mwl168

To be clear, are you saying that the SRD-7 MK II schematic was wrong and that R104 should be 4.7M and C108 should be at a different position in the circuit.?

I am a bit embarrassed. I did google it and came across this image but did not know it's what I was looking for ) Thanks Birgir! Edit: For reference for others that may be interested in this topic, here is the normal-bias SRD-7 schematic.

Hi Birgir: Resurrecting an old thread. I have a SRD-7 I am thinking about converting to Pro bias to fill in while I build my KGSSHV. The link you posted in this thread is broken. Any chance you can link me to a schematic? Thanks!

Really great work. Thanks for the internal photos.

It reminds me of Goldmund preamps. Also the Spectral preamps made in the 90's (I think). Never heard the Spectral but a couple of Goldmund preamps I listened to were very nice sounding gears. Nice build. It looks very slim. Does it use shorter heatsinks or it's an optical illusion? Some interior photos would be great!

I am out. Thanks!

I am a maybe - again depending on the cost.

Hi All: We are slightly ahead of schedule. I have received all but one confirmation payment so I went ahead and placed our order with SeeedStudio. I am happy to confirm that we have secured the free-shipping discount and I have received order confirmation e-mail from SeeedStudio. As I mentioned in my earlier post, it's Chinese New Year break over there and their normal work schedule will resume around next Tuesday, Feb. 24. I will post updates on this thread to keep everyone informed of the progress and status. Also, I checked with USPS and found out that they have a flat-rate, padded envelope, priority mail option which comes with tracking and $50 insurance for domestic US shipping. It ends up being about $1 more than the USPS first class mail option that I have originally planned to use. This only applies to the continent US shipping address. I suggest we use this service for those with US shipping addresses. PM me if you have objections. For the non-US location, I will have to wait till we receive the boards for USPS to weight the package and quote me shipping charge. Best!

Thanks for your interest. I'll put you on the waiting list.

I think the kgsshvpsminifinalstn9360 board can accommodate both KSA1156 and STN9360. The STN9360 will need to be mounted vertically while observing the pin out specification. See Kevin's post #4014 in this thread. Although I can use additional clarification about the use of 270V zener with KSA1156. It would be great too if someone can share some insights of the pro and con between the choice of the two devices.

This GB is officially closed. Thanks all for your interest, quick responses and participation. Anyone post with their interest for the board set from this point on will be put on the waiting list - please refer to the first post in this thread. I have good news for those participating in this GB. Since the GB was expanded and we will now be ordering 15 sets, the price per set is dropped to $23 USD before shipping from SeeedStudio. Since we should qualify for the free shipping from SeeedStudio (would have been another $63+), the only additional cost for the GB participants will be shipping cost from me to you and the PayPal fee. For comparison, it would have been $43 USD per set if only 5 sets of boards were ordered. Here is the list of GB participants: mypasswordis (2 sets), iwik, johnwmclean, chinsettawong, insanity, eggil, GeorgeP, kingofsnake, ChrisX, DefQon (2 sets). I will PM all of you with confirmation and my PayPal account. I need to figure out the proper amount for your down payment to me now that the per set price has dropped. This amount will be stated in my PM to you. If no one has objection, I like to move up the timetable and ask that you PayPal me the down payment by end of day Saturday, Feb 21 so I can put our order in the following day to secure the free-shipping discount. If this presents a difficulty for you, please PM me. Please let me know if I missed something. Best!

One set is 2 offboard amp PCBs (1 per channel) and 1 PSU PCB (see my first post). Below is the rough dimension of the boards. I cannot be certain - waiting for confirmation on the kgsshv thread. kgsshvampv16mini (amp): 182mm x 86mm, kgsshvpsminifinalstn9360 (PSU): 176mm x 167mm If someone has this information please confirm or correct me. DefQon, are you still in for two sets? (my bad, I had previously miscalculated number of participants)

Hi ChrisX: You are in - if I was not clear in my last post. Hi DefQon: As eggil stated, this GB is for the off-board version. Are you still interested? Thanks!

Wow! Thanks guys for your quick responses. This is going way faster than I expected. I have also received PM for boards as well. I am expanding the volume to 15 sets and closing the GB now. That means everyone posted in this thread is included. I will follow up with additional details soon!

Thanks Pars for the kind words. It was a pleasure to deal with you as well.

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

Thanks Birgir. I am planning to start a mini KGSSHV boards GB. I'll be using the kgsshv16mini.zip for the amp board and kgsshvpsminifinalstn9360.zip for the PSU. Can you confirm if the following board sizes are correct? Thanks! kgsshvampv16mini: 183mm x 99mm kgsshvpsminifinalstn9360: 176mm x 167mm

Thanks Kevin. Yes, now that you pointed it out, I did notice that the center mounting hole was relocated to the center location on the kgssmvampv16mini PCB. There are actually a few parts that were relocated to make this possible. The silkscreen identify this board as Rev. 0.91.

Many thanks Kevin and Birgir. What's the difference between the two versions? I tried compare the v15 and v16 boards using an online Girbir file viewer, it seems the only difference between the two is the 3.3K resistor (R43) being physically relocated to a different spot on the PCB. Did I miss something? I apologize if this was already mentioned in the thread. I just got done reading all the posts and taking notes but don't recall coming across this information.

That would be great. Much appreciated. I have seen an offboard version in Kevin's earlier post (#3608), it's named kgsshvampv16mini which also allow the option to use ixtp01n100d for CCS. Is this the board you are referring to? It still looks small with very little space between parts. I do remember seeing photos of a larger but similar boards with less parts in earlier posts but did not see the Gerber file for it in Kevin's library. For the Mafia boards, am I correct to assume running them at lower voltage (< 400V) would reduce the risk? Thanks!

Many thanks Birgir. I'll have to give it some serious thoughts which amp board to use. I have spent many nights now reading this thread to learn as much as I can to prepare for a build. I am looking at the Mafia board because I like to build a off-board heatsink version to allow some flexibility in tweaking output current and voltage swing. The Mafia version is the only off-board version listed on Kevin's site and uses current parts except for the 2SA1968. I am at page 137 of the thread now and have read about many firework and smoke shows. I may very well change my mind by the time I finish reading )

Thanks nopants and Birgir for your help. Hi Birgir: Can you elaborate what you mean by the Mafia version not being a forgiving PCB? Are you referring to the potential arcing problem resulting from less than careful soldering job and flux residual? Also, for the Mafia board, can I replace the 2SA1968 in the current source with ixtp01n100d? I know this is possible with other version of KGSSHV boards but involve chaning a few resistors as well. Best!

Need some advice here. Can the KGBH mini PSU that many have used to power the KGST be used to power the KGSSHV Mafia version? Would it compromise the performance of the KGSSHV? Your thoughts and advice are much appreciated.

I am interested in a set of amp + psu boards depending on version of boards and price. Thanks!

Sharing my findings with attempts to raise output BJT current as promised. I am running +/- 16V rails. Using 255R in R38 and R39, I got around 186mv voltage drop on the output resistors (20R) when the amp is fully warmed up (160mV at cold start). That's around 9mA current. I could barely feel a temprature on the output transistors at this operating condition. I finally settled on 301R in R38 and R39 which results in 250mV across the output resistors at cold start, rising to and stablize at 320mV after a few minutes. The output BJTs are quite warm to the touch but not hot. I am really liking the sound of the amp at this condition. For what it's worth, here is a few other values of R38 and R39 I tried and the resulting voltage drop across the output resistors: R38/R39 = 287R, 230mV cold start, 273mV warmed up R38/R39 = 317R, 300mV cold start, 360mV warmed up R38/R39 = 402R, 500mV cold start, did not wait for it to warm up. This amp really sounds great on both my Senn. HD650 and LCD2. Subjectively the best among the headphone amps I own and heard. Many thanks Kevin for your ingenuity and help!