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DF: How did you get into audio?

JS: Well, I can’t remember a time I have not cared about music. I had distinct musical tastes even as a child and recall hating the sound of junky speakers before I was in grade school. By the time I was a sophomore in high school, I’d spent more money on my car’s sound system than on the car itself. Unlike most other teenagers, though, I didn’t spend my money to make my car loud. I wanted it to sound good. Around the same time, I started upgrading my computers’ sound cards and I purchased a set of Sennheiser HD-280 Pro headphones. Since then, I’ve been quite critical of audio equipment.

I cannot single out any specific reason for my interest in audio. Rather, my interest is a byproduct of my personality. I played the alto saxophone for six years and have often been surrounded by musically-inclined friends. Plus, I tend to be a perfectionist. So, it was inevitable that a picky, musical person would take an interest in high-quality audio.

DF: What I'd like to know is how you came to build this yourself.  There's a small anecdote on your website, but it doesn’t say that much.  Did you have a mentor?

In the summer of 2006, I added optional auxiliary RCA inputs to my car’s stereo so that I could connect my iPod to the car. I found that even at full volume, the iPod did not produce a strong enough signal to drive my car’s high-end stereo at normal levels. I was already aware of headphone amplifiers and suspected a portable amplifier would fix the problem. I had meant to try out an amp long ago with my Sennheisers, but had decided then that I was happy enough with their sound, and I really didn’t need to spend the money at the time.

Anyway, I Googled “cheap headphone amplifiers” hoping to boost my iPod’s output to my car and came across the schematics for a basic cMoy. I almost ordered the parts than to build a cMoy myself, but realized I didn’t have the time to put the thing together. I wanted to fix the weak iPod output issue quickly. As an alternative, I found a respectable looking cMoy ad on eBay from a seller named Sanjay Vasu (aka “biosciencegeek” on eBay) and ordered his $50 “customized” cMoy.

I first tried the amp out with my HD-280 Pros when it arrived. To be honest, I was disappointed. The HD-280 Pros are known for their weak bass response. Maybe I had higher expectations, but the amp seemed to make the music louder with perhaps even worse bass response. Luckily, Sanjay’s cMoy performed as well as I had hoped with my iPod and car stereo, which is what I’d purchased it for anyway.

Since I was only satisfied with the cMoy for use in my car, I decided to hardwire it to the vehicle’s +12V line. However, the amp blew up (hardly kidding - there was smoke!). Sanjay had recommended I permanently wire it to the vehicle’s power in the first place and was baffled when I asked him what could’ve gone wrong. I sent the amp back for repair. I’d blown up the entire power circuitry. We concluded I must’ve shorted or reversed a wire at some point.

Two days after receiving the second amp, I blew it up, too. I sent Sanjay another message and told him I’d fix it myself that time. The man is a PhD biologist, but I decided that as an aspiring electrical engineer, I could more easily get to the root of the problem.

And that was the beginning of my DIY audio quest. I repaired the amp the same day, and by the end of the week, I’d researched the schematic and unearthed the electrical theory underlying the blown amps. In short, a cMoy has two ground circuits that must not be shorted. Sanjay had not realized this, even after building 500 amps.

A few months later, I finished my first serious electrical engineering courses (as a sophomore). Armed with a stronger knowledge of circuit theory and a breadboard left over from one of my lab classes, I re-investigated the cMoy. I ordered enough components to tinker with a cMoy on the breadboard. As mentioned on my site, the physical construction of my first amp took hours. I wanted to build an amp with bass boost then, but still did not have the knowledge. I set the project down for a few months and resumed it out of boredom following the end of my sophomore year.

With the additional engineering knowledge, I was able to build an improved cMoy with bass boost in July of 2007. My tweaked cMoy caught on quickly, so I designed and ordered PCBs from a manufacturer in China and ended up forming “JDS Labs.”

DF:  What school are you in?  What's your academic progress?...and do you intend to follow through with a career with a major audio manufacturer or maybe even establishing JDS Labs as a permanent fixture in the audio world?

I am nearly half way through my junior year as an electrical engineering undergraduate at the Missouri University of Science and Technology (previously known as the University of Missouri – Rolla). I hope to eventually work my way into the audio industry. MST/UMR has one of the top career centers in the nation. I actually accepted an internship offer with a large Fortune 500 company this afternoon. My girlfriend and I will both be working at highly prominent companies in Illinois this summer.

As for the future of JDS Labs, we’ll see where it goes. I would like to see it grow, but I admit family will always come first, and with my present state of affairs, it may be best to accept job offers with large companies. That said, JDS Labs will continue as long as I can afford to devote the time to it. I actually have a unique new amplifier in the works right now (sorry, I have no idea when/if it will be released).

DF: What manufacturers' products do you use (i.e. brand or model of headphones, amps, etc.)?

I still enjoy my Sennheiser HD-280 Pros (try the cMoyBB with a set of HD-280s if you can!) and also own a set of Grado SR60s with bowls. I primarily listen through an Audigy 2 ZS on my main PC - nothing too extravagant. On the go, I listen to a 5th generation iPod paired with a very old set of $10 Sony MDR-828 earbuds. I don’t like to admit I own or listen to such cheap earbuds, but I can’t tear myself away from them; they sound better than Sennheiser IEMs I’ve heard, so I haven’t yet been compelled to upgrade. I mainly listen to my own cMoyBB right now, but have also built other DIY amps, mainly from AMB.org, such as the new Mini3. Aside from headphone audio, I enjoy Infinity woofers and JBL amplifiers.

DF: What actual components are different between the old version and the new one?

I released two versions of the v1.xx Bass Boost cMoy. Besides the highly improved circuit board, version 2.00 adds an Alps RK097 volume potentiometer and a different bass boost switch (changed from a PCB mountable part to a panel-mountable part). The input filtering capacitors and bass boost resistors have changed since v1.45, too. Above all, the v2.00 circuit board utilizes a ground plane, which has had a significant impact on noise minimization.

By the way, the noise you described in the first article has no relation to the new ground plane (also, out of almost 80 amplifiers, no one else experienced that issue!). It was caused by interference along the dual gain switch’s wires. I theoretically calculated the importance of dual gain switch and found that as long as a volume control is present, dual gain is largely unimportant in the cMoy and is more liable to create noise than to improve anything. Hence, I no longer offer dual gain.

The noise is gone, which is great, but (and this is me being over-critical) when you turn the pot off and on there is a squelchy crunching noise like you just stepped on bubble wrap.  That's not a huge deal though, and overall it is a pretty sick hp amp.

Yep, that power-down sound is present with every cMoy I’ve heard that uses the OPA2227 opamp and TLE2426 based power circuit (including Mr. Sanjay Vasu’s). You probably didn’t notice it with my v1.4x cMoyBB because there was no off switch. The original cMoy uses two series resistors parallel with two series capacitors to create a resistor divider. It powers down quietly, but has some downfalls (namely, the power will never be precisely “split” as it is supposed to be). The Texas Instruments TLE2426 virtual ground chip I use, in conjunction with one buffering capacitor, splits the power much more precisely. However, it is noisier when shutting down. I could eliminate the sound with a more complicated circuit, but like you said, that’s being a bit critical. I care how the amp sounds while on, not off, and I wanted to keep the design simple for fellow DIY’ers.

DF: Do you take custom orders?  I play in a surf/reggae band.  There are two applications I can see your products in the musician's world.  Live, they'd work great as belt packs for personal monitor systems.  In the studio, I can envision four, six or eight of your cMoys mounted on a single rackspace plate as a studio multi-monitor system.  Signal routing options on the back could make it a versatile tool.  I'd like to know if you're into that kind of stuff.

I am regrettably too busy to take on new custom orders at this time. Those applications demand different enclosures, and finding proper housing can prove difficult. Aside from that, either of those ideas could be pulled off fairly easily. I’m interested to see what other builders do with my cMoyBB PCBs. One guy has already turned a set of my amps into a balanced amp system.

DF: John I forgot to ask, what does the frequency curve look like on your cMoyBB, both with the BassBoost engaged and disengaged?  Just tell me at what frequency the boost starts and at what +dB/octave, as well as where it peaks.  And if there is a rolloff, tell me where that occurs too.

The cMoy is a simple amplifier and I wanted to keep it that way. Consequently, the bass boost circuit is a simple shelving filter with a 6dB/octave rolloff. A plot of the frequency response of a breadboard cMoyBB is attached. The response of a cMoyBB v2.00 should not be too far off. Also, the oscilloscope I used for that test was not too accurate and the signal generator’s output was not steady - the response with bass boost off is actually flatter than the results from my 20 year old testing equipment can show. By the way, several high end DIY amplifiers use this same type of bass boost circuit; I’ll admit its frequency plot looks strange, but I do enjoy its sound.