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differential hybrid parafeed headphone amplifier

Construction - Setup

Some of you have built a Torpedo, designed by Dsavitsk of ECP Audio. The Torpedo has been around for awhile now and represents a true, output-transformer-coupled tube headphone amplifier. What made the Torpedo unique is that except for a single volume pot ground wire and a PCB safety ground wire, the entire high-voltage, tube-transformer coupled design is contained on a single PCB - no other wiring, no point-to-point construction, and with the supplied enclosure - no casework fabrication. The combination provided a lot of DIY-ers with the ability to construct a full-function, high-voltage tube/transformer amplifier safely and easily. (I count myself among the ones scared to death to ever try high-voltage construction with point-to-point!)

The Torpedo went through some teething pains early on in trying to reduce noise and hum. However, with the help and patience of many along the way - Dsavitsk, Morgan Jones, Kevin Gilmore, and Jim Cross of, several tweaks were discovered that resulted in a noise-free and high performance design. These consisted of 1) the zener diode tweak, 2) the rectifier snubber tweak, and 3) the discovery of the E90CC/5920 tubes. The result is a noise-free, high-performance tube-transformer (parafeed) amplifier.

Meanwhile, Dsavitsk continued to refine the basic planform using tubes, Edcor transformers, and 4 x 14" PCB. The Torpedo II was created and a couple of prototypes built. These used 6922 tubes, but resulted in more expense without a significant performance advantage over the Torpedo I, especially compared to a Torpedo I using the E90CC tubes.

Back to the drawing board, Dsavitsk decided to use elements of a solid-state, differential circuit in a tube-hybrid arrangement, all tied into output transformers, again in a parafeed arrangement. This is a singular and - to my knowledge - totally unique amplifier design. Learning from our previous experience in teething pains with the Torpedo, we built several prototypes ourselves and went through a number of changes before arriving at the DIY kit that you will see here. We think that many of you will find the cost and effort of assembling this kit well worth your while.

We won't go over the construction in excruciating detail as with the Torpedo I. The construction of that amplifier is highly documented and building the two amps are very similar. This is more an effort to note the differences in assembly from the Torpedo I.

Starting as I always do, you will note the assembly setup below:

We went with Red PCB and Gold plating/pads this time, all of which is ROHS compliant. To the right, you can see my trusty Hakko - still going strong after 9 years! Brass wool, which let me stop using the sponge altogether and it does not reduce the temperature of the iron tip very much, so the work goes much more quickly. Solder and de-soldering braid is to the left.

In the center, the PCB on my piece of high-quality 1 x 10 pine (also 9 years old!). The first thing you notice is that the PCB is longer than the building board. That's OK - we only need to access certain portions of the PCB at a time.

At the left, my collection of standard tools for assembling a through-hole PCB: scissors for opening the parts packs, cutting part tapes, etc., a lead-bending tool, flush cutters, and smooth-jaw needle-nose pliers. In addition, for those things that always seem to crop up that can't be handled by all the other tools - a trusty Leatherman multi-tool knife.

Solder, as always, is Kester 63/37 rosin core, 0.025" diameter. This is good for both through-hole and SMD work, too.

Besides the window, there is ample task-lighting both in the bench and a task lamp in the upper corner of the building bench. I simply used a table in the past, but moving a year ago gave me enough room to improve my setup. It's not needed just for the Torpedo III, though - a table with a lamp will do just fine.


file last changed:Saturday, October 31, 2015 6:53:23 AM
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