Announcing Codename “c421”

We’re past due on several announcements, but not due to a lack of content. In fact, we’ve been exceptionally busy this spring.

After returning from Silicon Valley last week, I was thrilled to see a package from Advanced Assembly at my office. Inside were two recently completed “c421” prototype headphone amplifiers:

A first look at codename c421, Prototype II (v0.84) - May 2011

Project History

Initial experimentation of c421 unofficially began in 2008, about a year after release of the cMoyBB. The goal at the time was to create a buffered headphone amp resistant to GSM interference. However, I ultimately spent 2008 and early 2009 designing microcontroller boards, a huge 4-layer, 2.4GHz quadrature modulator testbed, and miscellaneous audio circuits while finishing my BSEE. JDS Labs was still a very small company, so those first prototypes were stuffed into a box for many months.

Driving to a New Years celebration on December 31, 2009, for whatever reason, a new power supply circuit popped into my head. I jotted the idea onto paper as soon as I got home. Half a dozen Texas Instruments and Linear Technology evaluation boards later, we arrived at the first draft c421 schematic. An eager mechanical engineer contacted us around this time and custom enclosure design began immediately. By December 2010, the first c421 prototype PCB was in hand (pictured below).

c421, Prototype I (v0.83) - December 2010

The new ground/supply circuitry conjured almost a year earlier turned out flawlessly, but like many first draft designs, the PCB was far from perfect. With some trace chopping, I persuaded c421 v0.83 to behave, according to the oscilloscope.

Unfortunately, my ears were not pleased with the new opamp circuit (designed purely in LTSpice). For a mid-range headphone amplifier, it sounded weak, slow, and generally mediocre. Back to the drawing board!

Prototype II: Success

Starting over, I tweaked the opamp circuit and tried something very different: A triple-ground, dual-channel topology. Five “channels” in all. For a while, it seemed crazy. The 4-layer PCB would be split into a chaotic mess, but hey, it was worth a shot. [Edit 6/15/2011: The term ‘channels’ is used here in a non-standard fashion. C421 uses three opamps and two successive reference circuits in the power stage; hence, five stages. All grounds are at equal potential to allow usage while charging.]

We replaced the opamp, the power IC, and added two more chips. Practically every R/C/L component on the board changed and the layout grew significantly more dense.

c421, Prototype II (v0.84) - May 2011

Pending Release

I am pleased to announce that c421, Prototype II is a tremendous success! Typically I judge audio equipment by its capability to invoke the pilomotor reflex (hair raising brilliance). c421, Prototype II absolutely delivers. It’s powerful, fresh, and exciting to listen to.

Features and pricing will be announced closer to release, although much of the feature-set can be inferred from the photographs. And when might c421 be released? As soon as we jump through production hurdles, of course. Stay tuned!

67 thoughts to “Announcing Codename “c421””

    1. For now, I can say what is vaguely evident from the photo:

      -USB Charging
      -Lithium Ion Battery
      -Dual Gain
      -Bass Boost
      -Very small size (comparable to iPhone)

      Bass boost of c421 is similar to the cMoyBB, but the circuitry and general design is entirely different. For example, sound quality cannot degrade as the battery drains like it can on a cMoy. The price is hard to say at this point. The PCB is finished, but we’re awaiting quotes for the enclosure. It will be no more than $175 (USD)–likely much lower.

      I’ll post more pictures and information as soon as the prototype enclosures arrive.

    1. @Daniel: The circuit is finalized, but v0.84 is a very low quantity prototype. Final production amplifiers will be marked v1.00. We’re presently waiting for the enclosure to arrive…

  1. Thanks for the reply. This product is getting interesting, can you give any spoilers about how the final product will look? Dimensions, thickness, color, etc?

    1. Sure, we previewed four concept enclosures to about a dozen customers in December. Everyone was very enthusiastic about two of the four designs. Not too surprisingly, black was deemed most popular.

      We’re trying different finishes (plain anodized, brushed, etc.), so the final enclosure will have a unique look. Enclosure surface dimensions are 96 x 61 mm. The PCB and components are less than 10mm tall, although the enclosure will add some thickness. For comparison, iPhone 4 is 110 x 59 mm and the cMoyBB’s container is 117 x 64 mm, with a height of 21mm!

  2. Hey John I am a past customer. Two bbCMoy as gifts and 1 for myself. Sadly mine was stolen, and I am eager to replace. The c421 sounds great so I am going to wait for it.

    Are you sending out a release note to past customers? If you are, please add me to the list. If not, how soon should I check back to place an order.


    1. The official release announcement will be posted here and on Twitter, so you can follow us for instant news. We’ve never maintained a mailing list. Anyone who would like to receive an e-mail can reply to this comment thread.

      We’re aiming for release as soon as possible, which will be around July or August.

      EDIT: July is out. The enclosures will take longer to produce than anticipated, but we’re still on track for an August release.

  3. I am very interested in the C421. How much of a sound improvement are we talking over the Bass Boost cMoy v2.03 Amp? Will it have a more Sonic Sound and better soundstaging?

    1. How much? That’s hard to put into quantitative terms, but it will be worth it. I’ll leave that discussion to reviewers once C421 is released.

      We’ll begin posting pre-production progress to Twitter soon!

    1. C421 is a new design from the ground up. Only the bass boost circuit is similar to the cMoyBB, but deeper.

  4. Hi again John,
    I have both versions of your CMoy. Will you please let me know when this new toy comes out . Thank you.
    Les Netherwood. Isle Of Man U.K.

    1. No DIY, sorry. C421 was designed for machine assembly. Not many people have the skill or tools to solder 16 pin QFN chips.

  5. Will the op amp be changeable or will it be soldered on? looking at the pictures it seems like there isn’t a DIP8 socket as there is on the cMoyBB.

    1. All opamps are soldered to the board (SOIC-8). We’ll be releasing the enclosure as an open design. This means:

      1) We can design more products in the same, thin enclosure. If there’s demand for DIP-8 sockets in a thin portable amp, we’ll do it.

      2) DIY’ers will finally have access to a thin case designed for portable audio!

      1. Have you finalized which op amp you will be using on the retail version?

        If so which one are you going to go with.

        1. Yes, the main opamp is finalized and will be announced with the official release. It’s an expensive chip. πŸ™‚

          1. Something you should try is a ZIF socket for SOIC-8 chips, Don’t think I’ve ever seen that before, and it would be nice to roll without having to solder onto adapters.

  6. Will the C421 make it past TSA for aircraft flights? I would love to have a high quality headphone amp while flying again.
    Unfortuately the cMoyBB was a TSA magnet (looks like an improvised explosive) and a great hassle- that was only good if you wanted to be treated like Al Qaeda!

    1. TSA doesn’t like 9V batteries, period. Since C421 is professionally manufactured with a Li-Ion battery, airport security should no longer be a concern.

  7. I would like to know whether if this C421 will have more output power for a 300 ohm compared to cmoy? How far is it going to be before photo’s, spec and pricing will be release? What would the specs be in both voltage (v) and current (mw) in a 32 ohm

    1. Yes, voltage swing is much stronger than a cMoy, which is great for driving 300 ohm headphones.

      The enclosure is in production, but it’s a slow process because the machine shop must fabricate a custom extrusion die. Sample enclosures are scheduled to arrive in late August. Pre-production units will be sent to reviewers at that time and we’ll release features/specs/photos then as well.

      Due to the extraordinary cost of this project, we’re only producing 100 units for the first batch. Depending on timing, we may add c421 to our store for pre-order (no more than 4 weeks in advance). Later batches will not take so long.

      1. So does that means the production batch will be out in september? How bout the price would it still be lower than $175? How far lower would it be. And may i know who will be the first few reviewers to receieve them so i can read from their reviews. And one more thing is it possible to custom it into a op amp rollable design. (with extra charge) Thanks for your replies.

        1. The first batch will be ready in September if production goes smoothly. First batches are always tricky.

          The final price may not be as low as previously hinted. After much discussion, we decided that at this price point ($100-$200), it’s better to spend a little more to build the best sounding and highest quality amp for the money. Each thin film resistor in the audio path costs $1, for example. They sound much better than commonplace thick film components.

          As for opamps, please see the discussion above with Mark. πŸ™‚

          1. Thanks for fast reply JSeaber. So you did state that you have 100 Units for reviews. I’m wondering will Mike from Headfonia be in your list of reviewers? I really like his detailed reviews plus his sound preference and reviews are very similar to me. I hope that you can send one of it for him to do a shootout of difference with cmoy.

          2. There will be 100 total units in the first batch (most for sale, not all for review). Yes, Mike at Headfonia will receive one.

  8. Would you be interested in beta testing the C421 unit by releasing a pre-production version to a select few loyal fans of your work? You would benefit from impartial third party feedback which may result in some 11th hour tweaks before the production version is released. Perhaps the cost that you levy to the testers for the pre-production version can be credited to that user against subsequent purchases from you (either an upgrade to a post-production C421 or else against another CmoyBB. If this is of interest to you, I would be interested in participating in such a test.

    1. @Chris: We focused strictly on analog headphone amplification for C421. No DAC, so you know more money goes towards passive components. πŸ™‚

      It’s easy to implement a simple DAC, but those have become commonplace. I didn’t want to add another generic PCM2707 + Wolfson circuit to C421. A high-performance DAC is a distant project…

  9. Dear JDS labs
    I read this morning with great excitement of your new prototype headphone amp and wanted to comment on what I saw. As someone earlier in this blog has pointed out the CMoy is a real pain to take through airport security so this new design will make my life much easier. (have tried to find the best way to disclose and explain what this thing is in many different airports believe me !)
    One of the great things about your CMoy is its simplicity and robustness and as I travel with mine all over the world I appreciate that he on/off/volume is a solid knob (easily findable in the dark) and cant easily be moved if left in a shoulder bag in operation with my ipod. The new buttons/switches on the C421 hopefully will be robust and possibly slightly recessed. The volume control hopefully will be a solid and appreciably non-baggy and non-loose affair. Switches and dials are a really important part of the amp as longevity of the device on the road will depend on how well these can handle being in shoulder bags and travel cases in general. How solidly connected they are to the chassis/pcb.
    Personally I have never needed the bass boost so only the vol/on/off in an accesible place is important to me.
    RCA inputs as well as minijack would be amazing but hey !
    Rechargable from USB …yes thank you !
    Having now gigged my CMoy amp in most countries and PA’s of the world with the likes of Aphex Twin and Amon Tobin I cant tell you how much I have loved this little device, it makes my ipod sound huge through the channels.of a mixing always turns heads (and ears) and honestly I must have sent a ton of sound engineers to your website. It is my little portable hifi and perfect with a pair of Sennheiser HD650’s.
    Please tell me when you are sending the C421’s out …I will buy one immediately …even better send me one for review/beta roadtesting and I promise it’ll get a work out.
    best wishes
    Jamie Harley
    Harley Audio UK

      1. Looks smashing ..hoping the on/off button on the back will not get busted due to its extruded stick switch look …will be resting on its rear in a bag/case. On/off would be great as a flat switch or integrated in the volume on front fascia. Will the unit run from USB source and charge the battery at the same time ?
        As someone pointed out before a DAC/headphone amp of this quality for a Mac would be most most welcome.
        Sorry you did ask for comments on design.

  10. I loooooooooooooove this new design and will buy one as soon as it goes on sale. My only qualm with this product is the location of the power switch being on the opposite side of the other controls. It has me thinking twice about taking it out into public areas for fear of it switching off and on in my pocket. Other than that I look forward to pricing and availability information.

    1. Since a few have expressed concern, I’ll stick the prototype in my pocket and go for a jog. It was designed to withstand pocket use, so should not be an issue (more discussion here).

  11. I’ve got the v2 BB in the “unboxing” video my buddy put on his youtube channel. It is being used on the Grado SR60i’s he listens to most of the time. I purchased a few knock offs that don’t sound as good, just for references. The 18v version I have was loaned to Pete in temporary trade for the BB in his video. I’m pleased now and look forward to the C421’s release as well. As with any audiophile, I’m sure you have something “greater” in the works. But as an electrical engineer, do you have something “bigger” in mind? I have a pair of room specific rear loading horns designed by Pete for my Fostex FE166En’s. The CmoyBB is good enough for room listening, with a 3.5mm plug soldered to two 6′ pair of speaker wire running to my towers. I’ve sampled the DTA1 from Dayton and the Topping TP21. Topping takes the win, hands down. I’m wondering if you are even remotely interested in heading that direction?



    1. Full speaker amps? Probably won’t go that direction, as it’s a flooded market.

      Good to hear from you, Steve!

    1. We approved enclosure samples for production earlier this week, so release is getting closer. I’d say less than two months.

      Here’s a shot from the trip:!/jdslabs/status/109287740364947457/photo/1

      Note we mentioned 4 weeks there. That’s the timeframe for enclosures to be finished. It will take another week for shipping, a few days for final inspections, and at least two weeks to get the first units to reviewers. Pre-orders will be available around then and we’ll be assembling the first batch during that time.

  12. Hey John,

    I’m looking for a portable headphone amp. So please put me down to be notified when your C421 comes out.


  13. I am about to order your current Cmoy offering but would be interested in your new product offering as soon as it becomes available I am an avid headphone user having offerings by Headroom and Ibasso I am hoping the little Cmoy unit will set my brother in law off on the hi fi path and that things do sound different and better best wishes from Glasgow Scotland.
    Kind Regards Martyn R Marsh.

  14. I am definitely interested! Was about to buy your cmoy amp, but then I saw this and my tongue is hanging out of my mouth. πŸ™‚ Hope it comes out soon! The anticipation is killing me.

    1. Absolutely! We’ll e-mail everyone who’s replied to a C421 blog article.

      Enclosures are due for arrival sometime next week. I hope they’ll be delivered in time for the 2011 Rocky Mountain Audio Fest, but most likely I’ll already be on a plane to Denver. At any rate, I’ll be wandering around RMAF with a C421 in my pocket. Tweet to @jdslabs to catch me…

  15. Am very interested in this amp. Is it capable of properly “feeding” sensitive IEMs (SE535) and portable closed cans (HD25-1-II)?

        1. The AD8620 is more natural, while AD8066 is heavier (more thoughts on the pre-order page). I personally find AD8620 to be the most enjoyable, however, a few customers have listened to both and prefer the bass of AD8066.

          Eventually, we’ll offer more opamps for c421. Anyone is welcome to make a special request. It’ll take some time to build customer feedback on the dozens of popular opamps.

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