Integrated Amplifiers

Simaudio Moon 700i Integrated Amplifier


Design and Set-up

The Moon Evolution series has a common aesthetic. The products are visually and structurally anchored on each corner by metal pillars that sits on inverted conical supports. They have finned heat sink side panels and a red dot-matrix style display. You can have any colour you want – as long as it is black or silver. This look continues on with the remote - a ¾ lb milled aluminium slab that doubles as a personal security device. Despite all that the front display is fairly subtle with 8 buttons flanking the fully dimmable display and a large volume control.

The volume control knob on the front of the unit actually drives an optical encoder which controls two multiplying DAC (MDAC) circuits vs. being mechanically connected and will spin freely for a second or two if you give it a good yank. The two MDACs are part of the M-eVol2 circuit which allows the 700i to keep it's dual mono design and balanced differential operation in place and the signal completely in the analogue domain. Channel balance (L-R) itself is adjustable via the remote in 1% increments from 0-100%

The volume control is remarkably granular, with 1.0db increments from 0 to 30 db and then 0.1db steps from 30db to 80db (the max) on the amplifier. It's a feature I didn't realize I was missing until I had to go back to the usual 0.5db stepping with other gear. It makes dialling in the level you want much easier and matching levels on the bench a breeze. Although you really have to pay attention when you hold down the volume key on the remote, for the first second the increment will be 0.1db then the 700i switches back to 1db increments. You can look away for a second or so and all of a sudden you are up 20db.

The separate amplification stages and use of MDAC in the volume control rather than a potentiometer allows the 700i to (very) tightly control the gain of the analogue input and enables a very quiet -130db of crosstalk @ 1kHz.

Each of the inputs can be individually set with a max volume level and individual input offset levels (+/- 10db) in 0.5db increments. Each input comes from the factory set to +6db. The inputs can also be set in a full bypass mode in the event a user wants to use another component to control the volume and bypass the 700i's volume control.

There is one set of balanced connectors (XLR) on the rear panel and 4 unbalanced (RCA) inputs with a in / out pair of RCAs for a tape/monitor and an additional set of RCA line level pre-outs. The WBT speaker terminals were quite nice and if you are a spade lug fan this design should be your choice - finger tight will give you a near permanent connection. Of course they also accommodate bare wire (up to 10 AWG) and banana plugs. There are four 1/8" jacks as well, two for SimLink (proprietary Simaudio equipment interconnection), an IR in and a 12V out trigger.

The 700i has 68,800µF of capacitance onboard and uses two separate 0.5kVa toroidal transformers with a claimed 3% regulation factor (vs. a more industry typical 10-15%) giving more consistent output voltage as current demands rise with higher volumes or more difficult to drive speakers. The preamp stage also gets it's own separate power supply and a dedicated, separate board within the chassis for signal isolation.

The 700i operates as a class A amplifier up to 5W of output. Of course like any class A it's pulling power all the time which explains part of the 700i's 50W power draw even in standby mode. The highest draw I observed during actual use was 215W over a one second interval.

The final piece of the puzzle is the "Lynx" architecture. While Simaudio doesn't claim to completely do away with the usual amplification feedback loop from the output stage back to the input (there is still some local feedback to keep THD low) they do claim to provide "no global feedback". This presumably will have benefits in a more natural and accurate sound while still maintaining some of the advantageous characteristics of the feedback loop such as a relatively high damping factor of 400 or more and low distortion. Not to give away the farm but as you will see on the bench I saw less than 0.008% @ 0.5W and less than 0.007% @ 1W into a 8 ohm load with a 1kHz test tone.