DanEcho modification for harp players

The DanEcho is a digital echo/delay effect pedal made by DanElectro. It's priced reasonably, comes in a very sturdy housing, is easy to use and hence popular with many musicians – including harp (that's harmonica) players. Unfortunately, many harp players complain that the DanEcho "sucks the tone" from their playing. Specifically, the low-frequency "bottom end" is often weakened or lost when running the microphone through the DanEcho.

This page describes how to optimize your DanEcho for use with high-impedance microphones, especially crystal or ceramic mics, as used by many blues harp players. It describes a simple modification to the DanEcho's internal circuit board, using parts for about $3. Some soldering skills are required; of course, this modification will void your DanEcho's warranty. Alternatively, the last section will describe how to build an external buffer amplifier for using high-impedance microphones with any effect pedal.

Here's an overview of this page's contents:

The small print: This modification will void your DanEcho's warranty. Neither DanElectro nor myself will be responsible for any damages to the DanEcho or any connected equipment resulting from this modification. On the positive side, there are no dangerous voltages inside the DanEcho which could present hazards during your work! – If you have any suggestions or questions, please send an email to juergen@e–basteln.de – thanks!

(C) 2002 Jürgen Müller, Lohbekstieg 32f, D-22529 Hamburg, Germany

What's the point?

The input impedance of the DanEcho is much lower than the 1 MOhm typically found in tube amps – only about 100 kOhm for the DanEcho. Crystal and ceramic mics are especially sensitive to such a lower-impedance load; they will lose a lot of the low frequency part of their output. Dynamic microphones (including the older controlled reluctance types etc.) are not as sensitive to lower impedances. This would explain why users of dynamic mics, like the Green Bullet, may be happier with their DanEcho than JT-30 users.

The modification desrcibed here adds a little buffer amplifier to the input, which provides an input impedance of 1 MOhm or higher. It sits directly on the DanEcho circuit board, works from the pedal's standard internal power supply, and sounds fine to me.

If you don't like the idea of approaching your DanEcho pedal with a soldering iron, there are two outfits who will carry out a similar modification for you. Ron Holmes charges $75 for the mod, John Kinder asks $140. I assume they use the same approach as presented here, but since I have never seen a pedal modified by either Ron or John, that's just an educated guess. If you are handy with a soldering iron (or know someone who is), I would definitely recommend the do-it-yourself modification...

Mike Curtis has instructions for building his MikeMojo, or will build you one for $50. It's a buffer amplifier like the one presented here, but is intended to be mounted in a separate box outside the DanEcho. Hence, it can be used with other effects or amplifiers as well, but requires additional housing and connector hardware, and will need its own power supply (two extra 9V batteries for the dual supply voltages it requires). If you would prefer a separate unit, please also check the section "Building an external unit" below, which shows how to modify the single-supply design presented here for installation in a separate box.

By the way – the DanEcho has an additional quirk: Its electronics remain in the signal path even when the DanEcho is in "bypass" mode. Pushing the bypass button does not create a direct connection between the input and output jacks. Instead, the signal still goes through the DanEcho circuit – including the low-impedance input section –, just the echo effect is switched off. Hence the complaints that the DanEcho affects tone even when switched off. I am not aware of a modification which converts the DanEcho to "true bypass". Since the pedal sounds good after the modification, even in "dry" mode with the echo switched off, I don't think there's a need to go further.

Circuit diagram

If you are technically minded and want to look at the actual circuit change, here's the diagram of the DanEcho's input stage before and after the modification. (If this does not mean anything to you, I hope you can still safely make the modification by following the instructions below.) When comparing the diagram with the instructions below, please note that the circuit is on two different boards, as indicated by the dashed line.

Circuit diagram – click to open full-size image Circuit Diagram – Click the image for full-sized version.

The original input stage has a simple transistor input buffer. With the transistor itself, the 220 kOhm pull-up resistor and the 470 kOhm input termination, the overall input impedance is just about 100 kOhm at audio frequencies. The modification replaces the transistor with a unity-gain operational amplifier. This amplifier's very high-impedance input allows us to move to higher-impedance resistors as well. With resistor values of 2 to 3 MOhm each, an overall input impedance of 1 to 1.5 MOhm is obtained – as also found in typical tube guitar amplifiers.

It is important to chose an op-amp which works well with the limited 5V supply voltage available inside the DanEcho: There is not much headroom between the supply range and the signal amplitude, so the op-amp's input and output must be capable to swing over the full supply voltage range (this is called "rail-to-rail operation"). I used a TLV2460 from Texas Instruments. It is especially suited for battery-powered operation, because it offers single-supply voltage, rail-to-rail-operation, and low power consumption. It also has quite good noise characteristics. I don't use the TLV2460's shutdown mode, so the TLV2461 is an equivalent choice at a lower price. See the data sheet from Texas Instruments for details.

What you will need



Unfortunately, both the TLV246x, or similar single-supply op-amps, and the MegaOhm metal film resistors, are not-so-common components which are probably not available at your local electronics store. The components are available from online sources on the web; some examples are given below. However, it may be difficult to find a single source carrying both items. In the US, you might order from Digi-Key and go with 2 MOhm resistors; being based in Germany, I ended up ordering from two different suppliers (RS components and Conrad).


Only standard hand tools are required. You should be reasonably proficient with the soldering iron, especially when using a small-outline op-amp package.

Disassembling the DanEcho

Making the modification

That's it!

Re-assemble the DanEcho in reverse order of disassembly:

On the other hand, while you have the DanEcho apart, you may consider re-painting it. (If you happen to dislike the violet/pink color, like I did.) The "V" ornament and the footswitch button are screw-mounted to the case and are easily removed; the plastic insert for the connectors and control panel is just inserted loosely anyway. The stripped metal case can then easily be sanded and painted. Mine now has a charcoal hammertone finish. No, I don't feel this produced any further improvements in tone ;-)

Very Cool DanEcho – click for full-size image Very Cool DanEcho – click for full-size image.

Power supply notes

While I was looking at the DanEcho's input circuit, I also checked the power supply section, which is located on the piggy-back connector board. Since I had not ordered DanElectro's external power supply, I was wondering whether I could safely use a cheap, unregulated "wall wart" power supply instead, or whether the more expensive regulated type is required.

As can be seen from the circuit diagram below, the pedal itself includes a standard voltage regulator to create a stable 5V supply voltage for the pedal electronics. Hence, it is safe to use an unregulated supply, set to either 9V or 7.5V DC. (The regulator also confirms that it's absolute nonsense to use DanElectro's "vintage batteries". Rest assured that the DanEcho's electronics are well-isolated from any specific properties of the battery...)

Power supply circuit – click to open full-size image Power supply circuit – Click the image for full-sized version.

By the way, my DanEcho draws just below 40 mA of current – pretty much independent of whether the echo effect is active or "bypassed". The modification described here has not measurably changed the current consumption. With typical capacities of 500 to 600 mAh, an alkaline 9V battery should last 10 to 12 hours. Not great, but fair enough. I guess the reports of extremely short battery life, which occasionally show up on the web, are due to forgetting that the DanEcho is still powered when in bypass mode. (Since the LED indicator light is off, there's no reminder that the DanEcho is still on and drawing current.)

Building an external unit

As discussed in the first section of this page, there may be reasons for building an input buffer in a separate box, instead of incorporating it into the DanEcho – maybe you want to use your high-impedance microphone with a choice of different effects, or you just don't have a DanEcho but some other echo effect, and are not familiar with its internal circuit.

This circuit diagram shows how to adapt the circuit used for the DanEcho modification for mounting it separately. It's the same single-supply op-amp buffer, but modified for operation from a separate 9V battery. A few changes from the internal version discussed above:

I would appreciate any feedback on practical implementation and use of the stand-alone or integrated buffer version. Please send an email to juergen@e–basteln.de – thanks!