Need Help with Modified LaVache - Power Supply Filtering Issue?

[jasonstomps]

Hi,

So I recently made some mods to a LaVache pedal, really I just put the gain pot on a foot switch so I could toggle between a cleaned up sound and full dirt.  The other thing I did was add two extra LED status indicators for the gain foot switch and for the boost foot switch.  For the two new LEDs I just ran two additional leads from the power rail to 4.7k resistors connected to each LED.  So in total, the pedal has 3 LEDs.  

Now I noticed that I'm getting a "ssss" sound when the pedal is engaged.  I probed around and I think I pinned down the root cause to power supply noise.  I get the same "ssss" where R3 (3k3) connects to the transistor as I do if the audio probe is connected directly to the power rail.  I checked the connections and the resistance of R3 and everything checks out normal.  

So I'm wondering if the addition of the two extra LEDs messed with the power filtering?  And if so, would changing the value of C4 or C5 fix it?

Thanks

[jasonstomps]

I forgot to mention that this was on old LV that I did on vero.  I think this image might clarify what I mentioned about the power to the LEDs.

[stecykmi]

it seems unlikely that additional LED's would cause noise like that. Try running the pedal off a battery temporarily to see if the hiss goes away (since batteries are much less noisy than a power supply). If it doesn't, I would chalk it up to RF interference or some other noise (try turning off nearby lights).

[jasonstomps]

Thanks.  After a bunch of debugging I'm chalking it up to the nature of how the pedal handles input signal.  I didn't think it was being affected by the gain pot, but it is.  As I turn up the gain pot the hiss gets quieter, even with no audio signal being played.  It does the same thing when I bypass the gain pot and turn down the volume pot on my guitar.

[stecykmi]

hmm strange. double check all your ground and power connection for good solid connectivity. is there any change when the boost is engaged?

try grounding the input, then check again for the hiss.

[midwayfair]

hmm strange. double check all your ground and power connection for good solid connectivity. is there any change when the boost is engaged?

try grounding the input, then check again for the hiss.

Mine does the same thing. It's not a loud hiss or anything, it's just faint white noise when the gain pot drops below a certain point and there's nothing else going on. I've heard it in demos, too.

[jasonstomps]

Stecykmi, I checked all the grounds on the Input, Output, Vero and on the Gain pot and they were all good.  I made a stupid mistake while testing that amplified the hiss more than normal.  As Midwayfair mentioned, the little white noise comes out as you dial back on input signal, and when I was testing things out I didn't realize I already had my guitar volume pulled back some.  So the hiss was being brought out more than it normally would. 

Midwayfair, turns out you were right.  It's totally not a loud hiss when my guitar is at full volume.  It actually reminds me of the white noise from my fender champ...making the pedal even more Fender like.


Thank you both for your help.

I boxed everything up last night and I'm pretty happy with it.