Rat Debug (need help, full info inside)

[Evad Nomenclature]

Hey guys,

O.k.  I posted earlier saying I couldn't figure out what was wrong with the Tonepad Rat I did, but I just got home (1am!) and checked all of the voltages and stuff... here's the info if anyone can help.
The pedal has sound, all the pots do their thing... volume pot adds volume, gain adds gain and the filter filters, however... the pedal when cranked is a bit lower volume than my amp.  Also, it has some gain, but it doesn't have the Rat sound that I know at all... its kind of distorted and *very nasally* (almost like there is some sort of filter on it, no matter where the filter/tone control is set.)
Not sure how else to explain it... except maybe... it sounds like ass!
So here ya go...!

1.  Project: La Rata/Proco Rat build from www.Tonepad.com

2.  http://www.tonepad.com/getFile.asp?id=89 (schem and layout info)

3.  Followed the layout to a T, but made a few subs for missing parts... I tried to do the best I could with all the listed parts, but realized after I started building (always a good time!)
that I was missing a few things...

4.  Here's the list of Substitutions that I *did* make:

----Volume pot - I used a 1 Meg (other pots are the 100k's) Figured this was fine.... usually I find 1 mega's for volume, so.. yeah...

----The 4.7 electro cap off of the 3rd lug of the distortion pot- I used a 3.3 instead (ran out of the 4.7's used the last one in the other 4.7 spot on the schem)

----The 30 pf cap above the IC I used a 51 PF... (a little sketchy on that one) I just tried to find the nearest value that I had to the original...

----Diode 3... I used a 914 instead of a 4002.  I wasn't sure but is this just a circuit protect diode?  (bear with me, I'm still learning how all these parts work... and trying to recognize them in a circuit)

----the 47 ohm resistors in the layout I changed to 41 ohm resistors (pretty damn close, right?)

----and last but not least, on the tranny I used a 5457 instead of a 5458 (I read these were interchangable, just different gain levels for them...)

Everything else is right on the money, I even went through and measured and double checked the resistors (with my eyes as well as a multimeter) as sometimes my eyes can play tricks on me with orange vs. red and stuff

5.  Normal 9V negative ground...

6.  The battery is brand new... measuring at 9.56 V on the multimeter... and here's the readouts of voltage at the pins...

IC LM308

Pin1-9.02
pin2-8.87
pin3-8.84
pin4-9.41 
pin5-000
pin6-8.67
Pin7-9.56
Pin8-8.95

Q1-
Pin-1: 9.46
Pin-2: 9.47
Pin-3: 4.37

D1:
A=9.11
K=9.47

D2:
A=9.09
K=9.48

D3:
A=9.48
K=9.54


Thanks... I'm gonna check out pin 8 of the ic right now...

[RonaldB]

Hello,
After a first look the voltages on the LM308 seem wrong.
pin 4 needs to be 0v (connected to ground) and pins 2, 3, and 6 need to be half of 9v (4.5v) measure the Vb point on your board (see schematic).

good luck with it.

Ronald

[Evad Nomenclature]

changing them right now... had an oops... I forgot I swapped the IC... I read that the 741 was compatible and then saw that they were wrong (i'm pretty sure.?)
The 308 is back in and the voltages corrected are...

Pin1-9.02
pin2-8.87
pin3-8.84
pin4-9.41
pin5-000
pin6-8.67
Pin7-9.56
Pin8-8.95

From what you said... with these numbers something is still wrong...
still looking...

[frokost]

The parts substitutions should be all right. The electro cap sub will mess with the distorted frequencies, so you might want to sub that one to the original spec. Where's the other place a 4.7 is used in the rat? On the power section? You could put anything of a certain size there, 47 for example, the value isn't that critical. When it comes to frequency stuff, the value matters.

But most importantly - check your ground connections. Something is seriously wrong there.

[shadowmaster]

It's OK to put the 741 for the meantime to prevent damage to the proper IC (308, unless you have a stash of them in reserve) while still debugging your work. No need to get voltages for pin 1 and pin 8 if 741 is in use. Make sure that your pin 4 is not shorted to your supply voltage.

[Evad Nomenclature]

No luck yet.
Something interesting though... maybe this is another clue to figure out what the deal is.

The gain pot is adding gain, but also seems to be acting as a *filter* as well...
The filter pot is filtering, but it is doing so backwards... When I roll it left, the high end goes up... gets bassy as I go the other way.
The volume works as intended.

I've quadruple checked the pots and they are wired correctly as far as I can tell...
I made sure nothing was touching on the pot itself...

The voltages on the IC are still the same after checking for the shortout to power that shadow mentioned in his response... I used an exacto to  make sure that there wasn't anything touching that didn't need to be touching (i.e. if anything looked even close, I scraped out between the terminals)

I retraced the connections about 10 times over (with a pen, pointer and pad) and made sure that nothing was touching against the schematic that shouldn't be...

I know it has to be something, since obviously the circuit has been built before *_*  I screwed up somewhere, but I'm not having any luck finding it.

Oh yeah and last but not least... The pedal *is* working... I get distortion, it's a tiny bit lower volume than with the pedal bypassed, but I am getting something through it... and it has the Rat sound (sort of) but it is *wayyy* thinnner than any Rat I have ever heard.  Like I said before... it sort of sounds like there is almost an envelopefilter on it at times, it's real strange.

When I get home tonight, I'll see if I can take a close up of the top and bottom of the board and see if anyone has any ideas...

At least I'm learning something ^_^ I'm just not sure what yet =)

[shadowmaster]

The filter pot is behaving correctly based on your description. Bassy clockwise, trebly on the opposite. I switched terminals 1 and 3 on mine because I'm just used to having treble going up as I turn my pot to the right. Also pay close attention to the 1uF half-bias cap. Make sure it's working and that you get half of your supply voltage between the terminals. Try substituting it with a new one if it is acting strangely.

[frokost]

Any luck? My guess is ground - the diodes should read 0V on one end and about 4.5V on the other. They're both at about 9V now, which is seriously wrong. I'm guessing now, but I think that's what happens when ground isn't connected on the voltage divider. Make sure that every ground point actually reads 0V. Then check if Vb reads 4.5v. Then play some rawk.

[Evad Nomenclature]

Haven't had a second to dig back in yet.
It's waiting.
Ill try that when I have a minute to look tomorrow
Dave

[Govmnt_Lacky]

Dont rule out that you may have gotten a bad PCB from Tonepad. I have already DESTROYED two projects only to find that the PCB was poorly made and some of the circuit traces on the PCB were not there or were bad. Just a tip.

[oskar]

I think you have your wiring messed up somehow.
The PCB ground doesn't seem to be connect to the negative pole of the battery.

[Evad Nomenclature]

Ok here's pics... couldn't get the solder side of the board though... can't get my damn camera to zoom in and get a close up of it without it being blurry, so Im not sure if these do any good.

Thanks
Dave




Not sure I have time to do anything over the next couple of days, but if anyone sees anything , please let me know...
but then again, Im not sure if you can tell anything without the solder side =/

[oskar]

Trés chique! I can't properly follow the wiring but it looks OK. Is the ground wires going to the ground lug and the battery - to the ring lug?
Now I'ld check for continuity, battery minus to PCB, with the DVM in "beep thing" mode. Battery removed and a mono plug inserted for connection...             - Beep!

[Tony Forestiere]

Try checking for a solder bridge between pin 5 of the IC and the plus of the 4.7uf electro. There should be no voltage here. Just my humble thoughts.

[Evad Nomenclature]

yep.
no voltage at pin 5.
most of the others are reading too high I believe though.
Dave

[Evad Nomenclature]

uhhh 2 things...
just checked the suggestion about checking the half bias cap... checked it... 8.88 on the + side 9.23 on the minus.
Also... If I connect neg of the DMM to the neg terminal of the battery and the pos lead to ground... it should read 0 shoudln't it?
Because I'm getting... 9.27...
I have checked and checked everyone on both sides of the board and can't find a damn thing (and yes, I'm supposed to be doing other things atm, but I want to put this to bed... feeling a little OCD atm)!~

[asfastasdark]

If I connect neg of the DMM to the neg terminal of the battery and the pos lead to ground... it should read 0 shoudln't it?
Because I'm getting... 9.27...

On my multimeter it shows the voltage flowing over it with a "-" sign.

[oskar]

uhhh 2 things...
just checked the suggestion about checking the half bias cap... checked it... 8.88 on the + side 9.23 on the minus.
Also... If I connect neg of the DMM to the neg terminal of the battery and the pos lead to ground... it should read 0 shoudln't it?
Because I'm getting... 9.27...
I have checked and checked everyone on both sides of the board and can't find a damn thing (and yes, I'm supposed to be doing other things atm, but I want to put this to bed... feeling a little OCD atm)!~

Read my last post again....

Trés chique! I can't properly follow the wiring but it looks OK. Is the ground wires going to the ground lug and the battery - to the ring lug?
Now I'ld check for continuity, battery minus to PCB, with the DVM in "beep thing" mode. Battery removed and a mono plug inserted for connection...             - Beep!

[oskar]

When you're at it, check the battery clip. The wires from it could be going to the wrong poles.

[shadowmaster]

Some tips I would like to share.

Do not put your board  in an enclosure if you have not yet tested that it is working.

What you only need is your board soldered with all the components (offboard components like pots and switches, not bypass, should be included) and 4 wires. Those 4 wires should only consist of input, output, power and ground.

Do not solder your input and output jacks, DC jack, LED indicator and your bypass switch just yet.

To run power on your board, have spare battery clip that have alligator clips on both ends and connect this to your power and ground wires.

Have some spare jacks also with soldered wires on the terminals and alligator clips on its ends and use this to connect to your input and output wires on your board.

Now with these setup, you can now test your work if it is fully functional. If it is not then debug. If it is working then it is enclosure ready.

This will lessen the area of debugging, once your work is in an enclosure if you are quite sure that your board is perfectly working.