Onix OA-20/2

Heard my 1st Onix amp in 1988, a OA-20. Should have bought it then...

Front

Slant view

More than 20 years later, chance upon a OA-20/2 in good working condition - not making the same mistake twice!

The Onix deserve it's well earn reputation of a great performing unit with grunt- an excellent example of British audio quality. Although rated at a lowly 30W RMS and weight a mere 4kg, it is no push over. The unit was hardly warm after running for a few hours with the volume at 7 o'clock. This was more than enough to drive my honeycombs to a decent volume in a room 30ftx20ft.

After warm-up, the Onix was revealing. The mid and HF was fluid when playing a CD of well recorded piano pieces. Bass could be better but acceptable, may consider a recap later on (since it has been over 20 years).

Top

Back

Component view from back

Little wonder these units are seldom available in the resale market. And are quickly snapped up when they became available!

Update - 30Jul2011

Finally decided to perform maintenance on the electrolytic capacitors in the power amplifier section, as the reproduction seem a little muddle on critical passages.

Upon closer inspection, notice the unit had been repaired before and a unknown brand of EC, "Sun" was used in the power rectifier section as well as one side of the power amplifier. Replaced the 100uf 10V with Panasonic FC and the original 4.7uf 50V with Panasonic ECA of equal values in the power amp section. Left the Sun EC in the power rectifier section as that should be adequate for the task. Using better quality EC and substituiting the pairs of EC in the power amp section provided the desired results. Source is the Sony CDP-333ESA which is now connected directly to the Onix without the tube buffer. The Onix is now driving my Mission 753 Freedom's via 1.5m of the original QED Silver Anniversary (with enough silver to cover most of the cable diameter).

Original amp section

Capacitors replaced from power amp section

Musical Fidelity X-10D

With the help of a friend, I finally managed to purchase a X10D.

Front

Rear

Since completing and tweaking the Lite LS-29 (clone of the X10), though it would be interesting to compare the stock X10D vs the tweaked LS-29 @ http://myoldvintagehifi.blogspot.com/2010/11/diy-tube-buffer.html

Stock PCB

The stock X10D uses Philips 6922 valves and produces a rich mid, nice high with a lean low after power-on. About 15-30min later, the bass becames fuller but I find the high can be just a tad brighter than an actual presentation should be. The X10D seem to have a slight roughness around the edge as well, particularly on voices. I was using a gold CD recording of a singer whom I heard during a live performance for comparison.

The LS-29 produces a more authoritative low and  "richer" high while retaining the rich mid of the X10D. The reproduction of the LS-29 was more natural.

Finally decided to recap using lessons learnt from the LS-29.

Recapped PCB

Upon power on there was a immediate bandwidth improvement, compared to the stock X10D which was more reserve in presentation. Voices were now more natural and realistic.

After a week or so, decided to change the 0.22uF Wima(s) to the older MKS-C 0.33uF in the audio section. Initially sounded overly bassey. After a couple of weeks, it's sounding very close to my Tubelog when performing A-B comparisons - with a bit more HF extension, maybe due to the use of silver mica's in th output stage.

Update - 18Aug2011
Finally swapped the Philips 6922 with the Russian 6N23P-EV. Reproduction clarity improved.