version sounded way different to the soldered version. Not just noise wise but tone wise. We'll see, I'm gigging it tonight.

[Andrekp]

Used 100Rs in mine.  I think the gain is such on these that you're just not going to induce the sort of starvation sound that you might by slightly high value R in the power supply in a transistor based fuzz.  These CMOS chips just sort of go either on or off when you use them normally, they don't really do the fun stuff you can get a transistor to do. 

OTOH, check out the Robot Devil.  It has a starve pot that WILL get you these kinds of sounds.  I think it's only a 5 or 10k pot.  So I imagine if you go too far above the normal values for these power supply resistors, you could induce some sputtery stuff, but 100R won't do it.

You want some fun, put a Green Ringer in the same box with the Llama, switchable. 

[anotherjim]

Linear biased CMOS inverters are totally different if you were after a power supply sag effect. They actually present minimum load on the supply at peak swings and maximum load when idle or small signal in them. The resistor in the pin1 feed to the 4049 is to limit supply current which is otherwise quite high for such a simple pedal circuit. However, without also having a large bypass capacitor to ground from pin1, the effect is more like an expansion of signal as the supply volts actually rises as the signal reaches both positive and negative peaks and the voltage drop on the pin1 resistor decreases. Without the capacitor and with a largish pin1 resistor, there will be a double frequency signal on pin1.

In other respects, they are like a compressor that is always on with a very low threshold setting and fast attack/release. Gain is maximum around the bias idle point and continually reduces as the signal swings toward positive. Perhaps not surprising they can sound different on breadboard as the high idle gain picks up more noise outside of a box. The result is bursts of noise at each zero crossing that can sound like part of the distortion, because it occurs at signal frequency.

[Mark Hammer]

The late Charles R. Fischer published a 4049-based overdrive/fuzz circuit in Electronic Musician some years back that uses an LM334Z current regulator controlling the 4049 to achieve sag and splat.  One of these days I have to build it to hear how it sounds.  Goodness knows I bought all the parts years ago.  Many thanks to JD Sleep for hosting the images all these years.

[anotherjim]

To do sag on peaks like most amps can, the inverter output pin needs a significant load so it pushes/pulls more current at peaks than at idle. There is a variant of the Llama/tubesound that uses one of the spare inverters as an active load on the last inverter amps output.
The schematic looks odd because the extra inverter is wired by its input and output, so it just looks shorted out. However, it is biased to the same idle level as the existing inverter amp and at idle, does nothing to the signal. As the signal tries to swing up or down, the extra inverter is trying to hold it at bias and causes significant increasing current flow toward the signal peaks. Then the power supply can sag at the right times.
We did discuss that one here some years back, but I'm damned if I can remember more than that!

[Mark Hammer]

One of us is going to have to build it and see if the drawn schematic yields the described result.  There IS always the possibility that everything Fischer described is true, but the drawing has errors.  He did, after all, pass away before it was published.  So the opportunity for published errata from the author never really came up.  At least that I'm aware of.

My own plate is full, so I have to pass this one on to others, I'm afraid.  Sorry to dump it in your collective laps.   

[rankot]

I've built Pillar Shaker, obviously based on Red Llama. Sounds good, but it seems that most of the controls don't have a big impact on sound. I've found schematic on a site, but lost URL. This is the schematic:



It had a problem with mixing part of a circuit, so I altered it this way, it works better now (sorry for PDF, but it's faster to create and upload):

http://docdro.id/olumUz9