Hi everyone,
I traced the schematic of my Big Muff Pi USA reissue (2005 model, with true bypass), and I realize that it's different from all the schematics I've found on the Internet. And as I'm a newbie, there are some changes I don't understand. So I have some questions about those changes. It's just for curiosity :D
Here are the pics of the board:
(http://img262.imageshack.us/img262/6096/dsc001205xb.th.jpg) (http://img262.imageshack.us/my.php?image=dsc001205xb.jpg) (http://img262.imageshack.us/img262/949/dsc001269tc.th.jpg) (http://img262.imageshack.us/my.php?image=dsc001269tc.jpg)
Here is the schematic:
(http://img262.imageshack.us/img262/40/bigmuffusareissue3fd.th.png) (http://img262.imageshack.us/my.php?image=bigmuffusareissue3fd.png)
I've kept the same part names as the board. I've colored the parts I don't understand.
In green: it seems those changes are for LED. But as it uses a 3PDT footswitch, I don't understand the purpose of R25, R26 and C14.
In blue: why is the 2nd lug of the Sustain pot connected to the ground when the effect is bypassed? (Sw1a, Sw1b and Sw1c are the 3 poles of the 3PDT footswitch)
In red: the board shows 2 empty pads (look at the part-side picture, on the top left, near R15 and R25). What are they for?
By the way, I've changed C9 to 3,3nF and C8 to 47nF, and now the pedal kicks ass. It's a real beast! :icon_twisted:
I'm planning to mod it to the "Triangle" Big Muff specs, but with the Swollen Pickle tone stack.
Thank you ;)
The 2005 (or mine version, a bit sooner) is completely different from some of the other "found" schematics because it has the "modifications" suggested by numerous persons (search on Big Muff Pi mods). They just put some mods in their version.
It was real nice when I got mine and, because I did not like the stock version, tried to mod it: a lot of the named mods were already done so I could not do them and need to get used to the sound ;)
The blue one: I don't know why they still do this, but when you use a DPDT to switch the unit on and off (+ LED on and off), the unit bleeds like %$#^%. By grounding that point (as in the other side of the LED switch) the unit stops bleeding.
Quote from: Bernardduur on November 12, 2005, 03:39:08 PMThe blue one: I don't know why they still do this, but when you use a DPDT to switch the unit on and off (+ LED on and off), the unit bleeds like %$#^%. By grounding that point (as in the other side of the LED switch) the unit stops bleeding.
Actually, I use to see the input jack connected to ground when the effect is bypassed, by using the alternate wiring method for 3PDT footswitch. That's why connecting the 2nd lug of the Sutain pot looks strange to me.
Anyone for the green and the red questions?
???? input jack to ground when bypassed??? Wouldn't the signal then go to ground when the unit is bypassed and no signal would be heard at all???
R25 helps C14 & R26 C15;
red additionally helps green, if neccessary;
A circuit is only as good as its power supply!
:icon_mrgreen:
Quote from: puretube on November 13, 2005, 12:38:05 PM
R25 helps C14 & R26 C15;
additional info: these (R25 w/ C14 and R26 with C15) are low pass filters on the power supply.
Quote from: Bernardduur on November 13, 2005, 11:22:16 AM???? input jack to ground when bypassed??? Wouldn't the signal then go to ground when the unit is bypassed and no signal would be heard at all???
Oops, sorry I meant the
circuit input is grounded when bypassed ;D
Thanks to everyone for your answers ;)