A2PB turned into InvMon

As of February 20, 2025, InvMon.com is live. InvMon is the product I developed on the basis of A2PB. Here's a quick summary of what InvMon does:

InvMon is a personal finance program that offers a clear overview of accounts, savings, real estate, and investments, with easy asset structuring by family or company and analysis by liquidity or currency. It supports portfolio management with stock market data, exchange rates, and performance views, integrating with Interactive Brokers® for automated trading. Installed locally on a laptop or desktop, InvMon ensures data security with no cloud or mobile storage, delivering a complete financial picture and visually appealing graphs with minimal effort.

Check it out at https://invmon.com

My New Professional Project: A2PB.com

 I haven't posted in a while on this blog.

I have been more active on the blog A2PB.

A2PB is my new professional project that I've started around June of 2021. It's basically an automated stock trading and portfolio management system. Check out the homepage if you're interested: A2PB – Automatic Portfolio Balancing

I got a new rug -- corona triggered home improvement

Does a Celestion Gold fit into a Fender Pro Junior IV?

Short answer: No

The Celestion Gold is too big. Even with the aluminum cover removed from the back of the Celestion, the magnet of the loudspeaker won't get clear of the chassis of the Pro Junior by about 5mm.

Longer answer: It's possible if you want it bad enough and take out your tools. The following pictures illustrate the process.

The cover of the Celestion needs to be removed. Remove the screw and gently lift the cover off with a screw driver (there's some silicon paste between the cover and the loudspeeker that generates some resistance).

The pictures above illustrate what you save in terms of depth. 

But it's not enough. The problem is that the Celestion's magnet is also too big in diameter.

So the critical part of the chassis of the Pro Junior needs to be removed. It can be done with a Dremel like cutter. Make sure to protect the electrical parts and circuit board of the amp from the shavings (covering everithing with tape works good enough).

I took my time cutting - with ear and eye protection. This is about half way through. Each of the long cuts took 10 to 15 minutes.  

After cutting and cleaning the edges - not beautiful but effective.

Fits like a glove now.

The tubes have enough clearance.

My New Soulman Pedal Board

The finish company Soulman produces great looking and extremely functional guitar pedal boards.

I recently bought a Soulman S44 board and set it up with a Truetone 1Spot CS7 power supply.

Check out the pictures below about the setup and final result!

Optional patch and switch boxes can be ordered for the boards. This is an input patch box.

The Truetone 1 Spot CS7 power supply

Access to the dip switches of the power supply

All pedals powered up

The final result

Signal path:

• Guitar input starts bottom right into my buffered switch/fx box (see earlier post). The bottom right foot switch activates the tuner and mutes the rest. The left bottom switch on my pedal engages the whole board's pedal chain. (With the fx switch off, the guitar signal skips all pedals except for the reverb pedal (top-left.))
• The first real (sound) pedal in the chain is the MXR Custom Comp compressor.
• Then comes the Fulltone OCD overdrive.
• Then into the big muff.
• Next comes the Seymour Duncan Vapor Trail delay.
• Then to the Trio plus.
• And finally to the TC Hall of Fame 2.

Jam Box

This is my latest project. I call it "Double Trouble" - it is a two guitar input cross-switch with optional buffering and a switchable FX loop for each channel.

The purpose is to be able to connect two guitars to two amps and to cross-switch the guitars between the amps by pushing one button.

The top-right switch engages the buffer. There are two independent single JFET buffer circuits inside, one for each channel. The buffers are true by-pass using relais. This means that if the power goes out, the pedal switches itself to true by-pass and keeps operating (un-buffered).

The bottom-right switch switches the channels.

The bottom-left switch engages FX loop 1,

the top-left switch engages FX loop 2.

The following picture shows the circuit board with the components:

This is the schematic:

The following pictures show the strip-board layout, the templates for the cuts and jumpers, followed by illustrations of the work in progress and a couple of files for download.

DIY layout (http://bancika.github.io/diy-layout-creator/)

Position of strip cuts (copper side)

Jumper layout (component side)

Cutting the strip cuts

Running the jumpers

Resources:

• The LTSpice layout file: schematic
• The DIY routing and component layout file: layout

My messy pedal board

This is what it looks like. The bottom right pedal and the RT-1 in the top row are my own designs. The bottom right one is a dual input buffered cross-switch with FX loops. The RT-1 is a transparent overdrive / boost with a 12AT7 tube inside. The black bricks top-right are a TC Electronics tuner, a 12V lead battery for effects power and a 9V Sanyo Eneloop battery also for effects power.

To get this more organized, I'm planning to build a board for home use like this: it will be a more narrow design with space for three to four pedals across and three sloped boards on top of each other.

My favorite guitar

This is the guitar I've been playing since about a year:

• Fender Custom Shop 1965 built to spec Stratocaster with relic/closet-classic finish (Nov. 2012)
• Serial #R53483, Part # 11180111-49
• Black, alder body, rosewood fingerboard, white pick-guard
• Mid 60's style oval "C" neck with custom 9.5" TO 12" compound radius
• Mother of pearl inlays
• Abby hand wound 65 pick-ups
• Vintage 2 7/32" string spacing at bridge
• Vintage tone pot wiring (no pot on bridge p/u)

I found this guitar (or it found me) in January 2015. I walked into a guitar store with the aim to get a new guitar (my second one). I didn't have a specific model in mind but I always liked strats. It was a quiet afternoon in the store and I just sat down and took my time trying out about 10 different guitars. Of the ones I tried, this one was just different - the feel, the sound, the look! I didn't know it was a custom shop model until after I had played it. The price was about twice my target budget but I had to have it. Checking the specs against the Fender Custom Shop options and price list after I had bought it, I realized that I actually got a good deal from the shop (a 35% discount).  

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)