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 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. 

Saturday, July 29, 2017

retro-6L6 SE UL MKII power amp


















Ok you have seen it before and above the bonnet it is exactly the same. In the engine room most components are different. This was the prototype for "Silver Supreme" SE UL amp with the JJ 6L6GC tubes and Mundorf Silver Supreme inter-stage caps. That amp I absolutely love and has not moved out of my main system for some months. 
 
This amp (the original prototype) was a real rough build, had a hum and sounded too similar to the Supreme. So I tore it down and rebuilt almost from scratch. Only the initial stage of the PS remains even the ceramic tube sockets got swapped out. I want this amp with the 1944 JAN 6L6 metal tubes to have its own character. For that all resistors are 1W carbon film (and not metal film), inter-stage caps are the original Solens. No silver solder here just Jaycar off the shelf but I did use twisted pairs of Cat5 solid core as hookup. The PS has 475uf of electros and the final filter cap to the driver tube (a well used (tests 98) 12AT7 and not a high end Psvane "T" series) is a Russian 4uf PIO snubbed with a 220nf poly. All other eletros in the PS are snubbed with 0.1uf polies. I didn't split the HT feed to the 12AT7 this time as in the Supreme, again to endow a different image presentation. All filaments (AC) are cap snubbed. The HT was pushed up from 295V on the 6L6 to 300V and 280V on the 12AT7 to 290V.
 
After chasing down a horrid buzz it is all is now quiet but not absolutely dead silent as the Supreme but it passes the 1M test. Sound is warmer which is strange as the driver tube has no bypass cap which not only reduces gain slightly but drops a lot of the second harmonic. I did this once more to give this amp its own personality. On a short listen (wifes home) it sounded more mellow than the super fast Supreme and as above, warmer. Very different 6L6 tubes and not the ruggedized GCs in the Supreme.