2 problems with my ego driver

[zilla]

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]

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

[madbean]

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).

[zilla]

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]

This http://www.hobby-hour.com/electronics/resistorcalculator.php might save you a lot of time.... 

Paul

[zilla]

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]

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.

[zilla]

one thing i forgot - it may or may not be relevant..  I used a 1N270 in place of the 1n34a

http://ca.mouser.com/Search/ProductDetail.aspx?R=1N270virtualkey52600000virtualkey526-1N270

i will try replacing it with a 1N60

http://ca.mouser.com/Search/ProductDetail.aspx?R=1N6002B-TPvirtualkey54720000virtualkey833-1N6002B-TP