Paul Cochrane - Fat Bastard

sadrew · Post by **sadrew** » 24 Aug 2008, 21:31

i don't think it's a problem with the circuit, i double checked everything and it's all ok.

I will try 2N5457, so i can crank more the gain without having much distortion.

thanks modman for the quick reply.

sevinisthenumber · Post by **sevinisthenumber** » 18 May 2010, 21:28

Any tips/advice on adding some clipping diodes int this for a smooth-ish overdrive tone??

madbean · Post by **madbean** » 19 May 2010, 00:24

sevinisthenumber wrote:Any tips/advice on adding some clipping diodes int this for a smooth-ish overdrive tone??

I think adding another mu-amp stage would be better in this case.

madbean · Post by **madbean** » 20 May 2010, 12:00

Perhaps something like this.

FB+.gif

The T1 trimpot could be a 'saturation' control to tailor the amount of overdrive. C3 and C6 might need to be reduced to prevent it from getting to woofy: maybe 470n or 220n. Also, changing the trannys to J201 might give you some more OD.

Post by **mxrmxr** » 30 Sep 2010, 21:55

madbean wrote:Perhaps something like this.
FB+.gif
The T1 trimpot could be a 'saturation' control to tailor the amount of overdrive. C3 and C6 might need to be reduced to prevent it from getting to woofy: maybe 470n or 220n. Also, changing the trannys to J201 might give you some more OD.

What is the purpose of c3 and c6 in these mu-amp circuits ?

mcaviel · Post by **mcaviel** » 01 Oct 2010, 10:59

it controls the bass content before the signal is clipped more thoroughly.

new_anuzzerone · Post by **new_anuzzerone** » 03 Oct 2010, 20:41

I´ve built it this weekend! AWESOME!

I took the schematic from aron nelsons site (markMs gallery), put the described j201´s in it....awesome!

I used it in front of my Brunetti maranello Amp, clean channel is pretty useless with this, only small amount of gain added. Then I tried the Lead channel and it was way better than any F***drive, TS or whatever! It added just the right amount of gain / drive to make the amp sounding sweeter than ever before. Added a 4x12 to it and I dissected my MrBoogey, which I couldn´t get to work. Great!

THX again to this great board and especially paulc, for showing me, that you don´t need 200 parts, to make some great noise

Duckman · Post by **Duckman** » 22 Feb 2011, 22:17

I started foolin'round with the GGG schem recently and the "search" function lead me to this thread, so following Mr. Cochrane advises (improved input impedance and add output buffer) and taking values from other circuits, I drawn the schem below, but I'm not really sure about the values, so any help will be nice. Added parts are circled

Duckman · Post by **Duckman** » 23 Feb 2011, 21:26

"Viewed 40 times"...?? and no single opinion??

Hides-His-Eyes · Post by **Hides-His-Eyes** » 23 Feb 2011, 22:01

C1 is too small, the 10k on the first FET (and maybe the others) might be better off as trimmers (try 100k)

sinner · Post by **sinner** » 23 Feb 2011, 22:14

Duckman wrote:"Viewed 40 times"...?? and no single opinion??

Some of my layouts has almost 200 views and was added 3 days ago, just a single person pressed thanks button

Get used to it

I did...

Duckman · Post by **Duckman** » 23 Feb 2011, 22:25

But... I don't want to be "thanked"

just a little help with some values

"There's a jungle out there"

sinner · Post by **sinner** » 23 Feb 2011, 22:26

Duckman wrote:But... I don't want to be "thanked" just a little help with some values
"There's a jungle out there"

If I'll be able to find it, I'll PM you something tomorrow. It's gone from my HD, but I should have it @ my webmail

Duckman · Post by **Duckman** » 23 Feb 2011, 22:50

Hides-His-Eyes wrote:C1 is too small, the 10k on the first FET (and maybe the others) might be better off as trimmers (try 100k)

Big thanks!

I take the 10p cap from the AMZ mini booster input, but 10k resistors are original from the Fat Boostered.
Would you mind to explain me a little more about the advantage of using trimmers and what may I look for?

Thanks again!!

Hides-His-Eyes · Post by **Hides-His-Eyes** » 23 Feb 2011, 23:04

Duckman wrote:
Hides-His-Eyes wrote:C1 is too small, the 10k on the first FET (and maybe the others) might be better off as trimmers (try 100k)
Big thanks!

I take the 10p cap from the AMZ mini booster input, but 10k resistors are original from the Fat Boostered.
Would you mind to explain me a little more about the advantage of using trimmers and what may I look for?

Thanks again!!

Trimmers are for biasing the FETs to get as much clean as possible.

10k + 10p in that arrangement is a Low Pass Filter. Wikipedia that and see what it's doing

Duckman · Post by **Duckman** » 23 Feb 2011, 23:43

Hides-His-Eyes wrote:Wikipedia that and see what it's doing

I know what it's doing, but I missed the AMZ Mini Booster uses 1k resistor for biasing

Any way, and sorry for my noobness, the R-C filter still actuates with a FET in between? When I make calculations for the AMZ MB ( 1k/.00001uF) freq values are ridiculous.

Now, thinking about the low pass between R2/C1, C1 @ 220p will give me 10644 Hz wich seems more apropriate, don't you think?

RnFR · Post by **RnFR** » 24 Feb 2011, 04:17

you added an extra gain stage on the end. I would try simply adding another FET dc coupled onto the output of the mu amp with the drain going to 9v and a 10k resistor from source to ground. then put your output cap and treble cut control. check out geofex's mu amp article or some of the victor kempf stuff. as far as the input, I'll have to read up on what paul was talking about, because a jfet input buffer already has a rather high input z.

-----

ok, make q2 a FET. lower the source resistor on q1 for more gain. move the 1m bias resistor to the gate of q1, and use a trim for r3. upping the value of that 10p might be a good idea as well. that should do it.

Duckman · Post by **Duckman** » 24 Feb 2011, 06:01

Thanks, RnFR, a lot of help! Also added "noisless biasing" according with R.G. Keen Mu-amp article.
Ok, guys ... what you think?

Nikifena · Post by **Nikifena** » 14 Mar 2011, 21:59

I think that this is better

I put smaller input resistor, change protection with schottky diodie. Now we loose 0.2-0.3V, but the diode can't blow

Now we have lower output resistance

Duckman · Post by **Duckman** » 15 Mar 2011, 08:46

Nice! You breadboard it or just guessing?

Just joking. I will try it

Nikifena wrote:Now we have lower output resistance

How much lower? I mean... it was so higher to you?

Paul Cochrane - Fat Bastard [documentation]