Quick grounding question for Germanium Giant

[blorvak]

Hello everyone! Great site. I've learned tons just by reading through the comment sections. Thanks everyone for such a great resource!

And of course, I have a question. I'm boxing the Germanium Giant: http://tagboardeffects.blogspot.com/search?q=germanium+giant

Does it matter where you ground Volume 1? I have it currently grounded to the DC jack as seen in the Offboard section of the site (along with the board ground). I'm getting no distortion, and a high pitched whine.

I tested the board with my test rig, and had the same high pitched whine, but the pedal worked fine. I was able to audition a few transistors, and bias it. I figured the whine might go away when boxed, as I left the Volume 1 wire unconnected. But now I've connected Volume 1, I suspect I may be missing something very basic.

[PMowdes]

Hey,

It shouldn't make any difference where you ground volume 1.

Which version did you make??  There are three versions, two have a +9v supply and negative Ground, the third is -9V with a positive ground.

Take some hi res photo's and post the up, it's not a complicated build someone should be able to help you if we can see what you've made.

[blorvak]

Thanks for the reply!

I was pretty sure I could ground anywhere, but as I say, I'm new!

I built the PNP version of the Germanium Giant with the onboard inverter. Swallowing my pride and posting pics, even though they show off my very noob skills:





Trimmer was the wrong size, so I had to bend the poles to get it to fit. You'll see a tiny strip of electrical tape under it, to make sure it doesn't touch the link underneath.

I remember reading somewhere on the site that sometimes the inverters can cause squealing. I do have the 7660S, but it did come from eBay.

[PMowdes]

There's no need to worry about what it looks like, I remember what my first builds looked like 12 months ago, and whilst they weren't pretty they worked (and that's the important bit).

What is the transistor??  Looks like an AC128?  The description in the layout specifically says AC125 and AC128's wont work well.

Have you tried different transistors??  I get the impression that you might need to try different ones until you find something that works.

Can you provide a picture of the underside of the board and the rest of the off board wiring (switch etc)

[Travis]

That 1/2W 2k2 resistor looks like it's contacting the enclosure. Is that wired to 9V?

[blorvak]

PMowdes wrote

What is the transistor??  Looks like an AC128?  The description in the layout specifically says AC125 and AC128's wont work well.

Have you tried different transistors??  I get the impression that you might need to try different ones until you find something that works.

It's a GS109C, a German GE transistor. Worked (better) before I boxed and didn't have the ground connected. Also tried a few Russians: MP20A, and GT308. Nothing has changed the high pitched squeal.

PMowdes wrote

Can you provide a picture of the underside of the board and the rest of the off board wiring (switch etc)

Yes indeed! Tricky to take a photo without the solder reflecting, but see if this one is good enough.

[blorvak]

Travis wrote

That 1/2W 2k2 resistor looks like it's contacting the enclosure. Is that wired to 9V?

It is wired to the 9V. Bad angle, however, as it's not touching the enclosure. Just to be sure, I moved it so there was no doubt. Tested, but still generating nothing but squeal.

[Beaker]

I've noticed a potential problem - I'm not saying it is the cause of your squeal issues but you should definately check it out:

Your cuts have very ragged edges on the copper side, where you have drilled right through the board. Carefully check these with a magnifying glass to ensure you have not got a fragment of copper shorting across from one row to another.

If you have, carefully shave it away with the tip of a sharp knife or a scalpel.

[Travis]

Is clean 1 touching the enclosure?

[blorvak]

Finally got some time to get back to this. My wife cannot STAND the squeal this baby makes, so I have to find times when she's not around

Thanks for the tip, Beaker! Took a knife and cut all the jagged edges off the copper in my cuts... my cutting technique could completely stand some tweaks!  While I was at it, I cut between the rows several times. In the end... still had squeal.

Travis, good eye on the pot! As I'm still figuring stuff out with every build, I now know how not to solder to the lugs! I put some electrician's tape under the lugs, and screwed back on.  In the end... still had squeal.

But I had one more thing to try.

AND I FOUND MY NEMESIS!



So, I had just received a brand new shipment of 7660s in the mail, and I figured, what the heck? I'll swap it out.

And it instantly FIXED EVERYTHING.

Pedal works perfectly now. No insane, infernal squeal. Distortion is fantastic.

Lesson learned. Don't buy anything from the eBay seller who sold me the original chips.

Thanks everyone for the help!