Topics

I've built a Tweedy Bird drive that is a lot of fun to play.  My only problem is that the treble is a little much.  The J201's are Fairchilds and biased to around 4.5-5V.  I'm looking for ideas where I can cut some treble from the circuit without changing the character too much.  Playing with the Tone Stack calculator doesn't seem like there is much flexibility in the treble side (at least beyond what is already in there).  Between Q4/Q5 and Q6, it looks like there is some additional filtering where R13, C13, and R15 form a low pass filter (based on my limited electronics knowledge).  I think if I lower R15, that should drop the treble across the board.  Am I right?

So I populated an Autobahn board and fired it up...  Nothing.  Reflow all of the joints and clean up what appeared to be a couple unintentional bridges.  I did lift the traces in a couple spots, but I "fixed" that by using bits of resistor legs to connect the lifted area to the places it was supposed to go and everything checked out by continuity. 

OK, break out the multimeter.

IC1 (LM324) - Pin 4 is at 8.7V, Pin 11 at 0, everything else is at about 4.3V except pin 7 which I've measured at 7v and I've measured at about 80 mV.  Strange thing #1...

IC2 (LM13700) -
1 1.49V     16 1.49V
2 0.44V     15 0.97V
3 1.49V     14 4.3V
4 4.28V     13 4.2V
5 4.3V       12 7.6V
6 0            11 8.7V
7 0.68V      10 7.6V
8 1.7V        9 6.4V

Ground and +V are OK.  Don't know what to make of the rest...

Audio probe -
I have signal up to the C6/R17 junction and nothing on the other side, but I have audio on pin 14 of the LM324 (if the sense pot is wide open, with it "closed" there is nothing at 14).  No audio on pin 13.  Take the IC out (wondering if it is fried), and there is audio on the trace between R17 and the sense pot.  Put a TL074 (don't have another LM324) in its place and I get the same - no audio at pin 13.  With the LM324 in the circuit, the audio is really weak and heavily distorted later in that path (around R20) with a very weak signal feeding Q2.

On the LM13700 side, I have audio to the C2/R5 junction, but nothing past it anywhere on the LM13700.  Haven't tried taking that IC out, because at that point I was a fine mix of confused, frustrated and tired.

Any thoughts?

I know the PT2399 is designed as a delay for vocals.  I've built a couple delays for guitar (sea urchin and echo base) and was wondering whether there were any interesting DIY concepts out there for a vocal stomp box delay.  Any suggestions?

I've tweaked a layout for a Honeybee/Sparkling Yellow OD that I'm pretty happy with and want to build up.  I have vero.  I have a 1590A box.  Now the question of the hour?  Will 17x13 fit into the 1590A? (I'll only have two knobs and maybe one toggle).

On a side note, I'm also debating putting the resistor on the source of the 2N5457 on a switch to flip between 2 different values (one looser, one tighter and brighter) - I'm thinking 10K vs. 2x10K in parallel to give 5K.  Is there any good reason not to do this?

I've built a Bearhug vero based on the Tagboard layout (http://tagboardeffects.blogspot.com/2013/01/bearhug-fet-compressor.html) and I don't seem to be getting any difference in effect regardless of knob setting.  Actually, it looks like one of the 10K resistors in parallel to the high/lo switch is missing...  The hi/lo switch position doesn't change the sound either, so while that may be one problem, it isn't the main one.  My only substitutions were using 1n34A's for D3/D4 and tantalum caps for the 1uF's.  The one on the input has the - side towards the input and the + towards the BS170 (switched based on midwayfair).

Based on a couple ideas from midwayfair, here is what I have (all DC):

Q1 - D - 5.8V
       G - 2.1V
       S - 3.3V
Q2 - C - 7.4V
        B - 1.2V (drops to ~0.8V when playing)
        E - 0.72V
Q3 - D - 90mV (jumps to 180 mV when playing)
       S - 0V
       G - 55mV (drops to -0.6V when playing)
D3 anode - 9mV (goes to 2-3V when playing)
     cathode 45mV (goes to -1.5V when playing)


2N5457 drain to ground resistance is 370 ohm (goes up to 700 ohm when playing).  Gate to ground is 560k (drops to 70k when playing)

The compression knob is 1kB - when it's all the way one way, the 1-3 resistance is 0, the other way it's 0.97k.  Turning the knob doesn't seem to change the current on the Q2 emitter.

I've verified all the components (twice) and reflowed a couple joints (which is why the voltages are a little different than what I told midwayfair).  I also accidentally reported the voltage on the wrong side of D3...  Sorry!

Pictures to follow very shortly.  Thanks in advance for any help!

I've looked at a few projects that call for 1n4007 diodes in the power section.  I have a bunch of 1n4001 diodes hanging around.  The only difference I can spot is the voltage allowance of 1000V vs. 50V.  Is there any way a stompbox powered at 9V will see a swing of more than 50V?  Are there any places where a 1n4007 would be needed over a 1n4001?

builds 2-4 to report (that I've finished over the last few weeks).  I absolutely love the yellow shark (Clementine drive) and it will be my staple low gain drive.  I gave the echo to my other guitar player, but I've already put together another one on a breadboard that I'm playing with the filtering. The game of tones (Papa Smurf) is fun - i ended up adding a 1n34a , in series with the 1n914.  I'll play it loud tonight to see how that sounds.  What can i say, the building bug has bitten!

I'm building a Game of Tones board that will have 2 clipping options - LED and silicon (I'm leaning towards assymetric, but that's beside the point).  The diodes are switched with a SPDT.  The issue is that the LED's are substantially louder. 

Would it be possible/reccomended to use a DPDT instead of the SPDT and use the other side to bring in a resistor that would be on the volume pot to increase it's resistance?  I know I'd have to tweak the value of the resistor.  Which lug would be best to put it on?  Ground?  Out?  In?

I've finished my first build - Mudbunny to Civil War specs with the Jack Orman mids (fixed the capacitor and resistor that go on that side of the tone stack), and caps on the volume and sustain pots that Skreddy uses on the P19. 

What I would like to do is lower the clipping a little and smooth it up some.  I've seen people play around with the diodes. 

- My first question is whether the 1st or 2nd set of clipping diodes has more impact on the final sound?
- If I were to try germanium diodes, which have a forward voltage of ~0.3 (vs. the ~0.58 on the silicon ones that are in there), would there be a difference in tone of 2xGe vs. 1x Si?
- I've seen a couple mods that add a cap in parallel to the clipping diodes to bleed treble to ground, would this be effective in smoothing a little?

Thanks!

I just finished my first build last night - a Civil War Mudbunny.  After a minor hiccup (didn't order enough transistors because of how I read the parts list), it fired right up.  Sounded pretty cool last night through my solid state home practice amp (Peavey Vypyr) and headphones (sleeping kids, wife watching TV in the next room).  After playing for a few minutes, I did a minor tweak from the Skreddy threads- I added a couple caps (2nf across 2&3 of the sustain pot and 560pf across 1&3 of the volume pot).  That was interesting - made the tone a little smoother.

The thing I'm still thinking about is that the sustain pot doesn't have a lot of range - it is pretty much saturated by ~1/2 of the travel.  I've seen people add parallel resistors to play with the taper, so I may try that.

I did get lazy - nothing on the top yet...

OK, I've got my first pedal project built, but there is no sound.  I'm doing a Civil War Mudbunny.  I think I've figured out my problem though and just want to verify - the build sheet only specifies Q1, so I only bought 2 transistors (1+spare).  That leaves q2-q4 empty.  Is this right?  If not, what type of transistors should I put in those spots?

Thanks in advance!