Fosi BT20A Pro in a Grundig Console: Will It Fit?

The Fosi Audio BT20A Pro is one of the easiest modern amplifiers to fit inside a vintage console such as a Grundig. The one retailer listing that gives dimensions puts it at about 166 x 105 x 35 mm (roughly 6.5 x 4.1 x 1.4 inches) and 547 g. It also drives ordinary modern bookshelf speakers without trouble. Measure your opening before you order, because the real constraints in an old cabinet are height, airflow and the power brick, not width.

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The size figure, and how far to trust it

Fosi’s own product pages list the BT20A Pro as a 2-channel Bluetooth amplifier built on the Texas Instruments TPA3255 chip. Audiophonics lists 166 x 105 x 35 mm. Another reseller listing shows 5.59 x 4.21 x 0.16 inches, which is clearly a data-entry or packaging error. No official Fosi dimension table appears in the sources cited here, so treat 166 x 105 x 35 mm as a retailer figure.

Add clearance on top of the body:

• Rear connectors: RCA jacks, speaker binding posts, the DC jack and the antenna all stick out of the back. Allow several centimetres behind the amp, more if you use banana plugs.
• Knobs: the front controls protrude slightly.
• Antenna: the Bluetooth antenna is external. A radio-opaque wooden cabinet or a metal chassis can cut the range, so plan to put the antenna where it has line of sight to the room.

A measuring checklist for any console opening

The TPA3255 is a class D chip and runs far cooler than a class AB design, but it still produces heat at higher volumes. Reviewers describe the chassis as warming rather than hot at normal listening levels. If the compartment is sealed, drill vent holes or leave the back panel off.

Power, supply and speakers

Fosi sells the BT20A Pro with different supplies. Listings show a 24 to 48 V DC input range, with bundled adapters rated 32 V/5 A or 48 V/5 A depending on the version. Check which one you are buying: the 48 V version is the louder one, quoted at 300 W per channel into 4 ohms by Fosi and Parts Express, while Audiophonics quotes 2 x 225 W. Either figure is far more than typical bookshelf speakers need. PC Perspective covers the amp’s 2 to 8 ohm rating, RCA and Bluetooth 5.0 inputs, and 3.5 mm pre-out.

The external power brick is a separate object. It will not fit in a narrow slot alongside the amp, so plan to mount it elsewhere in the cabinet or behind it with an extension.

Two practical points:

• Noise: class D amps with a switch-mode supply can pick up a hum from an old cabinet’s wiring. Keep the supply away from any old transformer and keep the signal cable short.
• Op-amp rolling: the input stage uses socketed NE5532 op-amps (per the user manual), so a tonal tweak is possible without soldering. Most buyers will never need it.

Using the old radio and turntable opening

A Grundig console usually has the original radio chassis in the middle and a lift lid on top. If you remove the radio chassis, the amp sits where the tubes were and the opening above becomes the turntable shelf.

• Turntable: the BT20A Pro has no phono stage. A turntable with a built-in preamp, or a separate phono preamp, is needed. Without one you will hear a very quiet, tinny sound.
• Vibration: old cabinets are resonant. Put the turntable on a rigid shelf with isolation feet rather than directly on thin top veneer.
• Speaker cabinets: do not wire to the original speaker unless you have verified its impedance. Many vintage drivers are 4 to 8 ohms, but some are not, and the 2 ohm lower limit of the amp does not protect old paper cones from distortion.

What it does not do

The BT20A Pro is a stereo amp with no tone controls beyond what you add at the source. It also has no built-in phono input or DAC. If you want a built-in USB or optical input, look at a different model.

Alternatives if the BT20A Pro does not fit

The cheaper Fosi BT20A and the smaller Fosi Audio ZA3 are alternatives when the opening is tighter or you want less power. A bigger Fosi V3 Mono-style or larger stereo amp would not suit a small console: it is simply deeper and hotter.

Verdict

For most vintage console retrofits the BT20A Pro is a sensible buy. It is small, has plenty of power, and takes Bluetooth and RCA. Measure the opening first, confirm which power supply version you receive, and keep air moving around it. Skip it if you need a built-in phono stage or the opening is under 35 mm tall.