WHAMMY Pass Labs DIY Headphone Amp

Wayne Colburn of PASS Labs was kind enough to release a new DIY headphone amp circuit into the wild, the WHAMMY, standing for Wayne' Headphone Amplifier Must Make Yourself. It's a nice simple build, no need to match parts or make adjustments, so it's perfect for the budding DIY builder. It's also inexpensive. The PCB, parts and chassis should be under $200 without much effort. Jim Tiemann aka 6L6 of DIYAudio has been kind enough to coordinate the project and has been instrumental in making it accessible. Having a headphone amp of this caliber available at this price is an incredible opportunity and I hope many can take advantage of it. If you're not familiar, Pass Labs is very

You can read more about the project here and boards can be purchased for a very reasonable price at DIYAudio. And you can learn more about the circuit design by watching this Youtube video:

Wayne Colburn of Pass Labs, the designer of the WHAMMY

I'll be briefly walking through my own build. I encourage you to also check out Jim Tiemann's build as it is more granular. My parts choices are also going to be outside of the standard BOM to some extent and will be more expensive, but DIY is fun because you have the freedom to make some unique choices without deviating from the original circuit.

As I knew I would have a little bit of extra headroom in the chassis I'd be using, so I added a piece of Dynamat between the board and the transformer just for a little bit of extra vibration damping. There's electrical tape over some of the larger contacts to prevent any shorting with the aluminum on top of the Dynamat.

Dynamat mounted on the PCB

After this, the power supply components were populated on the board. Normally, you would populate the small components all across the board such as the diodes, resistors, etc., however in this case populating the power components first allows you to test the power supply and ensure it is running properly and within tolerance before moving on. Review Jim's write-up for additional information on the measurements.

Please note the snubber capacitor (C20) should be an X-type, so you might see X1 or X2 in the model number. Before buying the capacitor, check the datasheet to ensure it is X1 or X2 rated. The lead spacing is 22.5mm. I personally used part 594-2222-336-10224 from Mouser. The PSU caps are Nichicon "For Audio"... for whatever that's good for ;)

Power supply populated and ready for testing

After the power supply is tested, fully disconnected, and the caps allowed to fully discharge, I moved along to populate the smallest parts first. If you've read my blog in the past, you'd know I really like Kiwame/Koa Speers resistors. These can be found at Mouser under SPR2 and are 40 to 50 cents each, rated at 2 watts which is far above what's actually needed. Not all values are there, so you can get the remainder at a boutique provider like PartsConnexion or just get some Vishay Dales at Mouser. 

Adding the resistors

Then the rest of the parts are added. While Wayne mentioned that the Silmic IIs, which are now being produced in China, aren't as reliable as they used to be, I still like the sound of them so I went ahead and used them. They're over-rated too @ 50V, so hopefully they'll last a while. You'll notice they're a bit large, so some creative mounting is needed. Wayne suggested using Nichicon BPs (bi-polar caps, they're iridescent green) if you'd rather not use Silmics. C1 and C5 are the input coupling caps and should be of high quality as they're directly in the signal path. I personally used some vintage Sprague paper-in-oils, but you can likely fit some of the smaller narrow Mundorf EVO caps or Clarity Caps, either of which can be found at PartsConnexion. The lead spacing is roughly an inch. 

All PCB parts populated

I hate this picture as it looks terrible from all the flux (this is before I cleaned it with some isopropyl alcohol and a toothbrush), but It shows where the film bypass caps are. The units in the audio section are polypropylene and the units in the power supply are polyester. The twisted pair is pulling off the 22V secondary for a pilot light.  

WIMA film bypass caps on bottom of PCB

The chassis I selected is from IAG DIY Tube Audio Products. He lists his chassis on ebay and on his website. Hand-made in the USA and built like a tank. It would be a slightly tight fit so I needed to see where items would be mounted to the front and back of the chassis so they wouldn't bump into any parts on the inside. The IEC filter in particular needed to be offset from the center so it didn't bump into the PCB mounted transformer. I decided to mount the 0.5A fuse and socket on a blank part of the PCB so there'd be one less hole drilled in the chassis. 

Lining up the chassis-mounted parts

Once everything was lined up and the holes cut, the PCB was secured in the enclosure using 1/2" standoffs. The front panel has a four pin connector in addition to a locking Neutrik TRS as most of my headphones are wired that way, so it saves me from having to use an adapter.

Wiring is scraps of Cardas I had in my wire bin, 4x24, 2x24 and 2x21 and some 24AWG, all litz in teflon. The potentiometer is the $40 100K Audionote with solder tags. It's nice and small so I didn't have to worry about it bumping into a discrete opamp. The IEC filter is from Furutech, gold plated. I normally wouldn't spend the money on it but it was discontinued and quite a bargain. RCAs are Cardas rhodium plated. The switch is a simple 3A rated toggle I picked up from Radioshack when they were clearancing everything. The LED pilot light is one from a guitar shop typically used for an effects pedal. Everything else is from the BOM. 

Wiring everything up

Here's a few more images of the chassis with the wood panels.

Front of the WHAMMY amp in the chassis

Back of the WHAMMY amp in the chassis

I used a very simple circuit from ClassicValve for the LED. 

Pilot light circuit to protect LED

Here's an image with the bottom panel and feet installed. 

Bottom panel with vents

...and here's the WHAMMY almost done, just missing the knob. 

Nearly complete

It's quick and easy to swap the op-amp on the unit to slightly alter the sound. Dropping in a Burson Supreme Sound V5 soundeda bit less constricted than the Texas Instruments op-amp that's in the BOM. The difference was less pronounced than if you use a Burson in a DAC, but still an improvement and worth the price of admission (you only need one). I found the V5i picked up a little more noise in this particular amp, so stick with the V5 if you get one. I also swapped in and out the optional capacitors just in case they improved the sound with the Bursons, but wasn't able to hear any difference in any of the configurations. 

Final pics coming soon. 

Please remember that building/modifying circuits 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. 

The Objective2 (O2) Headphone Amp

People feel so strongly about audio reproduction that it often becomes akin to religion and politics and arguments ensue. Some listeners feel that a perfectly flat response curve and fully diminished THD levels (total harmonic distortion) are the holy grail, while there are others that enjoy the warm distortion and harmonics achieved with old triode technology and a frequency response that tapers the upper and lower extremes. Both are right in their own way, the former looking for perfect accuracy, the latter looking for a relaxing listening experience, and there are probably many listeners that fall in between.

The Objective2 headphone amp falls into the first category, where good measurements are the paramount objective. NwAvGuy has gone to great lengths to provide what many headphone listeners have been pining for, a low-cost headphone amp that achieves great measurements in a vast number of categories. While I don't fall into the category of pursuing perfect measurements (just look at all the number of tubes used in the builds on this site), I highly respect the effort that went into this build and all subsequent documentation.

Something that's quite impressive is that NwAvGuy does not make a penny from these designs. The PCB files are open source and circulated freely; users are encouraged to arrange group-buys on forums such as DIYAudio.com in order to procure the board and/or the front panel. Also, as of this writing, JDSLabs is offering both the O2 board and a unique front panel (to see the JDSLabs CMoyBB being built, please see my previous post). The total cost of the build is very reasonable and should fall under $100 including the case, custom front panel and wall-wart. Add a couple hours of soldering time and you'll have yourself an amp.

The Objective2 Sept 2011 PCB board

What's especially important with closely populated boards is starting with the small parts (resistors and diodes) and working your way up to the larger items such as capacitors and MOSFETs. If one doesn't follow this basic principal, it's much more difficult to fit your fingers into the small recesses between the larger items on the board.

Partially populated, all resistors and small parts in place

The battery clips may look crooked, but they were lined up carefully before soldering to ensure a perfect for for a 9V. This is something one doesn't want to try and adjust later as desoldering them can be difficult. The faceplate shown was procured from a DIYAudio group buy. Many thanks to MrSlim and FlynHawaiian for their efforts.

Fully populated board with faceplate

Faceplate from the DIYAudio group buy

There are a number of testing procedures on NwAvGuy's site to ensure the amp is working properly before you plug a pair of headphones in to ensure that you don't inadvertently damage them with high DC output.

A pair of Tenergy 9V rechargables were dropped in and secured with double sided tape and the unit was boxed up with the case specified by the bill of materials, a Box Enclosures B2-080. Gold was chosen as it's a bit more flashy than a plain black box. Screws were replaced with brass counterparts and the knob was a generic aluminum one from the parts bin, possibly made by Kilo.

Assembled Objective 2 amp

Once the amp had a few minutes to burn in, some cans were plugged in for a listen. All online reviews of this amp were avoided so the initial listening could be done without any pre-conceived notions. The amp reminds me quite a bit of the headphone output of the Benchmark DAC from a HeadFi meet. It's very crisp, clear and has strong, effortless bass. The bass may even be a bit better than the Benchmark was, if memory serves correctly. Both amps are quite analytical; I wouldn't choose them for my own personal musical enjoyment as my ears are sensitive and need the treble and upper-midrange to be a bit rolled off or fatigue sets in too quickly. One can see this amp being highly recommended for audio mastering work as it should convey every detail possible to the editor.

Immediately after building the amp, the input and output jacks were shorting with a variety of different plugs. It appears I received a bad batch as I didn't see any other documentation online regarding issues with the Kycon jacks. Rather than replace them with the identical items, Switchcraft jacks will be wired in as they are very trustworthy. The opamps will also be switched to the low-power versions made by Texas Instruments, which hopefully will be a little bit warmer.

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.