Tonepad small stone - partial success

[tonewill]

Hello,
I built the tonepad small stone phaser project using their own PCB. I've made no modifications and ordered the parts from small bear electronics as they suggest even thought I'm in the UK. It was easier as they emailed a list of parts required for this project and had them all in stock. Some resistors I already had. I (thought) I was very careful assembling it and checked all resistor values by colour codes and by meter.

Today I was ready to test it and as I don't yet have a box or main switch I wired the input jack straight to the input on the board and the output from the board to the output jack, so no bypass. I'm using a new battery as well until I get a decent adaptor.

To my surprise It worked, until I switched the colour switch whereupon I got an awful high pitched squeal.

As I'm a beginner at electronics can anyone point me in the right direction as to what I should be checking / testing for this problem? I know others have had this squeal problem but as far as I can tell that was due to them modifying the board to fix the 'volume drop' problem. I'm just using the standards values.

Thanks for any help,
Barry.

[tonewill]

Direct link to circuit diagram

There are a lot of threads on this forum about this project but the ones I looked at which had a similar problem all revolved around mods that had been made to stop the "volume drop when engaged" problem (which I haven't done).

Anyway, last night I went through every resistor with a magnifying glass and a resistor code chart hoping to find a wrong value but they were all correct. I then decided to separate the 'feedback' and the 'sweep width' from the DPDT switch. I wired the feedback so that it was off and the switch now just controlled the sweep width. The sweep width works fine so the problem is with the feedback part of the circuit.

I'm pretty hopeless at reading circuit diagrams at the moment, can anyone help me track this problem down please?

Here's a picture of the board in case anyone can spot a wrong capacitor or something. Taken with a camcorder, that's all I have. Click to enlarge:



I thank thee,
Barry.

[tonewill]

Is anyone able to help? Anyone able to tell me which part of the circuit could cause the problem? If you haven't read the other posts then the problem is with the feedback / regeneration part of the circuit causing high pitched sweeping tone. No mods done, same as circuit diagram. Everything else works including sweep width control.
Thanks,
Barry.

[edd29]

Hello,
I built the tonepad small stone phaser project using their own PCB. I've made no modifications and ordered the parts from small bear electronics as they suggest even thought I'm in the UK. It was easier as they emailed a list of parts required for this project and had them all in stock. Some resistors I already had. I (thought) I was very careful assembling it and checked all resistor values by colour codes and by meter.

Today I was ready to test it and as I don't yet have a box or main switch I wired the input jack straight to the input on the board and the output from the board to the output jack, so no bypass. I'm using a new battery as well until I get a decent adaptor.

To my surprise It worked, until I switched the colour switch whereupon I got an
As I'm a beginner at electronics can anyone point me in the right direction as to what I should be checking / testing for this problem? I know others have had this squeal problem but as far as I can tell that was due to them modifying the board to fix the 'volume drop' problem. I'm just using the standards values.

Thanks for any help,
Barry.

the awful high pitched squeal is come from R11 and R42  I suggest that  you need to change the value of two resistors 10k trimmer is fine for R11 and R42.
adjust the trimmers until the high pitched is gone. hope this will help.

EDD

[tonewill]

Thanks EDD for helping.
I've read about those 2 resistors needing to be changed when the bypass volume drop mod is done. I haven't done the mod so what I don't understand is how someone can make a unit with the standard parts and it works fine, yet someone else can use the same standard parts and get a problem. It doesn't make sense to me, I think there is either a fault with a component or a problem with my workmanship which is why I would really appreciate it if anyone could let me know which are the components that are required only by the feedback function so that I can check or change those components. Thanks again.

[tonewill]

I changed R11 to 10K but although it was better it was still unusable. I bought some 100k trimmers to try. What is the best way to fit them as they have 3 legs / prongs? They are square horizontal mounted types with 2 legs close together. I assume the furthest leg is the wiper. If so do I short the wiper to one leg and connect the other leg and wiper to the board? I've got a feeling I've bought the wrong type. I know it's boring for you experts, but thanks for your help.
Barry.

[tonewill]

Don't worry, this is my last post on the subject unless anyone else replies.

I have a 100k trim pot fitted in place of the 3k3 resistor at R11. Result? Same very loud squeal wherever the trip pot is set with little or no musical signal coming through. Looks like I have some other fault which means I'm pretty stuffed.

Thanks for all the help anyway,
Barry.

[edd29]

Don't worry, this is my last post on the subject unless anyone else replies.

I have a 100k trim pot fitted in place of the 3k3 resistor at R11. Result? Same very loud squeal wherever the trip pot is set with little or no musical signal coming through. Looks like I have some other fault which means I'm pretty stuffed.

Thanks for all the help anyway,
Barry.

hmm .. did you change R42 aswell ? what type of power supply you are you using ?

[tonewill]

hmm .. did you change R42 aswell ? what type of power supply you are you using ?

Well, no I didn't change R42 because I thought that was just for the volume drop problem, and I thought solve one problem at a time before doing any mods. I can put a 10K in there if you think I should. The power supply is a new duracell battery.
Thanks for helping, I really appreciate it.
Barry.

[tonewill]

Okay, I changed R42 to 10K. Now I also have distorted sound unless I turn the input well down. Input is from one of the outputs of my m-audio 192 sound card and I'm playing an audio file to test. The squeal is still there though more distorted and the trim pot makes no difference wherever it's set. I say I've failed on this even though I really took my time over it.

I dont know if this is relevant but there is one component that I had to substitute when ordering from small bear. They sent a spread sheet which had:

5 Capacitor Xicon Poly Film 50V .0068mf.

I couldn't find this on their site and ordered:

5 Capacitor, Panasonic ECQ-B .0068 mf

Could this have an effect?
Thanks for any help,
Barry.

[edd29]

Okay, I changed R42 to 10K. Now I also have distorted sound unless I turn the input well down. Input is from one of the outputs of my m-audio 192 sound card and I'm playing an audio file to test. The squeal is still there though more distorted and the trim pot makes no difference wherever it's set. I say I've failed on this even though I really took my time over it.

I dint know if this is relevant but there is one component that I had to substitute when ordering from small bear. They sent a spread sheet which had:

5 Capacitor Xicon Poly Film 50V .0068mf.

I couldn't find this on their site and ordered:

5 Capacitor, Panasonic ECQ-B .0068 mf

Could this have an effect?
Thanks for any help,
Barry.

Any types of caps should work , I'm not expert or engineer but only I can say double check your work maybe there is short circuit at the back of your pcb or wrong wiring
get the schematic from tonepad and compare it on your pcb I made mine from tonepad same problem with yours I just change the two resistors and works problem is solve
don't give up man  this is charge with your experience . good luck!

[tonewill]

Thanks edd29,
I cleaned up the back of the board, scraping between contacts and cleaning up with some alcohol and it works! Must have been a short all along. And I thought I'd been extra careful, just goes to show.

I also received some switches I've been waiting for and so I've now wired in the footswitch and have divided the 'colour' switch between 2 switches (width and feedback). So now I can test between bypass and engaged and like I've seen posted elsewhere, the 10k resistor in R42 hasn't cured the level drop problem and it has made it distort. Also, when the feedback switch is on, the level drops substantially.

So, it works, but there are still problems. If anyone has any ideas about that I'd love to hear it.

Barry.

[Fp-www.Tonepad.com]

A clean(er) solder job is usually all that's needed. Glad you got it working!

[edd29]

Thanks edd29,
I cleaned up the back of the board, scraping between contacts and cleaning up with some alcohol and it works! Must have been a short all along. And I thought I'd been extra careful, just goes to show.

I also received some switches I've been waiting for and so I've now wired in the footswitch and have divided the 'colour' switch between 2 switches (width and feedback). So now I can test between bypass and engaged and like I've seen posted elsewhere, the 10k resistor in R42 hasn't cured the level drop problem and it has made it distort. Also, when the feedback switch is on, the level drops substantially.

So, it works, but there are still problems. If anyone has any ideas about that I'd love to hear it.

Barry.

go here and read the build reports  http://www.tonepad.com/project.asp?id=11
scroll down at the bottom and you can see the build reports is all about volume drops issue.

[tonewill]

I put the 4K7 back in R42 as there was too much distortion with 10K, maybe it's alright if you're using a guitar. I might replace R4 as suggested in the tonepad build reports, perhaps with a trim-pot under the board though I can live with the difference in volume between bybass and engaged because I won't be using it live. What's more annoying is the volume drop with the feedback part of the colour circuit.

Anyway, thanks for all the help, much appreciated.

[tonewill]

I'm looking at this again after a break from it.

To adjust feedback some say change R11 to, say, 10K. I also read this:

...stick a 5k pot in conjunction with the 3k3 and 4k7 resistors, you can get some useful variable attenuation of feedback.  Here, ends of the two mentioned resistors should be lifted from where they normally meet, and the wiper of the pot would go there.  One outside lug of the pot goes to each of the two freed-up resistors.  What you have now is a variable resistive divider.  At one extreme, the attenuation is given by 3k3/(5k+4k7), and at the other it is given by (3k3+5k)/4k7.  That may or may not be enough range.  You might try a 10k pot as well.

How would this be better or different from just changing R11 please?