Aquaticwombat
Member
My friend's dad is convinced it is the greatest distortion of all time. I think he might be a Boston fan.
Upvote
11
COMPLETE Rockman Ultimatum
- Thread starter Aquaticwombat
- Start date
Just to be clear, as I wrap up this mouser order, I only need one 2N4338?
Any other exotic op amps/parts I'll need in hand?
caspercody
Active member
Where did you get a parts list
ICTRock
Well-known member
damn it
Robert
Reverse Engineer
The eventual plan is to be able to select the appropriate resistors for the transistor, so if you already have one hang on to it.
Just don't run out and buy one right now if you haven't already, it might be easier (and cheaper) to sort through a group of more commonly available substitutes.
Just don't run out and buy one right now if you haven't already, it might be easier (and cheaper) to sort through a group of more commonly available substitutes.
Cybercow
Well-known member
While Mouser does have the 2N4338 N-Ch JFET, you may want to take a look at some of the reliable sellers on eBay. Mouser wants 12 bux apiece for the 2N4338. There are some reliable sellers on eBay that have the 2N4338 for about 2 bux each.
EDIT: Note - the 2N4339 is the preferred JFET for Tom's compressor.
Last edited:
Cybercow
Well-known member
Roberman - mind you, while the 2N4339 N-Ch JFET is the preferred type, they come in a wide range of parameters that may or may not work with Tom's compressor (Ultimatum, X100, Soloist, etc). Tom apparently hand-selected them at the build point to match a specific range for Vgs(Off). It seems the magic Vgs(Off) range is very close to -0.90v - plus or minus about 10%
So finding the "magic" JFETs seems to be a matter of hit & miss.
It turns out that there are a few other JFETs that have specs within that golden range . . . .
CPH3910
J201 and
PF5102 to name a few.
Again, hand selection is important.
Pretty sure too that the magic Vgs(Off) range can be extended with careful biasing to reign in those JFETs with specs greater than (I suspect) about ±20% - maybe more. There are more than a few of us researching Tom's magic single N-Ch JFET compressor.
So finding the "magic" JFETs seems to be a matter of hit & miss.
It turns out that there are a few other JFETs that have specs within that golden range . . . .
CPH3910
J201 and
PF5102 to name a few.
Again, hand selection is important.
Pretty sure too that the magic Vgs(Off) range can be extended with careful biasing to reign in those JFETs with specs greater than (I suspect) about ±20% - maybe more. There are more than a few of us researching Tom's magic single N-Ch JFET compressor.
Last edited:
Cybercow
Well-known member
Ack! I need to make a correction! (I've already corrected the JFET type number in my response above.)
The preferred JFET for the compressor is 2N4339 - NOT the 2N4338. The Vgs(Off) parameter spec is vital to properly biasing the JFET for the right compression. The 2N4338 has a Vgs(Off) range at only half that of the 2N4339. So it's questionable that the 2N4338 will properly bias. The sweet-spot Vgs(Off) value is ~ -0.98 ± ~ 12%
I just finished auditing several 2N4339s, 2N4338s, J201s, 2N5457s and FP5102s . . . .
The 2N4338s and 25457s fall well short of the target range.
The other three (2N4339s, J201s and FP5102s) fall directly near the target value and should be easy to bias for the compressor.
Last edited:
JTEX
Well-known member
You might want to consider a surface mount JFET for the compressor. Far cheaper than through hole, and it's probably not too much to ask of people to solder just one 3-pin SMD component (or perhaps you can sell the boards with the JFET pre-selected and pre-soldered). I've had good luck with the batch of MMBTJ202 I bought, but as usual with JFETs, YMMV. To measure and sort them, you might want to invest in a SOT-23 socket (they do exist). The compressor JFET is the one critical part of the whole thing.
Please just get this pedal out there already, so I can stop thinking about whether I should make a Shockman Stomp... I don't want to build pedals anymore, I'm tired of them, but that's what everyone seems to want :/
Robert
Reverse Engineer
The PCB is laid out for SOT23 or TO-92. I have a reel of MMBFJ201's ready to go, considering offering them pre-soldered.
It'll be released this week.
JTEX
Well-known member
Cool! Any chance I can get the traced schematic of the Ultimatum? I love to compare the various Rockman design iterations.The PCB is laid out for SOT23 or TO-92. I have a reel of MMBFJ201's ready to go, considering offering them pre-soldered.
It'll be released this week.
Coda
Well-known member
The PCB is laid out for SOT23 or TO-92. I have a reel of MMBFJ201's ready to go, considering offering them pre-soldered.
It'll be released this week.
Just in time for the Labor Day Sale…womp.
fig
Village Idiot
Groovy!The PCB is laid out for SOT23 or TO-92. I have a reel of MMBFJ201's ready to go, considering offering them pre-soldered.
It'll be released this week.
Robert
Reverse Engineer
I hoped to have everything ready by this past weekend but it didn't quite work out.
Now between the sale, soldering FV-1's, and cleaning up the mess after transitioning the shop site to a new host last week I am absolutely swamped.
I have to clear off some bench space to sprawl out and measure a bunch of JFETs...
Yes of course, give me a bit to get caught up and I'll send it over to you.
