ZD50 Rev D7.12.108 Gerber Files

Enjoy. Click here to download.

Possibly the best relay for loudspeakers protection.

As you see there are two contacts: the first made of tungsten, the other one is golden (actually gold-plated silver). The tungsten contact closes first and opens last. It allows to have reliability of a tungsten contact relay (can switch 100A at 50V) and very low resistance of a golden contact.


The idea was to build an amplifier that has less than -120dB of any distortion products that lay in audio range. The goal was to design simple, easily reproducible (even with no measurement equipment) amplifier with the following parameters:

  • Maximum power 4Ohms: >50W.
  • THD and IMD of any frequencies in 20…20000Hz range:  <0.0001% (at maximum power, 40kHz bandwidth).
  • Frequency range:  0…20000Hz in 0…-0.1dB and 0…100000kHz in 0…-1.5dB (with no input/output filter).
  • Linear phase response.

As you may know it is relatively easy to reach -120dB or even less in a SPICE simulation, but there are a lot of hidden problems that prevent real amplifier to match model parameters. This amplifier wasn’t an exception. A lot of prototypes have been built and a lot of these problems have been discovered during more than an year long research.  Here is a list of some of them: incorrect grounding, distortions from an output stage (inductive coupling), distortion from power lines (ripple, power supply rejection), magnetic materials and components, feedback stability, etc. All these problem have been addressed and as a result ZD-50 was born…

ZD-50 Rev D7.12.107 THD and IMD

Here are 11kHz THD and 19+20kHz IMD tests results. The top graph(left) is the amps output, the bottom graph (right) is the amps input. Load is 4Ohm.

Building ZD-50 Rev D7.12.107 Bug

I finally soldered both channels and have found a mistake in PCB. Because of this mistake the speaker protection sometimes permanently turns off the speakers during amps power up. To fix that it is needed to cut one trace (red on the picture) and solder a piece of wire (green on the picture).

Building ZD-50 Rev D7.12.107

Today I’ve received top and back panels. They look nice !

And I still assembling the new boards…

ZD-50 Rev D7.12.107 Boards

PCB Board Rev D7.12.107

PCB Board Rev D7.12.107

Finally I received the new boards. I hope I’ll test them soon…

ZD-50 Rev D7.12.107 Doc

Here is D7.12.107 documentation – schematic, parts list, PCB layout.
And here is small article in russian article in russian