Australian manufacturer SM Pro Audio, a relative newcomer to the world of low-cost recording equipment, has brought an impressively large list of solid-state

Australian manufacturer SM Pro Audio, a relative newcomer to the world of low-cost recording equipment, has brought an impressively large list of solid-state products to market, such as microphones, an 8-channel optical compressor, and a variety of preamp-based products. To accommodate tube-based designs, SM Pro Audio has created the Red Valve series, which includes the single-channel TB101 ($199) and the dual-channel TB202 ($319) channel strips.

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FIG. 1: The TB202 front panel has two instrument inputs and switches for phantom power and the 20 dB pad.

The TB101 and TB202 have the same basic setup: a channel strip consisting of a tube preamp with DI, an optical compressor, and a 3-band EQ. Each preamp features push-button switches for phantom power, phase reverse, and a 20 dB pad. While the TB101 is housed in a tabletop box, the TB202 is a 1U device (see Fig. 1). Both units have the same electronics, but for this review I'll focus on the TB202.

Record or Mix

When I looked at the retail price of the TB202, I was astounded at its affordability: it offers a lot of features for a low price. Overall, it looks and feels solid, with metal knobs that allow you to see their positions clearly at a glance.

A pair of low-impedance, ¼-inch instrument-level inputs, which can also be used as insert points, are located on the front panel. The rear panel has balanced XLR and ¼-inch inputs, and balanced XLR and unbalanced ¼-inch outputs (see Fig. 2). The TB202, which is powered by an ungrounded lump-in-the-line adapter, uses only one 12AX7 tube to cover both channels.

The tube preamp/DI combination — ostensibly the primary function of this device — does what it's supposed to do. It fared best on electric guitar, an application for which you usually don't need much gain, and there isn't much in the way of high-frequency information. (Most guitar amps don't produce much above 5 kHz, so it is not as necessary for a mic preamp used in this application to have good high-frequency response, especially if you are close-miking the amp.) That is okay because while the TB202's preamps are rated as providing 60 dB of gain, I had to crank them up on quieter sources.

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FIG. 2: The rear panel includes balanced, line-level ¼-inch inputs so you can use the TB202 for processing tracks.

High frequencies were sometimes an issue with the TB202: it made cymbals sound a bit brash, and if male and female vocals tended toward sibilance, the TB202 emphasized it. The DI sounded fine on synthesizer and bass. For example, I plugged a 1975 Fender Precision into the DI using the onboard compression, which resulted in a nice low end and a lot of output before distorting. In general, the TB202 works well as a DI.

Except for the jacks, everything you need to reach is on the front panel, which, for a rackmount device, is very helpful. (If you've ever had to poke around behind a rack to find a switch, you're likely to understand what a hassle that can be.) Each preamp has dedicated buttons for the 20 dB pad, phantom power, and phase reversal. There is an LED indicator for the pad, but given that an LED was allocated for only one of the three buttons, I wish it had been used to indicate phantom power: it's reassuring to be able to look at a preamp from a distance and know the phantom power status if you're about to connect or disconnect a mic.

The Art of the Channel Strip

With compressors and EQs commonly part of the package, channel strips often come in handy for tracking and mixing situations. Many channel strips have mic- and line-level inputs, and the TB202 is no exception. Both inputs function simultaneously; if you plan to run a line-level signal into it for processing, however, be sure to unplug any mics that are connected to the TB202 or you may end up with more audio in the output signal than you bargained for. When you plug into the DI jack, the rear-panel inputs are disconnected.

With three fixed bands of adjustment, the EQ section is not as versatile as I had hoped. There are low- and high-frequency shelving filters at 80 Hz and 8 kHz, respectively, and there is a mid frequency adjustment centered at 1.8 kHz. Each filter has 16 dB of cut or boost, and the knobs have center detents with five levels marked on either side of the null point. The low-shelving filter is passable, but the mid frequency and high-shelving filters sounded harsh to my ears. The EQ section has a bypass switch, which is handy for performing quick A/B comparisons.

Dedicated buttons engage the optical compressor on each channel, and a colored LED indicates when compression is occurring. The compressor's controls include ratio (labeled Compression), which ranges from 1.5:1 to 10:1, and switches for fast/slow attack (1 or 5 ms) and release times (500 ms or 1.5 seconds). There is no adjustable control for threshold.

As far as I can tell, the compressor functions only when gain is applied to the preamp, and the effect that the compressor has on the signal depends on the amount of gain: the higher the gain, the more noticeable the compression. To use the compressor with line-level signals, you'll have to turn down the incoming signal at the source, increase the TB202's input gain, and adjust the output level until everything is just right. At high gain settings with a 10:1 ratio, the compression is relatively subtle, but it sounds good. It's neither transparent nor extremely dark and dirty, although it leans in the direction of the latter. The attack and release settings give you a bit of room to work, but again, any adjustments you make will produce relatively subtle changes in response. The lack of threshold and gain-reduction metering makes using the compressor a crapshoot.

TB or Not TB

Taking into account its price and feature set, the TB202 is worth considering if you are on a limited budget and don't already have a channel strip. Although the preamps are okay and the device provides a variety of functions, the TB202's overall sound is tempered by its poor-quality EQ and underfeatured compressors. Nonetheless, if you are just starting out, the TB202 could complete a bare-bones recording setup without breaking the bank.

Rich Wells oversees the Supreme Reality, a recording studio and band in Portland, Oregon

TB202 SPECIFICATIONS Channels 2 Inputs (2) XLR; (2) balanced ¼" Outputs (2) XLR; (2) unbalanced ¼" Output Impedance 51Ω Dynamic Range >100 dB Frequency Response 10 Hz-20 kHz (±1.5 dB) Gain 60 dB Noise -92 dB unweighted THD 0.05% Power Supply lump-in-line, switchable 110/220V Dimensions 1U × 6" (D) Weight 2 lbs.


dual-channel strip $319


PROS: Inexpensive. Two DI inputs.

CONS: EQ is harsh. No compressor threshold control. No gain reduction metering.

SM Pro Audio/Kaysound
(U.S. distributor)