New at runoffgroove.com: Professor Tweed

[Gringo]

Hey keko, i still have operational my "fet gainstage comparison jig". I'll run an A/B test between mpf102/2n5457 in it and see what happens.

[Ed G.]

I breadboarded the Prof. and initially had some trouble getting the fets to bias right. I did a search and came across the thunderchief thread, what with the 10k source resistors and all. I tried an 8.2k resistor and was able to bias to 4.5V.
Using that method, will it affect the gain or tone of the fet, or should it operate the same? The reason I ask is that it sounds like it could use a little bit "tightening up" in the bass range.
I'm going to reserve judgment until I can get all the parts and build it per the schematic. I only had (1) 1 meg pot, so I used it on the drive pot, but the tone pot is using a 500K pot now, so I'm not getting a full range from the tone control. Also, I need another .002 cap for the filtering on the end.

[B Tremblay]

What FETs are you using?  Just to clarify, you used 8k2 source resistors rather than the stock values?

I measured drain resistance around 2k5 when using 2N5457.

[Ed G.]

What FETs are you using?  Just to clarify, you used 8k2 source resistors rather than the stock values?

I measured drain resistance around 2k5 when using 2N5457.

8k2, 8.2k, that's it. I didn't have 10K. I'm using MPF102 from Rat Shack. They only had 2, I used a J201 in the first position, maybe the MPF102 would sound 'tighter'???
Like I said, I need the right tone pot and output cap, so I can't really comment on it until it's built right. THose sound clips sound damn fine, so it should sound real nice.

[Gary]

Ed,

You used 8k2 source resistors?  I don't recall 10k being used on the sources.  I would say you would need to adjust the bypass cap sizes on each resistor you changed.  It will affect the tone, but maybe only minimally.  4.7uF (for the 22uF caps) should be very close if you used 8k2 source resistors.

The best way to tighten up the sound would be to decrease the final drain cap slightly.  Maybe try a 15n or something like that.  The MPF102s sound brighter and are perhaps a little tighter.  You may want to try that, if you get the chance.  If all else fails, reduce that last drain cap.

[Lonestarjohnny]

Gary, can I use a J-201 and 2- 2N5614's or would the 14's be to high gain for this app?
Thank's, JD

[B Tremblay]

I just looked up the 2N5614 and it seems to be an NPN transistor.  Is that the correct part number?

[Lonestarjohnny]

Sorry Mr B.  :oops:
I'm still a sleep :shock: , worked on building the circuit late last night, got it about ready, the correct # would be a 2n5416, these are in a metal can, and i looked the data sheet up from fairchild.
JD

[B Tremblay]

2N5416 seems to be a PNP transistor...

[Lonestarjohnny]

Thank's Mr B, Looks like I need to go shoppin, I don't got a single fet layin around, I was hopin to try this thing out today, but I gotta go haul some resistors I just scored, I should have enough 1/4 watt resistor's here by days end to supply the state of Texas ! LOL.
JD

[guitarzan25]

okay so what does a newbie do with this stuff? I'm in a 12-step support group to exorcise the demons left over from my Vetta days and have been prescribed daily doses of my TopHat and boutique stompboxes. BUT, the fact remains that a pedal like "the prof" seems to be just what the doctor ordered for OD number 3 or 4 and I'm somewhat of a newbie in the DIY world. Any advise from the gearheads for someone who is 10 parts enthusiasm and 1 part experience?


thanks a bunch.

[Lonestarjohnny]

Go over to the Newbie page and build the clean boost pedal there, it's a great addition to my pedal board and I'm glad I built it,There's a bunch of talented people here that will help you get started, I'm on my fourth pedal build now and Have the fever for a few more :twisted:
JD

[guitarzan25]

I have built one pedal and just got a shipment from small bear today for my D. A. Orange Squeezer clone- I think the thing that is different about The Prof, though, is that those builds had parts layouts that held a newbie's hand. This one is a schematic and nothing more. For me, the breakdown is the space between the schematic and the parts layout diagram. I just can't visualize the board yet.

[george]

There is a veroboard layout for the Professor (and a no. of other projects) on runoffgroove ....?

[guitarzan25]

uh... yup.... there sure is. so if I scroll down on these web pages there's more words and pictures, huh? :oops:

i'm an idiot. thanks much.

[Lonestarjohnny]

Hey Guitarzan,

Your no worse off than the rest of us newb's here, I get so excited I get lost just tryin to get the parts rounded up,  :? But there are a lot of great guy's on here that'll help you get it right,
JD

[guitarzan25]

yeah, i know what you're saying. i've been online all morning trying to figure out why small bear elec won't sell a 4.7uf cap. I'm assuming they HAVE to sell it, I just don't know which of the caps with a 4 and a 7 in the rating are right. (I found it, by the way, at Radio Shack just now when they opened...) I want so badly to build this prof tweed (and now the matchbox too) but there's such a communication gap between what I can see in pictures and what I can actually own as personal knowledge and understanding. the learning curve is pretty steep.

[Fret Wire]

yeah, i know what you're saying. i've been online all morning trying to figure out why small bear elec won't sell a 4.7uf cap. I'm assuming they HAVE to sell it, I just don't know which of the caps with a 4 and a 7 in the rating are right. (I found it, by the way, at Radio Shack just now when they opened...) I want so badly to build this prof tweed (and now the matchbox too) but there's such a communication gap between what I can see in pictures and what I can actually own as personal knowledge and understanding. the learning curve is pretty steep.

Don't feel too bad, it can get confusing when cap values are posted in other than uf. Here's a little conversion chart to help:

http://www.justradios.com/uFnFpF.html

http://www.clintology.com/capacitor/

I have a chart printed up, and keep it right at the bench when I'm working.

[Phorhas]

The Fetzer will probably behave Jfet Smooth, once it's wired correctly.
The Rangemaster thing...not quite so fast, you might want to work with this one for a time er two.
Messing with bias, trying out different transistors helps find stable bias and tone.
These boosters are good fun stages to have around and experiment with. 1 2 3...Distortion, you can always separate them if they're not getting along, two on one board usually do ok.
Problem is with a PNP, it's meant extra battery for me.

Well, I've done a bunch of experiments with the RM (and there are alot more infront of me... with that little devil) and I've found that to MY ear an NPN AC187c sound great... meety and grouly like... plenty delicious when dirivung my beloved Classic 30...

I guess only testing will tell... onwards to the breadboard!!! I'll give that RM->Fetser->MiniB a shoot can't hurt (only to my neighbours)

[Lonestarjohnny]

finished my perfboard build of the Professor today, got it all wired out with LED, Total Bypass, mounted in a DOD empty pedal somebody gave me, hooked it up to my Peavey classic 50, I figured this was an ultimate test for the pedal, and to my suprise I got a nice clean Fender tone that has that Feelin Better, Birds jangly type sound, cranked up it has a great tweed tone, I ended up using the 2 MPF 102's and a 2N5457, all drains biased out at 4.5 volt's and the sources were all at or about 1 volt, all gates at zero, this is a neat pedal and I'm glad for the chance to build it, now to get it stripped and painted,
Thank's to the guy's at Runoff,
JD :lol: