A couple of months ago I managed to bag myself a PX303 for a very reasonable price from the bay. It arrived in near mint cosmetic condition. As already pointed out by the seller, it had issues with the sound being extremely quiet and also the parametric DSL just booming out.

Opening the unit up the PC board was in relatively clean condition. There were a couple of corroded capacitors. Noticeably the 100uF and the 22uF 2V SMD capacitors.

Just today I received a fresh delivery of capacitors from those resourceful people at Dig-Key. The 1989 TOTL AIWA just got bumped to the front of the queue for a new set of caps.

Testing the capacitors with an ESR meter, I got no readings at all from any of the 22uF or 100uF capacitors. The 220uF and 470uF capacitors gave slightly higher readings. On that basis I decided to remove all the capacitors from the PX303.

There was relatively little migration of electrolyte, so only minor cleaning with IPA was done. Some conformal had flaked off from underneath where one of the 100uF sat by the headphone jack. I will eventually go onto painting on some new conformal to replace this.

The connection pads were cleaned and re-tinned prior to fitting the new capacitors.

I have had to substitute tantalums for the 100uF 2V SMD as I am unable to source replacement aluminium electrolyte cans for this value. The 470uF surprisingly are microns of a millimetre small enough to fit inside their allotted spaces without any bulge to the PC board, and so would not need to be fitted sideways as previously thought.

The PX303 was reassembled and tested. I have to say, even without the DSL activated I get oodles of bass. There is a decent amount of treble. Selecting "1" and either "L" or "H" There is more deep and punchy bass, with "L" the bass range is lower than at the "H" position. Selecting position "2" and there is far to much bass for my own personal taste.

Without DSL activated the amplifier is loud but not as loud as some other models. I like the sound from the PX303 in this neutral setting, however activating the DSL and the loudness is there in full effect. This is definitely one model for all those bass lovers out there!

EDIT : Well I dug out an old pair of Sony MDR-G72 headphones I had kicking about. These are a slightly higher 24 Ohm rated and the PX303 is very comfortable driving them. Interestingly the DSL works really well with the G72 with settings of "L" and "2". Nice balanced rich deep bass on the G72. Not that the G72 is a  hard pair to drive, but I reckon there is plenty of power to drive the bass lower in more difficult headphones. This I would put down to the as specified 470uF DC blocking caps being able to accommodate such headphones with higher impedance.

I remember reading about how poorly the 3rd gen iPod did in frequency response tests because of using undersized capacitors.

Now that you fixed up your 303, how does it stand up against your other Aiwas?

Sorry I had to go away to do a few listening tests first

I do like the PX303 as a player in its own right. In a neutral configuration, the PX303 is balanced and does not seem coloured nor bright, it is almost like listening to a PX505 almost as accurate or sublime as the PC202. At the other end of the scale I also have a PX10 with 24 year old caps and listening to that without DSL it is very lower mid range heavy. I prefer my AIWA to be neutrally balanced (of which most are) with potential to go brighter or have more bass where required.

However when you crank up the Parametric DSL on the PX303, it turns into a bass monster. If you love bass, you'd love the fact that the PX303 has the potency and flexibility to give you bass where you want it with the "L" or "H" setting. Most of my other AIWA only have two modes of DSL. Some bass (when off) or extremely insanely powerful boomy bass when activated. Both this and the PX505 have two stages of adjustment. I like them both on level one as I wear IEMs that are quite bass receptive, and on level two it is too much bass. Interestingly from a technical point the PX303 and PX505 share the same audio amplification circuitry, and Parametric DSL "H" does sound very similar to regular DSL on the PX505. I have a PL30 that has Parametric DSL too, but this unit has three levels of adjustment and its internal circuitry is very different from either the PX303 or PX505 but similar to the PL50.

To fully appreciate level two (or level three on the PL30) would require a closed cup pair of headphones, but I don't favour those as my ears heat up.

Thanks Parkashan.

It is theoretically possible to replace most values of electrolytic capacitor with tantalum. However in practice this is not always possible or desired.

Good tantalum capacitors are typically 10-20 times more expensive than the equivalent electrolytic capacitors. The lower the ESR rating and the larger the capacitance; the even more higher the prices for them they go. Tantalum capacitors can also explode violently if their polarity is reversed!

There is a lot of chatter on the internet in various audio centric repair forums claiming that tantalum capacitors can distort the quality of the sound. Although I think this may be down to the use of cheap high ESR rated tantalum capacitors myself. Best to avoid using them if there is any doubt about it.

I am more than capable of replacing the old capacitors, so for me fitting electrolytic capacitors despite there being a possibility that they may leak is the cheaper option. To replace them all with tantalums would be very expensive indeed for the amount of walkman that I currently have. I use tantalum capacitors though where regular electrolytic capacitors are no longer available.