Slambox/ SHO high pitch tone

[Eljee]

Hi,
I build the slambox / SHO. But it produces a constant high pitch tone when powered by an adapter. With a battery there is no high pitch tone. Apart from the high pitch tone the pedal appears to be working correctly.
For all my other pedals this adapter doesn't cause any problem.

I changed the Cap C3 to 100 uF, and tried another BS170, but this is didn't solve my problem.

Any suggestion to make this build work correctly with a power adapter?
Thnx
Leon

[rullywowr]

It may just be that power adapter.  Some adapters are prone to emitting noise (even though it works with your other pedals OK.)  Try another brand/type of adapter and see what happens.

[selfdestroyer]

It may just be that power adapter.  Some adapters are prone to emitting noise (even though it works with your other pedals OK.)  Try another brand/type of adapter and see what happens.

I agree with this also, If you can hook up a battery snap just to test with it will be a good troubleshooting tool to see if its the PSU or the pedal.

[midwayfair]

Very much sounds like power whine.

You can improve the filtering at the power jack by increasing the resistance in the resistor-capacitor low-pass filtering network at the DC jack. You're probably like "What resistor?" Well ... most of the time, we just see a big cap from +9V to ground. Your power supply has a very small amount of resistance, so this forms a low-pass filter with the big cap. An additional 100nF film cap is usually used to filter higher frequencies because apparently film is better at that task than electrolytics. [Edit: there's no cap like this in the slambox, so you could solder it across the DC jack to add some filtering.]

Often, this is good enough, which is why a lot of your pedals work correctly. Sometimes, though, especially in high gain circuits, you need to increase the filtering. You can put a 47R in series with the +9v power and it will filter out more noise. Look at r24 in the mudbunny for an example. If you can still hear the noise -- if it just got higher pitched but didn't go away, use a larger resistor, like 100R. I'm suggesting the resistor in part because going any bigger on your filtering cap might involve a capacitor that's physically too large for the board.

There is a small price to pay for this, probably about a quarter volt, so you could lose a fraction of boost and headroom.

[rullywowr]

That's really useful information, Jon. Thanks!

[Eljee]

Hi Jon / midwayfair

Thanks, the 100 ohm did the trick (didn't had a 47R, but maybe I try two 100R's parallel).
Still weird, because my PSU never caused any problems, even with very high gain pedals. Just finished a devi ever soda meiser and the pedal is dead quiet.

Anyway. I'm happy now. thanks a lot.
Leon