Wider gain range for Red Llama

[AM]

Hi people,
A friend of mine tried my Red Llama and asked me to build one for him. He asked me to change one thing from the original though. He wants to have less minimum gain. I use my guitar volume control a lot so I always control mine this way but he likes to play with the guitar controls wide open. Does anybody have any suggestions? He likes everything else to remain as in the original circuit so I don't want to do any radical changes. Just less gain to start with when the gain knob is at zero. Thanks for reading.

Layout here:
http://www.aronnelson.com/gallery/main.php/v/MarkMs-Gallery/album15/album76/Red_Llama_LAYOUT.gif.html

[skiraly017]

Experiment with R2 (someone please verify). Increasing value will allow for less minimum gain and more maxium gain. I was messing around with the resistor in question last week and I think I dropped in either a 470k or 560k and liked what it did for the maximum gain but at the loss of being able to use it as a clean-ish boost with the gain all the way down. I would sub that resistor with a 500k pot and adjust with your friend there. Find the spot he's looking for, measure the resistance and replace pot with fixed resistor of same/close to value. You could also mod for a trim pot in that position which will give him the abililty to make changes as needed. Speaking for myself, what I like today isn't always what I'll like tomorrow. 

[frankclarke]

Reduce the resistor in series with the gain pot. The 100k, I think.

[skiraly017]

Frank's post made me realize that I read AM's post wrong. 

Don't listen to me, I have no clue what I'm talking about. 

[AM]

Reduce the resistor in series with the gain pot. The 100k, I think.

Thanks Frank. One more question: Would reducing R2 affect the maximum gain of the circuit too? Also what do you think is a good starting point for experimentation. Something like a 50k value or is this too much of a reduction?

[frankclarke]

I get confused all the time . If you short out the 100k, you will get a max gain drop of about 9%. 50k would be noticeable, try that. The 1M resistor (not the pot) also controls gain, a 500k would be less gain.

[Mark Hammer]

Here's a different approach you might consider.

The Gain pot has a wiper and two resistances that are inversely related (one goes up one goes down).  Flip the order of the pot and 100k resistor such that the 100k resistor goes to pin 4 ( http://gaussmarkov.net/layouts/redllama/redllama-schem.png ).  The wiper of the Gain pot now goes to pin 5, with one of the outside lugs going to the other end of the 100k feedback resistor.

So far, so good.  We now have the same 100k-1100k range of feedback resistance as before.

Interrupt the connection between C1 and pin 5, and insert the OTHER leg of the gain pot there.  Whatthis will do is insert a series resistance on the input that is zero when the gain is maxed and 1M when the gain is set to min.

Since you may not want to insert a lot of series resistance on the input, I would suggest tacking on a parallel 100k resistor on that leg of the pot, such that the amount of added series resistance will never exceed 91k and will generally be lower.

[AM]

Thanks guys. I'm waiting for some parts to arrive and I will start experimenting.

[DougH]

Mark's post reminded me of something. Another idea you could try is to wire the pot like the gain pot on a bluesbreaker:

http://www.diystompboxes.com/pedals/bbschem.gif

Note R7- as feedback resistance is increased on stage 1, input resistance to stage 2 is lowered. As feedback resistance is decreased on stage 1, input resistance to stage 2 is increased. This simultaneously controls the gain for both the first and second stage, which increases available headroom while maintaining the max gain possible if you had just used the typical setup with the 100k on stage 1.

So, on the redllama schematic referenced above try connecting the pot wiper to the junction of c2 and pin 4. Then disconnect c4 from the junction of c2 and pin 4 and reconnect it to lug 3 of the pot. This is sort of similar to what Mark suggested only the variable input R is on stage 2.

Of course a 1M pot wil produce a lot of input resistance in this scenario and may introduce noise. So you might try a parallel fixed resistor there as Mark suggested.

Just an idea, ymmv.

[skiraly017]

Not to hijack but does anyone else like using the Anderton TSF Lead/Rhythm switch? Kicking in the 10M resistor turns the Llama into a monster distortion/fuzz.

[AM]

Not to hijack but does anyone else like using the Anderton TSF Lead/Rhythm switch? Kicking in the 10M resistor turns the Llama into a monster distortion/fuzz.

Yeah but it's nothing you can't do by just maxing out the gain knob. Also, the issue with this current built is to have a smoother range of gain on tap, or let's say less gain when gain knob is set to zero.

[AM]

Here's a different approach you might consider.....

Mark's post reminded me of something. Another idea you could try is to wire the pot like the gain pot on a bluesbreaker:

Mark and Doug, thanks both of you for your input. I will try to draw a layout based on what you suggested. Would it be OK for you to have a quick look at it? I will have it done in the next couple of days and I can pm it to you or post it back on this thread (whatever you prefer). I'm not good at schematics but I think I could do a layout implementing your suggestions.

[Mark Hammer]

Doug's right.  That second leg of the Gain pot can actually be applied usefully in either direction.  Wire up the Gain pot so that the wiper goes to Pin 4.  One leg of the pot goes to the 100k feedback resistor in the first stage, anmd the other leg goes to the .033uf cap between stage 1 and 2.  As I suggested earlier, a parallel fixed resistor to constrain how much series resistance is added in before that .033uf cap is a good idea, and the suggested value (100k) is probably very close to what would be ideal.

[AM]

Ok guys,
I draw a layout based on Gaussmarkov's layout with the changes you suggested. It's here:
http://cid-90562a4f99e2b9cc.spaces.live.com/photos/cns!90562A4F99E2B9CC!122/?ViewType=4

Can you please have a look and confirm if I have followed your suggestions correctly? Also one more question: Would it be ok if I would reverse lugs 1 and 3 of gain pot and have lug 1 going to C4 with added R in parallel and lug 3 going to R2 without added R?
Thanks a lot for your help. It's been deeply appreciated.

[DougH]

If you draw it up as a schematic I'll take a look at it. It takes me too long to try to decipher layouts.

[AM]

If you draw it up as a schematic I'll take a look at it. It takes me too long to try to decipher layouts.

Ok Doug, I'll give it a try. I've never drawn a schematic before, because I'm not good at reading them. I'll try to draw one for the first time and post it.
Thanks for your help and suggestions so far.

[AM]

Doug (and for the rest of you who wanna have a look) I drew a part of the schematic applying the mods you mentioned.
The original schematic is here:
http://gaussmarkov.net/layouts/redllama/redllama-schem.png

My modified version of the section we have discussed about is here:
http://cid-90562a4f99e2b9cc.spaces.live.com/photos/cns!90562A4F99E2B9CC!122/?ViewType=4&searchtype=5&index=1&handle=cns!90562A4F99E2B9CC!124

Please have a look. One more question too. Could I have lug 3 of the gain pot going to R2 and lug 1 going to C4 with the Rnew=100k connected in parallel? This is probably a stupid question but if I can wire the gain pot thhis way it would help me to do a neat layout. Thanks for looking.

[DougH]

Looks like it should work. (Don't short out Rnew though if you want to use it.)

You can swap lugs 1 and 3 but the pot will operate "backwards".

[AM]

Looks like it should work. (Don't short out Rnew though if you want to use it.)

Doug I don't understand what you mean by "shorting out" Rnew. Is there something wrong with the way I drew the connection between Rnew and lug 3?

You can swap lugs 1 and 3 but the pot will operate "backwards".

Thanks for confirming this. That was exactly what I thought it would happen. I'll stick to the initial way of wiring the lugs.

One last thing. The stock circuit without any mods has a very good response to picking attack. Could you guess if that would change by applying the mods we've been talking about? I don't see the reason why it should change but I'm not experienced enough to be able to predict these things.
Once more, thanks a lot for your help.

[DougH]

I don't understand what you mean by "shorting out" Rnew.

Follow the path from C4 vertically above it. You have drawn a wire connected to each end of Rnew. Don't connect that wire if you want the effect of Rnew in the circuit.