Peer Review - Ampetronic ILD1000G

Alfred Sturma, CEO of ACS in Austria reviews Ampetronic's latest and greatest digital induction loop amplifier, naming it "The new king of IFILS". Read on to find out why.

Induction loop systems for the hard of hearing are a long way from being old fashioned technology. Constant developments and new discoveries are making induction loop systems the ultimate problem solvers for many of our current demands.

Induction loop systems have to fulfil the demands of International Standard IEC60118-4 after installation - the reference to which every induction loop installation should be tested. Additionally, during the planning and the mounting of the loops and associated devices, a lot of challenges are evident. One of the main problems is reinforced concrete with a high grade of core iron within the structure of the area the loop is being installed into. This may cause frequency dependent losses of up to 10dB and more.

Standard perimeter loops cannot solve these problems and there is, therefore, a need for special designs to cope with such high losses.

Most ‘normal’ loop amplifiers on the market are not capable of delivering satisfactory results under such circumstances. Generally, loops configured as phased arrays have a long cable run and consequently not only have a higher ohmic resistance, but also a significant inductive component.

In critical installations, values up to some millihenry (mH) are possible. Thus the amplifier must not only be capable of delivering the necessary high currents, but must also be in a position to deliver adequate output voltage to successfully drive the high frequencies. This is the point where most amplifiers on the market start to struggle.

Ampetronic has a longstanding reputation as a manufacturer of high quality amplifiers for induction loop systems. From my personal point of view, Ampetronic is the only producer of truly constant current amplifiers. All other brands only produce what I call ‘castrated’ voltage amplifiers with associated bad performance, so I was very curious about the new ILD1000G. Ampetronic promised a lot in technical terms: real 13A peak and 50V output voltage at full current are bold claims.

The unit comes in a standard 19”-1U size, with all important controls and indicators on the front panel. The controls are hidden in the front panel and can only be adjusted by the use of a screwdriver. This is a good safety measure as it should not be necessary to change anything after the commissioning of the system.

The ILD1000G offers three inputs: Input 1 (Mic, XLR, with switchable phantom power and sensitivity), Input 2 (XLR, Mic/Line switchable) and Input 3 (TRS-Jack, Line). In my opinion the three inputs are a nice extra, but not really necessary as this type of unit is only used in large professional systems where the signal comes from a professional mixer, matrix or other piece of equipment. I believe that this amplifier will seldom be used as a stand-alone system.

On the back, you will also find the insert socket for use with phase shifters (Ampetronic SP5), or to cascade more units for large and complex systems. The loop is connected via a Speakon connector, which ensures safe and reliable function.
The power stage of the amplifier is designed as a Class-G amplifier, which results in low power consumption and high efficiency.

It was very exciting to test the ILD1000G both in the lab and in the field. From the very beginning, the ILD1000G fulfils all expectations and more. It is a really great unit and, to my knowledge, is the best amplifier on the market.

Lab results – short version:

All parameters from the leaflet are adhered to and correct. This is an important point, and one where Ampetronic clearly differs from other manufacturers, whose leaflets seem to contain no traceable data.

It was interesting to measure the output impedance, which is a very important indicator of the performance of the amplifier.

We loaded the ILD1000G with different loads from short circuit (real approx. 0.1 Ohms) up to 4.6 Ohms. From these measurements we calculated an average output impedance of 22 Ohms, which is excellent.

As shown in the diagram, the frequency response is also very good. These are the best results we ever have measured.

The results with complex loads were also better then expected.

We loaded the amp with a dummy load of 1.6 Ohms + 330µH (this equals a low-pass-filter with a corner frequency of 772Hz), which is a common value for a medium sized loop. Independent of the set current, the performance was stable, the frequency response flat and the THD always less then 0.5%.

The next step was to test the performance of the ILD1000G on real loops.

First, we tested the amp on a small loop in a seminar room of approximately 40m² with the following loop data: wire AWG16, 0.7 Ohms, 60µH, low-pass-corner-frequency 1857Hz. The loop current was set to 3.14Arms @ 1kHz for 400mA/m at the middle of the room. The linear response, measured with pink noise, was (-3dB) 75Hz – 6,5kHz, which is much better than claimed in the standard. THD was less then 0.5%. Test with real speech and music signals confirmed the measurements.

The next real measurement was a medium sized auditorium of approximately 150m² with the following loop data: wire AWG14, 0.5 Ohms, 100µH, -3dB corner frequency 796Hz. The loop current was set to 5Arms @ 1kHz for 400mA/m in the middle of the room. The performance was exactly the same as described above.

In very complex installations the excellent performance ILD1000G comes to the fore.

A real challenge was the installation of an induction loop system in the “Passionsspielhaus Erl” in the Austrian Tyrol (pictured).

The whole building is made of reinforced concrete and can accommodate an audience of up to 1,600, all of whom needed to be reached by the loop system.

We solved this problem by installing a double phased array system with 2x(3+3) sub loops driven by four ILD1000Gs and an SP5 phase shifter.

For the loops, we needed around 1,200m of a special 25mm flat copper foil (approx. 300m per loop), each sub loop has a resistance of around 2.0 Ohms and a very high inductance, which I have not measured.

The four ILD1000Gs plus the SP5 and a line transformer (to prevent hum and noise) were mounted in a small lockable 19”-rack. The signal comes from an independent monitor-output from the mixing console. After commissioning there were no further adjustments necessary. The loop current was adjusted to approximately 4Arms @ 1kHz in each loop to reach 400mA/m peak level. Because of the carefully designed and installed loop system, good headroom is still available.

The frequency response is optimally flat in a range (-3dB) from 80Hz – 6kHz with a little peak (less then 2dB) around 2kHz, which increases the speech intelligibility (measured with pink noise) and is much better than stated in the IEC standard. The level variation within the whole auditorium is less then 2dB. Listening tests with real signals attested the very good performance of the system.


From my point of view, the Ampetronic ILD1000G is the best loop-driver on the world market today. Rugged design, reliable function and easy handling are the main advantages of this state-of-the-art piece of equipment. Even very complex and large designs are driven with absolute ease.

Ing. Alfred Sturma.

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