Category Archives: Hardware

The Last Stage …

“A box without hinges, key, or lid,
Yet golden treasure inside is hid.”
J.R.R. Tolkien, The Hobbit   

The Final Part?

At the end of the last Chapter I told you that I had decided to design an effects pedal-sized version of the vintage echo box that had started out as a rough prototype over three years ago.

Initially I made a few measurements to see if there was any chance that Piet’s original eTap2hw motherboard and my Arduino automation could be squeezed into a typical guitar effect enclosure, such as the Hammond 1590XX. It quickly became apparent that this wasn’t going to be possible so I started a re-design of the whole thing from scratch. At first I simply tried to stick with Piet’s motherboard design and designed a new PCB layout for it. One of the most popular PCB design applications is undoubtedly Eagle but I never really liked it or found it user-friendly and once team member Mick Taylor had pointed me in the direction of DipTrace, I immediately found it intuitive and easy to use.

Following various false starts I was beginning to settle on a two-board design with the audio circuitry on one PCB (basically this was Piet’s original motherboard design) and the ‘brain’ which consisted of the Arduino and the circuitry from Piet’s Universal I/O board on another PCB.

Two Boards

An early design with the Audio (L) and Digital ‘brain’ (R) on separate PCBs

This early design retained Piet’s original preamp including the Fetzer valve input stage but Steve and Mick had been quietly working on a new improved design that used four FETs which would end up as the Stanley-FX Baby Blue pedal, a replacement for the already successful eTap2hw pedal from the same company. (The Baby Blue, effectively a Blue Nebula with the original eight eTap2HW echo effects and without the ‘bells and whistles’ of automation etc., is already available to buy from the Stanley-FX website at £129.99.)

BabyBlue echo

The Stanley-FX Baby Blue

I had also discovered the Arduino Nano which is a much more compact little Arduino which still retained all the memory and processing capability of the Arduino Uno I had used in the original designs.

The team consisting of myself, Steve, Mick and Piet (by the way none of us has, as yet, ever met in the flesh) exchanged ideas and designs via email and Dropbox eventually ending up with a ‘final’ schematic that incorporated the 4-FET preamp, the Arduino Nano ‘brain’, the FV-1 DSP chip, two EEPROM memory chips for the DSP programs and another EEPROM that would store the User patches, allowing up to 128 patches to be stored.

Using Diptrace to capture the schematic from our various efforts I came up with an initial PCB design which Mick, who has vast experience in this area from his own Stanley-FX pedal designs, reworked to improve the layout, give better separation of the digital and analog circuitry and add ground planes that would ensure the Blue Nebula would enjoy excellent low-noise performance.

The design did end up on two PCBs: a Main Board (with most of the circuitry) and a Controls Board which had the pots and navigation switches. In this early design the LCD was a separate module that would be connected to the main board by a short cable. The two PCBs were interconnected with a short ribbon cable.

To ensure the design would all fit correctly in the proposed Hammond die-cast enclosure I used DipTrace to export 3D models of the boards and imported these into a 3D CAD package called DesignSpark.

3D Render Iso3D Render Iso Transparent

At this stage, with everyone happy with the progress so far, I ordered a batch of PCBs and eagerly awaited their arrival so I could start putting together the prototype. The boards arrived and I was very pleased with the quality so I got busy assembling the first working prototype.

Blue Nebula Boards

The prototype Blue Nebula PCBs, Controls Board (top) and Main Board (bottom).

By this stage I had come up with the name Blue Nebula for the new effects pedal and the other guys liked that so that name has stuck but, in honour of the original eTap2HW creator Piet, who is Dutch, I decided to built the prototype in an orange Hammond enclosure 🙂

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The prototype Blue Nebula – yes it’s Orange!

This initial prototype was put through extensive testing and enabled us to decide on a number of changes and improvements that would make the pedal better from both the user’s point of view and also simplify the assembly if anyone wanted to build one for themselves. For example we decided to

  • Replace the separate LCD module with one mounted directly on the controls board
  • Replace the small navigation/editing buttons with a larger Navigation switch
  • Have the Controls Board plug directly into the Main board so avoiding the need for special tools for making up a ribbon cable
  • Relocate the MIDI circuitry onto the Controls Board (it was originally on the Main Board)
  • Move the input and output jack sockets slightly further apart for a better fit in the enclosure
  • Move the Up and Down footswitches further apart so wearers of Size 12 boots wouldn’t accidentally stomp on the bypass switch 😉
  •  Fit a Lexan faceplate to protect the LCD from scratches and ingress of dirt and liquids (fancy a beer anyone?)

Mick quickly re-designed the PCBS and after more 3D modelling we ordered a batch which myself, Mick and Steve then used to build a number of final pre-production units to ensure all our modifications had worked out and we hadn’t introduced any other issues.

Blue Nebula 3D Model

Blue Nebula 3D Model

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A finished Main Board

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The Controls and Main Boards powered up and working.

The hardest part of the assembly is the machining of the enclosure to ensure everything will fit together correctly and we realized that this would be quite tricky for the average builder who would possibly lack either the ability and/or the tools to produce a sufficiently accurate result.

The pre-production Blue Nebula before it received its paint job.

The pre-production Blue Nebula before it received its paint job.

Mick invested in a CNC machine and after some trial and error and making extensive improvements to the machine itself he was happy that he could produce accurately machined Blue Nebula enclosures. Mick (proprietor of Stanley-FX) can also undertake powder coating and silk screen printing and the CNC and finishing processes have resulted in a fabulous result:

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The finished Blue Nebula enclosure as received from Stanley-FX

Everything fits together perfectly and the end result is really quite stunning to behold. So, at last, that effects pedal I had imagined way back at the start, is now sitting on my pedal board, looking and sounding great and with features I hadn’t even dreamt of when I set out on this ‘journey’ way back in February over three years ago!

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The Blue Nebula will soon be available from Stanley-FX as a fully built, tested and guaranteed unit at a very reasonable price (To be confirmed). If there is sufficient interest it may also be available in kit form with the finished enclosure as shown above. Further details will be published as soon as possible.

I want to finish this story by saying a big ‘Thank You’ to Piet, Steve, Mick, Ecca, Rolf, Johan and all the others who all played some part in this journey with their generous help, designs, ideas, suggestions and encouragement that kept me going. I hope you all agree that the end result has been well worth it 🙂

Phil.

If you’d like to be kept up to date on the Blue Nebula development including prices and availability, head over to the Stanley-FX website and subscribe.

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The Long and Winding Road

Part the Third

“You certainly usually find something, if you look, but it is not always quite the something you were after.”
J.R.R. Tolkien, The Hobbit

In this the penultimate part of the journey the path forks and I take a look at some experiments with using a valve preamp and improvements to the original FET preamp.

Opening the Valves

Eric Thacker, better known as Ecca, had demonstrated on the Shadows Music forum that Piet’s FET and op-amp preamp design could be replaced with a valve (tube) preamp that was available from a number of eBay sellers in Hong Kong and China. (Here, for example).

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The valve preamp and Eccamatic pcb mounted in an enclosure.

The circuit was originally designed to be used as a Hi-Fi stereo preamp using two 6N3 dual triode valves, one valve for each stereo channel. For the eTap2HW module we only require a mono audio pathway so the left channel of the stereo pair was used as the input preamp feeding the echo module and the right channel became the recovery amp, taking the echo module output and acting as a buffer and output level control.

Eric had produced a PCB for his ‘Eccamatic’ design which allowed the echo module to be plugged in, provided a step-up power supply to generate the HT voltage and the LT heater supply for the valves and had connections for the three pots that adjust the echo settings.

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The bits for Eric Thacker’s Eccamatic pcb.

Having already designed the automation circuitry it was easy to adapt the design so that the Arduino Uno would feed the pot inputs on the Eccamatic board, reading the required settings from pots mounted on the front panel.

The front panel also had input and output pots, controlling the signal levels.

I have described this valve EchoTapper build in a series of earlier posts and if you’d like more details just click on the Valve entry in the Categories list on the right of this page.

When the new unit had been completed, the sound was quite pleasing with less hiss and noise than the FET preamp but rather ‘sterile’ as might have been expected from it’s origins as a Hi-Fi design. As I am sure you will know, guitar amplifiers and the early Meazzi echo units have circuits that are far from Hi-Fi for a very good reason (at least in the case of the typical valve-based guitar amp) – the almost perfectly flat frequency response of a Hi-Fi design and it’s deliberate lack of harmonic distortion (achieved largely through the use of negative feedback) is really not what guitarists want or indeed need to get the sound they desire. The original Meazzi preamp is hardly a classic of valve design but somehow has that magic sound that we have come to love.

Piet’s FET preamp design had made use of the ‘Fetzer Valve’ circuit which uses an FET to emulate the sound of a triode valve so it does create harmonically rich sound when the input level control is set correctly to match the guitar pickup level to ‘push’ the Fetzer ‘valve’ into generating the pleasant sounding harmonics we all like.

Steve Mitchell soon had his thinking cap on and he came up with a number of modifications to the valve circuitry that, according to his simulations of the circuit which he had made using the TINA SPICE modeller, should tailor the frequency response better to the typical guitar pickup signal and also generate those desirable harmonics to give that rich sound we all love.

Steve and I came up with a three stage process that culminated in a final design that sounded great.

Stage 1: Remove the built-in stereo volume control pot and increase the input impedance

Stage 1 was essential to allow the input and output level controls to be separated and to provide a better match to the typical guitar pickup’s high impedance.

Stage 2: Remove the negative feedback from the preamp and add Meazzi-like tone shaping

Stage 2 was regarded as highly recommended to obtain a better tone and more gain which would encourage the desirable valve harmonics and tailor the frequency response which was very flat and resulted in a ‘lifeless’ sound, thus improving the sound for guitar purposes.

Stage 3: Add a separate Gain pot and three-way tone switching

The Stage 1 and Stage 2 modifications had resulted in a really good sounding preamp but Steve came up with Stage 3 which would take the whole thing to another level. Whilst not regarded as essential, these mods did make the unit even more flexible. There would now be three ‘level’ controls, the new Gain pot controlling the drive to the second valve stage in the left channel of the amp. The Volume pot controls the signal to the echo module and the Master pot controls the level from the output socket.

Modified Vavle Preamp Flowchart

Flowchart by Steve Mitchell (SCM)

Modified Valve Preamp Freq Responset

Predicted frequency response of the modified circuit

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Front Panel of the final Valve-based Echotapper

The 3-way tone switch provided ‘normal’, ‘vintage’ and ‘warm’ options by tailoring the bass roll-off. On the unit in the picture (built for Mario Voltolini in Italy) I also added, at his request, a Cutting Edge Filter (CEF) which could be switched in and out if required.

Biting the Bulletins

In parallel with the improvements to the valve preamp, Steve was also working on a series of modifications to Piet’s FET preamp design.

One of the problems with any FET is that individual devices, even from the same batch, can have parameters that vary over quite a wide range and this makes it difficult to design a circuit that will allow the FET to operate in the optimum part of its characteristics.

Steve and Rolf Holmberg collaborated and came up with a spreadsheet that would calculate the best resistor values to bias the FET into the optimum operating point. This would be a bit complex for the average user to get to grips with so Steve and I came up with a simpler ‘flowchart’ approach. This would allow the best operating point for the FET to be found using a simple voltage measurement and a little trial an error with a few preferred resistor values.

Steve put together a series of ‘bulletins’ that were published on Piet’s EchoTapper blog which also included simple modifications to improve positive signal headroom, improving the FET gain and reducing white noise (hiss). These mostly involved removing or changing some resistor values and adding some extra capacitors.

Piet has since modified his original preamp PCB design to accommodate these improvements and this is documented on his blog.

What Next?

Now I had two excellent sounding echo units but I had an urge to see if it would be possible to squeeze all this technology into a smaller package, one that would fit on a pedal board or sit neatly on the floor at my feet like a typical guitar effects pedal.

Thus began the germ of an idea that would result in the Blue Nebula. It had to be compact, so that ruled out the use of valves and it needed to be much easier to build, with minimal off-board wiring so that, hopefully, anyone with sufficient experience would be able to put one together from a kit or buy a completed built-to-order unit at reasonable cost.

We had to go from this …

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My first automated eTap2hw

 

to this …

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The final Blue Nebula Design

 

To be continued.

The Journey Continues

“Bilbo saw that the moment had come when he must do something.”
J.R.R. Tolkien, The Hobbit

 Chapter 2

As I explained in Chapter 1, while being very pleased with the sound of my newly constructed eTap2hw echo box I really wanted a way to store some settings for the tunes I played regularly.

My previous echo machine had been a Zoom RFX2000 with the EFTP programs from Charlie Hall. These programs or patches were numbered from 0-42 on the Zoom’s two digit seven-segment display and they came with a list of suggested patches for the common tunes by The Shadows.

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The Zoom RFX2000 displays two-digit preset numbers

Having been able to compare the sound of the RFX2000, which I had been previously pretty happy with, to the warmer and more ‘analog’ sounding eTap2hw, I decided to try to add the ability to store the settings for the tunes to the eTap2hw so I could recall them easily. The Zoom RFX2000 still required you to either remember or look up the patch number in a printed list of tunes.

My original short ‘wish list’ was something along the lines of:

  1. Ability to name patches, for example “Apache” or “Wonderful Land”.
  2. Be able to adjust the effect parameters by using real knobs,
  3. and store and recall these settings easily.
To which I added, as possible future additions:
  1. Interface via USB with a computer for backing up and restoring patches
  2. Addition of MIDI control to select patches, possibly by using a MIDI foot controller or by sending program change messages from a sequencer playing the backing track.

About this time I discovered some forum postings by a guy in the USA called Johan Forrer who had come up with a design for the automation circuit and had produced a simple version of the software to drive it, for the Arduino platform. When I got in touch with Johan he very kindly and with no hesitation, sent me the source code for his automation.

eTap2hw-Automation 014

One of Johan Forrer’s early prototypes with basic automation from October 2012.

Having studied his code I quickly realised it wouldn’t fulfil my basic requirement of being able to name the patches to match the tunes: he had allowed for 8 presets (basically one for each of the 8 emulations in Piet’s SKRM-eTap2hw module) and only four user patches which could not be named, only referred to by number. Each could use any of the 8 emulation presets and you could set the values of the three parameters of each by hitting the up and down buttons but there was no provision for setting the parameters with real knobs.

Johan’s code did, however, have the basic structure that would be needed so, with his permission, I started to ‘hack’ it and add the features I’d planned. First though I needed the hardware on which to run the automation and, whilst Johan had built his own Atmel Arduino-like microcontroller circuit I decided to go for an off the shelf Arduino Uno and an LCD/Buttons shield kit from Adafruit.

The latter would be more or less essential to leave enough free inputs and outputs on the Arduino to satisfy my ambitious plans. As it connects to the Arduino via the I2C bus, it required only two input/output lines to operate both the LCD and the buttons, rather than the more normal parallel LCD drive which needs up to seven of the Arduino’s precious digital pins.

In the manual eTap2hw design the three parameter pots are connected directly to the SKRM module’s P0, P1 and P2 inputs. These each provide  a variable DC voltage between 0 and 3.3V that is read by the DSP code running on the FV-1 chip on the module and can used to alter the parameters, depending on what the code has been designed to do. Piet’s eTap2hw code mainly used P0 to control the mix of wet and dry signal, P1 was a program or ‘heads’ control which usually emulated the heads switch on the Meazzi and Vox echo machines and P2 was usually controlling the feedback or ‘repeats’ of the echoes.

To automate the system these pots had to be disconnected from the echo module and instead the voltages they were outputting would be read by three analog inputs on the Arduino. As the Arduino operates at 5V logic levels and the FV-1 operates at 3.3V logic levels, the pots would have to be wired to GND and +5V rather than +3.3V and some sort of interface would be needed to drop the Arduino’s ‘analog’ outputs to a 0 – 3.3V range.

The P0, P1 and P2 inputs on the echo module would now be driven by dc voltages output from the Arduino. A complication was that the Arduino’s analog outputs are not true analog DC voltages. Instead they use a system of pulse width modulation (PWM) to generate the output and not a true DC voltage – the wider the pulse the higher the average voltage:

Johan and Piet together had already solved these two problems by coming up with a low-pass filter combined with a voltage divider that would both smooth the PWM to give true DC and at the same time reduce it from 5V max to 3.3V max. You can see one of these on the left hand end of the breadboard in the following photo of my first test-bed prototype.

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My first bread-boarded automation test-bed. January 2013

The blue trimmer pot on the right is connected to an analog input pin on the Arduino and the LCD is showing which button was last pressed and the analog input value being read from the pot wiper. The buttons board assembly which I built on Veroboard actually ended up being used in my first completed Echotapper Vintage Echo Unit – until the buttons wore out!

At this point Piet came up with a great little design for a shield that would do all the interfacing between the Arduino, the pots and the SKRM-eTap2hw echo module.He called it the Universal I/O Shield and it certainly simplified the wiring required as it would stack on top of the Arduino and the LCD shield would stack on top of that. The only wiring required would be to the external pots, the eTap2hw motherboard and the 12V dc power supply.

The Universal I/O shield takes care of all the PWM filtering and logic level shifting between the Arduino and the echo module.

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The Universal I/O Shield stacked on top of the Arduino Uno.

Having proved my ideas were going to be feasible I continued to develop the software for the automation, which I’ll refer to as firmware from now on to avoid any confusion with any software possibly running on the PC.

In parallel with the firmware development I looked for a suitable enclosure that could house the project and after much deliberation, measurement and ‘guesstimating’ I settled on a Hammond 1455N2201 Extruded Aluminium Enclosure measuring 223 x 103 x 53mm. As you’ll see below, it was quite a squeeze to fit it all in!

The finished unit turned out very well and I even managed to include the MIDI control that had been on the ‘nice but maybe later’ wish-list.

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The Automation Version Completed – January 2013

Word had begun to get around and this project seemed to be generating a good bit of interest from The Shadows forums. Steve Mitchell, who would come to play an important role in the Blue Nebula Team, was probably the first builder to take on the task of emulating my efforts. As he says himself

I eventually got into the Automated eTap2HW after managing to contact Piet who kindly pointed me in the direction of Newtone. Then I realised that there was also an Arduino based automation, which Piet was supporting with his interface shield PCB. So I contacted Johan, Lars and yourself and it went from there when I decided to “bite the bullet” and go for broke without ever building a manual version. Once I’d purchased the interface from Piet then off I went now firmly attached to your “Journey”.

Though doing a few things a little differently, such as using a larger enclosure  (good decision Steve!), by April 2013 Steve had become the proud owner of another eTap2HW plus automation or, as he called it on his excellent front panel, his “EchoTapper Vintage Echoes of the Sixties.”

eTap2build-USB-SCM

eTap2build-SCM

The Finished Project by Steve Mitchell

While working with Steve and helping him with his project we formed a close working relationship and soon Steve was coming up with some great suggestions for improving the firmware and some clever ideas to get an even better sound out of Piet’s analog preamp design – but that will have to wait for Chapter 3!

An Unexpected Journey

“Go back?” he thought. “No good at all! Go sideways? Impossible! Go forward? Only thing to do! On we go!”
J.R.R. Tolkien, The Hobbit

Chapter One

Back in February 2013 (is it really over three years ago?) I started this blog with the idea of documenting a little project that I  had been working on since the previous November.

Little did I know, like Bilbo Baggins in “The Hobbit”, where my ‘unexpected journey’ would lead. In the next few posts I’m going to recount how this …

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November 2012: The First Prototype. It won’t win any prizes for good looks!

ended up with this …

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March 2016: The Blue Nebula

I’d been using a Zoom RFX2000 with the EFTP patches for a couple of years but my ears pricked up back in November 2012 when I heard a couple of demos by Dave Robinson of a new (to me) echo circuit called the eTap2hw which had been designed by Piet Verbruggen.

I couldn’t find anywhere to get a kit to try it our for myself so I posted a question on the ShadowMusic forum and discovered that the kit could be bought from Newtone in Piet’s homeland of the Netherlands. Even then I had to email the guys at Newtone to find out the price and order details.

I managed to order a kit and it went together without any problems thanks to the very detailed instructions Piet had provided on his Echotapper blog and it worked first time. I’d had a lot of experience since I was a young ‘un of building and designing electronics so that probably helped so before November 2012 was out I had a working prototype that, while not pretty (I’d built it in a die-cast box from an old project lying in my garage), it sounded just wonderful. Not only were the echo timings apparently spot on for the various vintage echo machines it was emulating but the unit had a nice warm sound that belied the digital signal processing that lay behind those emulations.

Having heard my prototype in action at the Northern Ireland Shadows Club, my good friend and el-president of the Club, Des McNeill, also started raving (nothing unusual there) about how good and ‘analog’ the eTap2hw sounded so we ended up buying another three kits, two for Des to build and another one for me. What had we started here!

It was now time to produce a proper housing for the eTap2hw’s we were building and Des’ skill as an aero modeller came to the fore here. Des and I worked out a design for the front and rear panels which he then had made up by a company in Belfast. By the time of our next Club meeting Des had his new enclosure built and the first kit assembled and ready to try out and it looked and sounded great.

The boxes Des designed and made (remember I said he was an aero modeller) were constructed beautifully from precision cut plywood, lined on the inside with aluminium foil for screening and covered on the outside with a lovely beige tolex.

These proved so popular with the Club members that Des ended up building five or six more of them and they are still in use regularly on Club days and by the guys who play gigs.

While I was delighted with the sound of my eTap2hw there was one thing I thought it needed to make it even better: a way to store the settings for individual tunes – mainly because I kept forgetting which echo to use for a given tune – TMB syndrome (too many birthdays!).

Thus began the next stage of the journey – automation, as will be revealed in Chapter Two.

 

New Effects Pedal Launching Soon

As some of you will have heard on social media and various forums a new guitar effects pedal to be called the Blue Nebula will be launching soon. The Blue Nebula is a compact stomp-box style effects pedal design with a strong emphasis on accurately emulating the sounds of vintage tape-based echo units but with the ability for users to upload new effects that cover a wide range of other popular sounds.IMG_3108Designed by a four-man team including yours truly (firmware and software), Steve Mitchell (new analog preamp design), Piet Verbruggen (DSP programming) and Mick Taylor (hardware and PCB design), the Blue Nebula is released as an open source/open hardware project.

The Blue Nebula will be available as a kit or built-to-order. Prices to be confirmed.

Main Features

  • Accurately emulates many classic tape echo machines
  • Can be loaded with up to 8 additional general guitar effects such as chorus, phaser, reverbs, shimmer verb and other echo effects which can be uploaded via USB
  • Other effects in the pipeline include emulations of the classic Binson Echorec (think Pink Floyd) and an enhanced Vox Long Tom echo.
  • Three parameter control knobs which, for example, can control dry/wet mix, feedback or chorus rate.
  • Built-in USB and MIDI In ports
  • All firmware updates and new effect sets are uploaded via a normal USB cable – no need for additional special ‘programmers’.
  • Advanced built-in automation firmware controls the Blue Nebula and provides full editing facilities
  • Firmware easily updated via the USB port
  • 16×2 Character LCD display shows patch names, parameter knob functions and other details when editing
  • 22 built-in factory presets for classic Shadows tunes such as Apache, Wonderful Land etc.
  • 128 User definable patches to store any other settings you can come up with
  • Can also be used in a simple manual mode – just select your effect and tweak it by adjusting the parameter knobs in real time
  • Up and Down patch change footswitches and True bypass footswitch
  • Advanced low-noise 4-FET preamplifier designed to emulate the valve preamplifiers used in some of the classic tape echo machines
  • Gain and Pre Level knobs control the generation of ‘valve-like’ harmonics and match a wide range of guitar pickups from vintage single coils to ‘hot’ humbuckers
  • Master output level control to match the bypass level or maybe set it for a clean boost with a ‘No Effect’ patch
  • Fully-featured Patch Editor & Librarian application which is Free to download.

Some links to the Blue Nebula User Manual, the Building Instructions and the Bill of Materials are given below.

If you are thinking of building a Blue Nebula please read the Building Instructions thoroughly to determine if it is within your capabilities. Most of the components are through-hole types but there are a few surface mount components. The kit can be supplied with these already soldered in place for you.

Blue Nebula User Manual

Blue Nebula Building Instructions

Blue Nebula Bill of Materials

 

Optimizing & Modding

I finally got around to optimizing my FET-based eTap2HW, the one with automation. (I also have a manual eTap2hw that I already optimized a while ago now).

What’s this optimizing I hear you ask? It’s a well known fact that FETs are notorious for having widely varying electrical characteristics even when they come from the same batch and this makes it difficult to design a circuit that will work well with any FET you plug into it. Aside from buying a big batch of FETs and testing them to find the most suitable ones, it’s usually necessary to resort to trying different biasing resistors and measuring the source and drain voltages, and keep repeating this until the FET is operating in the desirable part of it’s characteristics. By doing this we are arranging that the FET will behave very much like a triode valve and thus give us the sweetness of tone that every guitarist seeks 🙂

This could all get very tedious but thankfully Steve Mitchell came up with a fairly straightforward ‘flow chart’ approach that will get your FETs biased nicely with the minimum of trial and error. Steve has kindly produced a set of ‘Bulletins’ that explain what’s required. You can download these over on Piet Verbruggen’s Echotapper blog. The ones required for optimizing your FETs are Bulletins 1 and 2 and Bulletin 5 is worth following as well as it improves the gain of the FETs and reduces the white noise or hiss that some people find problematic, especially for recording.

While I had the unit opened up I decided to make a few modifications I’d been thinking about doing for a while.

1. First up, I decided to cut a small opening in the end panel directly opposite the USB connector on the Arduino so I could easily connect the unit to my PC whenever I wanted to update the firmware and when I’m using the Librarian software to backup my patches and arranging them into a set list. Before this I had to unscrew the end panel to get access to the USB connector which was inconvenient.

The new USB 'easy access port'

The new USB ‘easy access port’

2. My second modification replaced the ‘Wet’ output mono 1/4″ jack socket with a stereo jack socket that will accept the patch change foot pedal I described in an earlier post. I never found a use for a ‘Wet only’ output signal so this jack socket was never used and it was easy to replace it with a stereo TRS 1/4″ socket. The sleeve (S) connects to Ground, the tip (T) goes to the ‘Up’ switch and the ring (R) goes to the ‘Down’ switch.

The footswitch socket labelled FS.

The footswitch socket labelled FS.

3. My original tactile push buttons were beginning to play up. Frankly I wasn’t surprised as I had always thought this type of little ‘clickety-click’ switch wouldn’t be very durable and so it proved. I decided to remove the strip-board sub-assembly that held all five switches and replace the Edit and Mem switches with panel mounted miniature momentary push buttons.

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The old buttons on their strip-board sub-assembly.

I was able to retain the ribbon cable and connector and make up a suitable matching connector for the new switches and patch change wiring.

As I was going to be adding a rotary encoder I no longer needed the Up, Down and Select buttons so the holes for the up and down were plugged with a couple of little rubber grommets that I happened to have lying around and the rotary encoder went in the  hole where the Select button used to be, after enlarging it with a reamer.

The new switches and rotary encoder. Colour coding will help me remember which switch is which!

The new switches and rotary encoder. Colour coding will help me remember which switch is which! Note the neat little blanking plugs.

4. I’ve described how to add a rotary encoder to the eTap in a previous post and I followed that when adding the new encoder to this project. The Sparkfun breakout board makes it easier to wire the encoder. I used an RGB encoder even though I don’t use the built-in LEDs as this type has a mounting bush to fit it to the front panel; other cheaper variants can’t be easily panel-mounted. I really recommend the rotary encoder as an alternative to punching the up and down buttons like a mad thing when choosing patches or editing  the patch name!

LCD/Buttons board and rotary encoder

Buttons and rotary encoder on its breakout board.

And here’s the EchoTapper Vintage Echo Unit with all it’s mods and optimizations completed.

Catalinbread ECHOREC pedal shown for size comparison.

Catalinbread ECHOREC pedal shown for size comparison.

I just wish there was room left for a bypass switch 😉IMG_2803_edited-1

And here it is on my new ‘Shadows’ pedalboard 🙂IMG_2816_edited-1

Another New Build

This unit was built for Mario Voltolini in Italy. It uses a new motherboard pcb and LCD display board designed by Eric Thacker and a number of new subassembly pcbs designed by yours truly. These new boards support the modifications devised by Steve Mitchell and myself to improve the sound and suitability of the Yuan Jing 6N3 valve preamp for use with a guitar input, rather than its original design purpose as a HiFi preamp.

There is also a neat little MIDI interface board and a switchable Cutting Edge Filter (CEF) as per the design by Charlie Hall.

Mario requested the ability to turn off the echo by using a remote footswitch so I added a bypass circuit using a signal relay to bypass the echo module. It’s not true bypass as we wanted to retain the tone of the valve preamp when bypassed.

Click on the thumbnails below for a larger picture and explanatory captions.

Test recordings