Stereo Base control, a little theory

A special feature is the possibility to adjust the stereo width. The perception of spatiality when listening with headphones differs from listening with loudspeakers. Instead of a cross-feed circuit, we use our stereo base width setting. It is based on the mid/side technique which is commonly used in professional studios. It provides additional benefits.

The stereo signal is converted into a mid signal (in simple terms, what L and R have in common) and a side signal (in simple terms, what distinguishes L and R). Summing mid and side signals in a 1:1 ratio will result in the original stereo signal. However, if you change the ratio between mid and side before summing them, you change the stereo base width. In our circuit, we leave the mid signal as it is. We only adjust the level of the side signal. If we lower the level, the stereo image becomes narrower, if we raise the level, the stereo image becomes wider.

Stereo Base control, what it does

You have direct access to the perception of spatiality. With a music programme which seems too "wide" in the headphones, one will turn the control one or two steps to the left. If you perceive a recording as too "dry" (centred), turn the control one or two steps to the right. The leftmost position is mono. This is the preferred setting for early stereo recordings, when individual instruments have been mixed to the extreme left or right - without spatial reference.

Professional users check the spatiality of their mix with this function and may discover possible problems, especially in the extreme positions.

Also important: With the DIR (Direct) button, this stage can be completely switched out of the signal path. In this way, the purist approach is taken into account.

A precision potentiometer with 21 detents is available for balance control. The centre position is perfectly calibrated and haptically clearly defined. In fine increments, left/right volume differences of up to about 2.5 dB - caused by music programme, headphones or individual perception - can be compensated.

XLR 4-pin, Pentaconn and ¼ inch jack connectors are wired in parallel and are intended for alternative use. Theoretically, you could use them at the same time, the power amplifier is strong enough. However, for a reference quality listening experience, we do not recommend such use.

Ideally, XLR 4-pin and Pentaconn are used in conjunction with balanced wired headphones. In this case, the signal currents of the two power amplifiers are not mixed with each other, mutual interference is impossible. The H1 can unfold its full quality (also refer to chapter "Dual Mono Design").

Dual Mono vs. Balanced amplifier design

With its dual mono design, the H1 features the same advantages as a balanced output stage but avoids the drawbacks.

The drawbacks of a balanced output stage are the significantly increased number of electronic components - a balanced output contains two output stages per channel which work in reverse phase. Two output stages result in doubling the output impedance. More components result in an increased risk of non-linearities.

¼ inch jack compatible

Another advantage of the H1 architecture is that unbalanced headphones with ¼ inch jack plugs can also be operated without any problems.

INPUT Bal/Unbal

Input can be switched between balanced and unbalanced mode.

• XLR connectors for balanced

• Cinch connectors for unbalanced

Balanced mode behaves transformer-like: hot or cold may be connected to ground without any loss. XLR and Cinch must not be connected at the same time

INPUT Gain

Basic amplification rate input to output: 6dB

3-position gain switch (-10/0/+10) to reduce or increase input gain by +/-10dB allows adjustment to sources with different output levels.

It is also useful for adapting to headphones of varying sensitivity.

The idea

The idea behind strictly separating left and right channels is to keep any interference away from the circuits. A term like “crosstalk” does not get to the core of the matter. Music signals usually have left/right references, so that an extremely low crosstalk value - moreover, usually measured with sine waves - does not mean so much. But with music highly energetic signal pulses occur, and then high currents are individually demanded by the output stages. It is extremely important that in these cases there is no coupling via a common power supply or via ground lines carrying signal current. Only this way an amplifier can produce absolutely undistorted output signals.

Realisation inside the H1

In the H1, the power supplies for left and right channels are separate, for preamplifiers and power amplifiers. The mains transformer has independent, completely potential-separated windings for each channel. Rectification, filtering and voltage regulation for each channel are individual. For logic circuitry and front-panel indicators, there is another winding and separate rectification, filtering and voltage regulation.

The ground potentials of the two channels are connected to each other at one point only, but this is done purely as potential equalisation; it is impossible for signal currents to be mixed.

Optimal output connection

If the XLR 4-pin or the Pentaconn output is used in combination with balanced wired headphones, the dual mono principle is implemented in full consequence.

When using the jack output, the ground wires of both channels are connected in the jack socket and the jack plug of the headphones. The use of headphones with jack plugs therefore is not that ideal. In the H1, however, an optimised ground routing ensures that the disadvantageous effects are as low as possible.

(also refer to chapter: Headphones Outputs / Balanced Connection)