Thursday, May 23, 2013

retro-thermionic\Oatley K272C headphone amplifier




























Oatley has continued to improve their headphone amp\preamp with the release of the K272C. I had something to do with this progression consulting directly with Oatley. In fact there was a K272B between the K272A and the “C”. Here are two K272C headphone amps, assembled from the new kits which sell for $40 from Oatley.

The improvements over the original K272 are:

  • ·         18V working
  • ·         Separate filament and B+ batteries
  • ·         Filament and B+ battery health LED indicators
  • ·         OPA2134 driver chip

The kits are very easy to assemble with the excellent PCBs being screen printed and solder masked with through hole plated. The sound has improved with better bass response.

In this build I Al lined the ABS compact enclosures and used switched 6.5 stereo phone jacks. Only with both source and headphone plugs inserted and the press button switched “on” at the rear will power flow. Wire-wrap wire has been used in the signal path and the battery health LEDs have been brought out to the front of the enclosure. The sound appears to have better bass than previous models but the tubes will ring if struck.

1 comment:

Especulóide said...

Hello, this is a very nice kit indeed (I have de K272B). Based on the K272C circuits, I made some alterations that might be worthwhile to test ( I am only a hobbyist and despite my ears and a multimeter do not have more adequate equipment or knowledge to test the real audio performance). The alterations was :
1) Changed de JAN 6418 for 1ZH18B (Soviet minitubes);
2) Changed C1 and C2 for 470nf PIO caps (also Soviets);
3) Excluded C4 and C5;
4) Instead of OPA 2134 I used the OPA 2107 (was on hand);
5) The rest was only minor alterations (power supply, etc);
Best Wishes,

Roberval