Introducing EL Amp II+ Balanced

JDS Labs EL Amp II+ Balanced

We’ve historically avoided building balanced amplifiers because well designed, single-ended amplifiers are all most need in a home audio setup. Yet, a growing number of customers have asked for balanced inputs. Maybe you have an audio interface or source with XLR or TRS outputs, and have passed on EL Amp II+ because there’s no ideal way to connect to RCA Inputs.

EL Amp II+ Balanced is for those who require balanced connectivity. Functionally equivalent to its unbalanced sibling, EL Amp II+, the amplifier is housed in a precision machined aluminum chassis, with plentiful power, button activated preamp RCA outputs, and a beautiful knob.

Hardware Overview

Balanced TRS

We chose balanced TRS input jacks because most customers requesting balanced inputs need to connect to audio interfaces equipped with TRS outputs. Additionally, TRS jacks share the same mounting height as other components on the rear of the amplifier, forgoing the need to double enclosure height just to accommodate XLRs.

Balanced Input, Single-Ended (SE) Output

Headphone drivers are inherently single-ended and we actively discourage balanced headphone outputs. Thus, EL Amp II+ Balanced provides 6.35mm (1/4″) Headphone output.

The balanced inputs are fed to quad buffers. The eight signals are then summed by quad balanced-to-SE converters, whose outputs are paralleled once more to minimize distortion products prior to headphone amplification. In total, 24 low-noise opamps are responsible for balanced-to-SE conversion.

Performance

It’s often assumed that Balanced connections must yield higher benchmark performance. This is a misunderstanding. We began prototyping balanced amplifiers years ago, and more often than not, there is no external noise to differentially cancel out, so a balanced amplifier yields no benefits while requiring more components in the signal chain. When no input noise is present, a single-ended amp will generally outperform the same amp equipped with balanced input circuitry.

For balanced signals, source impedance must be overcome in not one signal per channel, but two signals, identically. Any differential input error creates distortion products, thus, paralleled buffering helps average out potential errors. As more components and passives are involved, the base noise floor tends to rise, meaning power supply and amplification circuits must be designed for even lower noise than the average SE amp. With all of this in mind, it’s easy to understand why SE amplifiers perform so well (a case of “less is more”).

As explained in the recent Element III release notes, our goal is not to set benchmark records. SINAD > 110 dB is more than you should ever need! Today’s published performance of EL Amp II+ Balanced is a worst case snapshot, which will only improve as preferred passives for the differential summing circuitry become available. Obtaining precision resistors is a serious challenge these days, given global shortages.

EL Amp II+ Balanced
Frequency Response, 20Hz-20kHz +/- 0.01dB
SINAD @ 4VRMS, 1kHz > 114 dB
IMD SMPTE -94 dB
Noise (20-20kHz) 1.95 μV
Crosstalk @ 10kHz via 1/4″ Output -84 dB
SNR (20-20kHz) 126 dB
Dynamic Range (AES17) @ 4VRMS 125 dB
Input Impedance 47 kΩ
Output Impedance < 0.7 Ω
Max Continuous Power @ 600 Ω
153 mW (9.6VRMS)
Max Continuous Power @ 300 Ω
288 mW (9.3 VRMS)
Max Continuous Power @ 32 Ω
1.2 W (6.27 VRMS)

Availability

EL Amp II+ Balanced is In Stock and ships today! Samples to reviewers are in route.

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