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Step 3: Voltage Stage mod.


In the former "step 2" stage we explained that an ELTIM amplifier at leasts excists of two modules: a Voltage Stage and a Current Stage part. The current Stages are explained before. In this chapter we explain what a voltage module (VS-xx) is doing and why we are separating.

In order to achieve some serious currents feeding the connected speaker, some serious parts and copper tracks are required. These high currents cause a strong magnetic field around these tracks.
In about all amplifiers we are aware of, all required electronics for a power amplifier is on a single 2D board. This means that all small signal leading tracks "sense" these magnetic fields and interact with them. This effect is compensated by the feedback loop of the amplifier. On the testbench this seems to work perfect and wile a very tight feedback is used we come to the desired 0,000000000001% distortion as about everybody today believes is best, despite the FACT that this approach is totally killing the musicality of an amplifier. However, with our aproach where we hardly need to compensate, there is a lot more "tube-like" air around instruments and voices, normally simply killed by the feedback loop. We now hear you thinkig, show me some figures. OK, but only the ones effecting the sound of your music:
  • Frequency range:  DC (0Hz) - 350.000Hz (limited by us, unlimited > 1,5MHz)
  • Slew rate (rise/fall time of a steep signal): > 60V/uS
  • Harmonics distortion:  << -60dB (none specific and unnoticable)
  • Phase shift: 0-10º over the full audio band
  • Damping factor: > 200, influenced by type of CS-module and Power supply

Instead of  using a tight feedback loop as about everybody else uses to keep the amp under control, we decided to separate the small signal input part from the high current output part. While doing so, we were not only able to choose different input stage types, but also could turn the small signal tracks by 90 degrees compared to the high current tracks. The ones who studied physics know, that the magnetic interference becomes ZERO, without doing anything else. Also, while separating we build up a more 3D setup, resulting in a larger distance between the possibly interfering paths, also without compensating anything. The quite "loose" and current controlled feedback loop gives our amplifiers the musical "tube-like" sound. But unlike tube amplifiers, presenting an amazing strong bass fundament as well.
Without all the extra components others require, we manage to build a high-end, or according to some, a reference class amplifier just by using only 11 transistors/mosfets total.
 
Flat mounted to the heatsink a CS-80 Current Stage and L-mounted to that a VS-10 Voltage Stage board.
ONLY together they form a working power amplifier!
This picture also gives a perfect view of the symmetry of our designs.

The "finetuning" or refinement of this complete pack is defined by the type of input board (VS-module) you decide for. The schematics of both are similar; there are just some slight practical differences, like the transistors used for the input mirror stage and the driving transistors for the Current Stage. The wide range voltage is possible due to the use of some CRD's (Current Regulator Diodes) which appear hard to get. About no distributor of electronic parts is listing them. But, we have a lot of them in stock.

At his moment we have two types; one for the economic versions / rough work and high voltage range of ±20-100Vdc, or one with a rare, special transistor mirror IC, suitable for ±20-63Vdc. The first one is about noise free, the second one is totally silent, even with your ear close to a tweeter.

Check our Input stages (VS-modules) program under the > at left.