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This is a long time coming, but with the corona virus, I've finally got time to do this. This is my review of the KGSSHV Carbon I had commissioned from @joehpj (thanks!). I've purchased a pair of Stax L300 Limited to replace the Stax Lambda Pros I had been using for some 25 years before Hurricane Harvey flooded my house and destroyed my old headphones. I've upgraded the pads on the L300 with L700 pads--these make a noticeable difference for me, as the thicker pads allow me to get a decent seal even when I wear headphones. I've been driving them with a Stax SRM-252s, and it has become apparent to me that the amp was the weak link in the chain. After seeing photos of various builds on head-case forums, I decided that the ones joehpj was putting together looked among the nicest I have seen. I decided to take the plunge, despite Joe being in Taiwan, half way around the world from me. Working with Joe remotely was extremely pleasant. He is extremely professional, and allowed for/suggested various changes, from using the venerable Alps RK501 potentiometer, to upgrading the capacitors, to various colors for the chassis. I decided to stick with the stock black chassis to keep the looks similar to my existing equipment. I stuck with the default potentiometer Joe uses--I believe it's sourced from China, and I had heard good things from other people on these forums about it. I also stuck with the stock caps. The one customization I did ask for was to add the delay on power-on for the HV power supply, as I am intending to build a Grounded Grid amp in the near future, and figured I could use this power supply to use as a reference for comparison as I build the GG. Despite some hiccups during construction (Joe's amp-building partner apparently had a severe illness that added delays), Joe was always very clear with me about the delays and offered a full refund for the amp. Also, when the amp first arrived, something happened in transit that ended up compromising the power supply. After some investigations on the problem, Joe requested that I send the amp back for analysis. Unfortunately, the post office wasn't very kind to me, and ended up damaging the chassis and bending the heat sink slightly on one side. When sending an amp across the Pacific Ocean three times, I suppose this might be expected, and it doesn't bother me at all. The Carbon amps that Joe builds come in two chassis, one for the amp and one for the power supply. The cases are very nice, simple, and elegant, and very much look the part of a professional high-end amp. I'll post photos of them shortly. The inerts of the amplifier and power supply look as beautiful and professional as I can expect. My music tastes are all over the map. I'm a software developer, and typically use my headphones 4+ hours per day, usually listening to acoustic jazz (especially Blue Note--Miles Davis is a personal favorite); singer/songwriters (such as Damien Rice, Thom Yorke, and Nick Drake); rap, hip-hop, and rap fusions (including Beastie Boys, Eminem, Dr Dre, Rage Against the Machine, and Ozomotli); classic rock and prog rock (old Genisis, Yes, Pink Floyd, and the like); EDM (Chemical Brothers, Daft Punk, and Deadmau5); Alternative (R.E.M., Radiohead, and U2); and loads more. Basically, I like all styles of music, aside from country/western (unless you consider Johnny Cash country) and most bubble-gum pop music (although I might have a soft spot for my daughter's Taylor Swift music...shh, don't tell anyone). I listen to some classical, but rarely as a critical listener--usually when I'm trying to get some coding done. The sound is, as expected with a Kevin Gilmore design, stunning! Doing comparisons between my Stax amp and the KGSSHV shows that the new amp has substantial "authority" in the bass. The "air" in the midrange is closer to what I hear when listening to SR-Omega/SRM-T1S, the pairing that first brought me to the Stax world, even though it was far outside of my price range until recently. I'm afraid as I get older, my previously excellent high-end hearing isn't what it used to be--I used to have hearing through to 22kHz, whereas from my current testing it appears I'm only able to hear closer to 18-19kHz--still excellent for a male of my age (49). Despite that, this pairing between the L300 Limited and the KGSSHV Carbon is never the slightest bit fatiguing. In fact, with the higher quality front-end, I'm now finding that I don't turn the volume as high as I did on the SRM-252s, which ought to help my ears over the coming years. The noise floor on the amp, even when turned all the way, is non-existent, even though for actual listening I rarely turn it above about 15%. Balance between channels on the stepped pot is, to my ears at least, perfect, although I haven't measured it yet. I've not heard an amp with the Alps RK501, so I don't have a good reference here, but I am very happy with the Chinese pot that Joe used. The downside? I've always found Stax to be extremely revealing headphones, and they exaggerate poorly mastered music, and they are even more so with a better front end like the KGSSHV (old Genesis and Peter Gabriel--I'm talking about you). But on well recorded music, there's nothing better, in my humble opinion. The imaging and separation on old Miles Davis is absolutely superb--Sketches of Spain and Kind of Blue are regulars for me to evaluate equipment, as the simple mic placement, and quality of mics, used by Rudy Van Gelder can be extremely revealing, despite the recording being made 60 years ago. I've got a binaural recording from Stax--a sample disc they produced back in the 90s to show off their at-the-time new binaural microphone--that is absolutely stunning. There's one spot where a door is slammed...every time I hear it, I turn around to see who has come into the room. Likewise, the binaural bits on Pink Floyd's The Final Cut also make me feel like I am there in the room. These were stunning before with the SRM-252s, but they are more...involving, for lack of a better word...with the KGSSHV Carbon. To be honest, I'm afraid the pairing of the Stax L300 Limited with the KGSSHV Carbon has rekindled my never-ending hunt for higher quality sound. I've already determined I'm going to need a new DAC, and I've started experimenting with 24-bit and 96kHz or 192kHz sampled music. To be honest, now I'm beginning to look at higher-end Stax, like the SR-009s. I'm also looking forward to experimenting with tubes on a Grounded Grid. But I've definitely reached the point of severely diminishing returns. Thank you, Joe, for rekindling my old audiophile tendencies!

As several people have asked for the PSU boards, and some whether caps are available lets probe the interest. Group Buy moving ahead - collecting payments, and then ordering. Please bear in mind that lead time is 12 weeks ... edit: added: "Group Buy moving ahead - collecting payments, and then ordering.", and price confirmation.

EDIT 8/4: attach updated GB details and remov outdated chart EDIT 7/31: attach updated GB details and remov outdated chart EDIT 7/27: attach GB details and remov outdated chart EDIT 7/23: attach PCB cost quotes and limit first time poster to 4 set of amp boards max. EDIT 7/19: proposing use of HV Carbon V5 board to replace both V2 and V3 boards. See posting # 190. EDIT 7/13: attach snapshot of final order entries and board count. EDIT 7/12: This GB is officially closed as of 7/12/2015. Due to the changes Kevin made to the PS boards, it'll take a few more days for these boards to be checked before I officially request quotes from the fab houses. I hope to have information on the cost of the various boards to share in a week or so. I will post an image of the spreadsheet here for all to review. EDIT 7/9: Please double check and confirm or make any final updates to your record on the spreadsheet by end of day Saturday, July 11. On Sunday, July 12, I will officially close the GB, lock down the counts of the various boards, post a snap shot of the spreadsheet on this thread for your review and proceed to request final quotes from the fab houses. As promised, I am planning a KGSSHV Carbon GB which includes both the amp boards and the PS boards. First I like to gauge the interest for the GB which will also help me estimate the cost of the PCB boards. My plan is to make 2mm thick PCB with 2oz copper. (EDIT 0731: HV PS boards are upgraded to 3oz copper) For the amp board, we'll most likely use the latest board, kgsshvcarbonv2.zip and kgsshvcarbonv3.zip that Kevin posted on June 30 which has the cascode CCS and uses mostly current parts including the PZTA SMD parts. This board measures 5.45 x 4.05 inches according to Kevin. THIS BOARD HAS NOT BEEN CHECKED NOR TESTED AT TIME OF WRITING. For the HV PS board, we have the following options (these HV boards contain built-in LV supply): 1. the GoldenReference dual HV (kgsshvpssicfetdual2new.zip that Kevin posted on June 27, 6 x 6.48 inches). I have checked this board by tracing the PCB visually and Kevin has corrected the issues I spotted and updated the schematic accordingly (see Kevin's post #4802 on the KGSSHV thread for the schematic). I cannot guarantee I did not miss something. THIS BOARD HAS NOT BEEN TESTED. 2. the split/single, "skinny" PS boards (one board for each rail), they are kgsshvpssicfetsinglenewleft.zip and kgsshvpssicfetsinglenewright.zip which were also posted on June 28 (3 x 6.48 inches). THESE SINGLE PS BOARDS HAVE NOT BEEN CHECKED NOR TESTED. 3. the split/single, "fat" PS boards (one board for each rail), they are kgsshvpssicfetsinglenewleftfat.zip and kgsshvpssicfetsinglenewrightfat.zip which were posted on June 28 (4.05 x 5.45 inches). THESE SINGLE PS BOARDS HAVE NOT BEEN CHECKED NOR TESTED. For stand alone Golden Reference LV PS, two options (THESE PS BOARDS HAVE NOT BEEN CHECKED NOR TESTED): 1. the dual LV (goldenreferce3.zip) 2. the single LV (goldenrefernceplus4.zip and goldenreferenceminus4.zip) We'll need to at least check these boards before proceeding to have them fabricated for the GB. I will try to find time to trace them but can really use others' help for double-checking. To gauge the interest and to help get an idea of the volume in order to determine the cost, please respond with the following information (be specific) if you are interested in participating in this GB: 1. How many amp boards do you want. (one channel on each board, you need two amp boards for one complete amp.) 2. Which HV PS (dual, single skinny or single fat) and how many of them do you want. (you need at least one dual board or two single boards for one complete amp.) The HV PS has built in LV and bias sections. The separate LV PS and Bias boards are optional. 3. Please use this link to register your request: https://docs.google.com/spreadsheets/d/1GWDWwLfsIDtwn1HB-x76lS6WyWwLd5lwsORFKiUuuEQ/edit?usp=sharing The chart below is for reference only and not up to date. The spreadsheet contains the up to date information. Please let me know if I missed anything. It's advisable to read the the following posts at the minimal for relevant information to this GB: 16, 34, 42, 51, 68, 80, 89, 92, 113. More to come. Thanks! EDIT 6/28: updated information due to the newly released "fat" single PSU and updated gerber files for PCBs EDIT 7/3: added Golden Reference LV and Bias board options and start using sorenb's shared spreadsheet EDIT 7/6: remove early spreadsheet image Note: For the single PS boards, quantity of 2 indicates the participant will receive 1 left and 1 right boards (or 1 plus and 1 minus for the LV).

Hi: I am organizing a mini group buy of HGSSHV PCB boards. I intend to move very fast so please read this post carefully if you are interested. I'll be using the kgsshvampv16mini.zip for the amp boards and kgsshvpsminifinalstn9360.zip for the PSU boards. The amp boards are the one-board-per-channel, off-board heatsink version. Both amp and PSU boards have provisions for current production parts. See here for the Gerber files and the KGSSHV thread for more information. I plan to use SeeedStudio to fabricate the PCB boards. The boards will be 2 layer, 1.6mm thickness, 2oz copper, HASL surface finish and standard green color PCB. Each set of the boards includes 2 amp and 1 PSU boards. I call this a mini GB for a reason; I only intend to make either 5 or 10 sets of the boards. I am keeping 2 sets myself so I am looking for a maximum of 3 to 8 participants. If we get 5 sets made, the cost of each set is $50 USD, if we get 10 sets made the cost per set drops to $33 USD. This amount does not include PayPal fee and shipping cost (from me to you). SeeedStudio is having a free-shipping special for orders over $150 but orders need to be placed before Feb. 25. If we qualify for this special, per set cost will be reduced by about $5. Orders won’t be shipped till after Feb. 26 due to the Chinese New Year Holiday. I have used SeeedStudio for my SuSy Dynalo PCBs and was happy with the outcome. You can read my posts in the Multiamp/Dynalo MK II thread. The KGSSHV, of course, operates at much much higher voltage so participate in this GB at your own risk. You should read the KGSSHV thread before making your decision. Here is how I plan to organize this mini GB (I am a DIY hobbyist and have never organized a GB so I am sure I will miss some logistic details. I apologize ahead of time.): 1. Please respond to this thread with your firm commitment. If we have more commitments than can be accommodated, inclusion will be based on a first-come-first-serve basis (FCFS). 2. I will close the GB by 8pm central time Friday, Feb. 20 or when we reach the 3 or 8 sets commitments, whichever comes first. 3. At the close of the GB, I will PM each participant who is included in the GB with a confirmation and my PayPal account information. Firm commitment that did not get included in the GB will be put on a sequenced waiting list, again, FCFS. 4. The GB participants that receive my confirmation PM need to send $30 USD to my PayPal account by 8pm central time, Monday, Feb. 23 for down payment and confirmation. I can then hopefully send in the order in time for the free-shipping special. 5. GB participants that do not send me the PayPal payment by 8pm central time Monday, Feb. 23, are assumed to have withdrawn from the GB. The vacant spot will be offered to the next person(s) on the waiting list. 6. When I received the PCB boards from SeeedStudio, I will PM each of the participants with additional amount to cover the remaining PCB cost, PayPal fee and shipping cost to you. I will use your PayPal shipping address to calculate the shipping cost and it is where I will ship the boards to. Please PM me if you want your boards shipped to other address. 7. The board set will be sent when I receive the PayPal payment stated in 6. 8. If I do not receive enough commitment by Friday, Feb. 20, I will likely abandon the GB. We’’ll have play by the ear if this happens. Please let me know if I missed something. I’ve been reading the KGSSHV thread and am very excited about the prospective of joining the Stax Mafia. Hope this will be a fun and exciting project for all of us. Best! Michael