loud hiss on a treble knob of a FA-1 clone

[FredG]

Hello diyers,

I've just build this :
http://tagboardeffects.blogspot.com/2012/12/boss-fa-1-fet-preamp.html

Everything works fine, except the treble pot that makes a loud hiss (or whisper, I don't know how to say, a "shhhhhh") more and more loud as I turn this pot forward.
And I have a little bit the same with the volume control, but nothing critical.

The only changes I made is to use a 2N5457 in place of the 2SK246 (I matched the lead to the schematic) and adding a ground wire between Vol1 and Output wires (to go to input jack).

It's been a couple of days that I am looking around the net for some explanations. It seems that it could be several different things (bad grounding, pot too close to a power source, bad pot, etc.). I checked the ground points, they all look ok.
But as I am like John Snow (I know nothing  ) I'd like to see if somebody here can find an obvious mistake I made in the wiring or something else...

Here are some pictures.
Still have to arrange the wires more cleanly, but the hiss stays even with each elements not mounted and away from each other.
A part of the box is in wood.

The treble pot is the one between the diode + switch and the larger pot (volume control)

Thank's a lot for any advice !

[thermionix]

Have you tried powering with a battery?

[FredG]

I just tried and it works perfectly !
Thank's a lot !

But now, I really don't want to use batteries on my pedals, so how do I do ?

Could this kind of thing be a solution ?
https://shop.pedalparts.co.uk/Hum_Stop_-_power_supply_hum_reducer/p847124_6807259.aspx
(Or is it good only for the hum and not the hiss ?)

[ElectricDruid]

I suspect that "hum" filter might work on your "hiss" problem too.

It depends what's causing the hiss, but if you've got a cheap switched mode power supply (of which there are thousands these days) they can generate a lot of high frequency noise. In an audio circuit, these high frequency spikes seem to show up as hiss. They don't *look* like hiss on an oscilloscope, but our ears aren't a high-frequency instrument so it seems to all sound the same in the audio range. Since that filter will do a good job of removing such high frequency noise, I think it might work on your hiss, if that's what's causing it.

It's certainly cheaper than buying a better power supply, so I'd say it's worth an experiment!

HTH,
Tom

[FredG]

Thank's a lot for these explanations ElectricDruid !
I'll give it a try.

What califies a good power supply from a bad one ?
Wich specifications do I have to look for to have the perfect power supply ?

[ElectricDruid]

What califies a good power supply from a bad one ?
Wich specifications do I have to look for to have the perfect power supply ?

For pedals or audio in general, I'd say you just look for one that's been designed for that purpose. There are probably 9V supplies that run baby monitors, but you might find them pretty terrible plugged into your pedals. Audio/Pedal power supplies are designed to have low ripple (=less hum) and low noise (=less hiss). For many applications, these things don't really matter a great deal, and so the power supplies can have a much lower specification.

HTH,
Tom