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rustyd100 22nd August 2018 02:33 AM

Davisound TB7
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I've got three Davisound mic preamps, handmade by Hayne Davis in South Carolina. Two are within a TB-12 rack mount unit I picked up from Shoebox Studios when that facility moved on to something else. The third is within the TB-7 Channel Strip purchased directly from Hayne. All are of the "transparent" variety.

Here's the manual and specs page for the Davisound TB-7:

DaviSound TB-7 On-Line Manual

I've also got colored preamps out the wazoo but usually return to a Davisound for guaranteed results in recording acoustic sounds. It really is a desert island piece. When in studio, the TB-7 shares the rack with the Davisound TB-12, two 1968 RCA BA-71Bs, a Chandler REDD.47, a Portico, and four Universal Audio Unison preamps.

The Davisound preamps have no transformers in the audio path, unlike the rest of the pack.

General Description

Here are some details about the TB-7. This Davisound box is a Channel Strip using at its core the same preamp as the TB-12. Same exceptional specs. Almost no noise at any setting. No measurable distortion. Active variable-amplification (applies only the input gain necessary to reach a desired level, as opposed to the full input/adjustable output noise is always the same distance below the set level). It has a HPF 80Hz rolloff, Phase toggle, a 5-way EQ, and a LA2A-style compressor, all defeatable.

DI and Line Inputs
It also has a second line input that can be used as an unbalanced instrument DI, or as a balanced line-in. This input can be mixed with the mic signal via its own pot. There are TRS connections for the input on the back and in the front, with a switch that chooses which one (so one can have a lot of stuff hooked up at once!). The direct input stage also means the channel strip can be used as an analog insert for other signals in the control room.

Two Line Outputs
My unit has two 600ohm quasi-balanced outputs. A slight compromise, one might think...but mitigated by the fact I can drive two output in a fashion where one cannot affect the other (For example, in the case of a short, or when the cable is attached/detached hot, during a broadcast). One common scenario for me is when recording location sound. I can send one output to the dedicated recorder and the other to the camera. One could, I'm sure, request a single, fully balanced output. In any case, I can detect no induced noise, even at full gain.

Distortion Very Low at All Settings
The amazing thing is that output distortion specs remain stubbornly stable even with the EQ and Compressor engaged. The unit's headroom is +32dB above the max input setting!

Customized Features
My TB-7 has been altered from the standard design in a few ways. It's rack ears have been removed and it has no direct AC power connection. The unit has been fitted with a switchable headphone amp. This switch allows one to monitor the final output of the TB-7, or, to just listen to the incoming line-in (even if it's input knob is turned down to zero). This means the line-in can serve as a cue channel, or phone/IFB return for live shows like radio remotes or TV news, for example.

Hayne built this chassis out of solid red oak (the unit shown on his website is red padauk). He put beefy D-Rings on the sides (stainless steel gear cast for use on sailboats), and I use a nice padded leather shoulder strap to place the unit on my chest when recording in the field. The unit is lightweight, so there's little neck fatigue even after a couple of hours.

This particular unit has NOS bakelite RCA knobs from the 1950s that I've collected over the years. It's got a nice tactile feel!

The box has been altered to include brackets for four rechargeable 9V batteries, which last several hours. In the studio I power the unit with a full time AC to DC power supply attached to provided pole connectors. Despite the fact that the power supply is of the ultrasonic switching variety, I can detect no audible artifacts in the output.

Feature Wish
There is one feature that is absent...though I suspect it could have been added had I anticipated it. The unit has no level meter on the input. Not necessary in the studio, but appreciated in the field when I'm not close to the recording unit. A simple 5-LED display would serve the purpose. A workaround is to engage the compressor, set at 9:00, and adjust the input until the loudest peaks cause the compressor's LED indicator to flicker. That shows a good level. Now the compressor can be turned off...or left on...depending on preference.

Using the Compressor
I had to get used to adjusting the compressor. A very light touch will provide transparent and realistic leveling. Listening, I'm not always aware that it's working. Turn it up to get a clamp-down-after-transient effect that can lead to impressive results on bass, kick, and snare. Most of the time, though, I'm applying it modestly. Hayne lists the compressor as a LA2A type, and it may well be. My unit does use an opto-sensor, though Hayne also offers a FET version. However, this compressor doesn't apply the tube harmonics we have grown accustomed to from a real LA2A. True to form, then, the TB-7 remains quite transparent sounding with the compressor engaged.

It's my experience that microphones reveal more of their real character when passed through the TB-7. The clarity is quite amazing. Especially revealing is the bottom octave. Cleaner and deeper than most of my other preamps, devoid of any bloat and producing no masking effect on mids and highs. The response is ruler flat. The U87 is a smidge less nasal. The TM-1 tube mic and Horch FET tend to be favorites for male voices. The Peluso P-67? need to add transformer harmonics to what the tube and head basket already create. C414B-ULS...well, "you are there." Dialog mics like the Schoeps and Oktava SDCs, already known for their vocal clarity, sound really natural, without that very slight transformer-induced high-frequency edge I get on the Sound Devices field preamp. Sibilance is noticeably cleaner than produced by the other preamps. Preamp mojo? No, not as much as is sometimes desirable. I'd describe the sound as having a "sheen," though Hayne disagrees and says that I'm simply hearing what is, in fact, there.

Of course other preamps are sometimes useful for what they add and take away. I still prefer acoustic guitars to be passed through the RCA BA-71Bs, where the transformers add to the string transients. Rock-n-roll vocals get a bit more punch through the Portico, with its trannys and slight emphasis on the mids. Ballad singers, Indy vocals, and electric guitars are fatter through the REDD.47, as both it's tubes and big trannys do their worse. But, if I could only have one preamp, it would be the TB-7.

I Want Another One
I can't say enough about the TB-7. I'd gladly add another, as they would make up the front end of almost any acoustic or vocal chain. It is very satisfying to make basic adjustments to the analog input when recording digitally. Saves later processing and may even sound better by reducing digital noise from too much re-quantization. Don't get me wrong, I'm an avid plug-in user...but I'm also beginning to realize one is sometimes rewarded by minimizing digital processing where one can.

Davisound lists the standard TB-7 at $1695. The customized items added $200. In my experience, that's a pretty good price for the features, connectivity, and quality that make up this versatile channel strip.