falco_femoralis
New member
Hi all, The SB calls for two 2SK3557's for Q1 and Q2. Is there a thru hole alternative? I haven't gotten into surface mount soldering and I want to see if maybe something I have on hand will work instead. Thanks!
Skeptical Boost Q1&2 alts
- Thread starter falco_femoralis
- Start date
falco_femoralis
New member
Going to try out some 2n5457's since they are also N channel J fets
Mr. Strypes
New member
Did it work?
falco_femoralis
New member
I put them in but haven't housed the circuit board yet. Waiting on the chips to arrive
Chuck D. Bones
Circuit Wizard
JFETs are not plug-n-play, even when you have the right part number. Use sockets so you can audition them. I'd like to provide more help, but there are no build docs.
Attention newbies: wait for the Build Docs to be published!
Attention newbies: wait for the Build Docs to be published!
falco_femoralis
New member
Can you elaborate? Comparing the data sheets, they have similar forward voltages. What should I be looking for?
Chuck D. Bones
Circuit Wizard
Welcome to the Pedal PCB Forums.
I think you mean Vgs,off (aka Vp). JFETs do not have a "forward voltage" like BJTs.
The Vgs,off spec for a given part number has a large spread. For example, the Vgs,off range for 2N5457 is -0.5V to -6.0V. I don't know what Vgs,off that circuit needs, but I am 90% confident that if you get one near either end of the spec range, it won't work as intended in that circuit. If you want to know more about using JFETs in pedals, you can read about it here:
https://forum.pedalpcb.com/threads/why-are-jfets-such-a-pain-in-the-ass.4878/
There are other articles in Chucks Boneyard on the topic of biasing JFETs.
I just looked at the 2SK3557 datasheet. The Vp ranges of that and the 2N5457 barely overlap. Their Idss ranges do not overlap at all. Probably not a good sub. Again, I don't have the schematic, so I can't advise you on selecting a JFET.
I think you mean Vgs,off (aka Vp). JFETs do not have a "forward voltage" like BJTs.
The Vgs,off spec for a given part number has a large spread. For example, the Vgs,off range for 2N5457 is -0.5V to -6.0V. I don't know what Vgs,off that circuit needs, but I am 90% confident that if you get one near either end of the spec range, it won't work as intended in that circuit. If you want to know more about using JFETs in pedals, you can read about it here:
https://forum.pedalpcb.com/threads/why-are-jfets-such-a-pain-in-the-ass.4878/
There are other articles in Chucks Boneyard on the topic of biasing JFETs.
I just looked at the 2SK3557 datasheet. The Vp ranges of that and the 2N5457 barely overlap. Their Idss ranges do not overlap at all. Probably not a good sub. Again, I don't have the schematic, so I can't advise you on selecting a JFET.
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falco_femoralis
New member
It's been a minute since compared the data sheets, and tbh I really don't know what values to look for, which is why I asked here. I'll check out the link you posted.
