Big Muff, Transistor question. (NYC EC-3003 Rev_C)

[stonerbox]

I got a Big Muff Pi NYC (Blue board EC-3003 Rev_C) that I have installed lots of mods on.. Recently I managed to destroy Q3 Resistor (BC550) the ground lug snapped..  
All I got at home for replacement are BC309, K118 Y7A, C3378 GR 7K, K184 GR 8A, K118 YL7 and A1048 GR 7K.

Could any one of these work? If I had time I would buy a new resistor but time is not on my side right now. Please help the newbie.

I'm sorry if i posted in the wrong section.

This is the circuit (Q3 "Q2" Second Clipping Stage):

[frank_p]

Hi Stoner, welcome to the forum,

I think the version of your box is the current reissue  ,if so, the schematic you posted is wrong polarity.

http://www.pisotones.com/BigMuffPi/psst/schm-black.jpeg



For starting BC309 is :
PNP  Hfe 120 to 800
http://pdf1.alldatasheet.com/datasheet-pdf/view/50725/FAIRCHILD/BC309.html

A1048
is 2sa1048 is pnp audio Hfe 70 to 400
http://pdf1.alldatasheet.com/datasheet-pdf/view/29939/TOSHIBA/2SA1048.html

K118 Y7A and
K118 YL7
is 2sk118  is a JFET  so NO

K184 GR 8A
is 2sk184  is also JFET so NO


I suspect that is the only one that will work:
2SC3378:   = YES   because NPN

Si NPN Lo-Pwr BJT
Various
npn transistors,transistors
V(BR)CEO (V)=20
V(BR)CBO (V)=20
I(C) Abs.(A) Collector Current=2.0
Absolute Max. Power Diss. (W)=400m
I(CBO) Max. (A)=100n
V(CE)sat Max.(V)=.3
@I(C) (A) (Test Condition)=10m
@I(B) (A) (Test Condition)=1.0m
h(FE) Min. Static Current Gain=200
h(FE) Max. Current gain.=700
@I(C) (A) (Test Condition)=2.0m
@V(CE) (V) (Test Condition)=6.0
f(T) Min. (Hz) Transition Freq=100M
@I(C) (A) (Test Condition)=1.0m
@V(CE) (V) (Test Condition)=6.0
Package=SPAK
Military=N

-----------------------------------------------------------------

[stonerbox]

Your right! Thanks for the reply frank_p. Very much appreciated!! 

[frank_p]

My pleasure,
keep posted on how your mods turns out.

This topic might help you also:

http://www.diystompboxes.com/smfforum/index.php?topic=78111.0

[stonerbox]

Alright! now the pedal is in one piece again. Due to the poor quality of the EC3003C board I had to rewire the entire second clipping stage and the tone stage "outside" of the board. After a lot of hard work and tricky schematic reading (at least for a newbie like me) it is now functional again. Now with a 2SA1048 instead of the original BC550.

It sounds different now, lot less gaining going on, more of a fuzz/crunchy sound rather than the insane gain factor that was before. I barley use that much sustain, often around 10 o'clock. Now I get the 10 o'clock sustain sound at 3 o'clock. Go or bad? It all depends on the situation.


Thank you frank_p for the helping hand! Oh by the way, the schematic was not the right one, the EC-3003 Rev_C schematic seems to be nearly impossible to find out there.

[DavenPaget]

Alright! now the pedal is in one piece again. Due to the poor quality of the EC3003C board I had to rewire the entire second clipping stage and the tone stage "outside" of the board. After a lot of hard work and tricky schematic reading (at least for a newbie like me) it is now functional again. Now with a 2SA1048 instead of the original BC550.

It sounds different now, lot less gaining going on, more of a fuzz/crunchy sound rather than the insane gain factor that was before. I barley use that much sustain, often around 10 o'clock. Now I get the 10 o'clock sustain sound at 3 o'clock. Go or bad? It all depends on the situation.


Thank you frank_p for the helping hand! Oh by the way, the schematic was not the right one, the EC-3003 Rev_C schematic seems to be nearly impossible to find out there.

I am not bothered to check the 2SA1048 but it smells like it's a much lower gain tranny compared to the 550 .

[stonerbox]

I replaced the 2SA1048 first with a BC239... and then i added another BC309 on top of the BC239. Now it is starting to sound a lot better, more lows and more sustain/fuzz! I dig!  

[frank_p]

I replaced the 2SA1048 first with a BC239... and then i added another BC309 on top of the BC239. Now it is starting to sound a lot better, more lows and more sustain/fuzz! I dig!  

BC309 is pnp
Remove...
BC239 is npn OK

Alright! now the pedal is in one piece again. Due to the poor quality of the EC3003C board I had to rewire the entire second clipping stage and the tone stage "outside" of the board. After a lot of hard work and tricky schematic reading (at least for a newbie like me) it is now functional again. Now with a 2SA1048 instead of the original BC550.

It sounds different now, lot less gaining going on, more of a fuzz/crunchy sound rather than the insane gain factor that was before. I barley use that much sustain, often around 10 o'clock. Now I get the 10 o'clock sustain sound at 3 o'clock. Go or bad? It all depends on the situation.


Thank you frank_p for the helping hand! Oh by the way, the schematic was not the right one, the EC-3003 Rev_C schematic seems to be nearly impossible to find out there.

I am not bothered to check the 2SA1048 but it smells like it's a much lower gain tranny compared to the 550 .

BC550 is npn
2sa1048 is pnp
http://html.alldatasheet.com/html-pdf/29939/TOSHIBA/2SA1048/246/1/2SA1048.html
2SC3378 and BC239 is the only parts in your lot that will work if I am not mistaken.  Because it's npn polarity like the BC550.
If you put a pnp there your sound will choke.

Blue board sound like npn polarity...  Scroll down:
http://www.kitrae.net/music/big_muff_history3.html

Can you measure some voltage with the multimeter ?
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

IF YOUR BOARD IS NPN (NEGATIVE GROUND), PUT YOUR PNP ASIDE.

You have a power jack plug at the back of the box ?  If yes: put all the pnp in your drawer: I wrote next to the numbers.
You can piggyback the npn ones as you want for your mods, the others: you will just probably damage them.

[stonerbox]

BC309 is pnp
Remove...
BC239 is npn OK

BC550 is npn
2sa1048 is pnp
http://html.alldatasheet.com/html-pdf/29939/TOSHIBA/2SA1048/246/1/2SA1048.html
2SC3378 and BC239 is the only parts in your lot that will work if I am not mistaken.  Because it's npn polarity like the BC550.
If you put a pnp there your sound will choke.

Blue board sound like npn polarity...  Scroll down:
http://www.kitrae.net/music/big_muff_history3.html

Can you measure some voltage with the multimeter ?
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

IF YOUR BOARD IS NPN (NEGATIVE GROUND), PUT YOUR PNP ASIDE.

You have a power jack plug at the back of the box ?  If yes: put all the pnp in your drawer: I wrote next to the numbers.
You can piggyback the npn ones as you want for your mods, the others: you will just probably damage them.

You are right, the board has NPN Polarity, but I did not notice that the sound got "choked" by the BC309 C, rather a volume increase when I added it on top of the BC239 C. Strange..
One thing is for sure, they are a lot less gainy than the BC550 transistors. Maybe I should remove the BC309 C transistor, I would not want to risk damaging the other components.

Again, thanks for you support Frank.

[frank_p]

Hey, no problems, take care !