Amp Lab: Headway EDM-1 and EDB-2

This Article Was Originally Published On: February 3rd, 2015 #Issue 15.

Tone Shaping

The EDM-1:

The EDM-1 is a single-channel device featuring a ¼” TRS input jack with a trick up its sleeve. A switch adjacent to the input jack allows the user to selectively apply phantom power to the input. Moreover, the switch allows assigning phantom power to the ring or tip. The EDM-1 also features a balanced DI output on a stereo ¼” jack. The output jack has a trick, as well. Plugging in a stereo jack switches on the internal battery (where the provided external power adapter is not being used). As yet a further trick, the ¼” output jack accepts phantom power from a desk mixer, providing even more headroom than using a battery.

Turning to the front panel, the EDM-1 has an equalizer section featuring Bass, Mid and Treble controls, which are illustrated in Figs. 1-3, respectively. In these figures, the red trace is the control turned fully clockwise (full on position). The black trace is the control at “noon” (center position) and the blue trace is the control turned fully counterclockwise (full off position). 

Fig. 1 EDM-1 Bass sweep

Fig. 2 EDM-1 Mid sweep

Fig. 3 EDM-1Treble sweep

Referring to Fig. 1, the low frequency sweep shows a low shelving control with just under 15dB boost and cut. Note that the Bass EQ looks like a bell curve, especially on the boosted signal. This appears to be due to the interaction of the high-pass filtering, discussed below. Referring to Fig. 2, the Mid control is a traditional bell curve with about 13dB of boost and cut around 600Hz. Referring to Fig. 3, the Treble control is a shelving control providing about 12dB of boost and cut.

Referring to Fig. 4, the EDM-1 also features control that Headway calls the anti-feedback Range control. For some users, this label may be a bit confusing. Rather than providing anti-feedback in the form of a tight, adjustable notch filter, the “anti-feedback” Range control is actually a variable high-pass filter. As a variable high-pass filter, this control is worth the entire price of admission on the EDM-1. Did I mention that the Range control is, hands-down, my favorite feature of the EDM-1?

Fig. 4 EDM-1 Variable high pass filter

As Fig. 4 illustrates, the Range control provides a wide variety of low-end cut, without appreciable band interaction in the higher frequencies. The Range control is thus great for taming the low end of your instrument. In this regard, the labeling on the front panel provides suggested settings based upon instrument type.

One thing I like to do is dial the Range fully counterclockwise, then turn up the bass until I get the thump I want. Then, slowly dial up the Range to remove any ugly rumble, leaving full, tight low end.

Take a look at Fig. 5. I first set the Range fully counterclockwise, and set the Bass, Mid and Treble flat. This is the black trace. Then, I cranked the Bass fully clockwise (full on) for the remaining traces. The blue trace is the Bass setting (fully counterclockwise). The red trace is the Cello setting (9:00). The green trace is the Bouz setting (noon). The brown trace is the Violin setting (3:00). Finally, the orange trace is the Rock Acoustic setting (fully clockwise). As Fig. 5 illustrates, an impressive amount of low end control is available when the Bass and Range controls are used together.

Fig. 5 Bass vs. Range

Also, don’t overlook the power of the Range control as a “room equalizer.” By dialing the Range control, you can effectively remove the “boominess” of the room. As such, I appreciate the suggestions provided on the labeling, but do not hesitate to dial the Range control to taste.

EDB-2:

The EDB-2 is a three-channel device. Channel 1 features a ¼” TRS input jack with the same phantom power switching arrangement as that of the EDM-1. Channel 2 may be sourced from a stereo ¼” jack or an XLR microphone input. By default, Channel 2 connects to the stereo ¼” jack. However, a switch on the front panel allows selection of the XLR microphone input, with or without 18V phantom power. Channel 3 is an 1/8” post-EQ input intended for iPods, mp3 players and like audio devices. Whereas, the EDM-1 has a ¼” output, the EDB-2 includes both a ¼” line out and an XLR direct out, providing a bit more flexibility in signal routing. Note that the EDB-2 XLR does not accept phantom power from a mixing desk.

The EDB-2 divides tone shaping into three general sections, including a traditional main EQ section, a Notch filter section, and a Range section.

The main EQ section features Bass, Lo Mid, Hi Mid, Presence and Treble. The EQ section is switchable between Channel 1, Channel 2, or both Channel 1 and Channel 2. As such, this EQ section is always in at least one channel path. The EQ section is illustrated in Figs. 6-10. In these EQ plots, the black trace is all of the EQ controls at their noon position. The red trace is the control fully clockwise (full on position) and the blue trace is the control fully counterclockwise (full off position).

Referring to Fig. 6, the low frequency sweep shows a low shelving control with just over 12dB boost and cut. Note that the Bass EQ looks similar to the Bass control of the EDM-1. However, the peak in our test unit appears to be shifted about 15Hz higher (from about 55Hz in the EDM-1 to about 70Hz in the EDB-2). Like the EDM-1, there appears to be essentially no high-band interaction throughout the range of adjustments of the Bass control.

Fig. 6 EDB-2 Bass sweep

Referring to Fig. 7, the Lo Mid control is a traditional bell curve, with over 12dB of boost and cut around 590-600Hz. This control appears very similar to the Mid control of the EDM-1.

Fig. 7 EDB-2 Lo Mid sweep

Referring to Fig. 8, the Hi Mid control is a bell curve, providing about 12dB of boost and cut at about 900Hz.

Fig. 8 EDB-2 Hi Mid sweep

Referring to Fig. 9, the Presence sweep is a cool EQ addition. The Presence control sits above the Hi Mid control and provides a boost or cut of just under 8dB, centered at about 2.5kHz in our test unit. In my experience with acoustic instruments, I find a lot of mileage to be had through careful adjustment of EQ in this range. Careful control here can be the difference between cutting through a mix, controlling feedback, and eliminating dominating but ugly piezo tones affectionately referred to as “piezo quack.” The presence control is a nice, gentle, and wide equalization control, which should also allow the addition of air and clarity to your instrument.

Fig. 9 EDB-2 Presence sweep

Referring to Fig. 10, the Treble sweep is a shelving filter that resembles the Treble of the EDM-1, providing over 12dB of boost and cut available.

Fig. 10 EDB-2 Treble sweep

The Notch Filter section provides a semi-parametric EQ band, with user control of Q width and frequency. The Notch Filter can be assigned to either Channel 1 or Channel 2, and has a bypass switch to remove the Notch Filter from the signal path of both channels.

Referring to Figs. 11 and 12, the Notch Filter is illustrated in various positions. Particularly, Fig. 11 illustrates the frequency control at its minimum setting centered at just over 50Hz with the Q control set to wide (red trace), its middle position (dark blue trace), and narrow (blue trace). Fig. 11 also illustrates the frequency control at its maximum setting centered at 6kHz with the Q control set to wide (teal trace), its middle position (green trace), and narrow (mustard trace). Referring to Fig. 12, the notch filter is shown with the frequency control set to its noon position, centered at about 350Hz, with the Q control set to wide (green trace), its middle position (mustard trace), and narrow (purple trace). Notably, there is no control over the gain of the Notch filter. Rather, the gain is both frequency and Q dependent.

Fig. 11 EDB-2 Notch min and max frequency

Fig. 12 EDB-2 Notch min and max frequency

The notch control can be used to carve out unwanted frequencies with razor precision, or with wide coarseness, depending upon your need. As such, this control can be used to great effect as a tone shaping element, or to eliminate problem frequencies, e.g., prone to feedback, rumble, noise, etc.

The Range section provides a switch allowing selection of three possible high-pass filter settings. Referring to Fig. 13, these settings are Bass (black trace), Guitar (blue trace), and Violin (red trace). Comparing Fig. 13 to Fig. 4, it appears that the Violin and Guitar settings are not the same between the EDM-1 and EDB-2. The EDB-2 appears to be more conservative with the cut-off positioning, favoring more low-end interaction. While I believe that Headway selected reasonable ranges for the Range switch of the EDB-2, I much prefer the variable high-pass filter of the EDM-1. 

Fig. 13 Variable low pass filter

Gain

EDM-1:

We need to spend a minute talking about headroom and performance. With the volume control fully cranked (maximum clockwise), we swept an input signal from about 10 mVrms to 1 Vrms. Up to the point of overdrive, we measured a gain of about 23dB. What does that mean? If you put in 100 mVrms, you will get about 1.4 Vrms out. The maximum input before clipping with the Volume cranked, was measured at about 470 mVrms. For signals below this level, we measured an impressive range from 0.05% THD+N to about 0.2% THD+N up to the knee where clipping begins. In these tests, we also measured signal to noise ratios approaching 100dB.

Dialing down the volume control, we were able to inject signals as large as 5 Vrms with well under 1% THD+N. Likewise, tweaking the volume control, we were able to achieve clean output as high as 5 Vrms 0.3% THD+N by setting the volume to its maximum position and constraining the input to > 470 mVrms.

 EDB-2:

We performed the same gain tests as we did with the EDM-1. With the volume control fully cranked (maximum clockwise) and the Master fully cranked (maximum clockwise), we swept an input signal from about 10 mVrms to 1 Vrms. Up to the point of overdrive, we measured a gain of about 32dB. What does that mean? If you put in 100 mVrms, you will get just shy of 4 Vrms out. As such, the EDB-2 really ups the level of available gain compared to the EDM-1.

The maximum input before clipping was measured at about 150 mVrms with both the Gain and Master cranked to their full positions. For signals below this level, we measured an impressive range from 0.02% THD+N to about 0.1% THD+N up to the knee where clipping begins. Thus, the EDB-2 again outperforms the EDM-1 for cleanliness.

In these tests, we also measured signal to noise ratios over 90dB. Here, the EDM-1 might have slightly nudged out the EDB-2 in overall performance. Dialing down the volume control, we were once again able to inject signals as large as 5 Vrms with well under 1% THD+N. Likewise, tweaking the volume control, we were able to achieve clean output as high as 5 Vrms at under 1% THD+N.

 Miscellaneous

Turning attention to the EDB-2, since two outputs are simultaneously available, we took a look to see how well they tracked each other. We set the Master and Gain to their middle positions and injected a 1kHz sin wave. As illustrated in Fig. 14, the XLR output is about 10 dB lower in output compared to the line output (1/4” output).

Fig. 14 EDB-2 Comparing Line output to XLR output

With reference to Fig. 15, in certain situations, it is possible that the XLR output will clip before the Line output. For instance, we cranked the Master to its fully clockwise position and set the Gain to about 1:30. Applying a 400 mVrms, 1kHz sine, we observe the XLR output begin to clip, whereas the Line output remains clean. Indeed, we needed to up the input signal by about another 50 mVrms before we began to see signs of the Line output clipping.

Fig. 15 EDB-2 XLR clipping before Line output

A cool feature of the EDM-1 and the EDB-2 is the input impedance switch that provides Low, Hi and +Hi settings. This switch allows the device to present a low impedance input, optimized for low noise with active pickup instruments, a high impedance for passive pickups, and an ultra-high impedance for high impedance, non-powered pickups, such as piezo pickups.

Conclusion

Kudos for the variable high-pass filter on the EDM-1. This is such a simple concept, but the result is exceptionally usable and functional. Of these devices, this was hands-down, my favorite feature. The EBD-2 replaces the Range knob of the EDM-1 with a three-position switch. I understand this compromise. However, I would have loved to see one three-position switch for each input channel. Sharing a variable low-pass filter between channels misses opportunities for even more effective use in live settings, such as for solo musicians that might want to plug in an acoustic guitar or mandolin into Channel 1 and a bass or foot drum etc., into Channel 2. Better yet, if Channel 1 of the EDB-2 had the Range control of the EDM-1, and Channel 2 got away with the current Range switch, that would really be something.

With specific regard to the EDM-1, providing the ¼” to XLR adapter in the box is a nice touch. However, the adapter causes the XLR output cable to stick out about 4-1/2” and adds weight to the unit, which can cause the unit to become top-light. This weight distribution can cause the top of the unit to tip up. I understand that adding an XLR in place of the ¼” could complicate the output jack-based power switching, but I would be willing to forego a slightly larger package for an integrated XLR output. 

At least when configured properly, both the EDM-1 and EDB-2 are capable of handling extremely large signals. Indeed, I am currently unaware of an instrument that would be capable of clipping either the EDM-1 or EDB-2 if set up properly. Still, it would have been nice to see a clip LED, especially on the EDB-2, given the complex nature of the tool, serving as an equalizer, DI and mixer/blend control.

The weight of these units is refreshing. The devices simply feel pro-grade, which instills confidence in use. The belt clip and mic stand threading are nice touches, as well. The manuals look like they are intended to be part of the product, not just an afterthought. Take the time to read the manuals and the devices will be easy to care for and use.

1-5 (unacceptable to impeccable)

EDB-2 In-hand

EDB-2 Sonic Profile:

Lows: full, but otherwise neutral
Mids: wide range of midrange tones available
Highs: very present and easy to add definition to attack

TONE-O-METER:

Relatively transparent and clear, but not thick or rubbery on the bottom end. Very good for acoustic amplification. Would consider the tone great with a variable HPF.