Internal trim pot orientation question

Fuengi

Once bitten.... 

Can anyone advice me on which way to put this internal trim pot in to the PCB?

The instructions show a bias pot but this is in the kit, I'm assuming it goes in the three offset holes with Bias outlined below the external pot holes which will be unused? I don't know which way the pot should go though. 

Roland

Aren’t the three pins already bent so as to align with the three holes in the circuit board?

Fuengi

Roland said:

Aren’t the three pins already bent so as to align with the three holes in the circuit board?

Yes. I bent them to see if it would fit.

Paul_C

Well the pins are numbered, does the board or circuit diagram not show which goes where ?

ICBM

Yes, like that .

Paul_C

I've looked on the Fuzzdog site, and by the looks of things Pin 1 is on the left.

The only thing to bear in mind is that the trimmer you have is much harder to know where it's set, as it'll be multiple turns from one extreme to the other. (you can hear it click when it reaches either end)

Fuengi

ICBM said:

Yes, like that .

Paul_C said:

I've looked on the Fuzzdog site, and by the looks of things Pin 1 is on the left.

The only thing to bear in mind is that the trimmer you have is much harder to know where it's set, as it'll be multiple turns from one extreme to the other. (you can hear it click when it reaches either end)

Thanks again chaps.

ICBM

It doesn’t matter which end is which, it’s a linear potentiometer. Fit it how it fits, that’s all.

Fuengi

Another one I can't get working!

Been ultra carful to follow everything to the letter and checked the switching etc. I checked the voltages across the IC DIL socket as suggested but I don't know how to work out what they should be.

The bias trimpot seems to turn forever befor reaching a click. I got it to click one direction but must have wound it dozens of time the other way without any click.

I've got no idea how to test to see what wrong with it!

Danny1969

What kit is it ? if there's a circuit diagram I could tell you what voltages will be where 

Fuengi

Danny1969 said:

What kit is it ? if there's a circuit diagram I could tell you what voltages will be where 

The schematic is in the instructions on this page Danny. 

https://shop.pedalparts.co.uk/P45_Phaser/p847124_7971603.aspx

Danny1969

Ok, the opamps are TLO72 ... these are general use dual opamps so each package contains 2 opamps . 

Pin 8 should be 9V when referenced to ground
pin 4 should be ground ... so measure between 8 and 4 will give 9V 

Check that on both opamps

Signal comes in on non inverting input pin 3  .... that will be biased at half the 9v rail roughly so around 4.5V ... so read that between pin 3 and 4 of the first opamp. As a general rule this applies to any opamp used in that config with a single ended supply like a guitar pedal has to use

Check the FET's are the right way round .. this is easy mistake to make 

Check any diode is right way round too
 
Then see what you have 

Fuengi

Danny1969 said:

Ok, the opamps are TLO72 ... these are general use dual opamps so each package contains 2 opamps . 

Pin 8 should be 9V when referenced to ground
pin 4 should be ground ... so measure between 8 and 4 will give 9V 

Check that on both opamps

Signal comes in on non inverting input pin 3  .... that will be biased at half the 9v rail roughly so around 4.5V ... so read that between pin 3 and 4 of the first opamp. As a general rule this applies to any opamp used in that config with a single ended supply like a guitar pedal has to use

Check the FET's are the right way round .. this is easy mistake to make 

Check any diode is right way round too
 
Then see what you have 

Thanks for this Danny. I've checked the voltage across opamp 1 and have the following readings;

Pin 1 - 4.4v
Pin 2 - 4.4v
Pin 3 - 3v
Pin 4 - 0v

Pin 5 - 4.3v
Pin 6 - 4.4v
Pin 7 - 4.3v
Pin 8 - 9v

Checked the diodes and the FETs and they look right to me. I think I've even got the electrolytic capacitors in the right way this time! 

Danny1969

Ok if opamps good and FET's defo right way round it's likely to be a wiring mistake ... here a signal probe is a handy device but prodding pins with a small metal conductor will suffice .... if the pedal is connected to an amp then you can work backwards from the output ... if good then there will be a buzz when you touch the contact, bit like when you touch the lead before you plug into unto your guitar. 

Prod pin 1 of IC2 ... with the pedal turned on, do you hear a buzz ? if so go to pin 1 of IC1 and probe that ... if you have lost it then it's possibly  a switch problem, try jumping the switch 

Take heart that everyone makes mistakes building these things, I've built circuits I've designed myself and still f#cked up on something silly

Fuengi

Danny1969 said:

Ok if opamps good and FET's defo right way round it's likely to be a wiring mistake ... here a signal probe is a handy device but prodding pins with a small metal conductor will suffice .... if the pedal is connected to an amp then you can work backwards from the output ... if good then there will be a buzz when you touch the contact, bit like when you touch the lead before you plug into unto your guitar. 

Prod pin 1 of IC2 ... with the pedal turned on, do you hear a buzz ? if so go to pin 1 of IC1 and probe that ... if you have lost it then it's possibly  a switch problem, try jumping the switch 

Take heart that everyone makes mistakes building these things, I've built circuits I've designed myself and still f#cked up on something silly

Can't work it out. The only thing I get is a short between CI and Ground when the switch is engaged, but that's normal i think?

Fuengi

Danny1969 said:

Ok if opamps good and FET's defo right way round it's likely to be a wiring mistake ... here a signal probe is a handy device but prodding pins with a small metal conductor will suffice .... if the pedal is connected to an amp then you can work backwards from the output ... if good then there will be a buzz when you touch the contact, bit like when you touch the lead before you plug into unto your guitar. 

Prod pin 1 of IC2 ... with the pedal turned on, do you hear a buzz ? if so go to pin 1 of IC1 and probe that ... if you have lost it then it's possibly  a switch problem, try jumping the switch 

Take heart that everyone makes mistakes building these things, I've built circuits I've designed myself and still f#cked up on something silly

So Pin 2 and Pin 3 of each IC do give a buzz when I prod them. Does that help?

ICBM

Fuengi said:

Can't work it out. The only thing I get is a short between CI and Ground when the switch is engaged, but that's normal i think? 

Shouldn't be. CI is the circuit input so it should be an open circuit (assuming you haven't got a guitar plugged in and turned down!) when the switch is set to on and grounded when set to bypass. If you've used the switch PCB you can't have wired the switch backwards though...

Fuengi

ICBM said:

Fuengi said:

Can't work it out. The only thing I get is a short between CI and Ground when the switch is engaged, but that's normal i think? 

Shouldn't be. CI is the circuit input so it should be an open circuit (assuming you haven't got a guitar plugged in and turned down!) when the switch is set to on and grounded when set to bypass. If you've used the switch PCB you can't have wired the switch backwards though...

I have used the switch PCB, yes. Those switches can go either way I believe? 

ICBM

Fuengi said:

I have used the switch PCB, yes. Those switches can go either way I believe? 

If the holes in the PCB are round not oval, yes. You need to be careful to fit them so the flat terminals are lined up across the width of the pedal not along its length...

Like this:

Fuengi

ICBM said:

Fuengi said:

I have used the switch PCB, yes. Those switches can go either way I believe? 

If the holes in the PCB are round not oval, yes. You need to be careful to fit them so the flat terminals are lined up across the width of the pedal not along its length...

Like this:

Fuzzdog ones only go horizontally. I can't see what I've got wrong with the wiring? 

ICBM

Nothing I can see that's obvious - unless the spring terminal on the input jack is touching the casing?

(Just as an aside, why do these kits never give you shakeproof washers for the jacks? Or most boutique pedal makers fit them...)