Red Llama with Tone Control and Gain Mod

[Kost1978]

Hi to everybody!

While I'm waiting for some parts from Tayda to build a RedLlama, I found some info to mod it.

On "our" RL blog's post Dimitri Georgaras posted a link to his blog, where he describes a "Gain Mod": he simply omitted R3=100K (3d res from left) with a DPDT switch, adding the original value on one side and a 10M one on the other. Beeing something quite easy I thought I'd go with it, even if I don't know if it's worthed.

I also found an interesting article here:
http://www.diystompboxes.com/smfforum/index.php?topic=94088.0
http://hammer.ampage.org/files/SWTC.gif

So, I tried to implement everything in a new layout, starting from Mark's, obviuosly this one is NOT verified.

I'm still in doubt about the Tone mode, cause I cannot really translate "...10k tone pot, in series with a 10k volume pot, means the pedal will behave like it has a 20k volume pot on the output that can never be set above halfway" in something understandable for my little knowledge of this "game": does it mean the volume will be twice as loud? Do I need to use lower values (like 5K) for both pots, in order to have a 10K in total (original value of vol pot)?
Anyway, here's "my" layout.
I simply "moved" one column to the right (omitting the one where the 100K "gain RES" was sitting") and addedd 1K res, 18n cap and 3 cuts and a couple of new wires...

Hope someone will have a look at it and tell me if it's going to work, at least "on paper"!
As soon as I get my Tayda's order I will try it myself.
Red_Llama-ToneAndGain_v2.png

[induction]

Kost1978 wrote

I cannot really translate "...10k tone pot, in series with a 10k volume pot, means the pedal will behave like it has a 20k volume pot on the output that can never be set above halfway" in something understandable for my little knowledge of this "game": does it mean the volume will be twice as loud? Do I need to use lower values (like 5K) for both pots, in order to have a 10K in total (original value of vol pot)?

A volume pot is simply a voltage divider, which (in this case) is two resistors in series between the signal (lug 3) and ground (lug 1). The output comes from the junction of the two resistors (lug 2). Since voltage drops proportionately to resistance, the output voltage will be smaller than the input voltage, according to the formula: Vout = Vin*Rbottom/(Rbottom+Rtop).

Turning a volume pot clockwise moves the wiper toward the input signal point, meaning Rtop gets smaller and Rbottom gets bigger, and the output volume increases (up to the maximum value of Vout = Vin*1 = Vin). Turning the pot counterclockwise moves the wiper toward ground, increasing Rtop and decreasing Rbottom, so the the output volume decreases (down to the minimum value of Vout = Vin*0 = 0).

The SWTC puts a tone pot in series with the volume pot, which means that the value of the tone pot adds to Rtop. This means that you can never get Rtop to go to zero, and the signal will always be attenuated. If the tone and volume pots are of equal value R, then the maximum volume will be given by Vout = Vin*R/2R = Vin/2, i.e. 50% attenuation.

You can improve the situation by making the volume pot much larger than the tone pot. If you make the volume pot 100k and the tone pot 10k, then the maximum volume is given by Vout = Vin*100/110 = Vin*0.91, i.e. 9% attenuation. You can never get Vout = Vin with the SWTC, no matter what values you use.

Whether you need to start messing with values depends on how much volume you have on hand. If the Red Llama has a lot more boost than you need, then you can just leave it alone. If you need more volume, you can start messing with the values, but you'll need to adjust the cap value as well.

Mark Hammer explains how to select this value here. Or you can just go by ear. In situations like this, you definitely want to breadboard before you build.

[Kost1978]

A volume pot is...

Thanks for your reply, I'll read the post you linked and your explanation for sure and do my math to try to better understand.

Just to be perfectly clear, I don't have any "volume issue" with the RL, simply because I didn't tried one before. I only liked the idea to also have a tone control added and Mark's solution seems the easiest one.
So, maybe the one I discribed will work, maybe not, I'll see if after reading your info I'll still be "conviced" in modding it!

Have a nice weekend!

[induction]

Sorry, I should have put a summary in my long-winded post.

Bottom line: Adding the SWTC to the Red Llama will decrease the volume by 50%. If this is too much volume reduction, there are ways to adjust the SWTC for more volume.

[Kost1978]

I wasn't complaining Induction,actually quite the opposite!
Both of your post,the long and the short one,will help me to better understand if this mod(s) are worthed or not.

It'll be nice though to have some feedback from someone who built the RL: is it so loud that "half the volume" will be enough? Will it benefit from a tone control?

Thanks again!