Custom Designs

M2 Circuits does not only repairs analog electronics, we also build them!

Custom designs or clones can be requested, as well as modifications to existing gear. Requests can be sent via the contact page.

Below you will see some custom gear we have designed and built. Some work has been documented over on our YouTube channel here.

Model M7 Phono & Tape Preamplifier

The Model M7 is based on the classic Marantz Model 7, with a few alterations to make it a standalone preamp. It has two EQ settings, RIAA (for phono) and NAB (for tape). The NAB equalization has low and high speed positions, both fully adjustable. This means that the preamp will accept a wide range of tape heads with ease.

The M7 was the focus of the Tube Preamp series on our YouTube channel. A 4-part videos series about the design and build of the preamp.

Response characteristics using RIAA weighting.

Power Amplifier Load

As mentioned on the Repairs page, some of the test equipment we use is custom designed and built. One of those is a test panel designed to test power amplifiers.

For those more technically inclined, or just curious, we have provided the documentation for it here – AmplifierPowerLoadDoc_M2.

By taking a differential measurement across the load resistors, we are able to keep the loads completely floating. This is especially important with power amplifiers that do not reference the speaker output to ground. The calibrated meters allow for us to read the power output in Watts. The power amplifier test panel also interfaces with the audio test panel, so that the output may be monitored audibly.

The PCBs (Printed Circuit Boards) were custom designed for the test panel. In the future more of our custom builds will become modular and card based. Using cards allows for lots of flexibility, and many of the cards can be used in a variety of designs.


The custom PCBs used in the load panel.

Response characteristics, the upper frequency is limited by the QA401 used to measure the response.

This page is in the progress of being updated with more custom work, stay tuned for more!