Saturday, February 24, 2018

retro-Hiraga Le Monster

I bought the cct. brds. for the Hiraga Le Monster over twenty years ago and populated them shortly after arrival. But that's where it stopped. An enclosure I had designed for the amp was incomplete and thus the whole project stopped. Using an off the shelf 19" 2U enclosure the amp is now complete. The PS uses a 160VAC 12-0-12 volt high current toroid with 80,000uf total of filtering\storage. Bias is 700mA with a 10A bridge and 4ohm\20W filter\limiting resistors.

All wiring is Cat5 solid core twisted pair this includes most of the power wiring. No shielded cable is used and RCAs and speaker binding post are heavy duty and high grade gold plated. A internal 10A RFI\EMI power filter ensures clean power in the amp and the enclosure is earthed and fused.

Not only does the amp look smart with an ash black stipple finish but sounds excellent. With only 8W of pure class A power efficient speakers only will deliver good volume levels. The amp has an extremely natural relaxed sound about it I've not heard from other amps. Being a DC amp bass is extended and treble clean with controlled sibilance. It is an amp which has to be heard to understand.

Tuesday, December 12, 2017

"Sanctorum" - simple headphone amp on a Cypress base

Another simple two stage, direct linked headphone amp, Again using a RCA 6AS7 (also pictured with a 6080) and this time a E88CC Genelex Gold Lion gold pin. Ceramic sockets, choked PS and a stunning Cypress timber base. Alps Blue Velvet handles the volume levels and all Cat5 solid core copper wire hooks it all together.

Looks great sounds great and is quiet in operation. This proves once more that simple uncomplicated schematics can produce excellent sounding DIY gear and are easy to construct.

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.

Friday, October 6, 2017

"The retro-thermionic Valve Amplifier Book"

I have put together a book of my valve amplifiers. This covers most of my DIY better looking power amplifiers. It is more of a pictorial book than a technical one. There are 19 double sided gloss pages of good photos of the amps. Below is the name of each amp and a simple description.  

The book is hard covered and on the back is the underneath of two amps. The front has the retro-thermionic decal with the book name. I'm quite proud of a number of builds and each amp has its own characteristic look and produced its own sound. I'm also quite proud of the book. As a DIY friend exclaimed after viewing it, "what a great legacy". 

Sunday, August 13, 2017

Mimic - "Carbon" phono MM preamp

 After building and selling a number of Mimic MM  and MM\MC phono preamps, all based on Oddwatt's great design, I have here a Carbon film resistor version. All other builds use metal film 1/2W resistors. Carbon film 1W resistors have been used in a few of my tube power amps and the sound is rich and mellow. Here 1/4W fine carbon film resistors are used.

To make this build even more different with MKT caps I have also used Polypropylene and Russian Mil. PIO caps. The large red caps in the image above are 4uf PIO snubbed with 220nF polies. The usual OPA2134 chip and mil. spec. socket are used. Silver plated fine wire wrap wire is used for the short hookups. PS and amp exist on a 5cm square of vero-board. WBT silver solder holds it all together.

I had hoped this preamp would run from a single 9V battery but in the end two 9V batteries were required. This should provide 100hours of play between battery changes. A battery test point is at the front and an earth lug on the side. Initial test show good promise with a rich and warm sound from (at this point) limited listening. Interestingly on a short A/B test it sounded similar to my LM833 based two stage MM  preamp. Both have great warmth.