The ECP Audio / Beezar Torpedo Headphone Amplifier

It's been a long time coming; Dsavitsk started looking for builders for his prototype of the Torpedo, a CCS loaded, transformer coupled parafeed headphone amplifier back in March of 2010. The Torpedo is a simplified and more affordable version of the ECP Audio L'espressivo 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 Beezar 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 Torpedo Schematic from ECP Audio

The ECP Audio / Beezar Torpedo Shortkit

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. 

Tube sockets mounted

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 socket board wired up

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.

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.

 

Need a nice set of custom cables to take your audio rig to the next level? Contact Zynsonix for a custom solution today.

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

The Bottlehead Single Ended Experimenters (S.E.X.) Amplifier

If you've read my other posts, you'd know that I enjoy building Bottlehead gear. I have both a Bottlehead Crack high impedance headphone amp and Seduction phono preamp, both with the obligatory C4S upgrades. The Crack is excellent for high impedance cans (~300 ohms), but can't really handle the low impedance ones. The solution was to build a S.E.X for those more demanding headphones. ;) 

The S.E.X. kit is a stereo integrated single-ended-triode amplifier with 2 watts per channel output and has been available since 2004. From the Bottlehead site: The two stage zero feedback RC coupled circuit uses parallel feed (a.k.a. parafeed) output, a topology championed for use in modern single ended amplifiers by Bottlehead and MagneQuest. Parafeed output assures articulate, musical bass, great high frequency extension and minimizes the influence of the power supply on the sound. 

The Bottlehead S.E.X. Kit

There are a few special upgrades available for the S.E.X., including the C4S Constant Current upgrade which consists of a pair of small PCBs with mounted MOSFETs, LEDs and resistors (currently $45), and some higher quality MagneQuest transformers and chokes ($300-450 depending on nickel content). And of course you can throw in the nicer caps and such as well.

Building the amp is the typical Bottlehead affair; there's a wooden base to assemble and stain, a top plate made of aluminum you can paint or leave bare, and a nice big instruction manual that makes things easy for beginners. Because my build included the aforementioned upgrades, I had three manuals to look at.

My first concern was the MagneQuest transformers. They may be well made, but they aren't much to look at in my humble opinion. The chokes hide beneath the plate but the outputs would be visible. I sanded down the metal frame, taped off the center with painters tape, and spritzed it with metal primer, copper hammerite paint, a layer of clear coat, then more hammerite paint. It gives it almost a leather looking texture when the clear coat reacts with the hammerite. I then wrapped the center with some thin black leather (Doc's advice). You can see the difference below between the original look (left) and the modded look (right).

Magnequest choke, transformer and stock bell

I got the plate back from the powdercoater with my favorite antique copper finish, so the next step was to begin populating the plate. I had made a few enlarged holes for the Neutrik locking jack, Cardas RCAs and binding posts, Goldpoint attenuator and vintage lamp.

Teflon 8 pin sockets and boards, Goldpoint attenuator

The Goldpoint attenuator required a little bit of work to fit. In the stock hole position, it butted up against the wood frame and the plate couldn't be seated. The hole had to be enlarged vertically to allow clearance. A couple of the little solder strips required mounting to #8 screws to be enlarged. I recommend one takes their time if they use a drill for this, as I broke two of them :P

Further population included a few little tweaks to the stock kit, including rubber washers for the transformers and chokes, shielded Cardas output wire, bypass film caps for the power supply caps, a few nicer Nichicon caps, thicker shielded wire for the power switch, another solder strip for the Neutrik locking plug to keep the installation clean, and some big hulking paper in oil AmpOhm caps, which required the addition of a set of 2" standoffs. Below are a few progress pics of the amp being built. 

Getting Started

Additional solder post used for headphone output

Solen caps placed temporarily for resistance checks

One thing about the build that was a little difficult was soldering the bottom of two of the power supply caps. There were three or so things going into the top hole of terminal 4 with that little solder strip which made it quite difficult to ascertain whether you had a good solder joint or not. With a flashlight a couple minutes of investigation, it could be seen. 

C4S boards fitted

The little C4S boards got in the way of the standoffs for the large caps, so I flipped them 180 degrees and dremmelled into the unused part of the board for clearance. It's almost comical how large the AmpOhm caps are at a mere 2.2uF.

Finished inside - Front

There's a lot of parts shoehorned in here

Finished inside - Back

There's a lot packed into this little chassis, every inch counts ;) I originally had a set of EAR feet on the bottom of the wood frame, but the caps protrude far enough that I had to get larger feet. I initially entertained the idea of some little brass spikes, but the company selling them wanted $80 for a set of four 1" x 1" threaded brass spikes. I picked up a set of 1" black steel spikes and 1" rubber feet (both under a dollar each) from PartsExpress. I ended up liking the black spikes better, so I drilled out the bottom of the wood frame and threaded it for them.

This amp lets it's business hang out ;)

Finished Back

Finished Front

The emblem on the front I had custom made (I had two made in total). I created the logo and sent it off to a promotional company that makes the little metal emblems. 

UPDATE (3/22/11) I got to have a listen to this yesterday, Eileen got me a replacement set of RCA tubes, and I had a pair of Sylvania coin-bases arrive from another supplier. Sound is really excellent, even before burn-in. No lack in the bass department, a nice powerful sound with just enough detail.

I'm currently using a very special custom 10-3 right angle power cord with this kit (my own recipe). Take a look at the details here.

Wondering where I got all my parts for this build? Check out a list of my favorite online vendors here.

UPDATE (3/29/11) Replaced the stock sandcast 0.1 ohm 5W resistor with a Vishay Dale wirewound in the power supply. Can't tell if it made a sonic difference, but would likely be a little more reliable over the years.

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind. 

The Bottlehead Crack OTL Headphone Amplifier

Bottlehead has been known to me many years before I purchased my first kit from them. Doc and Queen have been in the business of selling tube-based kits for quite some time and have earned an excellent reputation for providing easily accessible and excellent sounding kits. All of the kits follow a rather unique naming structure: S.E.X., Foreplay, Seduction, Quickie ... you get the idea ;)

The Bottlehead Crack is a very inexpensive kit, for only $219 (as of Feb 2011) you get all of this:

The Bottlehead Crack Kit

The amp runs on a single 9 pin 12AU7 and an 8 pin 6080 / 6AS7. I'd recommend a little bit of tube rolling on this little guy as it can sound very nice with the right compliment. The manual is included on the CD in PDF format with step by step instructions. The kit includes an aluminum top plate that comes pre-drilled for the stock parts. Since it's aluminum, it's a piece of cake to drill out any additional holes or enlarge existing ones if you decide you'd like some different parts in there. I used a Hammerite spraypaint to add a bit of personality to the top plate and transformer bell cover. A Northwest Alder wood base is also included, you glue it together and finish in the color of your choice. I used a combination of MinWax products to get the wood to a deep red finish and a Polyurethane finish to preserve it.

Below are a few of the initial build photos:

After a number of steps into the build, with DACT mounted

Fitting the large Solen 100uF Film Caps

I decided that I wanted a little more than the standard Bottlehead square emblem adorning the wood base. I managed to find a promotional products supplier that fashioned metal badges. I designed a vintage looking logo in Adobe Illustrator and fired it off to them, the results turned out well.

Finished Wood Base with EAR Feet and Custom Emblem

Bottlehead offers an excellent upgrade to the Crack called the Speedball... again with the crazy names. This, more specifically, is the Camille Cascode Constant Current Source upgrade. Bottlehead states on their page: The most immediate thing you will notice is a better sense of clarity. Things get tighter and quicker, bass and midrange get cleaner and more dynamic sounding, and the background gets more quiet.

Speedball Upgrade Fitted

Final Build with PSU bypass cap and Pilot Light

Custom made 10 gauge power cord for the Crack

Obbligato Bypass caps peaking out from the vent holes

The Final Build

As always, a few tweaks here and there are always welcome. This Crack features the following upgrades:

• Cardas Rhodium RCAs
• DACT 100k stepped attenuator
• Kimber TCSS wiring
• Kiwame Resistors
• Neutrik Locking Plug
• Obbligato 1uF Copper coupling caps (hidden under Speedball board)
• Solen 100uF Capacitors
• Teflon Tube Sockets
• Woo Audio Tube Socket PCBs
• Auricap Bypass
• Vintage Pilot Light

The Crack, with Speedball, is an excellent sounding headphone amp for high impedance headphones (think ~300 ohm like Sennheiser's higher end cans) and a great value for the price. It can be a little bright with certain tube compliments in my humble opinion, so be sure to get a few to roll. 

UPDATE (5/1/11): It's been a little while since I worked on the Crack, so I figured I would give it a fresh upgrade :) I managed to squeeze in a Solen 220uF film cap in the final electrolytic power cap location, sitting on a pair of standoffs. I also took the time to bypass the other two power caps with a pair of low-cost Audiophiler 2.2uF film caps.

All these parts just narrowly fit in the stock case

Leads were cut and longer Kimber TCSS wire was run

2.2uF Audiophiler bypass caps on left and right

UPDATE (5/18/11): Since I can't leave well enough alone for longer than 5 minutes, I opted to add a choke to the power supply for even further refinement. I selected a Triad C7X with a rating of 270ohms to take the place of the final resistor in the power supply (also 270 ohms). Since pretty much all the real estate has been used up on the plate, I opted to add two 2" aluminum standoffs to raise the choke above the capacitor near the RCA inputs. This required adding 1" spiked feet to the bottom of the wood base for adequate clearance, just like in the Bottlehead S.E.X. build. I think this baby is finally done.

Triad C7X choke right above the power supply cap

Spiked feet for added clearance and ventilation

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a build or modification posted above and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind.