TELEFUNKEN TDA-1 Mono Active Direct Box

Product overview

The TELEFUNKEN TDA-1 Mono Active Direct Box is a single-channel active FET transformer direct box built around a custom-wound output transformer, a rugged extruded aluminium enclosure and hand-assembled through-hole circuitry, assembled and tested by TELEFUNKEN in Connecticut, USA.

The single-channel TDA-1 is phantom powered and uses top quality components in a modern take on classic circuitry. Discrete Class-A FET circuitry paired with a high quality, European-made transformer and a rugged metal enclosure delivers a full, rich sound that both complements and retains the natural tone and character of the instrument, with a harmonically rich low end and a detailed, open high end. The front panel carries the balanced XLR output, the ground lift and the +48V LED; the rear panel carries the 1/4-inch INPUT and THRU jacks and the -15 dB pad.

Key features

• Discrete Class-A FET circuitry: a modern take on classic circuitry for a full, rich sound that keeps the natural tone of the instrument
• Custom-wound output transformer made in England, at the heart of every TELEFUNKEN direct box
• ±2 dB from 20 Hz to 70 kHz: extremely low distortion and self-noise; every unit manually tuned for the lowest possible distortion
• Mono, single channel: one 1/4-inch INPUT, one THRU and one balanced XLR OUTPUT
• Recessed heavy-duty metal toggle switches for the -15 dB pad and ground lift
• +48V phantom powered: powered from the mixer through the XLR output, with a +48V LED indicator
• Gold-plated circuit board traces, hand-assembled exclusively with through-hole components
• Extruded aluminium enclosure built to withstand the wear and tear of the road

Discrete Class-A FET circuit

The TDA direct boxes use top quality components in a modern take on classic circuitry to deliver a full, rich sound that both complements and retains the natural tone and character of the instrument. Discrete Class-A FET circuitry is paired with a high quality, European-made transformer, giving what TELEFUNKEN calls the perfect balance between clean, high headroom performance and warm, saturated tone. The circuit boasts a frequency response of ±2 dB from 20 Hz to 70 kHz with extremely low distortion and self-noise, and each individual unit is manually tuned for the lowest possible distortion figure in TELEFUNKEN's US facility. The result is a harmonically rich low end and a detailed, open high end.

The transformer at the heart

At the heart of all TELEFUNKEN Elektroakustik direct boxes are custom-wound output transformers made in England. The transformer converts the unbalanced, high-impedance instrument signal into a balanced microphone-level signal on the XLR output, ready for any mic preamp, stage box or mixing console, and gives the TDA-1 its rich, warm character. Running the signal through a transformer also isolates the instrument from the mixing system, which together with the ground lift switch helps keep hum and buzz out of the signal path.

Connections and controls

The TDA-1 has one channel with its controls split across two panels: the 1/4-inch INPUT, the THRU jack and the -15dB pad switch on the input side, and the XLR OUTPUT, the LIFT / GND switch and the +48V LED on the output side, labelled TDA-1 MONO ACTIVE FET TRANSFORMER DI.

• INPUT (1/4-inch jack): accepts the instrument, keyboard or line source
• THRU (1/4-inch jack): passes the unaltered input signal on to an instrument amplifier, tuner or effects
• OUTPUT (3-pin XLR, male): balanced microphone-level output to the preamp, stage box or mixer
• -15dB switch on the input side: lowers the input by 15 dB for hot sources
• LIFT / GND switch on the output side: disconnects the ground to help remove ground-loop hum
• +48V LED: lights when +48V phantom power reaches the TDA-1

Built for the road

The circuit boards feature gold-plated traces for maximum conductivity and are hand-assembled exclusively with through-hole components, which TELEFUNKEN chose for a secure and reliable connection compared with common surface-mount technology. The circuits are housed in an extremely durable extruded aluminium enclosure, and the heavy-duty metal toggle switches are recessed so they are not knocked by feet, cables or flight-case lids. TELEFUNKEN describes the construction as virtually indestructible, able to easily withstand the wear and tear of gigging.

Sources it suits

With clean, high headroom performance and warm, saturated tone, the TDA handles everything from electric bass and acoustic-electric guitar to hot keyboard and synthesizer outputs, especially with the -15 dB pad engaged. TELEFUNKEN uses TDA boxes in its own LIVE FROM THE LAB sessions, tracked at its South Windsor, Connecticut facility, for bass DI, and records synth and keys comparisons through its direct boxes. The TDA-1 is equally at home on a touring stage, in a house of worship or on a studio desk.

In the box

• TELEFUNKEN TDA-1 Mono Active Direct Box (SYTM-084)

Make all connections and mute the channel before switching on +48V phantom power. Check the positions of the recessed -15 dB pad and ground lift switches before each soundcheck.

TELEFUNKEN TDA-1 Mono Active Direct Box: frequently asked questions

Does the TDA-1 need phantom power?

Yes. The TDA-1 is powered by +48V phantom power from the microphone preamp or mixer through its XLR output. The +48V LED on the output panel lights when phantom power is present.

What does the -15 dB pad do?

The recessed -15dB switch on the input side lowers the input level by 15 dB. Use it for hot sources such as synthesizers, keyboards with strong line outputs or active basses, so the signal stays clean before the transformer and the preamp.

When should I use the ground lift?

If you hear hum or buzz when the instrument and the mixing system are on different power circuits, flip the LIFT / GND switch on the output side to LIFT. This disconnects the ground between the two sides of the DI and often removes ground-loop noise. Leave it on GND when the system is quiet.

Can I use the TDA-1 for a stereo keyboard?

Yes. Use two TDA-1 boxes, one for the left output and one for the right, each on a channel with +48V phantom power switched on.

Can I still use my instrument amplifier?

Yes. Connect the THRU jack to the amplifier input. The amplifier gets the unaltered instrument signal while the XLR output sends a balanced signal to the mixer, so you can blend the direct sound with a microphone on the speaker cabinet.

Where can I buy the TELEFUNKEN TDA-1 Mono Active Direct Box in India?

The TELEFUNKEN TDA-1 Mono Active Direct Box is available from Shivansh Electronics, Kolkata, West Bengal, India, with delivery across India.

Workflow 1: Bass guitar DI on stage

A bass player who wants a clean direct feed to the mixer and keeps the amp on stage.

Connections

Setup

1. Connect the bass to the INPUT jack and run the THRU jack to the bass amplifier.
2. Run an XLR cable from the OUTPUT to the stage box or mixer channel.
3. Switch on +48V phantom power for the channel at the mixer or stage box and check that the +48V LED on the TDA-1 lights.
4. Set preamp gain while the bassist plays at full level; engage the -15 dB pad on an active bass if the signal is hot.

Tip: Blend the DI with a microphone on the bass cabinet for punch plus definition.

Workflow 2: Acoustic-electric guitar

Singer-songwriters and worship teams sending an acoustic-electric guitar straight to the PA.

Connections

Setup

1. Plug the guitar into the INPUT jack.
2. Connect the XLR OUTPUT to the mixer or stage box.
3. Switch on +48V phantom power for the channel at the mixer or stage box and check that the +48V LED on the TDA-1 lights.
4. Raise gain slowly while the guitarist strums hard; switch the ground lift to LIFT if you hear hum.

Workflow 3: Stereo keyboards and synthesizers

Keyboard players with left and right outputs, live or in the studio.

Connections

Setup

1. Use two TDA-1 boxes, one per side: connect the keyboard's left output to the first and the right output to the second.
2. Connect the XLR outputs to two adjacent mixer channels and pan them hard left and right.
3. Switch on +48V phantom power for the channel at the mixer or stage box and check that the +48V LED on the TDA-1 lights.
4. Engage the -15 dB pad if the keyboard's line output overloads the input, then match gain on both channels.

Tip: TELEFUNKEN recorded its own synth and keys sessions through its direct boxes.

Workflow 4: Studio bass: DI plus amp microphone

Tracking bass with a direct signal and a miked cabinet at the same time.

Connections

Setup

1. Connect the bass to the INPUT and the THRU jack to the amplifier.
2. Send the XLR OUTPUT to a preamp and record it on its own track next to the cabinet microphone.
3. Switch on +48V phantom power for the channel at the mixer or stage box and check that the +48V LED on the TDA-1 lights.
4. Check the phase between the DI and microphone tracks and blend to taste.

Workflow 5: Drum pads, samplers and playback

Electronic drum pads, samplers or a laptop playback rig feeding the front-of-house mixer.

Connections

Setup

1. Connect the pad or sampler output to the INPUT jack (use both channels for stereo where available).
2. Engage the -15 dB pad, as these devices usually have hot line-level outputs.
3. Switch on +48V phantom power for the channel at the mixer or stage box and check that the +48V LED on the TDA-1 lights.
4. Run the XLR cable to the stage box and set gain at the loudest sample.

Workflow 6: Removing hum with the ground lift

Engineers fighting ground-loop hum on stages, in churches and in rehearsal rooms.

Connections

Setup

1. Connect the instrument, amplifier and mixer as normal.
2. Switch on +48V phantom power for the channel at the mixer or stage box and check that the +48V LED on the TDA-1 lights.
3. If hum or buzz is audible, flip the recessed LIFT / GND switch on the output side to LIFT.
4. Listen again with the instrument volume up; keep the setting that is quietest.

Tip: The recessed switches stay where you set them, even in a busy stage set-up.