BTL operation, Theory of Operation, Connections

The PA-30 rear panel includes a switch that selects either normal stereo mode or a special mode termed BTL (Balanced Transformerless). The setting of this switch determines the maximum power available to the load from the PA-30, and also decisively affects how the load is connected to the ampliﬁer. This section explains the BTL mode, and describes how to use it.

Theory of Operation

BTL mode (also called 'bridged' mode) uses both channels of the PA-30 to form a single monophonic ampliﬁer with signiﬁcantly higher power capability. If your loudspeakers can handle the increased power, BTL mode will give you more headroom - resulting in undistorted reproduction of program peaks and signiﬁcantly greater 'punch' from your system.

When the MODE switch is in the 'BTL (MONO)' position, only the Channel A input is active; the Channel B input is disabled, and signals present at either of the Channel B input connectors are ignored by the ampliﬁer. The signal at the Channel A input is ampliﬁed and sent to both outputs of the PA-30, but the

polarly of Channel B is reversed with respect to

Channel A. In other words, the two channels are intentionally out of phase.

The single load (remember, BTL is a monophonic, or single-channel, mode) is wired across the two channel output 'hot' (red) terminals, and the black output terminals are left unconnected. The minimum allowable load impedance is 8 ohms (not 4 ohms, as is the case in stereo mode), and the available power to the load is 50 watts continuous (at 8 ohms).

BTL mode is electrically identical to push-pull transmission at line level (the signal level is simply much higher): the two channel outputs deliver the same absolute signal voltage, but with opposite polarities. So, when the Channel A output is at +10 volts, for example, the Channel B output is at –10 volts. The difference between the two (which is the total voltage across the load) is then 20 volts.

BTL operation

The voltage across the load is thus effectively doubled

– which doubles the power.

Notice there is a crucial difference between BTL mode and what is normally termed 'mono' in the HiFi world. When we select 'mono' on a HiFi preamp or integrated ampliﬁer, what we intend - and what we get - is the same signal from both speakers with the same polarity. It is very important to understand the distinction between this and BTL mode, because if two speakers are connected to the PA-30 in a normal stereo conﬁguration and the MODE switch is set to 'BTL', the system still works but the two speakers are out of phase. This will cause acoustical cancellations at low frequencies, resulting in poor sound quality. In rare cases, it can even cause a woofer to blow out!

Connections

Before changing the position of the MODE switch or making any input and output connections, turn OFF the PA-30. To select BTL operation, move the MODE switch to the 'BTL (MONO)' position.

Figure 9 illustrates the connections for BTL mode. The input signal is connected to the Channel A input, using either the –10 dBV (RCA) or the +4 dBm (XLR) connector. The Channel B input is left unconnected.

The load is connected across the two output 'hot' (red) terminals, and the black terminals are left unconnected. Be sure to observe correct output polarity: Channel A is positive, and Channel B is negative. Note that the minimum permissible load impedanoe in BTL mode is 8 ohms.

Connecting loads with a lower impedance will result in current limiting, and may trigger the Protection circuits to shut down the ampliﬁer.

120V

NO CONNECTION TO BLACK TERMINALS

Figure 9. BTL Mode Connection

TASCAM PA-30 9

PA-30 specifications

The Tascam PA-30 is a professional power amplifier designed to meet the demands of demanding audio environments. Known for its high sound quality and robust construction, the PA-30 is an ideal choice for both live sound applications and permanent installations.

One of the standout features of the Tascam PA-30 is its power output. It delivers 30 watts per channel into an 8-ohm load, making it suitable for driving a variety of speakers in moderate-sized venues. Additionally, it can also handle 50 watts per channel into a 4-ohm load, providing the headroom necessary for high-energy performances and dynamic audio playback that requires extra power.

The design of the PA-30 emphasizes durability and reliability. Built with a rugged chassis, the amplifier is capable of withstanding the rigors of touring and frequent use in commercial environments. It also features a fan-less design, which minimizes noise and enhances the listening experience, ensuring that no distracting sounds interfere with the music or spoken word.

For connectivity, the Tascam PA-30 includes balanced XLR inputs, as well as RCA connectors that allow for various audio sources to be connected easily. This flexibility ensures that the amplifier can integrate seamlessly into different audio setups, from small gigs to larger events.

In terms of technology, the PA-30 is designed with advanced thermal protection, ensuring that the unit operates safely even during extended use. This feature prevents overheating, which can lead to unexpected interruptions in performance. Moreover, the amplifier is equipped with short-circuit protection, providing peace of mind and safeguarding connected equipment from potential damage.

The user interface is straightforward and intuitive, featuring rotary knobs for volume control and basic EQ adjustments. This simplicity allows audio engineers and operators to make swift adjustments during live shows without any hassle.

Overall, the Tascam PA-30 stands out for its combination of performance, reliability, and user-friendly design. With its impressive fidelity and robust features, it is an excellent choice for anyone looking to enhance their audio systems, whether in live sound situations or in fixed installations. This amplifier continues to be a trusted option for audio professionals around the world, ensuring quality sound reproduction in a variety of settings.