Proco RAT - no sound after diodes added

[Brynngar]

Hi folks,

I recently built me a RAT clone. I tried it out and it worked, but gave a clean signal. That's when I noticed that I forgot the diodes.
After installing those, it gave me no more sound whatsoever. Pretty frustrating, especially for such a relatively easy build...

The layout I used:
http://tagboardeffects.blogspot.de/2012/01/proco-rat.html

Here are the EXPECTED measurements :

Max Distortion

1 8;40
2 4,52
3 4,09
4 -5 = 0
6 4,52
7 9,06
8 4,37

D = 9,06
S = 1,77
G = 0

Min Distortion

1 8,43
2 4,53
3 4,10
4 - 5 = 0
6 4,53
7 9,09
8 4,58


D = 9,09
S = 1,71
G = 0

---
And my measurements:
Max Distortion

1 1,97
2 7,83
3 2,26
4 = 0
5 0,27
6 8,66
7 9,33
8 8,9

D = 9,33
S = 0,87
G = 0

Min Distortion

1 1,97
2 2,65
3 2,27
4 = 0
5 0,31
6 8,66
7 9,33
8 8,94


D = 9,09
S = 0,39
G = 0


---

I have already checked for bridges, but could not find any. Here are the pics I made:









Since my last builds all worked just fine, this is getting really frustrating...
Maybe one of you can find a solution 

[antonis]

I should start from the voltage divider resistors followed by non-inverting bias resistor...

[Brynngar]

I should start from the voltage divider resistors followed by non-inverting bias resistor...

..would you care to elaborate that, please? Do you mean mine is wrong or what exactly?

[antonis]

I mean that you should measure about 4.5V (half the power supply) at pin 3...

Try to fix this and we'll proceed with compensation values difference between pins 1 & 8...

[Brynngar]

I mean that you should measure about 4.5V (half the power supply) at pin 3...

Try to fix this and we'll proceed with compensation values difference between pins 1 & 8...

Here is my "flow" and the measured voltages. I get 4.5, but then there is the 1M resistor and I just don't get how there could be 4.5 at pin 3 with the 1M before it...
Or did I miss something here?

[Elijah-Baley]

Did you have used the same components of the layout? (Transistor, IC...)

Do you use often that kind of board to build veroboard layout? Seems very easy to make some mistakes.
Anyway, don't worry, have to be simply something wrong. We have just to find out it.
Checked already the values of the resistors (looking and measuring them with the multimeter) and caps? And the working of the pots? And wires contact?

Maybe you could check the contacts in your circuit looking at the schematic. It is an alternative way, maybe it helps.

In these days I'm building another veroboard layout of this pedal with some mods. When I finish mine (if it will work), I'll try to help you again.

[antonis]

Op-amp inputs appear VERY high resistance so you may consider that there isn't any noticable voltage drop across 1M resistor..
(no practically current flow..)

But you've probably dominated input impedance with your DMM impedance and I suspect it didn't happen only once.. 

[Brynngar]

Did you have used the same components of the layout? (Transistor, IC...)

Do you use often that kind of board to build veroboard layout? Seems very easy to make some mistakes.
Anyway, don't worry, have to be simply something wrong. We have just to find out it.
Checked already the values of the resistors (looking and measuring them with the multimeter) and caps? And the working of the pots? And wires contact?

Maybe you could check the contacts in your circuit looking at the schematic. It is an alternative way, maybe it helps.

In these days I'm building another veroboard layout of this pedal with some mods. When I finish mine (if it will work), I'll try to help you again.

Yes, I already did all that. Checked that the cuts are in the right place, that the connections exist where they should etc. I even built a pharao clone lately (appr. double the size of a Rat) and it worked
perfectly..

Op-amp inputs appear VERY high resistance so you may consider that there isn't any noticable voltage drop across 1M resistor..
(no practically current flow..)

But you've probably dominated input impedance with your DMM impedance and I suspect it didn't happen only once.. 

But then still, I don't get how instead of 4.5 - 4.5 on 2 and 3 I get something like 5 - 2 on 2 and 3.. seems like half of pin 3 goes to pin 2 instead 

[antonis]

I've a strong feeling that you placed IC 180 degrees reversed...

[Brynngar]

That would be annoying to redo but I'll try!

Oh and also, on a second glace: The IC is a LM801AN, while the original layout used a LM308N (but I couldn't get one of those)

[antonis]

That would be annoying to redo

Only if you didn't use socket on your board..

P.S.
Perhaps you mean LM108 - not LM801..

[duck_arse]

I have questions.
is LM801 an LM301?
what fet type are you using?
why is your 3n3 cap at the top of yr build so much larger than the other caps? just voltage rating?

[whatever the opamp is, it seems to be pointing in the specified direction correctly.]

[Brynngar]

I have questions.
is LM801 an LM301?
what fet type are you using?
why is your 3n3 cap at the top of yr build so much larger than the other caps? just voltage rating?

[whatever the opamp is, it seems to be pointing in the specified direction correctly.]

Sorry for the typo, again:
Should be a LM308
Is a LM301

The cap is bigger because of the voltage rating (couldn't get another one :/ )

[GGBB]

Check that neither the diodes nor the 4u7 coupling cap are shorted (solder damage?). If either of the diodes are shorted, well that's obvious. If the coupling cap is shorted, bias DC won't be blocked and will bias one of the diodes forward allowing all signal to pass to ground. Can't tell from the photo, but make sure the polarity is correct also else the cap will die, possibly to a short.

[Brynngar]

Sooo

interesting going-ons here. I removed both diodes to check if it's there fault, just to find out that there is still no signal -
Even though just this morning it worked without the diodes. Seemingly, something else must have been damaged in the process or idk.


The 4u7 caps seem to be fine though...

[antonis]

I should suggest to pull out IC from socket and measure DC supply (pin 7 & 4) and Vbias (pin 3) taking in mind your multimeter's impedance (parallel loading)..

Next step should be C4 (100pF) in the NFB loop - if it's shorted it creates a buffer (no amplification..)

Next follows testing C1 (22nF) Input cap - if it's open there is no incoming signal..

It should be a good idea to check discontinuity between pin 2 & GND and pin 3 & GND - it also secures that none of C2, C5 & C6 is shorted..

Last (but not least) check for the correct value of R6 (1K) - too low -> loads amp's out, too high -> loads signal's current (can't drive what comes next..)

[Elijah-Baley]

In these days I'm building another veroboard layout of this pedal with some mods. When I finish mine (if it will work), I'll try to help you again.

I built the circuit. It is a mod version layout by Sabrotone, with three kind of clipping. My circuit works. I used a LM308 as suggested for the original version.
Tell me if I can be useful.

For solve your fault circuit, did you tried with an audio probe testing? You could find out where's the sound got wrong.

[Brynngar]

Hey, thanks for the replies! I decided to just order a vero board, sockets and new parts (since it's not expensive anyway) and redo it on vero.
Finding the error in this one would probably drive me crazy... Once the vero version is finished (and works, I hope) I'll come back to this one here 

[Elijah-Baley]

Meanwhile we wait you, I do some tests, I socketed some parts. I'll let you know what you could try.
I tell you now you could socket the diode of course. I added a switch to replace the 47R resistor (on the left on you layout) with a switch. I can chose the 47R stock resistor or I can control a 1k pot for the Ruetz mod. It add some bass (if it need) but seems to me it get the gain smooth, too.
I'll let you know something else if you need.

[Hatredman]

Any news?


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