Fatter sound? Turn your pick!

I play with my pick turned 90 degrees, the pointy side pointing to the neck. I started doing this because for me, the pick stays in place with less pressure coming from my thumb and index finger.

Over time I noticed a positive change in tone compared to the normal way of holding the pick (warmer, fuller tone). The effect is subtle but consistent across different types of picks.

To analyze it, I recorded a picked A string into my laptop and ran it through Audacity's frequency analysis (Hanning window).

The result is shown below:

• With the turned pick, I get a few decibels more of the 3rd and 4th order harmonic, which explains the fatter sound.
• There also seems to be more overall distortion/noise in the -70dB range with the turned pick. However, I never noticed that through the amp.
• The main frequency is at 220Hz (A3). The harmonics depicted in the diagram are: 440Hz (A4), 660Hz (E5 - harmonically the fifth with respect to A4) and 880Hz (A5).
• I ran several samples through the frequency analysis. The increase on the 3rd and 4th order harmonic was consistent in all the tests.
  

On the side: I recently read in the German magazine "Guitar" (issue 9/2015), that Stevie Ray Vaughan allegedly played like this.

DigiTech TRIO Band Creator Sound

I recently got a DigiTech Trio. A really cool device. I use it to add some background to my blues practicing.

Out of the box, plugged into my guitar amp, there was a problem though. I didn't like the sound of it. It actually hurt my ears. I kept going back to the DigiTech web site to check for firmware updates hoping that the scratchy sound of the drums and snares was something that might be corrected with a software update.

There were no updates and I started thinking about other ways to improve the sound. The solution is actually simple: don't run the bass and drums output from the Trio through your guitar amp. Use a dedicated, linear loudspeaker.

Check out the following video for a sound sample:

Electric Guitar Output Voltage Levels

I was recently interested in how much output voltage you get from guitar pickups. To find out, I connected a guitar to an oscilloscope and did some measurements. Here are the numbers:

• The values are peak voltages in millivolts (double the values for peak-to-peak)
• The 'A' values represent the maximum transient peak voltage I observed (just after the string leaves the pick)
• The 'B' values are measured after about two seconds into the tone.
• I picked (strummed) hard. That's obviously a very subjective statement. Your mileage will vary.
• The values are averages over three to five repetitive measurements.
• The scope used has an input impedance of 1MOhm and an input capacity of 18pF. Probe attenuation was at 1X.

The guitar I used has a volume control and a tone control. For the measurements, volume was on maximum output and the tone control was on minimum impact.

I used the following pickups:

• Single coil (neck and middle): GFS Pro-Tube lipstick
• Humbucker (bridge): Artec Vintage Humbucker LPC210N

The measured DC series resistance of the pickups are as follows:

• Neck: 4.8K
• Middle: 6.2K
• Neck & middle (parallel): 2.7K
• Neck & middle (series): 10.9K
• Humbucker: 8.3K

The difference between soft, medium-hard and hard picking was in my case about a factor of 2 to 3. Meaning: picking the open A string softly I got about 10mV, medium-hard 20mV and hard 30mV (which you'll find under 'A' in the table, above).

And here the screenshots referred to in the table:

a.bmp - neck pickup, open A string.

b.bmp - neck pickup, open E chord. This is one of the lower samples. Most other measurements came in higher.

c.bmp - bridge humbucker, open A string.

d.bmp - bridge humbucker, open E chord.

April 22, 2025: Thanks for all the comments so far. If I wont reply it's probably because I'm busy working on my new thing: InvMon, a professional investment monitoring and portfolio management application.

Scratchy Pots?

Your pot is...

• either too old (resistive layer worn off; wiper doesn't connect well anymore...),
• is dirty (has dust particles under the wiper),
• has DC on the wiper,
• or... (let me know if you've experienced other sources)

For a lot of people obvious, for me something I learned recently: If you have DC voltage at the pot in your audio circuit, your pot will sound scratchy as you adjust the level. Once adjusted, no problem, but as you move the dial you hear an annoying scratchy noise.

A typical cause for the DC are defective caps that leak DC into the circuit. In my case, however, it came from an error in the schematic.

Here's the problem area in my tube overdrive circuit (see the earlier RT-1 post):

And here's the fix to the circuit:

To fix it, I added an additional cap after the pot wiper (C17, you may have to scroll to the right to see it). This reduces the effective coupling capacitance by 50%. To remedy this, I roughly doubled the input impedance of the following buffer circuit (R26 & R27).

By the way, see this very useful page about pots in general: http://www.geofex.com/article_folders/potsecrets/potscret.htm

Low noise 9V to 33V DC/DC converter

This DC/DC converter is well suited for guitar effects projects where you have 9V input power but need 33V for your circuit as well (e.g. for tubes or for discrete transistor circuits with a lot of head room). The boost converter IC in use switches at high frequencies. It is very quiet for the guitar (audio) projects I used it for.

The output voltage can be varied by using different values for R1 and R2. 33V is about as much as you can get out of the converter (I actually measured 32.6V with R1 and R2 as shown). See the LT1613 datasheet for the formula to calculate the values for R1 and R2 for lower voltages.

R3 in the schema above is optional. It is not needed for the LT1613 (input voltages of less than 10V). There's a jumper in the diagram below (just above the 39K resistor) in place of R3.

C2 is optional too. It helps reduce output ripple. I simply soldered a small ceramic 2.2nF cap over the resistor.

Layout is the most crucial design aspect for obtaining low noise (and to actually make it work - because of the high switching frequency it won't run as a bread-board prototype). Use big area trace to minimize impedance. The LT1613 GND pin (center left pin in the diagram below) carries high speed, switched current; its path to the circuit's power exit should be direct and highly conductive at all frequencies. R2's return current (bottom left pin), to the extend possible, should not mix with pin 2's large dynamic currents (center left pin). C1 and C3 should be located close to pin 5 (top right) and D1 respectively. Their grounded ends should tie directly to the ground plane. Pin 1 (top left) has a small area, minimizing radiation. (Source: Analog Circuit Design Volume 2: Immersion in the Black Art of Analog Design, Volume 2 and LinearTechnology LT1613 data sheet.)

The following picture shows a possible component layout on a small PCB using both sides for the components. The components drawn in black are visible (front side), the components drawn in gray are located on the back side. The 5-pin component in the center is the LT1613.

Component selection is also important. I used the following components:

• Inductor: Coiltronics DR73-100, 10uH
• Capacitors (C1, C3): Kemet T495D226K035ATE300, Tantalum 22uF 35V
• Schottky-Diode: ST 1N5819RL, 40V

Creating the PCB

This PDF (editable with Adobe Illustrator) shows the mirrored trace layout in actual size. Use the PDF to create your own PCB. I did it as follows:

• Print the layout file on transparent laser printer foil using a laser printer
• Put a flat board on your work desk
• Put a piece of circuit board (one sided 35um copper layer) on the board. Copper up. Make the printout slightly smaller than your circuit board
• Put your printout on top, Toner against the copper.
• Use Scotch Magic tape to tape your printout to the copper around the edges.
• Put a thin piece of linen cloth on top.
• Fire up your household iron. Set it to high (linen or similar)
• Iron the toner onto the copper using a lot of pressure and, in my case, one to two minutes of time. You may have to experiment a little at this point to get perfect results.
• Peel the foil of the circuit board. All toner should stay on the copper.
• Cut your board to size
• Put the board in a bath of natrium persulfate (a little more than hand-warm) for an hour or two (you'll see when it's done). Don't put your hand in the solution. I actually used to baths: a bucket with hot water and a small tupperware container with the persulfate solution - the tupperware container swimming in the bigger bucket.
• Here's a site that provides much more info on this process: https://www.smallbearelec.com/HowTos/DirectPCBoards/DirectPCBoards.htm

And here some pictures for illustration

A laser printer printout ironed onto copper and then peeled off.

The PCB in the natrium persulfate bath

Not pretty but effective: thick short straight connections from the IC to the caps.

I first used a conductor with through-hole leads. I then switched to a different surface mount inductor which required improvised solder pads. 

Ready for a test drive.

The DC/DC converter in my RealTube-One pedal. L2 and C4 are for additional noise filtering.

Without additional noise filtering.

With additional LC noise filter (L2 and C4)

RealTube-One - A 12at7 Tube Overdrive Pedal

In an earlier post I presented the BluesBox - my own design of a valve-based overdrive pedal. It was a great learning experience but didn't quite hit the sweet spot I was looking for with respect to sound and usability.

I'm presenting now the RT-1 pedal. A complete overhaul of the original BluesBox design. This time... yeah! Exactly what I was looking for. A fantastic sounding pedal. My specs to start with:

• very transparent and open
• very dynamic
• a large amount of sweet sounding even order harmonics
• full, rolling tube clipping and distortion
• tone controls which, at their 12 o'clock position, provide a linear (or near linear) frequency response

The Result - RealTube-One

Technical Specs

• two valve (triode) gain stages (a 12AT7 twin triode)
• three discrete transistor gain stages
• maximum gain of 30dB (mileage varies based on component selection)
• controls for level (volume), "crunch" (gain/distortion), treble, bass
• 9 to 12V DC power input at about 170mA
• 33V DC from an internal DC/DC converter (top-right in the picture above) to run the triodes and two of the transistor stages
• 1M Ohm input impedance
• 3.3K Ohm output impedance
• high quality foil capacitors in the signal path

Below I'm providing the schematic, strip-board layout and other helpful resources. 

The Schematic

Download LTSpice (.asc) file here (Note: I used LTSpice just for drawing. The schematic cannot be run as a simulation). LTSpice is from Linear Technology.


The Strip-Board Layout

Download the layout file as PDF, or as a complete DIY project file. The DIY file opens with the DIY Layout Creator.


The Jumpers

Download the jumpers file as PDF.


Trace Cuts and Solder Bridges

Download the file as PDF. This file is a mirror image, looking at the board's trace side. The blue jumpers are provided as a reference. They help locate the correct positions of the cuts.

Notes on the DC/DC converter and a PCB layout for it will follow in a separate post.

I used the Type BB enclosure from Musikding. It's easy to work with (like drilling the holes) and has pleasing dimensions. Fitting everything into the box, however, was a bit of a challenge.

One of the coming weekends I'm planning to spray-paint the box and put some nice white lettering onto it (using the DecalPro system).


Possible Modifications

• The two bias trim pots are not too important. They can be replaced with 100 Ohm resistors.
• The first transistor stage in the design is a JFET based input buffer / booster. With a 1.2K drain resistor (or 1.3K as shown in the schematic), it provides very little gain. By incrementing the drain resistor you can get a little more gain out of the input buffer stage. At the same time, you will also start to get distortion from the transistor. The level of this distortion depends a lot on the output level of your pickups. By tickling the MPF102 just a little, you get very nice first and second order harmonic distortion. By pushing it too far, you get some pretty bad sounding distortion. However, this can be used in an interesting way: driving the signal further, through the next transistor stages and finally through the tube stages, you will get some pretty cool fuzz-like sounds out of the box. The modification I have in mind is a three way switch allowing to switch between three sizes of the drain resistor: 1.2K, 1.6K and 2K (clean, harmonic and fuzz).
• The tone controls allow to adjust for bass boost, bass cut, treble boost and treble cut quite nicely. You can also get a nice mid scooped kind of frequency response. Mid boost is more difficult to get. I'm considering modifying the tone stack to also be able to shape a mid-boost kind of frequency shape.

Disclaimer: The schematic and all other resources of this post are provided "as is". I put a lot of effort into reviewing the schematic and layout for errors. However, I do not provide any guarantee as to their correctness. Do not use the pictures as a reference (for example, the transistor orientation is wrong on some of the pictures). Always refer the provided PDFs and DIY file.

Should you decide to build this for yourself: it is not an easy project! If you can't read the schematic at all you will not be able to turn it into a functioning device. I will not be able to provide any support. General questions and comments, however, are welcome.

Copyright notice: All resources provided are my copyright. I'm granting you the right to use these resources for your own use with no limitations, except when used as a basis for commercial production of sound effect products. 

April 22, 2025: Thanks for all the comments so far. If I wont reply it's probably because I'm busy working on my new thing: InvMon, a professional investment monitoring and portfolio management application.

BluesBox - Tweaks and Samples

The source of a lot of noise and the chirping sound turned out to be the tone stack driver. The noise could be eliminated by bypassing the tone stack. So the noise was obviously added to the signal path. However, the chirping sound remained even after bypassing tone stack. Therefore, the tone stack driver circuit introduced the chirping sound on the signal ground. Nasty!

Since I had enough of overall gain to work with, I decided to go for a simple solution. I disconnected the tone stack driver circuit (the recovery amplyfier part of it) and put the passive tone stack after the tube gain stage. To be able to model the sound going into the distortion stage a little bit, I added a sinple passive variable bass cut between the pre-gain stage and the tube stage.

The following movie shows the final result. The second movie shows the BluesBox in action.