What could be wrong with my Proco RAT breadboard build ?

[kaushikwavhal]

Help! My rat sounds like thrash as i turn up distortion knob. If i try to play individual notes, they sound muddy/fuzzy  and it sounds like two tones in  (not sure if they are the same not and different octave or two different notes) .
I've built a proco rat clone on a breadboard using this schematic.

I've used two 27nf capacitors instead of the two 22nf ones in the circuit as i couldn't find 22nf ones.

I even tried routing the pin 6 straight to my amp in an attempt to divide and check the circuit but it still sounds the same. i.e when i turn the gain up, it doesn't sound crisp at all.

[GibsonGM]

Hi, and welcome!  It is ok, we often have problems with our first builds!

First, go over EVERY part and connection again...look closely! It is very easy to mistake the value of a resistor, or to place a component leg in the wrong hole!

Do you have a multimeter?  I believe you need to make sure you have the 4.5V bias voltage going to R2.   If this voltage were not present, you would have an ugly sound.   It is one quick thing to check.

If that is not the problem, please check out the "debugging" page, and try to post the information requested!

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

Be patient, you will learn how to work the problem and find what is wrong      

**Be careful apply the opamp output directly to an amp, be sure it is through an appropriately rated cap to block DC....not often a problem, but one day it COULD cause some damage....try making an AUDIO PROBE (search the forum or internet for instructions) to listen to your circuits!

[GGBB]

When you say thrash, does this mean that you know what a RAT normally sounds like and this isn't it? RATs have a thrash kind of sound - in my mind anyway.

[strungout]

I have breadboarded a rat using that schematic you posted and I can confirm it works as any other rat schematic I've tried. Recheck all your connections, rebuild it if needed. But you might have tried that already.

Do you have an audio probe? http://www.diystompboxes.com/pedals/debug.html or http://diy-fever.com/misc/audio-probe/ This would help you point out where the sound gets muddy/fuzzy at every single connection. Then you can play with either resistor or cap values to get a sound that'S less muddy/sounds like a Rat. Look up highpass and Lowpass filters formula to help you out.

The two 27n cap subs shouldn't matter much. It's not high enough of a value sub to drastically change the tone. Unless you have crazy good ears!

[dschwartz]

Sounds like crossover distortion...check the diodes connection and the opamp bias

[GibsonGM]

^ This.  Symptoms aren't really of a thrash tone, he seems to be reporting some partial rectifying or something (?)

[kaushikwavhal]

@GibsonGM Thanks for good to know that everyone has problems with their first build. This is my 4th attempt (previous three were with a faulty opamp) and the first successful where i could at least get a sound of it. I've spend 8 weekends trying to get this up. I feel i am close. Definitely not going to give up.

Yes, i have a Multimeter and will check those connection. I'll also post a link to the sound sample from my build. That would help to describe the sound as i find the sound to be just weird.

@GGBB Yes,i've heard other RAT builds on YouTube. I called this sound thrash as there's no way one can make use of such sound. Its very unpleasant.

@strungout. Yes i am going to do a quick rebuild of this on two breadboards now. That'll give me enough space to tinker components without disturbing other components. Right now its very difficult to even remove the opamp. Instead of a audio probe, i tried routing the sound directly thorough my cable by removing its input wire from the end of the circuit and inserting at pin 6 of my opamp. The sound was a little louder but had the same weird tone.

@dschwartz: Yes, i am going to rebuild the whole thing.

[Elijah-Baley]

Do you have the rat circuit on breadboard yet?

Maybe this could be useful:


This is the link where it come from:
http://www.diystompboxes.com/smfforum/index.php?topic=110103.0

[GibsonGM]

@GibsonGM Thanks for good to know that everyone has problems with their first build. This is my 4th attempt (previous three were with a faulty opamp) and the first successful where i could at least get a sound of it. I've spend 8 weekends trying to get this up. I feel i am close. Definitely not going to give up.

Keep trying, you will succeed    It is like learning to ride a bike.  After you make the Rat work, the next one will be easier.  Right now, you are learning the 'tricks' to using the breadboard and how to read schematics, and diagrams.   In time, they will become easy.

Builds that used to take 2 days will soon only take an hour!    We will wait for your sound sample.

[illuminatiNPS]

For what its worth, I built the rat from guitarfxlayouts on vero and had problems too. I was getting weird voltages on the pins of the LM308. I ran my pencil soldering tip down each rail and must have broke up a bridge that occured or maybe even a frgment of copper from the cuts. The Rat is very fuzzy on high gain settings, almost sounds like it clips out. This, from what I have read is do to the IC's slew rate

[GGBB]

The Rat is very fuzzy on high gain settings, almost sounds like it clips out. This, from what I have read is do to the IC's slew rate

Very fuzzy indeed - quite compressed and mushy. The slew rate is part of it, but that mainly affects bandwidth. The primary reason is the extremely high gain, which is by design and contributes to that signature RAT sound.

[kaushikwavhal]

I tried and have rebuilt that thing . I thought there would have been some mistake in the connections but i am facing the same problem again after rebuilding.

Here's the sample recording. (I am using Liner Taper 100k Pots ).  i can only hear clean-ish sound in the first 2% of the knob. At around 7-10% of the knob turned i hear the below sound. If i turn it halfway or completely, i dont get any noticeable sound, i only here random fuzz which doesn't change even if i hit the strings hard.

I cannot understand how should i go about debugging this. I've tried with multiple LM308 and also NE5534. I think the OpAmp is doing its job. I suspect there is something wrong in the pre-input stage.

https://soundcloud.com/kaushik-wavhal/proco-rat-sound-debugging

Note: i am using film capacitor (27nf) in place of both the 22nf capacitor in the schematic.

[bloxstompboxes]

Do you have an audio probe? http://www.diystompboxes.com/pedals/debug.html or http://diy-fever.com/misc/audio-probe/

This.

[kaushikwavhal]

Yes i do have one. I've traced it to pin 6 (Post-Amplification) of the opamp and pin 3 (Pre-Amp sound) of the opamp. Except the sound levels , i didn't notice much difference. The major bad fuzzy tone still exists.

[Kipper4]

What are the voltages please?

[kaushikwavhal]

Voltages for LM308:
Pin 1: 7.72V
Pin 2: 4.05V
Pin 3: 2.02
Pin 4: 0V
Pin 5: 0V
Pin 6: 4.14V
Pin 7: 8.39V
Pin 8: 3.96V

Voltages At Transistor (2n5458):
G: 0v
S: 1V
D: 8.4V

Power Source: 9V Battery

[Markw5]

Sometimes there can be layout problems that lead to instability or oscillation. That can make the pedal sort of work, but sound bad. And you wouldn't necessarily hear the oscillation itself, since it might be occurring at several hundred kHz or maybe a few MHz. More about that type of  consideration here: http://www.diystompboxes.com/smfforum/index.php?topic=114555.msg1063679#msg1063679

[LightSoundGeometry]

Sometimes there can be layout problems that lead to instability or oscillation. That can make the pedal sort of work, but sound bad. And you wouldn't necessarily hear the oscillation itself, since it might be occurring at several hundred kHz or maybe a few MHz. More about that type of  consideration here: http://www.diystompboxes.com/smfforum/index.php?topic=114555.msg1063679#msg1063679

yeah man, you have to stick with it. I watch a lot of engineering type videos on the interwebs, along with reading to haha, but noticed there is a failure rate in the field..not everything turns out 100% of the time all the time; and you have to learn to live with it lol..now I know there are some skilled sob's out there as well who have a very LOW % of failures and are mind blowing with their creativity and craftsmanship.

[kaushikwavhal]

If the failure was due to improper placement, it should have been rectified when i rebuilt the circuit. I am getting the same output in both the builds.

Also the input wire to the circuit is isolated to a great extent. I suspect the problem lies in some faulty resistor or capacitor.

[Markw5]

What are you using as a signal source? A guitar? If so, humbucker pickups?
What is the output connected to?
What happens when you try turn down the guitar volume half-way or so?
Is your circuit inside a shielded enclosure?