FEMTOVERB /Wavefrontsemi/ PCB layout

[MetalGuy]

do you mean pins 14 and 15 of the AL1101 or the AL1201?

Peter, do you mean pins 15 and 16?

[Peter Snowberg]

Peter, do you mean pins 15 and 16?

Yep, sorry. Make that 15 and 16.

[MetalGuy]

Hey Mark, did you get the thing running?

[Mark Hammer]

This is my first time back at the bench in a while, so no, not yet.

[gaussmarkov]

would someone please check me on this?  i think there is a problem with the version 2 layout.  to find it, note that on the schematic (http://dstockett.50megs.com/femtoverb.gif) there are a pair of 10uF cap/200 ohm resistor combinations between IC2 and pins 1 and 2 of the AL1101.  and there's a 4700p cap across those pins.  on the layout the 10uF caps hook up directly to the 4700p cap instead of having the 220 ohm resistors in between.  it's like the caps and resistors are switched.

edit:  or does that even matter?  i guess order is not important there. 

[MetalGuy]

it's like the caps and resistors are switched

Yes, they are.
This was suggested by Peter Snowberg with some mods in mind. Maybe he can give you some more details.

I'm almost done populating my PCB and next week I hope to be able to power it up.

[gaussmarkov]

it's like the caps and resistors are switched

Yes, they are.
This was suggested by Peter Snowberg with some mods in mind. Maybe he can give you some more details.

I'm almost done populating my PCB and next week I hope to be able to power it up.

cool and thanks for the reply.  fwiw, i am going over the layout carefully and i hope it's helpful.  i put the schematic into eagle and now i am laying out your layout again, using the rubberbanding and the design rule checker in eagle to confirm everything.  i haven't started to build it yet because i still have a few components (crystal and regulator) and some pnp blue to get.

i hope yours works first time! 

[gaussmarkov]

metalguy,

i just finished tracing your layout and here are some additional questions.

• i wonder whether the 78L05 is backwards, with IN and OUT switched?  if i read the layout right, OUT is currently connected to +9v and IN is connected to +5v.  my (inexperienced) reading of the datasheet says they should be the other way around.
• the 2M2 pulldown resistor on the OUT looks to me like it is connected to Vr when really it goes to GND, one hole over
• two 1uF caps in the schem are 10uF in the layout:  the dc blocking cap on the OUT and the supply filter cap on the Vr supply
• is the +9v supply missing the 100uF filter cap and the 1N4002 polarity protection diode?

everything else matches the schematic as far as i can tell.  i put the schematic into eagle and then built up your layout from there--so there's a pretty good chance there's nothing else different.  i guess the cap values aren't critical, nor the polarity protection and the 100uF cap.  maybe peter changed those, too?  and i admit that i do not know how regulators are supposed to be hooked up.  so maybe it's all good. 

--gm

[MetalGuy]

i wonder whether the 78L05 is backwards, with IN and OUT switched?

You're right -  it's backwards.

the 2M2 pulldown resistor on the OUT looks to me like it is connected to Vr when really it goes to GND, one hole over

You got me one more time!

two 1uF caps in the schem are 10uF in the layout:  the dc blocking cap on the OUT and the supply filter cap on the Vr supply

I don't think the values are critical but I'll correct them.

is the +9v supply missing the 100uF filter cap and the 1N4002 polarity protection diode?

They are omitted intentionally - to save space and because I usually mount them directly on the DC jack.

Thanks for noticing and informing me for these details on time.
Below is the corrected layout:

[gaussmarkov]

metalguy, thanks for the new layout and the additional comments.  i like to move stuff like the power supply filter off the board sometimes, too.

everyone, i have a different sort of question about the circuit design itself.   i hope someone will answer.  are some of the caps on the schematic by davetv supposed to be physically close to the pins of the ICs?  i remember puretube making a comment about this sort of thing in another thread about R.G.'s variable stutter circuit. 

if not, then what's the deal with all the .1uF caps across the +5V and GND rails?  i am thinking of the ones across pins 12 & 13 of the AL1201, pins 14 & 15 of the AL3201B, pins 12 & 13 and 6 & 7 of the AL1101 (because digital ground and GND seem to be the same thing).  you could also throw into this list the cap on pin 6 of the AL1201.  that could just as well be across pins 5 & 6.

if these caps should be physically close to these pins, then how would anyone know this just from looking at the schematic?  and how close should the pcb designer put them?  how should other neighboring components be treated?

thanks in advance, gm

[TELEFUNKON]

you can find IC-sockets with built-in decoupling caps - that`s physically close as it can be! 

[gaussmarkov]

you can find IC-sockets with built-in decoupling caps - that`s physically close as it can be! 

ah, a clue:  "decoupling caps."     thanks TELEFUNKON!  for those who were unsure (like me):

• Re: Amp-op decoupling and unused XOR gates by R.G.
• Coupling vs. Decoupling Capacitors by R.G.
• Understanding 'decoupling' by R.G.

there are probably many other threads.  these come up first in a search and seem to cover the ground.  check out the related comments by niftydog and puretube.

[MetalGuy]

I got mine working from the first time! Populated the board, checked everything several times, connected it to the power supply and heard the slapback echo.
I didin't have time to experiment too much but all programs are working it sounds good so far. I'll post some pictures later today.

[TELEFUNKON]

CONGRADZ!!

[gaussmarkov]

this is very good news!     excellent.     i still have to order that crystal and the regulator ...

how are you going to box it?

[MetalGuy]

About boxing I'm thinking a standard 1590 box but I'm also thinking about  adding a PIC control unit which will be able to memorize 3 settings for my 3 channel amp. Because this will complicate things maybe I'll leave this one as standalone FX unit and make another one for my amp. Unfortunatly I didn't have time to play with it too much but this weekend I'll take some more time to experiment. Below are some picures of the unit:

[gaussmarkov]

beautiful!  thanks for posting the pics!

[Peter Snowberg]

 

[MetalGuy]

Today I spent couple of hours playing with the unit and noticed that the effects switcing order is somewhat different from what it should be. Looking at the schematic I'm assuming that I'm facing the encoder /the shaft side/ - that's how I connected it. The effects order goes like this /backwards/: Rotary - Vocal - Chorus Room /Wah/ 2 - Chorus Room 1 - Delay 2 - Delay 1. So far so good. The following should be Flanger  - Chorus but in fact three rooms/halls/plates follow then Flanger - Chorus and again four rooms/halls/plates. I'm using the same encoder as from the schematic.

Any ideas what could be wrong?

[A.S.P.]

encoder "pinout"?