Noise and Mosfet

[kristoffereide]

All builds I've made with mosfets have the same high pitch noise. I'm using bs170's and it's the same noise whatever I build, be it the sho or theROG EA-tremolo. The effects are working like they should, so I don't think they are the wrong way. Any thoughts? Should I order a new batch, or add a DC-filter, or just give up using mosfets???

[DDD]

MOSFETs are noisy by themselves. JFETs like 2SK170BL are low-noise, and you may try them to surprise yourself. 

[kristoffereide]

Yes, however Jfets arent the same as Mosfets

[Cliff Schecht]

The relatively high noise of a MOSFET a "defect" of the MOSFET design. 1/f noise is the most dominant force in a MOSFET under typical linear biasing conditions, but there is also Johnson (thermal) noise from the typically large gate resistors as well as other noise sources. You aren't going to get away from the 1/f noise unless you choose a quieter part or switch technologies completely i.e. JFET's (rebiasing may be required).

The lowest noise JFET that I know of is the U310. I think the noise spec is down in the 1 dB range (1 kHz at about 15 mA quiescent drain current). It's also got a relatively remote pinchoff voltage (2.5 V) and makes a great candidate for a low noise, high gain preamp.

[anchovie]

Do you get the high-pitched noise even when using a battery?

[Cliff Schecht]

Yes, the noise is inherent in the device. But 1/F noise is usually stronger at lower frequencies and so the high-pitch whine may not be what you think it is. There are a lot of other culprits that can introduce noise including bad grounding (weak grounds and star grounds), bad solder joints, misbuilds, etc...

[Joe]

P-channel MOSFETs are less noisy. I did the Obsidian this way and it worked out much better:
http://www.diystompboxes.com/analogalchemy/sch/obsidian.html