eTap2hw Flowchart

Steve Mitchell has produced an excellent and very easy to follow ‘flow chart’ that shows the signal paths through the eTap2HW circuit. It shows clearly how it all fits together without being too technical. Well done Steve!



A version V2 board build, taking most retrofits directly into the newbuild

A version V2 board, it’s the same old classic board but now with special solderpins so the resistors belonging to the FET transistors can be replaced during the optimalization process developed by Stephen Mitchell. A small 1cent part (qty 8) but a big step in enabling this optimalization without damaging the motherboard. Yes, some values of resistors and capacitors did change also and even two resistors are not required anymore!

Changes to the original build:

The exact changes to the existing kit is a small set of components: Firstly, 8 solder pins are added to allow easy exchange of the resistor pairs per FET transistor. this is key to optimize the triode behaviour of eTap2hw: R13 and R24 are now 1K5 Ohm as an initial value (was 2K2) R12 and R23 are now 15K Ohm as an initial value (was 6K8) R9 and R17 are now 22K Ohm (was 10K Ohm) The R22 and R26 resistors are not used, location is to be kept empty C11 and C12 are now 220pF capacitors (was 120pF) A further improvement is to replace the IC1 and IC2 with TLC2272 OpAmps for slight sound improvements.

The manual presents a procedure to optimize the resistor pairs belonging to each FET transistor. it is initiated by measuring the voltage over two resistors and a feedbag through an eMail of recommended values. this process is required as the spread in FET transistors is just too much to guarantee optimal settings.

A build manual is available to support this version





When ordering parts from Newtone request the V2 kit as an extra kit. in the event that the TLC2272 is required make this also known. The TLC2272 is slightly more expensive and provides more headroom and less noise.

EFTP (Echoes From The Past) discontinued

Due to copyright concerns it has been announced that the ‘Echos From The Past’ patches will no longer be available to purchase. Regrettably, all listing information pertaining to Charlie Hall’s EFTP software being settings only  are also removed from my site on his request by PM d.d. 15-Dec-2014


What is required in addition to the Universal I/O board when the 38 mm LCD is selected as best choice?

The RGB Negative LCD Display is stacked on-top of the 38mm I2CtoLCD board and connected to the Universal I/O board through a cable. This allows for the display to be mounted upright into a 19″ enclosure. Each picture is supplied with a link to vendor information.




38 mm I2C to LCD board (kit) to be ordered through Piet

A general statement applicable for each configuration presented is that the actual switch locations are not regarded as used for the actual switch placement but more a area to solder the wires to for the switches outside the area if the LCD display. In the kit are buttons supplied , with using the rotary pot possible redundant.










arduino-unoNote1: This Adafruit RGB LCD unit is including the required RGB LCD display!

Note2: In most cases the button positions are not used and act as connections to your buttons

Note3: For the buttons you need to establish what is best fit for your enclosure.

Make yourself- A small circuitry to decouple computer with analog devices (ask for link)

What is required in addition to the Universal I/O board when the Adafruit LCD shield is selected as best choice?

The Adafruit LCD shield is stacked on-top of the Universal I/O board and both boards are stacked onto the Arduino UNO making it a appr. size of 80mm x 54 mm x 38 mm (LWH)

For order information select  the description








arduino-unoNote1: This Adafruit RGB LCD unit is including the required RGB LCD display!

Note2: In most cases the button positions are not used and act as connections to your buttons

Note3: For the buttons you need to establish what is best fit for your enclosure.

Make yourself- A small circuitry to decouple computer with analog devices (ask for link)

Bulletins to improve eTap2hw workings and support on automation

Bulletin 1:

In the last year it became evident that there are opportunities  to improve the performance of the eTap2hw unit further. Extensive investigations carried out by  ChrisG revealed that headroom could be much improved by removing two (2) bias resistors at the first operational amplifier.

Bulletin 2:

In measurements done on a large batch of J201 FET’s by both Stephen C Mitchell  and Philip Hawthorne  it became clear that a simple (laymen) procedure (CAD/flow done by Philip) could be used to achieve the most optimal setting of both FET’s.

Although a procedure on optimizing FET’s was already mentioned in the build instructions manual this procedure was aiming for engineers with sufficient knowledge. Now, thanks to both Steve and Philip, it is in a format that’s easy to apply for most of the DIY builders.

Bulletin 3:   Update  26/1/14

Issued by Steve to share the special power-interface board when automation is considered. This board with capacitors and inductors was designed after a dialog with Johan Forrer this to avoid cross-talk of the computer with the analog eTap2hw unit over the power connecting wires.

Bulletin 4:

Describes  the Cutting Edge filter that can be applied to also the eTap2hw unit. The frequency response characteristics are done by Philip and Steve.

Bulletin 5:

Improving FET gain and lowering white noise in eTap2


A ‘thank you’ to all who participated in this ChrisG, Johan, Philip and Stephen for all the endless hours to achieve this excellent work result. It is a true reflection of the ‘open source’ approach demonstrating that the ‘sum of many’ provides results exceeds over commercial products in both cost and performance.

Also a big ‘thanks’ to Steve for the effort taken in understanding and applying the technical papers of Dimitri Danyuk on FETs simulating triodes and improving his maths!


eTap2hw automation, an introduction


Philip Hawthore’s hybrid project including automation


Some additional info…..

A next step in the evolution of the eTap2hw unit is the addition of automation so the user can select particular patches both pre-loaded and self programmed.


The automation I would like to introduce is fully based on Johan’s excellent efforts and the additional features added by Philip resulted in the presented approaches al based on the next schematics designed and tested by Johan:


As the core microprocessor system of choise is the Arduino UNO there is an requirement to allow for a simple interface shield  to the outside world. This interface goes on top of the Arduino UNO and looks like:


The connections between this universal interface board and the Arduino is here shown with pin connectors. In the event that an Adafruit LCD shield is going to be used those pin connectors should be changed to stackable pin connectors. The above universal interface is presently available as a kit supporting all acceptable configuration being:

  • Use of parallel LCD display
  • Use of I2C LCD display

in both display configuration offerings there is also a connector allocated for the buttons. Here is an overview of the two different configurations being stackable and non stackable:


When the Adafruit LCD shield is used it’s going to be used the I2C connection is used and the button connection can be used to support Philip’s feed-trough potentiometers. Here some pull-up resistors are redundant.

A matrix visualisation of possible configurations supported:



Lets go through all the configuration modes step by step:

The I2C connector. note the use of rainbow colours to make assembly easy!

Screen Shot 2013-02-10 at 2.51.20 PM



The potentiometer connections, remember that pull-ups are not required.

Screen Shot 2013-02-10 at 3.31.34 PM


The parallel LCD connector

Screen Shot 2013-02-10 at 2.51.42 PM


The button connector (if the potentiometer feature is not used)

Screen Shot 2013-02-10 at 3.31.17 PM

And last but not least the interface connection to the eTap2 unit.

Screen Shot 2013-02-10 at 3.18.08 PM


The Adafruit solution as designed by Philip:

A picture of that complete installed Adafruit shield:


The buttons assembly, not shown here are connected to this shield replacing the ‘on board buttons not installed)

Obviously the size of this complete assembly is to be considered as it will not fit in small or 19″ enclosures (90Lx60Wx36H1…46H2) all mm. were H1 is flush without display and H2 top with display mounted. Between H1 and H2 is then your height requirement. Activities are ongoing to also support a 19″ solution with integrated buttons.





status: living document



An Introduction to eTap2hw


This unit, as shown in this poster, is available from Newtone in the Netherlands at around 67 Euros excluding shipment cost. At the present use Newtone’s email address  to start queries and/or acquisition of this vintage echo unit.

  • The cost of the kit is based on only material cost so no uplifts like profit and recovering development cost are added
  • In addition, a preferable metal enclosure, 4 potentiometers, 1 digital BCD rotary/thumb wheel switch, a couple of input/output sockets and a mains adapter is required to build the complete unit.
  • On the right side of the header are two buttons marked  ‘SM ‘and ‘ST’ those are your entries to fora with more information on eTap2hw. Those two locations are also available for questions raised to a growing community of eTap2hw users.



DIY automation eTap2hw

A next step in the evolution of eTap2hw is adding DIY automation to the unit. In the spirit of ‘open source’ I would like to present a simple interface between the unit and an Arduino UNO single board computer also designed with ‘open source’ in mind. Obviously commercial designs are also on the market (soon) if the effort of building it yourself is not within your scope or interest.

The actual software required is presently designed by an engineer (Johan) in the USA and is reaching maturity now. For the early adaptors, who are possible interesting in an interface solution, I would like to share a first simple interface board that’s rather easy to assemble. In a later post I’ll address the special board (shield it’s called by Arduino specialists) that adds directly on top of the Arduino unit hence making the assembly a complete dedicated interface to the eTap2hw unit. For obvious reasons this shield design is rather complex to design and requires a ‘do it once’ approach to avoid timing and cost impact.

This board is sized in a way that utilizing terminal blocks (8 in a row x2) are possible. The unit is limited to 3 snubber networks and 3 logic ports. The snubber networks are there to smooth-out the possible ripple from the microprocessors pulse train while the logic ports are to manage the BCD connection of the eTap2hw.


A real size impression of the little single sided board

PDF file of board




simple components layout


A visualisation aid

On Pouchi site in France I found an enclosure of the eTap2whw that would allow for an easy 3D view of the inners of the unit and its surroundings. I guess a picture tells more then 100 lines of text.

by permission Pouchi

For obvious reasons I would not recommend building eTap2hw into a plastic enclosure as screening is a good way of keeping external distortion away from the unit. Anyway, a big Thanks for Pouchi for sharing this ‘insight’