TS-808 layout for confirmation, please!

[jlullo]

hey guys,
i used tonepad's schem to do my first layout:
http://tonepad.com/project.asp?id=1

does anyone see any mistakes?



Red traces are +9V
Blue is Vb
Grey is ground

[johngreene]

does anyone see any mistakes?

Yes.

[jlullo]

would you mind giving me a hint as to where they are?  Or is the whole thing f'ed?

[johngreene]

would you mind giving me a hint as to where they are?  Or is the whole thing f'ed?

The mistakes I see are:
1. the Vb trace is shorted to R2/C2.
2. R5 should be connected to the emitter of Q1, but Q1 emitter is connected to ground. The signal will die here, and the transistor will probably smoke.
3. R3 is connected to pin 1 of IC1. Should be connected to the other side of R2.
4. C1 is connected across D3 only. Should be connected across Pins 1&2 of IC1.
5. R1 is connected across the drive pot and Pins 1&2 of IC1. This is wrong, it should be in series with the drive pot only.
6. The tone pot is connected across pins 5&7 of IC1, should be connected between pins 5&6.
7. The base of Q2 is connected to the wrong side of R12
8. The emitter of Q2 connects to R13 but nothing else.
9. R14 is grounded.

Just to name a few.....

I'd say the whole thing is pretty much F'ed.

Then there is the subject of placement.....

--john

[jlullo]

alright... thanks John.  I'll try again tonight!

[markm]

Ummm, it looks like Tonepad's layout........

[jlullo]

Ummm, it looks like Tonepad's layout........

does it really?  i made a point of not looking at their layout at all while i was doing it!

this is a lot harder then i thought 

[johngreene]

While you are at it, try to follow the 'straight line' method for your layout as best as you can. In other words, keep the input and output (Q1 and Q2) as far away from each other as possible and try to have the signal flow in a line as much as possible. For pedals, if you run it left to right, the input and output will land on the correct ends of the board.

A comment on your routing of Vb. You have it going all over the board but the only bypassing is at the very end of its long run. The 47uF should be placed as close to the 2 10k's as possible. Then if the trace gets long, like you have, add another bypass cap or two along the way.

Make the ground trace as fat as you can.

--john

[jlullo]

thank you john.  i'll give another shot at this with your advice in mind.  i might try with another schematic, as this was my 3rd attempt with the tonepad schem

would you suggest starting at input and running to output?  i had been branching out from the IC

[pyrop]

Try building the layout in blocks (i.e. input buffer - distortion section - tone section - output buffer) then work out how to put them together.
I good thing you can do is drawing the layouts on paper first. It's a lot quicker.
Btw a good circuit to help learn doing layouts using opamps is the Distortion+.

paulw

[jlullo]

paul,
thank you!  i actually just finished reading RG's "Technology of the Tube Screamer" (which i admit i should have read long ago!).  I'm going to try his schematic and see where i'm at with that.

One question on that, though- how do i take the "footswitching" stage out of the schematic?  since i use 3pdt switches, i shouldn't need this, right?