DIYstompboxes.com

DIY Stompboxes => Building your own stompbox => Topic started by: B Tremblay on May 03, 2004, 01:27:54 PM

Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 03, 2004, 01:27:54 PM
The Professor Tweed is a FET emulation of the Fender Princeton amp.  Check it out!

Article, schematic, and perfboard layout: http://runoffgroove.com/professor.html
Sound clips:  http://runoffgroove.com/salvo.html#professor
Title: New at runoffgroove.com: Professor Tweed
Post by: puretube on May 03, 2004, 01:37:19 PM
wow! a new record in the C/W *  score !

[* : Circuits per Week]
Title: New at runoffgroove.com: Professor Tweed
Post by: Mark Hammer on May 03, 2004, 01:52:51 PM
Okay, now yer pushin my buttons, Tremblay!!!

As the proud owner of a 5F2-A since 1976, my sense of identity is challenged by the notion that 3 FETs could replace this marvel of glass and iron (and tweed).  Now I'm gonna have to put them to the test.

One thing I am glad to see, though is the implementation of the one-knob tone control which many of those whose viewing of schematics is limited to effects may not be familiar with.

Imagine the following.  Imagine the wiper (2) has been rotated fully so that it rests at point 3.  What you have there is a volume control with a treble bypass cap (470pf) and a treble bleed cap (4n7) with a 1meg resistor in series (severely restricting treble bleed).  As you start to rotate the knob, the resistance in series with the 470pf treble bypass cap increases at the same time as the resistance in series with the treble bleed cap decreases.  So the one knob adjusts treble boost and treble cut at the same time.  Pretty neat, huh?  The thing to remember is that, like all treble bypass caps on volume controls, its effect interacts with the volume control setting.  The lower the volume setting, the more impact the treble bypass has.  As you turn the volume up, you need to turn down the tone more and more to notice any audible change from having the tone full up.  On the one hand, the interdependent nature makes more work for the player/user.  On the other hand, it means a lot more interactivity.  Since this designs also includes a master volume (which my little tweed baby doesn't), the flexibility aspect wins hands down over the inconvenience

I might point out that my 5F2-A, as well as being fabulous for blues guitar,  is one of the finest harmonica amplifiers I have ever heard.  One harp player I jammed with years ago had a complicated setup with the requisite bullet mic and a Twin.  I suggested he plug into mine and it was like we had been instantly beamed to Pepper's Lounge.  In his words "You're not leaving here with that amp tonight".  So, if it emulates as well as you hope this may well be an interesting project for those harp players who want a little box that will make them sound like "instant Chicago".  Who knows, you may not even need your bullet mic anymore. :D
Title: New at runoffgroove.com: Professor Tweed
Post by: Gary on May 03, 2004, 03:09:35 PM
I wouldn't lay down that bullet mic, yet!  I'll be looking for a report of the pros/cons.

I've seen one of these amps and the guy that owned it refused to let me touch it!  Oddly enough, he was a harp player.  He owns a few Valcos, too.
Title: New at runoffgroove.com: Professor Tweed
Post by: Marcos - Munky on May 03, 2004, 03:22:49 PM
Cool, another circuit!!!
Title: New at runoffgroove.com: Professor Tweed
Post by: koolimy on May 03, 2004, 03:23:29 PM
Wow... You guys are posting up new stuff like crazy now... :o
I remember that the Matchbox came out not too long ago...
Title: New at runoffgroove.com: Professor Tweed
Post by: Gary on May 03, 2004, 03:36:45 PM
Last week was the Matchbox.  Since the Matchbox seems to be a slow burner (pun), we put the Professor out for those that don't have access to J201 fets.
Title: New at runoffgroove.com: Professor Tweed
Post by: Mark Hammer on May 03, 2004, 03:52:49 PM
I might point out that on a real 5F2-A. lifting the negative feedback resistor (22k) puts one squarely into the icepick through the forehead tone-zone.  Does the negative feedback have the same roll here, that of keeping the harmonic distortion in check?  If so then some sort of variable, or at least switchable (e.g., 22k / 100k / 500k)  resistance there would be a worthwhile mod.  

You will note as well, that the locus of traditional "presence" controls was in a parallel RC network alongside the 1k5 resistor on Q2.  The 22k feedback resistor and 1k5 resistor (well, its equivalent, actually) served as a voltage divider for the feedback signal.  A variable resistor in series with a cap would set a differential amount of feedback (i.e., attenuation of the feedback signal from the output transformer) for the higher-frequency content so that there would be more and/or less feedback for the high-end.  With less negative feedback, all the added grit to the signal would be cancelled and the amp would sound cleaner.  One of the reasons why early amps without the negative feedback, or with the ability to adjust the amount of negative feedback are desirable and sound so great.
Title: New at runoffgroove.com: Professor Tweed
Post by: puretube on May 03, 2004, 03:58:44 PM
Quote
"instant Chicago"

would be a very nice name for a new pedal...
(with an equivalent sound, i.e.)
Title: New at runoffgroove.com: Professor Tweed
Post by: Mark Hammer on May 03, 2004, 04:23:10 PM
... as opposed to an early Liverpool emulator called the "Instant Hamburg"?  :lol:
Title: New at runoffgroove.com: Professor Tweed
Post by: puretube on May 03, 2004, 04:32:52 PM
you mean: "The Beatler" ?

(rather a name for a starkey rhythm ace...)
Title: New at runoffgroove.com: Professor Tweed
Post by: Gary on May 03, 2004, 04:51:01 PM
Mark,

Lifting the 22k does drive the distortion way up.  We omitted the "presence" setup since it seemed a bit redundant.  The value of the coupling cap (10n) on the feedback loop makes a huge difference and you can indeed tune the feedback via this cap.  It seems to do exactly as you mention.  I highly recommend playing with this cap's value, as the effects are very noticeable.  10n got the nod from both of us, so that's what we've stated as the "stock" setup.  As you work up through the values from, say 10n to 1 micro, you'll hear the diffrences.  As always, breadboard this circuit before you build.  If you work up something different with the source side of the second jfet that sounds more like the real thing, let us know.  I'm dying to know how close this thing is to the real deal.  Having only heard one of these amps once, we kinda shot for a conglomeration of tweed tone.  Please tell us how far off we are.

BTW, I guess "instant Chicago" is much better than "instant Air Supply!"
Title: New at runoffgroove.com: Professor Tweed
Post by: Gringo on May 03, 2004, 04:56:23 PM
Wow, do you people at ROG actually sleep?

Another one that goes to the (almost endless) build list :D
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 03, 2004, 05:21:38 PM
Mr B.
You guys are cookin the Midnight oil at Runoff, I just put the finish on my Sili-Face, tried it out with a Gibson GA-5, It work's like Gangbuster's for sure, It's a nice addition to my board, now I know what my next build's gonna be, where's my J201's, :D
JD
Title: New at runoffgroove.com: Professor Tweed
Post by: Bucksears on May 03, 2004, 09:20:40 PM
You's guys are fryin' my brains ova heah!!!! I'm OD'ing on OD's!!!!
Man, my 'to do' list is growing by leaps and bounds.
The Matchbox and the Professor would pretty much round out my versatility of OD's and distortions.
Top notch work guys!!
Title: New at runoffgroove.com: Professor Tweed
Post by: Ed G. on May 03, 2004, 09:24:04 PM
Hah! I thought woodshedding was in my future. WRONG! I'm breaking out the breadboard as I type (well, not exactly this moment, but...)

Seriously, those sound clips sound fantastic.

One question: Does the tone control give a wide range from bright to dark? (I suspect it does) because playing a strat through a super reverb, I find a lot of pedals too bright/harsh. I always have to add extra tone filtering and I don't usually like the end results.
Title: New at runoffgroove.com: Professor Tweed
Post by: RedHouse on May 03, 2004, 10:20:30 PM
Wow that actually did sound Fender'ish, I'm impressed.

Ok then, it's time to dust off the good'ol 2204 schematic and see if that can be done.

Any thoughts on how to implement a CF with the FET's?
Title: New at runoffgroove.com: Professor Tweed
Post by: Ed G. on May 03, 2004, 11:28:17 PM
The BSIAB and Doug's "Sweet Thing" series of pedals use a fet as a source follower. Try that.
Title: New at runoffgroove.com: Professor Tweed
Post by: puretube on May 04, 2004, 02:51:41 AM
imho a presence control plays its best role, when deriving the F.B. signal from the actual power output at the speaker...
Title: New at runoffgroove.com: Professor Tweed
Post by: bwanasonic on May 04, 2004, 03:14:56 AM
Quote from: Gary

BTW, I guess "instant Chicago" is much better than "instant Air Supply!"


Is there a pedal that does "intant Poughkeepise" ? That,  and "instant Idaho" , are the tones I've been searching for.

Kerry M
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 04, 2004, 07:10:19 AM
Quote from: Ed G.
One question: Does the tone control give a wide range from bright to dark? (I suspect it does) because playing a strat through a super reverb, I find a lot of pedals too bright/harsh. I always have to add extra tone filtering and I don't usually like the end results.


I used a Tele bridge pup extensively when we were developing/testing the Professor and found the Tone control to have a very useful range.  At the lowest Tone setting the punch is still present, but much smoother than the usual twang.  The treble bleed cap preserves brightness at the low gain settings as Mark Hammer described earlier, so it doesn't get really dark when playing clean.
Title: New at runoffgroove.com: Professor Tweed
Post by: Mark Hammer on May 04, 2004, 10:01:47 AM
Quote from: puretube
imho a presence control plays its best role, when deriving the F.B. signal from the actual power output at the speaker...


I certainly can't speak from experience, but I would lean towards your view, if only because the output transformer and speaker play a factor in what it is that is being fed back through the loop.

As to the properties of the tone control, call me crazy, but in the 28 years that this has been my main amp, I can't think of many times where I found the tone control a shortcoming on how I wanted to sound.  Indeed, sometimes I wonder if the pot hasn't rusted in place because I simply don't move it most of the time.  On the other hand, I'm the sort of guy who likes to have more flexibility in tonal control on the guitar itself, and via pedals.

Still, that being said, there have probably been a number of FET-based projects posted, involving mu-amps or other topographies, where insertion of a tone control like this around a gain/attenuation pot earlier in the circuit might be interesting and worthwhile pursuing, particularly insomuch as it permits for variable treble accentuation at lower drive settings.
Title: New at runoffgroove.com: Professor Tweed
Post by: RDV on May 04, 2004, 10:11:48 AM
Yes. I'd like to place an order please? I'd like a one of your lovely J-Fet simulations please? One of my Supro "Super".

Here's the schem file(thank you schematic heaven!):
http://www1.korksoft.com/%7Eschem/bargainbin/gretsch6150.pdf

Please & Thank You!

RDV
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 04, 2004, 10:38:23 AM
Quote from: RDV
Yes. I'd like to place an order please? I'd like a one of your lovely J-Fet simulations please? One of my Supro "Super"


The coolest feature of Doug's method is the ease of converting to FETs.  Read the Professor Tweed article for the technique.

Take a stab at it on your own and if you get stuck, we'll help you out.
Title: New at runoffgroove.com: Professor Tweed
Post by: Doug H on May 04, 2004, 11:03:05 AM
Well, this isn't really "my method" or anything but I appreciate all the kudos guys. :D  I was inspired by Jack's use of the minibooster with the mini-tubes, as well as his use of JFETs in the Fet-Muff, and Brian Mena's work among others.  In all honesty the Meteor was a hack, just a brute-force approach of blindly subbing fets in a tube circuit (at 9v) to see what would happen.

My only comment about the NFB loop is I would think you would take it from the "speaker" (your output LPF).

But man, that sure sounds tweedy! I have some soundclips of a strat through a 5E3 and hear some similarities.

Nice work!

Doug
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 04, 2004, 11:08:20 AM
Regarding Supro amps, I should probably mention that we've already developed a terrific-sounding FET emulation of my Supro 16T, which is not too different from the Super.

We've been debating whether to release it; we don't want to be over-saturating the market with emulations, especially since the 16T and Princeton amps share a similar circuit and tone.

Our goal is not to be the leaders in the FET emulation field, but rather to help teach the technique to the DIY-FX community with examples such as the Thunderchief, Matchbox, Fetzer Valve, and Professor Tweed.
Title: New at runoffgroove.com: Professor Tweed
Post by: puretube on May 04, 2004, 11:15:04 AM
wanna know a secret?
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 04, 2004, 11:15:51 AM
Quote from: Doug H
Well, this isn't really "my method" or anything but I appreciate all the kudos guys.


They're quite well deserved, since your "brute force" approach just happens to work beautifully!

I hope that more people will apply the technique to the vast number of tube amp schematics now available on the web.  Creating a pedal version of a favorite amp (or using various stages from different circuits to develop an original design) is much less mysterious and daunting thanks to your work.
Title: New at runoffgroove.com: Professor Tweed
Post by: Ed G. on May 04, 2004, 11:33:37 AM
hmm...can you say Dumble???
Title: New at runoffgroove.com: Professor Tweed
Post by: RDV on May 04, 2004, 11:36:37 AM
Quote from: puretube
wanna know a secret?
YES!

RDV
Title: New at runoffgroove.com: Professor Tweed
Post by: Phorhas on May 04, 2004, 12:21:43 PM
mmmm... Dumble...

I had an Idea: take a range master and stick it before a fetser-valve type thingy right to a mini-booster type thingy... to emulate an over-driven-amp-with-a-hot-pocker-stuck-up-it's-*ss...

Blues Braeker ClapTone?

Well, what ya say? I'm so busy right now so I can't seem to find the time and check it out... if it tickles anybody's fancy, be my guess...I wonder what that will sound like...
Title: Probly pretty coool..
Post by: petemoore on May 04, 2004, 01:56:28 PM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Gary on May 04, 2004, 01:57:40 PM
Quote from: Ed G.
hmm...can you say Dumble???


Ed,

We worked out a draft for the '97 Dumble ODS and an earlier '70s model.  There's a lot of jfets in there and it will require a bigger board, but I'd love to see if you take it somewhere.  I don't think we ever breadboarded it.  Since these things seem to work right off the bat, I'll bet you can get it going.  Please let us know if you do.

puretube,
What is that secret?  The curiosity is killing me.

On the subject of where the feedback loop is taken from, I tend to like the sound better if the feedback is taken from the last coupling cap.  For some reason, it seems more "lively" than going straight from the drain.  As Doug says, you can go from just infront of the master volume control.  That setup seems to sound a little thicker to me, which can be good.  We've stuck with tapping from the output side of the last drain cap for no particular reason.  There is a lot of room for experimeting here, as you are crudely trying to emulate the output transformer and the effect of the speaker(s).  There are arguments that can be made for taking the tap from just about anywhere.
Title: New at runoffgroove.com: Professor Tweed
Post by: Doug H on May 04, 2004, 02:38:00 PM
Quote from: Phorhas
mmmm... Dumble...

I had an Idea: take a range master and stick it before a fetser-valve type thingy right to a mini-booster type thingy... to emulate an over-driven-amp-with-a-hot-pocker-stuck-up-it's-*ss...

Blues Braeker ClapTone?

Well, what ya say? I'm so busy right now so I can't seem to find the time and check it out... if it tickles anybody's fancy, be my guess...I wonder what that will sound like...


3-4 yrs ago there was a diy-er that designed a pedal with a si rangemaster driving a couple miniboosters. The web site is gone and I can't remember the name of it but it had the word "ballz" in it.  That's all I remember, I used to have the schem but I don't think I do anymore. Anyway, he had a few sound clips and it sounded pretty nice from what I remember.

Doug
Title: New at runoffgroove.com: Professor Tweed
Post by: Mark Hammer on May 04, 2004, 02:58:46 PM
T'wer the Ballz Booster by Alexandro Charissis, and I'm looking at it right now.
Title: New at runoffgroove.com: Professor Tweed
Post by: Doug H on May 04, 2004, 03:34:45 PM
Quote from: Mark Hammer
T'wer the Ballz Booster by Alexandro Charissis, and I'm looking at it right now.


That's it!

Doug
Title: New at runoffgroove.com: Professor Tweed
Post by: Johan on May 04, 2004, 04:13:52 PM
this method seems very interesting, perhaps I should make a version of MY favorite amp..Orange Graphic-80 ( think early AC-DC )
I remember seeing a schematic for Trace-Elliot a few years ago doing it this way to make an amp with two channels, Marshall and Fender style. I didnt reflect on it then, but obviusly I should have... allthou they run their amp at 24volts ( I think ), the aproach was very simillar.
I think the trace amp was called either Speed-twinn or trident..I also think I have the schematic at work...

Johan
Title: New at runoffgroove.com: Professor Tweed
Post by: keko on May 05, 2004, 02:38:37 AM
All around the article you talk about using MPF102´s.

How does it compares to 2N5457? They are the only ones I've got around, so, is it worth it building it with those and only those in mind?

Great release...again!
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 05, 2004, 06:35:17 AM
Quote from: keko
How does it compares to 2N5457? They are the only ones I've got around, so, is it worth it building it with those and only those in mind?


The circuit has been tested with 2N5457 and the results were quite close to using MPF102.
Title: New at runoffgroove.com: Professor Tweed
Post by: Torchy on May 05, 2004, 07:13:23 AM
While on the subject of "pet" amps, anyone got/investigated the Hughes&Kettner Tri-Amp ??

Saw it demo'd by a guy called Thomas Blug (?) and sounded awesome ...
Title: New at runoffgroove.com: Professor Tweed
Post by: Gringo on May 05, 2004, 08:14:06 AM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Ed G. on May 05, 2004, 10:20:51 AM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 05, 2004, 10:36:59 AM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Ed G. on May 05, 2004, 10:56:26 AM
Quote from: 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.


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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Gary on May 05, 2004, 11:27:36 AM
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.
Title: Q1 Q2 Q3 ?
Post by: Lonestarjohnny on May 05, 2004, 12:58:27 PM
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
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 05, 2004, 01:02:13 PM
I just looked up the 2N5614 and it seems to be an NPN transistor.  Is that the correct part number?
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 05, 2004, 01:10:55 PM
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
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 05, 2004, 01:17:10 PM
2N5416 seems to be a PNP transistor...
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 05, 2004, 02:00:30 PM
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
Title: New at runoffgroove.com: Professor Tweed
Post by: guitarzan25 on May 05, 2004, 05:52:24 PM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 05, 2004, 05:57:59 PM
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
Title: New at runoffgroove.com: Professor Tweed
Post by: guitarzan25 on May 05, 2004, 06:17:37 PM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: george on May 05, 2004, 11:06:53 PM
There is a veroboard layout for the Professor (and a no. of other projects) on runoffgroove ....?
Title: New at runoffgroove.com: Professor Tweed
Post by: guitarzan25 on May 06, 2004, 12:29:45 PM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 06, 2004, 01:16:45 PM
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
Title: New at runoffgroove.com: Professor Tweed
Post by: guitarzan25 on May 06, 2004, 01:28:40 PM
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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Fret Wire on May 06, 2004, 01:34:06 PM
Quote from: 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.


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.
Title: New at runoffgroove.com: Professor Tweed
Post by: Phorhas on May 07, 2004, 08:28:15 AM
Quote
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)
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 17, 2004, 01:00:18 AM
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:  :D
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 17, 2004, 06:28:17 AM
Thanks for the report!  I'm glad that you're enjoying it.
Title: Perfing from Schem...
Post by: petemoore on May 17, 2004, 09:20:45 AM
Most sections of any perf on a schematic, will have something in common with already available perf builds layouts...
  Transistors...I simply follow the schematic's general layout, adding a space here and there for buildability and access.
  Opamps is where I really like to leave some space around the IC socket. These can get tight real quick if spaces around the IC socket are not provided.
  Get the schematic, and the perfboard template printout [at Runoff Groove], that way you can try drafts of your layout on paper.
  I have not too much troubles anymore builing 'freehand' on perf from the schematic, just by following the simple rules laid out above^.
  When I see a really tight spot, or if I need a cramped layout, I use 'upright' resistors [these only take two adjacent holes of perf spacing],  or make above board connections.
  Leaving enough lead above the board for the DMM's probe to touch it, is, IMO, a very good way to make debugging a whole lot easier...
  If youre like me, ..Use alot of sockets for certain voicing and active components. A specific Schematic is easier to refer to...
Title: New at runoffgroove.com: Professor Tweed
Post by: Gilles C on May 17, 2004, 09:46:49 AM
"especially for blues playing."

Hey, how can I resist.

I'm still trying to find some time to build something, that you come up with something else...

Now it's really time for me to remember where I put the few J201s I had left from my other projects... unless I decide to steal them from a few pcbs that never got their place in my collection of effects.  :twisted:

Btw, do any of you know the Crate V15 tube amp?

I could have a good deal on one (for a 2nd amp, when I don't want to use my 40W Hot Rod Deluxe), and a Fender Princeton sim could give him back  some Blues tone.
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 17, 2004, 12:48:27 PM
Rickey, the perf Board is a lot of fun for me, I use a lot of socket's also, makes it easy to get the voicing to sound right for the amp I choose to play it through.
Hey Gilles, that Crate is built better on the inside than most of the new amp's that are mass produced, you can get yourself a nice Vox Chime outa that amp with the right tube selection and some tuning on the circuit.
JD
Title: New at runoffgroove.com: Professor Tweed
Post by: Gilles C on May 17, 2004, 02:44:56 PM
Thanks JD,

You answered 2 of my questions:

1st, >>built better on the inside than most of the new amp's that are mass produced<<<

That's how it look from the outside...

2nd, >>you can get yourself a nice Vox Chime <<<

That's what I thought, because of the design. I am also hopping for some crunchy Marshall vibes...

Now, the only thing left to discover is: is it loud enough to be useable.

Gilles
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 17, 2004, 03:42:21 PM
Yes to both count's, if you like more of a marshall crunch, try a ecc 83 as your first preamp tube, it'll darken and compress more like a marshall.
JD
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 17, 2004, 08:14:01 PM
mr B or Gary,
On your Schem. of the Prof. you show a 1 uf axial cap that is pointed towards the source of Q2, then on the layout you show it pointed towards the 22n cap hooked to the drain of Q3, which way do it go ? I hoping you say it would be pointed at the 22K resistor hooked to Q2's source. I also ended up useing 5K trim pot's, seem's like all my MPF 102's biased at or about 3 K.
Thank's,
JD
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 17, 2004, 09:32:28 PM
The schematic shows the correct orientation.  I'll update the layout shortly.
Title: New at runoffgroove.com: Professor Tweed
Post by: Lonestarjohnny on May 19, 2004, 11:58:16 PM
Mr B. or Gary,
I have finally figured out { NOT to get in a Hurry} Biasing these Jfets until they have had voltage applied for several min's, I like Ed had problem's on biasing the Q2 on the Professor,
After change'in the 100k trim pot's out for 10k's I was starting to get a Lil worried that I had screwed up the Circuit, what's funny I got frustrated and walked away for 10 or so min's and when I came back all three MPF 102's biased out to 4.5 V. with no problem, I had the same thing on the Eighteen, and now I'm perfboarding the Supro, when I finish it I think I have enough insight as to what I'm doing to tackle 1 by myself, I'm gonna try the Magnatone 440 with and somehow, someway I'm gonna add the Maggie vabrato to this, I've seen a pedal thats called a wobulator that get's very close to this so I know it can be done,
Thank's to you guy's and Doug, the rest of the Gang around here for make'in Jfet's so much more interesting,
JD :D
Title: New at runoffgroove.com: Professor Tweed
Post by: jrc4558 on May 20, 2004, 12:27:08 AM
Hi, everybody!
I have just finished the Professor. It is anice sounding cirquit, dynamic and probbly excellent for blues (that is if I only played blues).
However, as with many J-fet builds I did so far, I had to increase the sourse resistors considerably to get ANY output signal at all.
Those that were 1.5K are now 10K and the 470ohm one is 4.7k.
I used MPF102 for all three transistors.
What can be a reason for that?

Thank you runoffgroove for an excellent pedal!
Title: New at runoffgroove.com: Professor Tweed
Post by: B Tremblay on May 20, 2004, 07:07:03 AM
Please post your pin voltages.  It's very odd that you needed to change the source resistors.  How were the drains biased before you change the source resistors?

I've used MPF102, 2N5457, and J201 in the circuit and haven't needed to adjust anything other than the drain trimmers.
Title: New at runoffgroove.com: Professor Tweed
Post by: jrc4558 on May 20, 2004, 10:14:44 AM
Ok, I remeasure them this evening.
I still suspect that there's smth wrong with the way those guys label these J-fets at the factory... :)