Red Llama BASS mod question

[anotherjim]

One thing to keep in mind is the power consumption in linear mode. It's easy to get a hot chip if too many inverters are biased up and it gets worse over 9v supply.

The app note AN88 is ancient and went with National Semi's old 74C range. The inverter, the 74C04 was an unbuffered CMOS version of the TTL 7404 hex inverter and happened to be functionally identical to the CD4069U. The 74C range is long gone, but the part does kind of live on in some Tiny-Logic in SMD packaging containing 1 or 2 inverters.

The CD4049U that the pedal world seems to be so fond of, was originally intended as a logic level converter to TTL/DTL systems and having high output current sink capability. It's a bit different than the 74C04 so the linear data is only generally true for a 4049.

[Mark Hammer]

I think I have a 74C04 or two sitting around.  I know I have some Japanese schematics using one of those instead of a 4049 for an overdrive.

[PRR]

> tend not to look for appnotes.

I knew it when it was new, but it has become obscure since then.

Raising the supply raises gainbandwidth and output headroom but paradoxically *reduces* gain. However the INput headroom at 3V rail is really teeny.... 1Vrms max out at 50+dB gain is under 3mV.

[iainpunk]

Good to hear that you are happy with the result!

A question to all: does anyone know a good EASY TO USE schematics editor? I'm very happy with KiCad right now but I wouldn't necessarily recommend it to anyone who is just starting out drawing schematics. The drawing of schematics is superbly easy with KiCad but the component libraries are massive and confusing unless you know exactly what you need and where to look for it. Something like bancika's DIY Layout Creator but for schematics would be great for beginners. Is there any such thing?

how about http://falstad.com/circuit/circuitjs.html
its quite easy to use and does some good simulations.

[snk]

Hi,
I took some time today to box my modded Red Llama.
I am really, really happy with the way it sounds (thank to your help !) : very transparent, just with more presence and "fatness". It's amazing on bass... and with just everything

[OiMcCoy]

Brining this thread back to life to say thanks to everyone who contributed. Working with the red llama circuit right now and this has pointed me in the right direction to make the changes I wanted to make. Really cool how different it sounds now.

This was one of my favorite DIY pedals to make back when I first got into making pedals. But back then I always wanted more and more gain. now I am happy to see how it sounds with less and less gain.

[snk]

Hi,
I'm glad this thread has been useful (it has been to me!)
I enjoy my modded Red Llama a lot. It's very, very low gain, but it makes everything beefier.

[marcelomd]

Some time ago I was looking for inverter-based overdrives. Lots of suggestions to use a resistor/trimpot to lower the supply voltage and/or limit the current available.

I didn't try it then, but maybe it's worth a try.

[Fancy Lime]

Hi snk,

Do you mind sharing a schematic of your final version? Maybe even sound samples?

Cheers,
Andy

[snk]

Hello, Andy

Do you mind sharing a schematic of your final version?

I'm afraid I don't know making schematics. I'm working with veroboards, and I write stuff with a pen on the printed layout
But I took notes of the mods which have been suggested to me, and ended up in the final circuit.

Here they are :
- DRIVE pot : 500K (instead of 1M);
- 100k resistor going to the 51pF cap lowered to 47k;
- Increased the first feedback loop cap from 51pF to 68pF;
- I have put the second feedback loop cap on a switch for a brigth/dark toggle : 51pF/82pF. I like this a lot : "bright" allows for more transparency and wider frequency range, while "dark" is not too damped either. It's quite subtle, but efficient.
- 68nF input cap on a switch : 68/220nF. 220nF is ballsy 68nF is the stock value, but along with the other mods, it really usable on a wide range of sounds.
- Increased the coupling cap from 33nF to 68nF (I think, not sure about the final value).

I hope these informations are useful, instead of a schematic?

Maybe even sound samples?

I should be able to record and post something, but I am not a guitarist : I'm using the pedals I build to process drum machines and synths, so I don't know if my sound samples would help to get an accurate idea?

Cheers!

[OiMcCoy]

Thanks for the rundown of your mods.

I think I am going to try your bright switch idea. I think it will add a lot of tonal options depending on where you set the gain.

[iainpunk]

> I have yet to see a gain/bandwidth product graph in a datasheet for a 4049

General curve for CMOS inverters:



http://bitsavers.trailing-edge.com/components/national/_appNotes/AN-0088.pdf

why haven't i seen this graph before? i think i might want to lower the voltage on my ''perfect overdrive" R&D project.
a little less bright and less headroom are both positives in my case.

cheers

[snk]

Thanks for the rundown of your mods.

I think I am going to try your bright switch idea. I think it will add a lot of tonal options depending on where you set the gain.

You're welcome.
I would advise to try different values for the switch, because in my case I had it set up with slight cymbal damping in mind, which may be to high for your taste if you want to use it with a guitar.
With the values I used for the "bright" switch, it wouldn't reduce all the hiss from a low output instrument (like a guitar or an electric piano, for instance), but it really helps taming harshness without changing the tone too much.