Upgrading a Sony micro system

A while back, I was browsing the local charity shop when something caught my eye. A Sony micro hi-fi system.

Now normally these things are garbage, but this one was a bit older (early 2000s), and it had two things on it that were of interest. A minidisc deck, and an optical input.

Essentially you can connect a digital source to this thing via the optical in and it'll use the internal DAC. So an el-cheapo PCM2704-based USB audio device from China off eBay can connect between a PC and this thing and in theory it should sound decent.

For £12 I wasn't leaving it there, so I bought it (following a quick test playing a CD in the shop just to be sure) and took it home. Tried it out, first with some CDs, then a couple of minidiscs, then finally I connected a 'spare' Squeezebox to the optical input and gave it a spin.

Initial impressions were pretty good. This thing sold for about £300 when new, so one would expect that it would sound fairly decent. However, as always with 'mainstream' audio kit like this, there were some corners cut.  Being a hardcore geek, the next thing I did was to dismantle bits of it to find out how well it was built.

With a bit of kit at this price point, you'd expect it to be reasonably good. And it was. The speakers, however, were a bit of a let-down. To be fair, the speaker drivers were pretty decent, a 4" polypropylene bass / mid, and a 1" mylar film tweeter. However, there was no damping material inside the speaker cabinets, no cabinet bracing and no proper crossover. Instead there was merely a bipolar electrolytic in series with the tweeter.

The unit has a function called "DSG", which is turned on by default and has to be turned off via the remote. This function, Sony's so-called 'dynamic sound generator', appears to apply bass and treble boost (the 'loudness curve') followed by a multiband compressor. So rather than building the speakers properly with acoustic damping and a proper crossover, Sony did things 'on the cheap' and used a DSP to compensate for the shortcomings of the speakers. Indeed I tried hooking the unit up to some better speakers (a pair of Celestion 1s) which, with the DSG turned off, were a vast improvement.

So I set about improving the speakers.  I did note that they had a proprietary Sony plug fitted to the captive speaker lead, which was far too thin to sound decent. I'd already managed to obtain a couple of these plugs from eBay, and made up some new speaker cables using decent 105-strand speaker cable, with the Sony plug on one end and a pair of 4mm 'banana' plugs on the other. This meant I could try connecting standard hi-fi speakers to the main unit, which did actually sound pretty decent.

The first thing I tried doing was cross-bracing the cabinets, then stuffing them with acoustic foam:

Connecting the unit back up and testing it produced a fair improvement; the response from the speakers was much flatter. In fact it now sounded better with the DSG turned off, as the cabinet resonance had been somewhat tamed.

Compared with the Celestions, however, the speakers were lacking some top-end definition. The treble sounded a little fuzzy, and whilst I'd originally put this down to the mylar tweeter (the Celestions have a metal dome) I suspected it could be to do with the bipolar electrolytic capacitor that was being used as a high-pass filter for the tweeter. There was also still a 'peak' in the midband, where the bass-mid driver wasn't being rolled off. Basically the speakers needed properly-designed crossovers, not a cheap 'bodge'.

Whilst not expensive, a proper crossover costs more than just pennies, and Sony obviously thought that it was more economical to use a switchable EQ in the main unit to dial out the midband peak. Unfortunately this can degrade the audio in all sorts of nasty ways.

The thin 24-gauge speaker wires also weren't helping matters, they needed to be replaced by something thicker. (No 'audio woo' here, it's a known fact that the thinner a cable, the higher the series resistance, so your amplifier's power ends up being used to heat up the speaker wires rather than move the speaker cone.)

A quick look on eBay and I located some suitable crossover modules for about £7 for a pair. These also had a proper terminal plate with binding posts and 4mm sockets, enabling the use of proper speaker cable. So I ordered a pair and waited for them to arrive.

A few days later and they duly arrived. A decent quality terminal plate, with what appears to be a 6dB/octave filter on both the high-pass (for the tweeter) and low-pass (for the bass-mid) at just below 1kHz, complete with provision to attach decent thick speaker cable for the internal wiring on the speaker.

The crossovers were supplied without any wiring attached; I've soldered some lengths of Gale XL105 cable to them (105-strand OFC, about 69p per metre at Richer Sounds). Nothing esoteric, no silver-plated cryogenically treated directional audiophool nonsense. Just some decent quality multistrand cable of a much thicker gauge than the cheap garbage that Sony fitted to the speakers.

Once again I set about dismantling the speaker, having to temporarily remove all the modifications I'd previously made (the damping foam and dowelling to brace the cabinets). With the cabinet completely empty, I then set about marking up the rear panel and drilling out for the new crossover panel:

The next step is to install the crossover, secure it to the rear panel, then attach the flying leads to the existing drivers. I wrapped some self-adhesive foam around the back of the terminal plate (sourced from Hobbycraft of all places) in order to make the panel as airtight as possible.

Now all that remains is to re-assemble the cabinets:

The modified speaker, as well as having uprated internal wiring, can now accept standard banana plugs, allowing the use of much thicker speaker cable.

So of course, the big question is, how do they sound now?

I hooked them back up to the main unit in place of the Celestions.The bass is tighter, probably due to the improved wiring and speaker cable. The mid-band peak is gone. And most noticeable is the treble, which is much clearer and crisper.

Looking at what these units tend to go for on eBay etc, it's effectively cost me a fair bit less than the regular selling price. And I've ended up with a very nice sounding little hi-fi system - which, following the modifications, is actually worthy of that term. No, it's not going to give the reference system downstairs anything to worry about (Arcam AV receiver with Monitor Audio Silver RX series floorstanding speakers), but it's great for a bedroom, workroom etc. And it has a digital input which works as a line-in (not just as a recording input to the MD deck unlike some similar units), the usefulness of which cannot be overstated.

Plus it's given me something to do in my spare time for the last couple of weeks!