Tag Archives: mimmo

Emergency Room #9: Delta Labs Super Timeline ADM2048 Battery Burst

This is quite possibly the most interesting circuit I’ve worked on so far. I’ve always wondered how a digital delay works, and this late ’80s digital IC-based technology allowed the opportunity to reverse engineer the general concept. (I’ll share those findings in posts to come!) But before I could reverse engineer anything the unit had to be repaired to a working condition, as it had suffered the results of a failed board-mounted 4.6V battery:

Figure 1: Showing the Damage from Battery Leakage

There is an SRAM chip (NMC6504) used on this board to store 4 preset configurations (A, B, C & D), this is obviously being powered by the battery and was confirmed when I replaced the blown fuse, powered up the device, and no presets were able to be saved.

I couldn’t find the specs for this battery model online for a direct replacement, so I had to dig into many forums to find information and, eventually, a schematic. For legal reasons I won’t post the schematic here, contact me for more info if needed.

The schematics yield a 4.6V battery, and the test point for the battery voltage is labeled +5VB after the zener. I settled on a Varta 4.8V NiMH from JLS Batteries on eBay. It’s a through-hole component, but doesn’t match the footprint of the original battery, so I soldered wires from the + and – sides to the appropriate vias. To secure the wiring to the battery’s body I used electrical tape and twisted the wires together to provide additional support. The electrical tape may also help in preventing a large amount of damage to occur in the case that this NiMH fails in the future. A square piece of Velcro was used to secure the battery to the main board.

The use of a NiMH is based on the color of the corrosion that occurred on the copper traces and component leads. NiMH batteries contain the hydroxide anion (OH-). In the presence of an electrical current and physical contact, the hydroxide anion and copper can react to form copper (II) hydroxide, which is blue in color.

Copper (II) Hydroxide suspended in a Test-Tube

Copper (II) Hydroxide suspended in a Test-Tube (WikiMedia Commons)

To reiterate, this reaction is corrosive and literally eats away the copper traces on the board. If enough corrosion takes place the board may become irreparable! (Or at least extremely hard to repair without re-engineering and rebuilding the affected circuit). Luckily, this was not the case for this unit.

Once the replacement battery was installed I powered up the Super Timeline and presets were operational!  The contacts for the presets, however, were extremely unreliable. They would make contact maybe 60% of the time, so I ended up removing all of the preset button switching actuators. I tinned a thin, even layer of solder onto each contact and reinstalled them; that worked very well.

Figure 2: Programmable preset switches. The switch to far left has its' actuator removed. This is done by applying a precision flat-head screwdriver to the plastic lip between the lug sets.

Figure 2: Programmable preset switches. The switch to far left has its’ actuator removed. This is done by applying a precision flat-head screwdriver to the plastic lip between the lug sets.

After tinning the preset contacts I took aim to the copper (II) hydroxide build-up near the power and LFO circuits. I cleaned a toothbrush with distilled water and started brushing the corrosion build-up off the leads. I quickly noticed that the component labeling was getting scraped off as if they were old stickers. From that point on I was very careful in removing the corrosive material and mainly focused on relatively open areas between components. It’s not perfectly cleaned, but the unit was working and I didn’t want to ruin the labeling scheme, as it may prove useful down the road. (If anybody has an abrasive-free solution for cleaning copper (II) hydroxide from PCBs I’d be highly interested!) To remove the distilled water I used some combination of paper towels, a hair dryer, and an air compressor.


Thanks for reading! Notes on the circuit’s operation will definitely be a topic for future Talk Theory To Me posts. Stay tuned if you’re interested!

This fix was done for DMS Productions located in Ransomville, NY!

“With over 22 years experience in audio, 16 years experience in photography and over 5 years in video, DMS Productions has become a true multimedia company.”

In The Spotlight: Matthew Fantini of Space Junk

Welcome to the first In The Spotlight session! This new category of posts will highlight individuals in the effects pedal community, mostly encompassing guitar players and effects pedal builders. Today we’ll be taking a look at Matthew Fantini’s board and how he utilizes it with the Buffalo-based band Space Junk

Matt Fantini of Space Junk

In The Spotlight Interview:

[Mimmo] Q: What’s your story? How did you end up playing with Space Junk?

[Fantini] A: Space Junk began as a 3 piece live EDM/Jam band that I formed in college with Kevin Rogers (drums/keys/DJ) and Will Thompson (Bass) in 2004 at SUNY Fredonia. In 2015 we added keyboardist Cary Meehan to complete our current lineup. We are all huge fans of experimental, electronic, and jam music but we also incorporate elements of blues, jazz, and funk.

[Mimmo] Q: Give us two Space Junk songs that allow you to utilize your pedalboard in a unique way.

[Fantini] A: Two Space Junk songs that allow me to use pedals in a unique way are: “Gas Pump” and “L Way.” In “Gas Pump” I use a combination of a Strymon Timeline set to an Ice Delay paired with a Strymon Blue Sky set to a shimmer reverb. This combo = ambient space for days. In “L Way,” I use an EHX POG2 and an EHX Micro Synth to recreate the sounds of an analog keyboard during the verses and outro.

[Mimmo] Q: What are some songs, artists, or guitarists that have influenced the way you utilize your pedalboard?

[Fantini] A: (a) Nels Cline – Wilco/Solo, (b) Robben Ford, (c) Bill Frissel, (d) Adrian Belew (King Crimson), (e) Vernon Reid (Living Colour) …can I name a million more??!!

[Mimmo] Q: What amp do you use live? In the studio?

[Fantini] A: Amp live = John Nau Engineering Crown Victoria (2×12 Combo). In studio, same as above and also an ENGL Fireball with my side project: Free Man

[Mimmo] Q: Are there any sounds you’d like to emulate that you haven’t quite found out how to do yet?

[Fantini] A: I am always working on getting analog keyboard sounds to cut through my mix better. I have an original EHX micro synth in addition to the reissue. When I push them a little hard with a boost, I sometimes have clipping issues. Pairing with a compressor does help, so maybe I need to put them on a loop together. Is there a pedal that will make me sound like Jimmy Herring?!

Q: Time for Quick-Fire Favorites! Favorite Overdrive/Distortion/Fuzz?

A: Hermida Audio Zendrive

Q: Favorite Chorus, Phase Shifter, or Flanger?

A: EHX Small Stone

Q: Favorite Tremolo or Vibrato?

A: JHS Honeycomb

Q: Favorite Wah or Expression Pedal?

A: RMC Picture Wah

Q: Favorite Compressor?

A: CMATMODS Deluxe Compressor

Q: Favorite Boost?

A: Xotic Effects EP Booster

Q: Favorite Octaver or Harmonizer?

A: EHX POG2

 

Pedalboard Order:

TC Electronics Polytune –> RMC Picture Wah –> EHX POG2 –> EHX Small Stone –> EHX Micro Synth –> CMATMODS Deluxe Compressor –> J Rocket Archer Ikon –> Hermida Audio Zendrive –> Vox Volume Pedal –> Strymon Blue Sky –> Strymon Timeline –> BOSS RC-20XL Loop Station

___________________________________________________________________________________________________

A huge thank you to Matt Fantini for participating on In The Spotlight! Catch Space Junk at their next show by following them on Archive.org and Facebook. Their sound emulates a wall of pure psychedelic energy that toys on experimentalism, yet manages to firmly keep itself together by way of masterful musicianship.

Decimator Title Pic

Emergency Room #8: The Discharging Decimator

Introducing: the iSP Decimator Noise Reduction unit! This is quite probably the best noise reducer I’ve played through thus far. There’s only one problem..it pops! You had one job Decimator!

Deal with it.

In any case, it’s a good thing the Decimator is in our hands. What’s happening is the pedal works correctly when set to -30dB and below. Problems are only seen when disengaging the pedal with the potentiometer past the 12:00 position. Engaging the pedal is fine but once we decide to disengage, it lets out a noticeable “pop” in the output. Turning the potentiometer clockwise from 12:00 makes the popping sound even more noticeable.

So we see two things here: (1) The popping intensity is dependent on the position of the potentiometer and (2) the popping only occurs when disengaging the pedal. Keep these in mind as we continue.

Okay, so now we have some clues. As an aside, when pedal-popping complaints arise it is usually a result of a DC current snaking its way into the signal path and eventually into the pedal’s output signal. Now I will admit to not knowing all the ways this can happen, but the primary cause is a build up of charge. This charge build-up only results in pedal pop when it quickly affects the output signal. The quicker the discharge, the “shriller” the pop. The slower the discharge, the “duller” the pop.

The same can be said on how filtered the pop is. If a pop is filtered enough it can be transformed into a “thud”-like sound. You can read more about that here.

After some careful thought the next thing to do is take a look at the schematic and try to pin-point possible areas where charge build-up can occur. But first…we need a schematic. I was pointed to Fred Brigg’s La Revolution Deux blog and found a schematic for an iSP Decimator model similar to what I had. Along with the schematic it’s nice to have the datasheets handy for any ICs or transistors onboard. This Decimator only uses 3 types of ICs:

  1. THAT2181C – Voltage Controlled Amplifier
  2. LF353 – Dual JFET Op Amps
  3. HEF4013 – Dual D-Type Flip-Flop

And 3 transistors:

  1. 2N5484 N-Channel JFET
  2. KSP222A NPN Gen. Purpose Amplifier
  3. 2N5551 NPN Amplifiers

Reading through some of the datasheets I suspect the THAT chip is intercepting a DC input voltage. Though, this is ruled out since there happens to be an input coupling capacitor which should thwart any chance of a DC voltage popping up at the input of the VCA.

Eventually I take another look at the schematic and realize the switching circuitry for the model I have isn’t conveyed. This is in fact directly related to the original problem, so maybe the solution lies in that area of the board…

I pull flex my reverse engineering muscle and trace out the Decimator’s switching circuit. This is important since it reveals a 2N5484 JFET transistor used to switch the pedal on and off. It’s important to understand conceptually how this switching circuit interacts with the rest of the circuit. I’ll explain the inner workings of how the pedal switches ON and OFF. (I’ve made a mock-schematic for you in Figure 1).

Figure 1 - Mock Schematic for Conceptual Use

Figure 1 – Mock Schematic for Conceptual Use, Final Mod is in Red (discussed later)

When the pedal is disengaged, the gate terminal of the JFET is too low of a voltage to allow current to pass through the source and drain terminals. This effectively severs the dependency of the input signal from the VCA’s operation, leaving only a virtual ground (4.5V set by an on-board potentiometer) applied to the Ec+ control pin (pin 2) of the VCA. This DC voltage is constant and, at 4.5V, the pedal sees virtual ground. (This is because the ground, pin 6, of the VCA chip is also seeing 4.5V, so in the chip’s perspective it’s ground.)

If we take a look at Figure 2 we see that when the chip sees a control voltage of 0V (in relation to it’s ground pin) the VCA gain is set to 0dB. This means the chip doesn’t amplify or attenuate. Whatever signal you put into it should also be received at the output.

Now let’s understand what’s going on when the pedal is engaged. Take yet another look at Figure 2. If we decrease our control voltage the amount of gain we apply to the input signal proportionally decreases. Essentially, when engaged, the circuit varies the DC voltage at this Ec+ control pin and this controls the amount of gain the VCA applies to the input signal.

Figure 2 – Note that the control voltage is in relation to virtual ground, so in this case our virtual ground and the control voltage are equal at 4.5V.

The control voltage is a function of two things: (1) the amplitude envelope of the input signal and (2) a user-controlled threshold voltage set by the potentiometer. If the input signal’s amplitude envelope is below the threshold voltage the circuit decreases the control voltage accordingly and the VCA attenuates the signal. If the input signal’s amplitude envelope is above the threshold voltage the circuit increases the control voltage such that the VCA eases off with the attenuation.

So how does the circuit increase or decrease the control voltage? By way of current! Firstly, both the input signal amplitude envelope and the threshold voltage are sent to a differential amplifier (which we can think of as a comparator for ease of discussion). This component increases or decreases it’s output voltage based on the comparison of its two input signals. This voltage is seen at the cathode side of a diode. The anode side sees the drain terminal of the 2N5484 FET. If the voltage across the diode (which is based on the comparison above) is positive enough, current starts to sink through the FET and resistor R37. This current produces a voltage difference across R37 that pulls the control voltage lower than virtual ground. This in turn provides the attenuation and, hence, “noise” reduction based on the plot in Figure 2.

Pretty cool, huh?

Now for the main take-away: This control voltage is only there because the FET is allowing current to pass through it. When the pedal goes from being engaged to being disengaged (i.e. when the gate voltage of the FET is suddenly hit with 9V from the switching circuit) the current providing the drop in control voltage ceases and the control voltage increases (or decreases) back to it’s original virtual ground of 4.5V.

This self-correction of control voltage is sudden. So sudden that this popping sound could be originated by it’s occurrence. If a fast voltage transition is the suspect, why not find a way to slow down this voltage transition?

Take your thinking cap out: what causes the voltage transition? In this case, it’s the step change generated by the switching circuit applied to the FET gate terminal. This type of step-change signal is depicted in Figure 3. All we need to do is smooth out this transition (Figure 4) while making it last long enough to not hear a “pop” in the output. We can achieve this by constructing an RC circuit at the gate terminal while choosing component values that allow a slower voltage transition.

Square wave/periodic step-changing signal

Figure 3 – Square wave (periodic step-changing signal)

Figure 4 - Same signal as Figure 3 showing the affects of applying an RC circuit

Figure 4 – Same signal as Figure 3 showing the effect of applying an RC circuit

The circuit already utilizes a 1M-ohm resistor at the gate terminal. What needs to be added is a capacitor between the gate terminal and ground (0V). I tested the pedal’s operation with a 103 ceramic capacitor branched between the gate terminal and ground. This allowed a softer fade out of the current through the FET which ultimately eliminated the “pop.” Awesome!

All that for adding a little capacitor! We got a bit technical this time around but nonetheless I hope you enjoyed this post! This one’s for Deadwolf guitarist and Afterglow Studios’ owner/producer Cody Morse. Look out for Deadwolf at Buffalo, NY’s HerdFest, June 17th at Dreamland!

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