Tag Archives: phono

Link: Phono MM/MC Preamp

DC4300 Digital CameraSome phono enthusiasts prefer audio equipment with vacuum tubes. I’m also fascinated by these “old” equipment, but did not build a tube amplifier or preamplifier by myself. While the circuits usually are quiet simple, most of the performance of tube amplifiers come from the realisation. The grounding concept or the placement of transformers can make the difference between a great and a bad amplifier – even with exactly the same circuit.

If you still think, that you want to build your own phono preamplifier based on tubes and even want to use it for very low MC signals, check out this project: MC/MM phono preamp. Even if you can’t understand the german text, the pictures of the mechanical construction are worth a look

Low Ron analog switches for audio use

14-SOICFor the comfortINA project we were looking for analog switches with a very low resistance. They should be able to use a symmetrical power supply with at least +/-5V.

There are more ICs available for unsymmetrical power supplies. These might be an interesting alternative if you can shift the level of the logic inputs.

Here are the interesting switches with a symmetrical power supply that we’ve found:

Analog Devices ADG1401/1402

These single switch circuits have a Ron of 1Ohm with supply +/-15V. Unfortunately the MSOP package with 0.65mm pitch  requires serious soldering skills.

Analog Devices ADG1411/1412

This quad switch has a Ron of < 2 Ω at +/-15V supply. Unfortunately it is only available in TSSOP package, which makes is not so easy to use for DIY projects.

Analog Devices ADG451/ADG452/ADG453

Another (older) quad switch from AD. Unfortunately Ron is about 4 Ohm with +/-15V power supply. The good thing about it: it is available as SOIC an even DIP version.

Maxim MAX4602

The Ron of this chip is 2.5 Ω, It is available even in DIP packages which is great for DIY (I still would recommend to use SOIC package, which allows a more compact layout. Unfortunately it is relatively expensive (about 10 US$ in small quantities).

You can see, that the more modern ICs provide lower Ron values. Unfortunately this comes in packages that are harder to solder.

A digital controllable phono input stage

When connecting a MC or MM system with a phono stage, the most important things to consider are input capacitance (for MM systems) and input resistance (for MC systems). Usually this is done be DIP switches or external connected capacitors. That means you cannot do this from your listing position and it is not easy to hear the differences between different settings. This the following input stage, all switching is done by low-resistance analog switches. These switches can be controlled by a digital circuit (e.g. a microcontroller). That makes it easy to implement a switching of capacitance and resistance using a remote control.

The selected analog switch is the ADG1411 from ADI. It features 4 independent switches, can run at +/-15V 8 and has an Ron of only 1.5Ω.