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+28dB of clean gain. Zero extra cables.

Your dynamic mic isn't broken.

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+28dB Class-A JFET gain, so your interface knob
-128dBu EIN noise floor for silence between words
Plugs straight into your mic or interface, with
48V pass-through switch lets condensers work without unplugging

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Built to Fix the Quiet-Mic Problem

Four engineering decisions that separate the GainTube+ 28 from budget boosters and bulky stompboxes.

+28dB of Clean Gain

A matched Class-A JFET stage adds 28dB before your interface preamp, enough to bring an SM7B or PodMic to broadcast level with the knob in its quiet range.

Ultra-Low Noise Floor

Rated at -128dBu EIN. In editorial testing on a Scarlett 2i2, the measured floor dropped from -71.2dBFS to -86.4dBFS.

Selectable 48V Pass-Through

Boost mode keeps phantom DC away from dynamic and ribbon capsules. Flip the recessed switch and condensers get their 48V as normal.

Direct Inline Connection

Male-to-female barrel design plugs directly into your mic or interface. No extra cable, no box on your boom arm.

How It Works

Class-A JFET Gain Stage

Inside the aluminum shell, matched JFET transistors give your dynamic mic a steady high-impedance load and add +28dB of low-noise gain, all powered by your interface's phantom supply.

Plugs Straight In

Connect it to your interface's XLR input or your mic's output, plug your existing cable into the other end, and turn the gain knob back to around 11 o'clock.

Phantom Protection and Pass-Through

A recessed selector keeps 48V away from dynamic and ribbon mics in Boost mode, or passes it through for condensers. Gold-plated pins and a spring-loaded latch keep the connection tight.

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Cosari GainTube+ 28

Inline +28dB Class-A FET Microphone Preamp with 48V Phantom Pass-Through

Hear the difference tonight.: Click it in, press 48V, and turn your gain down. The hiss drops away right away.
No extra cable to buy.: Plugs directly into your mic or interface, unlike box-style activators.
Safe with every mic you own.: Boost mode protects dynamics and ribbons, and pass-through powers condensers.
30-day money-back guarantee.: If your recordings aren't quieter and fuller, send it back within 30 days for a full refund.

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$89.99 ~~$179.99~~ Free Tracked Shipping (5–7 Days) Included

In Stock: Delivers in 5–7 Business Days. Free insured US delivery with tracking.

30-Day Money-Back Guarantee plus a full 2-Year Warranty.

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Description

Who it's for: Podcasters, streamers, voiceover artists, and anyone on remote calls using a low-output dynamic or ribbon mic with a USB interface or mixer that has 48V phantom power.

What it fixes: Quiet levels, audible hiss at high gain settings, thin-sounding dynamic mics, and having to press your lips against the windscreen to be heard.

What it needs: An XLR mic and an interface or mixer with 48V phantom power. It doesn't work with USB-only microphones or 3.5mm inputs.

5–7 Day Shipping & 30-Day Returns

Free 5–7 Day US Shipping: Every order ships free with full tracking and delivers in 5 to 7 business days.

30-Day Trial: Try it at home for 30 days risk-free. Need help? Email us anytime at support@buycosari.com.

2-Year Warranty: If anything goes wrong within 2 years, we replace it free of charge or refund your order in full.

Why Choose the Cosari GainTube+ 28?

Shielded Against Interference

The thick anodized aluminum shell blocks hum and digital ticking from PCs, monitors, and Wi-Fi routers on a crowded desk.

Your Interface in Its Quiet Range

With 28dB added up front, your gain knob can sit around 11 o'clock, well below the hissy top of the dial.

30-Day Quiet-Headphones Trial

Plug it in, put on your headphones, and listen. If the hiss doesn't drop, return it within 30 days for a full refund.

Cosari GainTube+ 28 vs. Ordinary Alternatives

Cosari GainTube+ 28Standard Competitors

Feature	Cosari GainTube+ 28	Standard Competitors
Clean gain added	+28dB Class-A JFET	+25dB typical
Extra XLR cable needed	No, plugs directly in	Yes, for box-style units
48V pass-through for condensers	Yes, selectable switch	Usually no
Size and weight	98 × 21mm, 78g	Box on desk or boom arm
Price	$89.99 (50% off)	$149 plus cable

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What's Included

In the Box

1 × Cosari GainTube+ 28 Inline FET Microphone Preamp
1 × EVA Protective Carry Case
1 × Reusable Hook-and-Loop Cable Tie
1 × Gain-Staging Quick-Start Card

Technical Specifications

Gain: +28dB (Class-A JFET)
Equivalent Input Noise: -128dBu
Frequency Response: 10Hz–50kHz (±0.5dB)
Power: 48V phantom (required)
Phantom Mode: Selectable Boost / 48V Pass-Through
Connectors: 3-pin XLR male/female, gold-plated contacts
Dimensions & Weight: 98mm × 21mm, 78g
Housing & Warranty: CNC-machined 6061 aluminum, matte black anodized; 2-year warranty

Care & Safety

Turn off phantom power before connecting or disconnecting the preamp to avoid a loud pop in your headphones or monitors.
Store it in the included case when traveling, and keep the XLR contacts free of dust. Wipe the barrel with a dry microfiber cloth only.
Backed by our 30-Day Money-Back Guarantee & Full Cosari Warranty
Customer Support: support@buycosari.com

Set Up in Under a Minute

Swipe left for steps 2 and 3

1
Click It Inline
Plug the GainTube+ 28 into your mic's XLR output or your interface's input, then connect your existing XLR cable to the other end.
2
Press 48V and Turn the Gain Down
Switch on phantom power, then turn your interface gain back to about 11 o'clock, roughly half where it was.
3
Record Without the Hiss
Sit back comfortably and talk. Your voice comes through fuller and louder, with silence between the words.

Give Your Mic the Clean Gain It Needs

$89.99 ~~$179.99~~ Free Tracked Shipping (5–7 Days) Included

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Frequently Asked Questions

Will the Cosari GainTube+ 28 fit directly on a Shure SM7B or Rode PodMic?

Yes. The barrel is 21mm wide and cleared the yokes on both mics in our testing. If your mount is tighter, plug it into your interface's XLR input instead. Performance is the same either way.

Do I need an extra XLR cable?

No. It's a male-to-female inline barrel, so it sits between your existing cable and either your mic or your interface.

Can 48V phantom power damage my dynamic or ribbon mic?

In Dynamic Boost mode, the GainTube+ 28 uses the 48V to power its JFET circuit and keeps DC voltage from reaching your mic. Switch to pass-through only when you're using a condenser mic that needs phantom power.

Which audio interfaces does it work with?

Any XLR interface or mixer with 48V phantom power, including Focusrite Scarlett, UA Volt, Audient iD and EVO, Behringer UMC, PreSonus, Motu M2, GoXLR, and Rodecaster units.

Does it need batteries or a power adapter?

No. It runs entirely on your interface's phantom power. Press the 48V button and it's on.

Will it change the sound of my voice?

It's rated flat from 10Hz to 50kHz (±0.5dB), so it adds level without EQ coloration. Many dynamic mics sound fuller with it because they see a steadier load than a budget interface provides.