Sunday, November 26, 2017

Xover with ferrite choke and PIO cap

After experimenting with different Xover points, with my high efficiency Beyma speakers (VoXGrandious), I finally settled on 1100Hz. Also I went back to a first order Xover. I wound the choke on high frequency ferrite as a short rod. This allows the use of heavier wire and reduced turns compared with air core. The cap is a PIO Russian Military cap with another PIO across it. Total inductance is 1.16mH and total capacitance is 4.47uf into 32ohms (tweeter and limiting resistor).

VoXGrandious is a very dynamic speaker typical of most high efficiency drivers. I found that by using Ist order Xover I could hear the greatest dynamics. Also the PIO cap presented the clearest and most dynamic treble. All Cat5 wire used with heavy brass and gold binding posts.

Saturday, November 25, 2017

retro-Oatley 6J6 Headphone amp

Its been some time since I have bread boarded an amp but this prototype headphone amp from Oatley was just to pretty to hide. I happened to have a Pete Evans chopping board unused. So as not to mark the board all cct. brds. etc. are stuck down with either double sided tape or sticky standoff. Once dried these are hard to remove but not impossible.

To zippy boxes house the 240V power cord,switch and fuse while a front box holds the headphone connection, pot and RCAs. I did not assemble the brd. it came fully assembled. My job was just to bring it all together. The valves are 6J6 in two stages. Input goes direct into the phase splitter then into the push-pull power stage. Custom wound 35K/32ohm OPTs couple the headphones. 

The PS is separate in an effort to isolate any hum. The power transformer is also custom wound and though gets very hot is within spec. The passive parts are quite ordinary which when this is released as kit, from Oatley Electronics, will keep the price down. Better parts can be substituted.

A ground plane runs through the two brds. which I have connected to mains earth along with the power tranni and OPTs. DC is provided for the filaments and two stage power filtering helps to make a quiet amp. High and low output taps help cater for different phones. The amp sounds good on two of my pairs of 32ohm headphones.

Tuesday, November 7, 2017

"Sanctum" - simple tube headphone amp

Yet another very compact tube headphone amp. This time SS rectification. Hammond power tranni and 5H choke. Ceramic valve sockets and Alps Blue Velvet pot and solid brass black knob. NP (snubbed) output caps and all silver soldered. Tubes are RCA 6AS7 and Ozzie Miniwatt 12AU7. Great sound with good bass. Base is Australian Spotted Gum, top pate ABS.