Reviewed by Rick Lindquist, N1RL

Senior Assistant Technical Editor

    By and large, amateurs are not audiophiles. With a few exceptions (mainly traditional AM aficionados who pride themselves on flat audio response), hams are content with “communications-quality audio,” so at first glance, a tuned-port speaker with a built-in audio equalizer (plus peak and notch filters) might not be high on your wish list. But, if you enjoy “good” audio or are not content with the audio quality of the typical built-in transceiver speaker or even the available external speakers, the Model VRC Variable Response Console might be just the solution.

    The VRC is a solid little block (the case is a heavy cast aluminum with a black matte finish) containing a 4-inch speaker and a tuned port baffle. As we indicated, this is more than just a speaker (although Alpha Delta also offers the Model VRC-2—just the tuned-port speaker and no electronics). An ac wall-outlet adapter cube supplies 12 V dc to the unit via a rear-panel coaxial connector. During ARRL Lab testing, we found that the wall cube would not power the VRC to full audio output (greater than 2 W). We measured approximately 1.3W of audio into an 8 Ohm load using the wall cube, but 4.7 W using a huskier 13.8-V dc bench supply. We’d recommend using a bigger supply for best dynamic range.

    The front panel is nearly equally divided between the speaker grill on top and the control subpanel on the bottom (the PC board containing the electronics is directly behind this subpanel). The most prominent feature of this subpanel is the x-y style bar graph of green LEDs. This graphically displays low-frequency boost or cut in dB (vertical axis) and high-frequency cutoff point in kHz (horizontal axis). By the way, we discovered a “typo” on the kHz scale on our unit’s graphic display. Instead of “1” at the 1 kHz LED, the scale reads “.1” (which would be 100 Hz). The graphic display also serves as a pilot light. You turn on the VRC with an orange pushbutton. Three black pushbuttons engage NORMal mode, PEAK or NOTCH (peak and notch functions are mutually exclusive). Four rotary controls set the desired equalization and adjust the response of the peak and notch filters. There’s also a tiny set-and-forget ADJust VOLume control; although this is an amplified speaker, Alpha Delta instructs users to set volume level using the AF gain or volume control on their transceiver or receiver. The ADJ VOL knob controls an audio attenuator that comes after the filtering networks but before the AF power amp that drives the speaker. If you turn it up too high, you might hear some strange noises resulting from internal audio heterodynes generated in the filtering circuits. Under some circumstances, you could hear this when using headphones, but it’s not noticeable with the ADJ VOL knob at a typical setting—approximately 1/4 turn.

    A centrally located 1/4-inch monaural PHONES jack provides output to headphones or an auxiliary 8 Ohm speaker. A phono jack on the rear of the VRC provides approximately 0.5 V of audio through a separate amplifier to feed a tape recorder or other device. This level is independent of the ADJ VOL control setting, but not independent of your receiver’s volume control.

    The VRC is very easy to use, but the little six-panel Instruction Manual (a brochure, really) explains all quite well and even includes a block diagram and various frequency response curves that describe the effects of the front-panel controls on the audio. As the block diagram explains, audio entering the unit from your transceiver or receiver via the rear-panel mini-phone jack (a connecting cable is supplied) passes through a low-frequency network that permits increasing or attenuating low-frequency audio via the LOW FREQ control on the front panel.

    The response curves in the Instruction Manual suggest a maximum boost of approximately 6 to 12 dB and an average roll-off of approximately 15 dB at 100 Hz or less. In the ARRL Lab, we found approximately 9 dB of boost (maximum boost setting) and 14 dB of cut (maximum cut setting) at 100 Hz. The boost/cut adjustment primarily affected frequencies from approximately 25 to 400 Hz. On the other end of the spectrum, the HIGH FREQ control adjusts a low-pass filter (an active four-pole Butterworth design). Lab tests confirmed that this sharply attenuates frequencies above the setpoint (adjustable from approximately 500 Hz to 10 kHz. You can tinker with the equalization in any of the unit’s three modes. In the Lab, 0 dB low-frequency boost and minimum high-fre-quency cutoff settings yielded an overall –6 dB bandwidth of nearly 11 kHz (from 20 to 11,000 Hz). The minimum –6 dB bandwidth we obtained by just using the boost and cut controls was 469 Hz (from 21 to 490 Hz).

    For the peak and notch functions, the VRC uses separate SCAF filters. Pushing the NORM, PEAK or NOTCH mode pushbuttons creates an annoying pop in the speaker (it also pops when you first turn on the power). A P/N FREQ control sets the peaking or notching frequency (from approximately 400 Hz to 10 kHz), while the P/N BW control sets the peak or notch response—from wide to sharp. Alpha Delta’s response curves for the sharpest P/N BW setting, suggest a maximum peak of up to 20 dB and a maximum null of up to 25 dB or so (approximately what we measured in the ARRL Lab in both cases). In practice, the peak and notch filters worked very effectively. On CW, I found the peak filter worked great. It was also a nice complement to my external DSP box (plus, you can roll off the higher frequencies to further reduce noise). The notch filter would be especially beneficial to those who enjoy listening to shortwave broadcasts and need to eliminate the occasional heterodyne. But it’s superb for those who like to work 40-meter SSB among the broadcasters in
the evening, too.

    The VRC really shone when receiving SSB or AM signals. Voices I was already familiar with sounded more natural, and the ability to boost the bass provided additional presence, while the high-cut eliminated annoying high-frequency noise. I caught some especially good audio one evening from a couple of fellows on 160-meter SSB who had taken pains to tinker with their audio using various high-quality microphones and external equalizing units. Their efforts would have been lost on a lesser speaker, but on the VRC, they started approaching AM-broadcast quality. Of course, you can also take advantage of the VRC’s electronics with a good pair of headphones.

    While the VRC (and the passive VRC-2) is designed to provide high-fidelity audio, it’s not going to make your transceiver sound like a Bose Wave. This is because most MF/HF transceivers and communications receivers are designed with a limited “communications-quality” audio passband that rolls off higher and lower frequencies accordingly. (This is even more true of the typical FM transceiver.) And, if you feed the speaker via another intermediary device (as I did going from my HF transceiver through my external DSP box for some of the time), the speaker probably won’t sound as good as it might if it were working with “flat” audio from your stereo, for example. While the bass boost feature will help to recover some of the lost or rolled-off low frequencies, the VRC offers no way to brighten the treble end of the scale. With these limitations taken into account, the VRC delivers lots of nice, clean, clear, crisp audio, and it can make good audio sound even better. The QRM-fighting features are icing on the cake.

Manufacturer: Alpha Delta Communications Inc, Box 620, Manchester, KY 40962; tel 606-598-2029; fax 606-598-4413. Manufacturer’s suggested retail price, $250;

Model VRC-2 (tuned-port speaker without equalizer or filters), $99.