I've been building a few pedals which call for BS170s lately and I've experimented with using 2N7000s because every pedal i have built with BS170s has sounded a little harsh in the high end.
Take the Box of Rock (or '59 Sound) for example. I can't quite put my finger on it but the original circuit has always sounded great but also slightly fatiguing to me. So far I'm finding the 2N7000 similar but maybe a little smoother. I believe it is less powerful - maybe that's why? I have experienced similar issues with other pedals using the BS170 - a kind of brutal, harsh high end which gets wearing after a while. Is it just me?? Is it a mosfet thing?
Any opinions/actual scientific observations are welcome! It's ok if you think I am crazy too!
Some people are like that princess who can feal a pea underneath a whole stack of matrasses, and I'm in the other camp, to me they all sound the same. Which I think also applies to most dirt boxes, especially overdrives. Maybe when you just built one you're superstoked about it, cause its new, but eventually that wears off. And then the only thing I care about is will it cut through a mix or not.
Also one man's harsh is another man's clarity and one man's warmth is another man's muddy. Maybe more so once you get older and your hearing in the high frequencies starts to suffer. Even more so after a life time of being subjected to high volume doesn't exactly help either.
I certainly see where you are coming from. With all the loud music I have been exposed to over the years I shouldn't be able to hear a lot of the frequencies i still can. Life is unfair, eh? I don't believe in mojo but I do believe good sound. :-)
The 2n7000 and bs170 do have opposite pinouts, so remember that if you're swapping them. The datasheets indicate that they have identical specs, but manufacturing tolerances being what they are it's possible that one brand may sound slightly different than another.
I remember than the first time i've tried the BS170 (it was in a sho) I was impressioned by the power, but with the time I fund there was something unpleasant in the sound. I don't have yet tried the2n7000 but Ioften choose the j201 for the sweetness when the gain isn't crucial.
Okay, I'm pretty new to building, and haven't heard either of these transistors, but I think I may have found some relevant info on this. Comparing the datasheets for the two devices from the same manufacturer (ON Semiconductor), all the specs in the tables seem very close if not dead-on, but looking at the graphs is showing me something not in the numbers. In this image, the 2n7000, on the left, seems to be pulling a lot more current, drain to source. If we follow the 5.0 V gate to source curve (a lot of pedals seem to be biased at 4.5), the 7000 is leveling off at more than 750 mA, compared with around 500 on the BS170. As I said, I'm certainly no expert on datasheets and such, and I do find this graph a little puzzling for a device with an absolute max current rating of 500mA, but if the 7000 is truly drawing 50% more current, it would probably be more linear and sound less harsh in a power amp config than the BS. IDK if this matters, but the 7000 also has a built-in diode, I think for ESD protection.
Oddly enough, I'm only considering it for a Millennium Bypass circuit, so it won't be in my signal chain anyway.
I only built them back in the day because they were a lot cheaper together with DPDT switches then 3PDT switches. And that was with J201's for the transistor. Nowadays even good 3PDT switches are cheap to be had, let alone a single genuine J201. And the only reason to use anything else then a 3PDT switch is to use a relay switch for better low noise switching.