It's been a long time coming; Dsavitsk started looking for builders for his prototype of the Torpedo, a CCS loaded, transformer coupled
headphone amplifier back in March of 2010. The Torpedo is a simplified and more affordable version of the
spud headphone amplifier and works with 6J6 tubes and equivalents, including the 5964 and 5844. The shortkit was just recently made available in December 2011 on
after a number of DIY enthusiasts built the initial prototype and includes the chassis, custom transfomers from Edcor and the PCB. The remainder of the parts are listed in the bill of materials and can be purchased from the usual suspects (Mouser, Digikey, etc.). The total build cost, if not going crazy, should fall under $300.
The most unique facet of the Torpedo is the length. At 14" deep, it's a very unique looking unit. The length was designed to keep the output transformers as far away from the power transformer as possible to minimize potential flux interaction. As anyone who's built a headphone amplifier with output transformers can tell you, this is a real concern; noise is very apparent when a sensitive driver is right next to your ears.
In the interest of a unique looking build, an antique copper / bright copper powdercoat color scheme was selected. Holes were drilled every inch in a line along the top left and top right for copper pop-rivets to embellish the chassis. The rear vent was cut out in favor of copper colored perforated metal above the power transformer. Also, holes were added to the bottom of the case for EAR isolation feet.
|Fancy powdercoated Torpedo case (Bottom and Top)|
The EAR feet were installed with a combination of a #6 screw and washer on the bottom and a lock washer and nut on top to ensure that they remain screwed in.
|Case bottom with EAR isolation feet|
The initial population starts with the smaller parts, resistors, diodes, etc. This build won't deviate much from the bill of materials as the specified parts are of high quality, however the obligatory Kiwame carbon film resistors were dropped in. Since Kiwame / Koa Speers doesn't offer their resistors in 1M values, Takman carbon films were used in their stead. Also, the Neutrik 1/4" jack was substituted with the gold-plated version as their isn't much of a price difference.
|Initial population of the Torpedo Board|
A matched pair of 4.7μF Clarity Cap ESAs were used as the parafeed caps. The ESAs are the same size as the SAs but with slightly nicer specs and tighter tolerances. The price was right at about $34 for the pair as of this writing and they're a perfect fit. The purpose of these caps is to block direct current (DC) from the output transformers.
|Clarity Cap ESAs at 4.7uF|
|Almost fully populated|
According to TomB and Dsavitsk, there is a small bit of audible noise when the top of the case is fitted on a completed Torpedo amp. Unfortunately at this point, builders have not been able to isolate the issue, despite trying things like grounding the heatsinks and adding grounded shielding to try to isolate the power transformer from the tubes. This build will be trying a slightly different approach; the tubes will be raised up out of the chassis using a custom fabricated metal panel that the tubes will mount to, hopefully protecting them from the power transformer noise. The PCB will be wired to a pair of chassis mount tube sockets which will sit on the metal panel raised by a set of nylon standoffs. The ideal measurement for the standoffs seems to be about 40mm, or a hair above 1.5 inches.
Below is the metal panel designed in Front Panel Express that Dsavitsk and I worked out. There are three holes to attach the nylon standoffs and two holes for the 7 pin tube sockets and the accompanying chassis mounts. This will necessitate two holes being drilled into the PCB to accommodate the left and right standoffs, which will be used to ensure a rigid mount so tubes can be swapped without the panel flexing.
|Tube mounting panel designed in Front Panel Express|
Below is the FPE fabricated panel in their nice bronze anodized color.
|Tube socket mounting board|
Unfortunately, the panel was a little too wide at 39mm, so it was trimmed down a bit with a cutting disc. Also, underneath one of the screw holes are the traces on the PCB for the left and right channel inputs; we wouldn't want to knock those out, so a new screw hole was made a little closer to the tube socket on that side. Since the screws are so close to the top of the chassis, they were depth mounted to avoid any clearance issues. Finally, the ceramic tube sockets had to be sanded ever-so-slightly to fit in the holes.
Now came the time to wire up the tube socket board. Because some of the pins are interconnected on the PCB, they would be shorted on the socket to decrease the amount of wiring necessary (1+2) and (5+6). A hundred ohm resistor was used to connect pins 5+6 to the PCB. This was done at the advice of Dsavitsk. Also added was a twisted pair of wires coming from pins 3 and 4 (the heater section) that will be powering an LED-based pilot light. Kimber TCSS wiring was used, it's my preferred hook up wire in tube amps as it's relatively thick (19ga) but easy to work with and has a Teflon coating. The pins of the socket were covered with heatshrink tubing to prevent shorting.
|Tube sockets mounted|
Holes were drilled into the PCB (into the ground plane area) and the nylon standoffs were mounted. The wires were carefully trimmed to the right size and stripped at the end and tinned (covered with solder) so that the wire strands wouldn't stray when inserted into the PCB holes. The board was screwed to the nylon standoffs. Finally, the amp is fully populated.
|Tube socket board wired up|
|Fully populated Torpedo amp|
|Wiring detail under the mounting board|
When the cover is added, the sockets come right up to the top of unit, perfect for rolling tubes without having to unscrew anything.
|Sockets once the cover has been mounted|
The amp assembly can now be completed. The pilot light with bayonet style LED was wired up, the front panel holes were tapped for 4-40 screws and screws installed, the grounding screw and standoffs secured, and a Kilo aluminum knob installed on the Alps Blue Velvet potentiometer.
|Completed Torpedo Amplifier|
|Completed Torpedo - Back|
|Completed Torpedo - Front|
Initial testing was done with a pair of headphones with 32ohm impedance.
There is a smidge of audible noise that sounds like it's from flux interaction, but it's barely audible and hardly worth mentioning. I'd definitely consider it a non-issue. The amp sounds excellent. Highly recommended!
Update: Beezar has introduced an additional Zener Diode tweak
to derive even better sound from this kit.
Amazing job - it's beautiful!ReplyDelete
That's just beautiful.ReplyDelete
Digging the net above power transformer. BTW, how does it sound compared to Jonokuchi?ReplyDelete
How does this compare with Crack?ReplyDelete
It's a more resolving amplifier than the stock Crack. I prefer my highly modified Bottlehead Crack a bit more, but it was a much more expensive build.ReplyDelete
Where to buy LED pilot light cover ?ReplyDelete
Pretty sure it was from Angela Instruments - Angela.comReplyDelete