Most amplifiers or preamps give you about 4 or 5 inputs. This is fine for most, but after 2 years of lockdown-fueled eBay and Gumtree HiFi buying sprees, I need at least 12 - and counting.
My plan was to make a switch box using relays and a microcontroller, but once you factor in the cost of multiple switches, relays, RCA jacks and a decent case to put them in, the cost of this is putting me off.
So I thought I would give this a try...
This is an Extron MPS 112 Media Presentation Switcher. It's a professional AV switcher that will switch 12 audio and video inputs to a common output (outputs actually, but we'll get to that).
Being a professional audio product it's well made, with a powder coated aluminium chassis and decent buttons, and gold plated RCA jacks on the back.
The 12 inputs are selected using push buttons on the front panel (which I'll need to label somehow) and there is also a control to mute and adjust the level of the output. You can mix in a microphone input as well, if you're into karaoke.
Round the back we have two sets of four gold plated RCA inputs and one set of four 3.5mm jack inputs. Plus a load of video inputs we can ignore.
As well as a pair of RCA jacks forming the main output, each set of four inputs has its own output too. The unit can be configured either as a single 12x1 switcher or as three completely separate 4x1 switchers (with the ability to also send one of the three outputs to the main output jacks).
Here's what it looks like with it's shirt off. On the right is a switchmode power supply regulated to +/-5v and +/-9v. In the middle is the switching and volume control circuitry and to the left are the audio switches and op amps.
Having all that circuitry in the signal path would make most audiophiles turn their noses up at this, and it isn't ideal, but the circuitry in here is reasonably decent stuff.
Level controls use Burr Brown PGA2310 chips which are used in such insanely priced audiophile products as the £3000+ Bel Canto Pre6 and the £5000+ Classé CP800. They have a very low THD+N performance of 0.0004%. Presumably headroom is limited a bit by using a +/-9v power supply rather than the +/-15v this chip can normally handle.
TL084 JFET op amps (0.01% THD) are used as input/output buffers. Switching is done using 74HC4052 analog switches. Sine wave distortion for these is quoted at around 0.02%.
The overall THD+N for the unit is quoted as 0.08%@1khz - not great, but also not that bad. Lower than a lot of the audio sources that will go into it (cassette, 8 track etc). Other specifications are pretty good: S/N is >90dB, crosstalk between inputs is -105dB@1kHz and stereo channel separation is >80dB.
I haven't noticed any audible degradation in the sound since adding this to my HiFi, and for the cost (£13 eBay) and convenience of having a 12 input switch box, I'm not going to go looking for it. There are much bigger factors affecting the quality of sound from the system (the room for starters).
I have the output of the MPS112 hooked up to one input of my integrated amp. Turntables go directly into the phono input of the amp (odd things seemed to happen when I put them through the switcher first for some reason, possibly the low level of the signal).
The tape-out of the amp goes to a simple mechanical switch box to feed the record inputs of various tape and minidisc recorders.
There is no power switch on the unit - it has to be turned off from the mains, which is slightly annoying. Buttons will need labelling too. But I'm pretty happy with it as a solution to the input problem.
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