Author Topic: 2 problems with my ego driver  (Read 1407 times)

zilla

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2 problems with my ego driver
« on: May 13, 2013, 10:33:18 PM »
HI all,

I just finished building my first madbean project - an egodriver.

This is my first PCB build, but i have experience with veroboard builds.

I have run into 2 problems and was hoping to get some help on them:

problem 1:  when i set the gain up i get squealing. I know that squealing is usually due to feedback between the input and output wires;  I am using shielded wires for the board in/out connections.  WHen i get the gain above about 10 or 11 o'clock it starts to squeal/hum.  I don't have a problem when i crank the volume to max, only the gain knob.

problem 2:  i wired a swith to the clipping connectors. I'm not sure which is which but in one position both LEDs light up. in the other position, the LEDs go out and there is a high pitched hum. I'm not sure what's going on here?

I've made sure that the back of the pots are insulated from the board. 

can anyone help?

Thanks

Tim

ichilton

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Re: 2 problems with my ego driver
« Reply #1 on: May 14, 2013, 02:01:14 AM »
The 2nd problem - if it's ok on the LED side, but not working on the other side, there must be a problem with the mosfet clipping.

I'd check your connections around the 2N7000's and the 1N34A - check there are no shorts etc, and consider swapping them out in case they are faulty....

Ian

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Re: 2 problems with my ego driver
« Reply #2 on: May 14, 2013, 06:11:59 AM »
As well as looking into those mosfets, an incorrect resistor value in the feedback loop could cause the squealing (ie too much gain).

Verify that you have used 2k2 for R4, 39k for R8 and 150k for R9. If you aren't sure, post a pic of the PCB and I can read the color codes for you (or you can just look them up online).
I own madbeanpedals (duh). I am part owner of Function F(X).

zilla

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Re: 2 problems with my ego driver
« Reply #3 on: May 14, 2013, 09:05:19 AM »
Thanks. I'll take a look tonight.

I am almost positive that the resistors are fine. ordered from mouser, double checked the BOM, and then verified the label when the parts were delivered (I didn't actually verify by measuring or reading the colour code tho)

Even with the LED side "working" there is still squealing/whistling when the gain is raised.

I'll check the transistors tonight.

Thanks

DutchMF

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Re: 2 problems with my ego driver
« Reply #4 on: May 14, 2013, 09:57:15 AM »
This http://www.hobby-hour.com/electronics/resistorcalculator.php might save you a lot of time....  :)

Paul
"If you can't stand the heat, stay away from the soldering iron!"

zilla

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Re: 2 problems with my ego driver
« Reply #5 on: May 14, 2013, 09:14:47 PM »
here's a photo of the board.

re-seated the transistors and it didn't make a difference.  it's not clear, but the flat side of teh transistors faces left on Q1 and right on Q2




jimilee

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Re: 2 problems with my ego driver
« Reply #6 on: May 14, 2013, 09:20:05 PM »
This http://www.hobby-hour.com/electronics/resistorcalculator.php might save you a lot of time....  :)

Paul
That's cool man! There's an awesome app that I use also.
Pedal building is like the opposite of sex.  All the fun stuff happens before you get in the box.

zilla

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Re: 2 problems with my ego driver
« Reply #7 on: May 15, 2013, 11:10:07 PM »