My Mission Cyrus One amplifier is a very simple affair, which is indeed one of it’s strengths. With the exception of the phono stage the pre amp is purely passive.
Normally this is a good thing. However In my system I want to connect several devices to the tape-output sockets simultaneously. This just won’t work well.
The Cyrus connects the selected input device directly to the tape-output via one of the two big rotary selector switches on the front. There is no electronics in the signal path, which is what you want for maximum fidelity. Unfortunately connecting multiple devices to the Cyrus output is equivalent to connecting them directly to your input device. This could result in loss of sound quality even damage to the source equipment.
The connection and protection problem is solved by my tape selector. To solve the sound quality issue some sort of amplifier is needed between the source and other devices.
Originally I was going to build my own circuit on strip-board. However I found this amplifier module on eBay. It’s pretty much what I would have built myself but without the hassle and at just £11.99. Cheaper than I could have made it and a lot neater.
It is a stereo module using a pair of NE5534 op amp. This IC is commonly used in HiFi, indeed the Cyrus uses them in it’s phono stage. The chips are in sockets, so I can experiment with other types if I like. Through hole components are used rather than surface mount. Again this is useful, so I can get in with test gear and a soldering iron should I want to tweak the design.
To get the best out of OP amps like this you want to power them from a dual power supply of +15V and -15V. This ensures that the amplifiers are operating comfortably in their most linear range and minimises the risk of overload and distortion. Inside a typical HiFi Amplifier most of the circuitry needs +-15V, so it makes sense to build a good stable power supply that is shared by the whole unit. In an ancillary unit like this that is less practical and would add massively to the cost.
I previously modified my Cyrus to fit a power output socket, specifically with this project in mind. This socket delivers a rather dangerous +-30V which would immediately kill the 5534’s, and quite likely do the same to a human. A simple regulator is required. Again my plans to build my own regulator circuits were thwarted by a £4.86 module from eBay, visible on the left in this picture. It uses standard 7815 and 7915 regulator chips to derive +-15V from the power output from the Cyrus umbilical power cord.
All of this fits perfectly into a rather nice aluminium case( £6.41) and looks professional. Connected into my system between the Cyrus tape out sockets and my switch box it provides the necessary oomph to drive my recording devices and a long cable to a headphone amplifier. This let’s me enjoy headphone listening in the comfy chair. As it should be.