professor tweed...I'm not passing his class

[bluesman69]

Love every sound sample I've heard of the prof tweed.  Received the components and completed populating my perfboard.  Plugged it in to my trusty tiny giant amp build.  Had the prof tweed switched off to start with.  Great bypass tone straight to the amp.  I thought "ok, so far so good".  Switched on the prof tweed switch and nothing.  When I touch the pots leads, plenty of electronic noise, but nothing from the guitar.  Switch it off again and I get the nice clean amp tone.  I'm a beginner at this electronics, and I think I've followed the schematics carefully.  It's my first perfboard build.  I must have gotten the components and leads on the board correctly or else I assume I wouldn't even get amplifier tone when the pedal is switched off...But I could be wrong there.  I'm thinking it must be in the way I've got my jacks or pots wired or both.  I still have a hard time with jacks.  This time I'm using an enclosed stereo Jack for input, and enclosed mono for output.  The stereo Jack has three lugs on each side.  I have the tip (farthest from where the Jack gets plugged in) wired as positive.  I believe the center lug is ring and the lug closest to where the cable is plugged in is the sleeve.  I will try to get a pic up tomorrow after work.  I just can't seem to track down why I get no sound through the pedal when it's switched on.  I really thought I had it set up right and can't wait to get that sweet sound I've heard from other's prof tweed samples.  Please help.

[bluebunny]

Assuming you're using bypass switching, then getting a bypassed signal through unfortunately tells us nothing about the state of the board and its components.  Check out the sticky debugging thread at the top of this forum.  And do post those pictures of your build (and a layout).  We'll get it cracked!

[antonis]

The stereo Jack has three lugs on each side.  I have the tip (farthest from where the Jack gets plugged in) wired as positive.  I believe the center lug is ring and the lug closest to where the cable is plugged in is the sleeve.  I will try to get a pic up tomorrow after work.

Propably you've wired the signal as positive...

In cicuits with negative ground:

TIPS are ALLWAYS wired as signal (IN & OUT)

SLEEVES are ALLWAYS wired as GND...
(sometimes through the metal casing)

You can use the RING as a switch closing (or opening) the GND loop...

(if you follow these "regulations" it will help you a lot in troubleshooting prosedure..)



Pay some attention at the jacks wiring (lower part of scematic..)

edit:Corrected thanks to tubegeek..

[tubegeek]

THIS PICTURE IS INCORRECT

Pay some attention at the jacks wiring (lower part of scematic..)

Indeed, pay attention - the labels are wrong.

Tip, Ring, Sleeve:

Tip is at the the tip of the plug, it is connected inside the jack by the contact furthest from the wall of the enclosure;
Ring is the middle section of the plug, it is connected inside the jack by the contact closer to the wall of the enclosure but NOT contacting the wall;
Sleeve is the section of the plug which is also connected to the cover: it is connected inside the jack by the contact closest to the wall of the enclosure which contacts the wall.

Where did you get that picture from? It has "Sleeve" and "Ring" reversed.


If ever you get confused, look at a TS (Tip, Sleeve) plug, which is simpler. Ring is the contact that that plug doesn't have, the middle one. See above.

Also:

Let's use "Signal" for the Tip connection, not "Positive," which can get confusing with regard to the DC power connection. Another option, "Hot."

For an unbalanced connection,  which covers over 99% of all guitar gear, there are two interconnections running along cables between guitar and pedal, pedal and amp, etc. along one cable. They are "Hot" and "Shield."

Shield in an unbalanced interconnection is 0 Volts and is steady. "Hot" varies, to carry an AC signal from one end to the next.
Shield is also physically arranged to protect the "Hot" conductor, forming a continuous tunnel that begins inside one piece of equipment, surrounds the "Hot" conductor for the length of the cable, and only ends once it is inside the next piece of equipment. Lokking at the plugs, you can see that the "Sleeve" connection is surrounding Tip and Ring (if present.)

In guitar gear, as mentioned above, a very popular trick is to use the Sleeve portion of a TS plug to make a connection between Sleeve and Ring inside a TRS jack, most often at the input of a battery-operated pedal. This allows a connection between the battery and the circuit's Ground connection to be made (turning the power ON) or broken (turning the power OFF) depending on whether a cable is inserted, which saves battery drain when the device is unused.

The 1st drawing attempts to show this, but the incorrect labeling doesn't really help. I'm late for work or I'd Photoshop it into line. Look on Small Bear Electronics web site for a correct illustration please.

[SuzukiScottie]

The labels on that stereo jack are incorrect too. You can clearly see that the ring contact is not the same part as the ring solder tab.

[tubegeek]

The labels on that stereo jack are incorrect too. You can clearly see that the ring contact is not the same part as the ring solder tab.

Uh oh.

I'm taking it down, you are correct. Someone help me out with a proper pic? I have to leave for work....

[antonis]

My bad...!!

(I was in a hurry drawing the above scheme  - so I've labeled it in reverse ...)


P.S.
I'm not confused at all...
(despite of the fact that I've seen some mono jack pics naming the shield tip as ring - after all, the correct connection doesn't mind about how we "name" it..)

[antonis]

True and Correct now....

[bluesman69]

Thank you for all the good advise.  I should have mentioned that the switch I am using is a six post spider switch.  I certainly will take the time to follow the debugging instructions and post my results (probably tonight or tomorrow morning).  Getting this thing to work would be a great Christmas gift to myself lol.

[bluesman69]

Ok, finally got all the voltages measured.  Did it today during break between shifts at work.  I have pics and my layout drawing for both front and back of board.  When I get home tonight I'll post the pics and the voltage measurements for each component.  I thought I found a solder bridge and scraped it out while I was checking component voltages.  I decided that maybe that was the problem and decided to hook it up to the amp and guitar and see.  Well, no dice.  Then I got to looking at the trim pots and wondered if maybe they needed to be adjusted somewhat to get anything out of the pedal.  So, I found my little screwdriver and did a little twisting...and I got some sound!  There is certainly a signal boost in the pedal and a very small amount of gain.  I built my perfboard exactly as shown on the perfboard layout on the ROG webpage.  Looking at the perfboard layout you will notice that there are 3 semiconductors.  I used J201 in the first (Q1) spot, nearest the corner of the board that shows the +9v lead, then Q2 in the middle and the last one to the right of the board is Q3.  When I adjust Q1 to a towards the left, I got some volume.  The trim pot adjusted mostly counterclockwise produced this volume to finally come through.  Then I adjusted the center trim pot (Q2) and I move it also mostly towards counterclockwise and I can get a little bit of gain/ overdrive by slightly turning it clockwise but I get to a point where it becomes glitchy sounding the volume of a sustained note is not evenly maintained...that is, it goes out fairly quickly at times and the glitchy distortion sounds like garbage to my ears.  So I adjusted that trim pot to point where the overdrive just began and left it there.  Moving on to Q3 trimmer I adjusted it all the way to clockwise, then counterclockwise and then back clockwise, as that seemed to brighten the tone.  I notice that the Volume pot is the only pot that gives any significant difference when turned.  The Tone pot gives a little difference, but not much at all, and the master volume pot makes no difference in the tone, it's as if the master volume pot does not even exist.  I checked to see if I have the Master Volume pot leads in the proper place and if I switched them around the pedal stopped working until I switched them back. 

  Now, I have read about the trimmer adjustments based on voltage readings.  I have not been able to find the voltage measurements for the trimmers that everyone keeps saying are ideal.  Also, does it matter on which trimmer lead that I make my reading for the biasing (?) adjustments?  Does anyone have any idea why the Tone control has very little effect on the pedal and why the Master Volume has no effect?  I will post my voltages and schems/pictures when I get home to help make this a bit easier to diagnose....but anyway, at least it is working now, if not at 100% yet! 

[antonis]

I used J201

duckarse will slap your hand by way of congratulation..

[bluesman69]

Ok everyone, got my voltages finished.

  As per the debugging page:

1.  At first, the build was getting no sound but some electronic hum.  Now that I've fiddled with the 100k trimmers a bit, I can get a boosted, barely overdriven tone from the pedal.  The Master volume pot seems to do nearly nothing for the circuit except darken the sound a bit.  The Volume pot kind of controls the volume but also affects the tone.  The tone pot does change tone, but not to the extent that I expected.  When I turn the R3 trimmer all the way to the left and then back to the right a hair, I can get sound from the pedal.  If I go all the way to the left or too far to the right, the sound cuts out completely.  The margin for adjustment on the R3 is a very small window and the only changes are from silent to a pretty good boost to silent without much of a graduation between.  When the R7 trimmer is adjusted all the way to the left I get a very nice clean tone with just a ghost/ hint of overdrive.  When I turn R7 a bit to the right from that position, the clipping becomes horrible sounding and if the volume knob is turned down a bit the clipping sound is followed by these really strange bumping or popping noises until I turn the volume control back up.  The clipping is nothing like what I expected, it sounds very electronic and horrible.  When R 10 is adjusted it seems to control the tone from dark and muddy (all the way to the left) to somewhat sparkly (all the way to the right).  Overall the pedal does boost the signal significantly but it does not sound very much like the sound samples I have heard, and the overdrive is almost non-existent. 

2.  Name of the circuit:  ROG Professor Tweed

3.  http://www.runoffgroove.com/professor.html

4.  The only modification to the perfboard layout that I made was by accident in layout only:  C3 (470p) should have been placed one hole lower on my perfboard in order to faithfully copy the perfboard on the website.  To compensate for that and to keep the ground "rail" (?) at the bottom of the board from coming into contact with C3's lower lead which goes to tone lug 3, I used a bit of wire with the insulation still on to jump the ground over that C3 tone lug 3 leg without touching it.  Other than that, everything is the same.  I used a J201 on R3 and MPF 102's on R7 and R10.  All of my parts were purchased from Pedalparts.com.

5.  No substitutions.  I don't know enough about what I'm doing to feel confident in substituting parts yet.

6.  Positive Ground to Negative ground conversion?  I'm not sure what that means.  I just copied the perfboard layout from ROG's professor tweed page nearly identical.

7.  With my meter set to 20V on the DCV scale my voltages are as follows:

Q1   Drain: 9.31, Source: 9.31, Gate: 9.30
Q2   Drain: 9.27, Source: 9.28, Gate: 0.05
Q3   Drain: 9.34, Source: 9.34, Gate: 7.68

R3   Pin 1: 9.74, Pin 2: 9.53, Pin 3: 9.51
R7   Pin 1: 9.74, Pin 2: 9.26, Pin 3: 9.26
R10 Pin 1: 9.74, Pin 2: 9.35, Pin 3: 9.35

For schnitz and giggles I measured every component on the circuit board but I will only post the results if needed to help diagnose the problem.  I don't want to use up more space the required.  All my polarized caps are correct by my voltage readings.  The thing that troubles me is that on the ROG sight for this build, they say that all Q gate voltages should be 0.  Only Q2 (MPF102) has the gate voltage low enough, and that still is at 0.05v.  I have no idea how to get the gate voltages down and it seems like all the other Q voltages should be a good deal lower than they are based on the chart provided on ROG.  Please help me pinpoint my problem (other than the fact that I'm a newb who knows next to nothing about this stuff, except that I want to do it and learn to do it well).  Thank you

[bluesman69]

by the way, I'm using a DPDT switch, not a 3DPT.

[bluebunny]

Check all your connections - your transistor readings are way off (drains and sources look shorted).  The ROG page that you linked to has baseline readings to aim for.  You also need to adjust the trimmers so that you get 4.5V on the drain of each JEFT, as indicated in the schematic.

[PRR]

Basically ALL (but one) of your voltages are 9V, or so close we do not care.

You do not have a connection from battery "-" to circuit common. Find that.

Q2G probably has an additional problem.

[bluesman69]

Yes, I was trying to get my d,s,g voltages right but it was no use.  I'm out of town for Christmas eve but will get back to it tomorrow to have a look for the battery -.  That may have something to do with it.  By the way RG, how could you tell from my posted voltages that there was no connection to the battery grnd?

[PRR]

> how could you tell from my posted voltages that there was no connection to the battery grnd?

Just as I said: "ALL of your voltages are 9V, or close"

NOTE: many pedals use the Input jack as an on/off switch, by returning the "-" to GND via the plug sleeve and a "ring" contact. Be sure you have a plug in the input jack!

> how could you tell from my posted voltages that there was no connection to the battery grnd?

Draw it out:



The pedal guts are resistors and stuff with values from maybe 100 Ohms to 100K Ohms, stacked up and down between "+" and "-". When working normally, we expect various voltages over the WHOLE range from -9V (read as zero) to +9V.

Now break the "-" wire. We have a bunch of low resistances that only go to +9V.

Poke your voltmeter at it. In this case it seems your meter black probe did find -9V (zero). But everything you poked (almost) went to +9V, not zero. The meter internal resistance is much higher than (almost) any of the circuit impedances. A 1Meg meter probing 1Meg to +9V will read around 8V; to 100K from +9V about 8.9V. All your readings are in this 7.8V to 9.3V range.

(*) Q2 Gate reads near zero. Why? The Gate is a diode, and in this connection the diode is working in reverse-bias and should pass "no" current, infinite resistance. If the meter has any resistance (they always do), the reading should be zero. In fact real diodes (or JFET Gates) don't have infinite reverse resistance. Maybe 100 Megs to 1,000 Megs. This is consistent with a 0.05V reading, and the exact reading is of no interest. However, Q2 Gate should *also* have the Volume pot to ground. If the Vol pot is grounded off-board, this may be right. If returned to board, I suspect a second open connection.