Hello and help with the Cot50

[Waldo]

  Hello , i am a new forum member but i have been a lurker for a few years and would like to thank all the contributors and especially IvIark for such a great siteand effort involved  .  I have built a good few pedals from all your layouts and i did think it was about time i gave a thank you regardless of the help question below .  I am sure there are many more that use and appreciate this great site who don't sign up but i am sure like myself , make good use of it .  I know there haven't been so many new projects on the main pages lately  so that's why i came over to the forums  , hopefully the site won't dissappear and stays up for many years , it is an encyclopedia for pedals .

And the help ....
 
  So i just built the Cot50 and it's an interesting one , it does sound good as a sound improver/boost and very reactive on guitar volume without diodes in the circuit .
However i have wasted hours messing with the diodes . They don't seem to make any difference in or out of the circuit which is puzzling as the original has them in the schematic but why if they don't do anything ?
    I have checked my soldering , it's all good , no bridges and works fine - apart from these diodes doing nothing ?
The only other thing i can think of is that you need to use the Cot50 at ear shattering volume for them to come into play ( i believeit is supposed to be used loud).

  Did anybody manage to find a solution to this as plenty have had the same result .


   Also posted on main Cot50 page , perhaps if someone knows the solution it would be good to answer there .    I know people seem to have made the Cot50 up and have it working  but there seems to be a few with the same issue  .  
     
       Regards Waldo

[induction]

Hi Waldo,

The diodes should make a noticeable difference in both the volume and the tone. If they don't there could be several explanations, but to make any intelligent suggestions we need a few questions answered:

1. Can you confirm which layout you are using? (This one?)

2. What transistor are you using?

3. What kind of diodes are you using?

4. Any modifications to the circuit or layout?

5. Do you have a DMM to take voltage readings and check continuity with?

The best chance for us to help you troubleshoot would be if you answer the above questions and post hi-res photos of the front and back of the board and all your wiring (especially the diode selector switch).

[Waldo]

Hello ,
     Yes i have used this layout  http://tagboardeffects.blogspot.com/2010/07/lovepedal-cot50.html#comment-form  .
 
  I have tried different jfets - no problem - (nothing to do with orientation or type) .
 
 I have also tried different diodes and led's .  They are in the circuit but make no difference .

  There is no problem with my build (easy for me to say ) , i have had a magnifiying glass on it there are no solder bridges and been through with a dmm , the circuit is as per the layout . All components checked before  soldering and after everything checks ok .
  And i have put the link in between the two caps.
   
I know this is verified but i think there is an error in the layout because it appears to work (and it actually does well)  but that is regardless of the diodes - that make no difference whether installed or left off .

   On the main page there are plenty of others who found this and no mention of the solution . And yet it is such a simple circuit .

       Regard Waldo

[Travis]

The 2N5088 is a BJT. You’re using JFETs?

[induction]

Waldo wrote

I have tried different jfets - no problem - (nothing to do with orientation or type) .

I assume you mean bjt's? There are no jfets in this circuit.

I know this is verified but i think there is an error in the layout because it appears to work (and it actually does well)  but that is regardless of the diodes - that make no difference whether installed or left off .

There does not appear to be any error in the layout as compared to the schematic. The fact that the circuit is working but the clippers are not indicates that only a few possible issues are likely.

1. Your clipping switch is not connected correctly.

2. Your diodes are not connected correctly.

3. You have an incorrect component value that is causing the gain factor to be too small to activate clipping in the diodes.

4. The clipping is actually working, but the effect is too subtle for you to hear it (this could be the case if you are overdriving your amplifier; the amplifier distortion could cover up the pedal clipping)

There are other possibilities, but without access to the pedal or photos, I think these are the most likely culprits.

I'm happy to help you troubleshoot, but there's not much more I can do until you answer the questions I asked and post photos.

One more question: how are you comparing the sound with and without the diodes? Are you physically removing them from the circuit, or are you using the switch?

[Waldo]

  Yes , 2N5088  - BJT   should have just said transistor .
 
  I had forgot , i did make one change , i didn't have any  47 ohm resistors so used a 75 ohm  instead  .
      I thought that would have been close enough ?    I had also ordered some 47ohm's anyway but they won't arrive for a couple of weeks .    I guess i could solder 5 x 10 ohms together to try ?
   Tried the amp totaly clean , it made no difference .

  The diodes are socketed so i tried a load .

  Struggled to get a good picture these don't look to bad on my pc .
 Diodes and transistor taken out for better view .

 

[induction]

Thanks for the pictures. Can you add one of the whole circuit, including the pot and switch?

The 75R is fine. You can leave it if you're happy with the range of gains that you get from the pot. Can you confirm that the pot is working correctly? It should be noticeably louder with the pot turned all the way up compared to all the way down.

I see no build errors.

My current guess is that your spdt is cooked. Can you check it for continuity with your DMM?
Switch down: pins 1 and 2 shorted, pin 3 unconnected
Switch up: pins 2 and 3 shorted, pin 1 unconnected

[Waldo]

Hello the pot and "switching" work fine , no switch at the moment for testing , i have connected them (the yellows) together with a push in connector and also by touching the top output yellow directly to the diode track  , it makes no difference  ,
 
    I appreciate there was possibly doubt on my build but as i mentioned in my original post i had been through it and checked properly .  I knew my build was fine  and when reading the posts on the main page plenty of others have had the same result .

  I have also checked from a couple of schematics i found ( i admit i am not to good at reading them - something i should probably re-learn , been a while) and the layout does look correct from those .     But , could the actual schematics be wrong , unless taken from the actual Lovepedal one , is that available  ?

 

     Regards Waldo .

[induction]

I understand your frustration, and I know it can feel insulting when people assume that there is a problem with your build, but I promise you, if the diodes don't do anything, there is a problem with your build. To solve the problem, we have to find out what the problem is, so we start with the most common problems, eliminate them and move on to the less common problems. The number one most common problem in any circuit is a build error. Based on your pictures, it doesn't look like that is the case, so it could be a faulty component, cold solder joint, cracked vero track, or something else. This is why we ask very specific questions: what type of diodes have you tried, what type of bjt have you tried, can you confirm that the volume increases when you turn up the bias pot, can you confirm that your diode switch properly connects lugs 1 and 2 in the down position, etc. The possibilities for what is wrong with the build are constrained by the answers to these questions, so it is easier for us to help when you specifically answer the questions, rather than saying "it's fine". This is a game of details.

The one thing that I can be fairly certain about is that the schematic and layout are not the cause of the problem. First: This is not a complicated circuit. It consists of two building blocks: , a a common emitter amplifier with treble-bypassed variable emitter degeneration for gain control and collector feedback biasing (which appears to be working in your case), followed by a hard clipping stage consisting of antiparallel diodes to ground (which does not appear to be working in your case). It is one of the simplest pedal circuits in existence, and we confirm its operation by very basic electronic principles (it is literally a textbook circuit) and by the fact that it has been built hundreds of thousands of times by myself, many other people, and dozens or even hundreds of companies.

It does not matter if the schematic matches the 'original' Lovepedal circuit, the fact is if you build the circuit as drawn, the diodes should have a noticeable effect on both the volume and the tone. The lower the forward voltage of the diodes, the more of an effect they will have (which is why we asked what type you are using). In fact, there is no such thing as the 'original' Lovepedal circuit, because Lovepedal's business model mainly consists of tweaking one or two components of this circuit and releasing it under a different name (Woodrow, Tchula, Champ, Englishman, Englishwoman, Les Luis, etc., etc., etc... Here is one of many millions of guides on the internet for just this purpose), and the Electra is the well-known distortion circuit that predates the existence of the Lovepedal company.

Sorry for the rant, and I hope I haven't offended you. The point I am trying to make is only that I and many others can simply look at the schematic and the layout and say with a great deal of certainty that the electronic design is sound, the layout should work, and if your diode clippers are not working then there is a problem with your build. If you are willing to troubleshoot the build, take measurements, and answer questions precisely, I am confident we can fix it.

If you are willing, the next two steps are to take voltage measurements and perform a socket connectivity check.

1. Install your transistor and your diodes. Power up your circuit and connect it to your guitar and amplifier. Using your DMM, connect the black probe to the ground leg of the 100u cap, and use the red probe to measure the DC voltage on each leg of the transistor, and both legs of the 100n cap. Report those voltages here. Take a photo of the circuit in this arrangement and post it here. (The goal here is to confirm that the transistor is producing enough gain to activate the diodes, and to check whether the output cap is shorted, which could leave enough DC offset voltage in the signal path to interfere with the diode clippers.)

2. Remove the diodes from the sockets, and replace them with jumper wires while playing through the circuit. Test each jumper individually, and then both at the same time. Tell us what happens. (The goal here is to check whether your sockets are allowing a solid connection between the signal path, the diodes and the ground rail.)

[Waldo]

  Hello all ,
               can't explain how much simple a circuit has bugged me .  I knew the build was ok but i have spent hours messing with this thing to get the clipping working .  A couple of nights ago i was still awake at 01.30 thinking about this  s so idecided to build another to see if there was a difference ( yes at 01.30 in the morning),  result = exactly the same .  
   Then last night wondered if my guitars were the issue , most of them are high output pickups , were they pushing it to much ?

    So today i tried again , different guitar and amp . Success !!!!!  It was working correctly all the time .

   I think it was down to , mostly the  diodes that i tried hardly made any difference , i should have kept trying more. But also as some of you mentioned the amp .

   Using a different amp/set up to normal , i could really hear the difference with some diodes ( terrible) so then i knew it was working as it should.    
   But after all that , i think it 's better without the diodes anyway .

     Still shocked and also annoyed how much time i put into this and it was just down to my normal set up and was much more obvious on a cheap amp .

    Lesson learnt ( and now i will be able to sleep) ,   thanks all for your help .
   
        Regards  Waldo .

[induction]

Great news. Glad you got it figured out.