Studio Projects VTB1 Variable Tube Microphone Preamp

No longer available at zZounds
Shape guitar, bass, and vocal sounds with a turn of the VTB1's Tube Drive knob. This mic preamp/DI lets you blend in a little (or a lot) of tube distortion.

The new Studio Projects VTB-1 is the ultimate in low cost mic preamplifier technology. Incorporating true class A/B switching, the VTB-1 is a totally discrete circuit. Unique to the VTB-1 is the "Tube Drive." The Tube Drive is a variable drive to a 12AX7, that allows the user to blend as little, or as much of the Tube Drive they want. This VTB-1 allows the user the most flexibility of any mic preamplifier in it's price class.

The VTB-1 allows you to go from a pristine solid-state sound, to any combination of Tube Drive you choose -- even hard distortion for guitars and bass! The VTB-1 is must have device as the perfect mic preamplifier for any microphone!


- 48-Volt Phantom Power
- Phase Reverse
- Variable Input Gain Control On Detented Pot
- 1/4 in. D.I. Jack On Front Panel
- High Pass Filter
- Discrete Solid-State Class A/B Design
- TRS Insert
- Mic/Line Switch
- VariableTube Blend On Detented Pot
- Meter Read Select Between Input and Output level
- Switchable Impedance between 50/200 Ohm
- 5 position LED metering
- XLR mic input
- Balanced outputs on XLR and 1/4 in.
- External AC Power Supply For extreme Low Noise Operation (Included)
- Output Gain Control On Detented Pot


- A superb vocal mic pre with warm transparent character
- Great for use as a Tube DI Box
- Great for production, broadcast, and voice over work
- Perfect for the professional and home project studio
- A quality vocal mic preamplifier suitable for all vocal styles read more

Circuit Topology:

Mic Preamp
Discreet, current-source fed, paralleled-transistor balanced input stage feeding a bipolar opamp balanced-unbalanced converter. Dual feedback design for low distortion performance. 2-Stage design for increased performance; transistor stage provides up to 45dB gain, 2nd stage contributes up to 15dB gain.

Line Input
FET-input opamp buffer with hi input impedance to avoid pickup loading when used as an instrument preamp. 2nd stage provides adjustable gain from 10dB to 30dB, constant hi-impedance is maintained.
Hi-pass filter:

75Hz hi-pass filter for low-freq wind and rumble elimination (3-pole filter @-18dB/oct).

Tube Blend
Constant-level blend control allows the user to smoothly change from an all solid-state path to a tube-based preamp. This allows the user to add the desired amount of tube sound to the signal without having to deal with complicated "tube drive" controls and such. Alternately, it allows the user to use only the solid-state portion of the preamp to get a very low distortion, un-colored sound when desired.

Tube Stage
12AX7 vacuum tube with DC filament supply for minimum hum and noise. 1st half of tube is operated as a hi-gain amplifier stage, 2nd half operates as a cathode follower to minimize loading of the first stage. A low-voltage plate supply is used to create a "starved-tube" condition for enhanced sound.

Output Stage
Bipolar, lo-noise, hi output-current opamp used for best performance. 1st stage is used to provide additional gain (6dB) and drives the Line out jack and Pin-2 of the balanced out. The 2nd stage provides signal inversion and drive for Pin-3 of the balanced output (effectively an additional 6dB gain).

For Best Tube-Sound Results

The tube operates best when provided with a solid signal. The best way to accomplish this is to use the onboard metering to set the internal levels. Press the Meter Select switch IN, the meter will now display the signal level within the preamp, just before the tube stage. Adjust the Gain control to get a meter reading within the 0 to +8 range. With the Output control at "0", start turning the Blend control clockwise until the desired sound is heard. Depending on the source material, more or less Blend will be needed. If the output level is too high or low for your following equipment, adjust the Output control to compensate. This won't change the sound of the blended signal, just the overall level.
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Maximum Gain :
Mic In to Bal Out: 72dB (60dB preamp gain, 12dB output gain)
Line In to Bal Out: 42dB (30dB preamp gain, 12dB output gain)

Distortion/Noise (THD + Noise):
-20dBu input-Mic; 0dBu input-Line
Both measured at +15dBu output
Mic or Line In to Bal or Line Out: <0.0015% (Blend set full CCW- no tube)
Mic EIN: -128dBu (150 ohm source, 60dB gain)

Frequency response (20-20kHz, ref 1kHz):
-20dBu input, +15dBu output
Mic In to Bal Out: +0 /-0.25 dB
0dBu input, +15dBu output
Line In to Bal Out: +0 /-0.5 dB

Phase response (20-20kHz, either input): <+/- 15 degrees

Input impedance:
Mic Input (Rear switch in 200 ohm position): 2000 ohms
Mic Input (Rear switch in 50 ohm position): 300 ohms
Line Input (Front panel TRS jack): 1.5 meg ohms

Output impedance:
Male-XLR Balanced Output: 100 ohms (50 ohms each leg)
TRS Line Out: 300 ohms (Impedance Balanced)

Insert Jack (TRS):
Nominal level approx 0dBu
Located between SS preamp stage and tube/output stage
Tip=Send: 50 ohms output impedance
Ring=Return: 7500 ohms input impedance

For support or warranty questions, please contact the manufacturer:
Phone: 310-323-9050

Reviewers gave this product an overall rating of 5 out of 5 stars. (26 ratings)
Submitted January 5, 2011 by a customer from
"Worth every penny and more!"
Overall: 5 out of 5 stars
(see rating details)
Verified Customer zZounds has verified that this reviewer made a purchase from us.
I expect it to last......

I am giving the VTB1 a 10 for sound because for $149 bucks it is extremely quiet, very clean and uncolored on the solid state side w/o being harsh, has more gain than moist will need, and has a variety of musical tones from clean to warm and fuzzy. It is a very musical preamp with a wide ranges of possible sounds making it extremely useful for a variety of needs.

I am surprised at some of the lower feature ratings. All the standard features are there (pad, 48volt, phase reverse, direct/instrument selector, input impedance selector, meter select), plus you can also simultaneously use all three outputs and use the insert jack a total of three different ways including as a straight path out from just the pre and pre gain. That is more flexibility than many much higher priced units and a lot more than anyone should expect from such an inexpensive yet extremely quiet and nice sounding pre amp. As for the on/off switch, just plug it into a power strip with a switch...DUH! One final note, ignore anything you have read about modding this thing with Burr Brown op amps. I bought 4 before buying and when I opened it imagine my surprise to find it already has the Burr Browns in all four slots! The stock tube is a Sovtek 12AX7LP, already a premium tube but I did install the LPS version of the same tube which is the newer and slightly more musical of the two. I mean really, what else could read more people possibly want for $149???

Ease of Use
It doesn't get much easier! I do recommend going to the website though. It has a more extensive manual with more wiring options.

So far so good! It is built like a tank, even on the inside and I anticipate quite a few years of use.

It is easily worth more, perhaps even twice as much...

Manufacturer Support
I am not impressed with their support. I asked about the BB mods before I bought the unit. Instead of telling me it already had them, the response was "open it up and leave it open so you can decide" instead of telling me it now comes with them. When I asked them about it, they support guy said "well, you were bound and determined to replace them". I told him not if he had said it already had them...

Musical Background:
Recording Engineer, musician, live sound tech

Musical Style:
just about anything....
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