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Studio Projects VTB1 Variable Tube Microphone Pre Amplifier  From Studio Projects

Tube Microphone preamp.

Studio Projects

What We Think

The least expensive preamp that we have available (and probably ever will offer). We honestly couldn't beleive the performance this little preamp gave us... While no Avalon 737, this little VTB-1 is a great little solution for someone looking to get into a step above their sound card or mixers preamps, or someone who simply needs a decent phantom power preamp solution for a condenser mic.

Manufacturer's Description from Studio Projects

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" D.I. Jack On Front Panel 
  • High Pass Filter
  • Descrete 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"
  • External AC Power Supply For extreme Low Noise Operation
  • 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
Studio Projects

About Manufacturer

Many microphone manufacturers on today's market bring microphones in from Asia with their brand name on it. It's a very common thing, and they are all pretty good. Some buy all their parts from Asia and assemble them from down under somewhere. Other's go so far as to deceive you by making you think they actually make their own mics right here in the USA or other Country of origin. We won't mention names, but during our travels to many different manufacturers in Asia, we saw plenty of brands come off the assembly lines. Now not all brands do this, but many do. You need to know this. Not that the product is bad, but no one wants to be tricked! Studio Projects partner company, 797 Audio, has a long history (more than 40 years) in the production of professional microphones. The photos to the left and below are from their early 1950's models when their first vacuum tube microphones hit the market The company has a strong contingent of engineers engaged in electro-acoustic products and structural design. With a complete set of B&K electro-acoustic measuring instruments, a first class anechoic chamber, and a high level testing facility, Studio Projects microphones are manufactured at the highest standards available. You wont find real cool new ?buzz? words on this site, or stories of how long it took to create our mics from the latest and greatest materials known to both humans and little green men from outer space. We won't go into how passionate we are for our microphones by showing you our esteemed leader holding his microphone with a look of love in his eyes, as we think that is a bit kinky, and quite frankly, what has that got to do with microphones! After all, we are talking microphones here, and with so many on the market, why should you buy ours, especially since we are a new company? Well, that is a good question so let's address it. We think it's quite simple. Our mics are every bit as good or better at a fraction of the cost you would pay for a world class German microphone. No, we are not a German mic, but we sure do sound like those $3,000.00 models. We use an outstanding capsule based on a 1950's German design, but we have made it sonically better due to advanced manufacturing techniques. We know as much as about mics as any microphone company out there with the exception of what we charge for them. After all, PMI Audio Group knows good sound and by bringing Studio Projects in directly without the added middleman stepping all over the product, we can make them very affordable. If you're not convinced just yet, you will be soon enough. We have plenty of time to wait it out. So keep the Studio Projects name in the back of your mind as you have nothing to lose, and everything to gain. You see, we may be priced like the other low cost brands, but the quality and sound you get will compare with the expensive German models.


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)

(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

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).





VTB1 User Manual

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