mwl168

A suggestion - maybe rename the thread to something like SRX Plus build thread?

And the regulated voltage is rock steady too. In the 7 weeks or so I've been using my GR HV PS, the voltage has not varied more than 0.5 VDC from cold start to fully warmed up. Quite remarkable! Thanks again to Kevin and Kerry for a great creation!

Yes, if you have a continent US shipping address, the $6.1 covers the shipping from me to you. Shipping charge from PCBNET to me has already been figured in in the board cost.

It's time to wrap up this GB. I like to start collecting payments from the participants so we can proceed to ordering the PCB. Below is the list of the participants, order quantity and total payment for boards in USD. For participants with continent US shipping address, please add $6.1 to your total which will cover the USPS Priority Mail shipping to you. For non-US shipping address, I'll need to let you know of the shipping charge individually when I receive the boards. My PayPal ID is [email protected]. Please use PayPal Gift for your payment and include your HeadCase ID and shipping address in your payment note. Soon as I receive all payments I will submit our order to PCBNET. All boards will be 2mm thick with 4 oz copper. SRX AMP ($25) Shunt PS ($20) Total MLA 2 2 $90.00 UFN 1 1 $45.00 blueman2 2 2 $90.00 gepardcv 1 1 $45.00 jose 1 1 $45.00 DefQon 1 1 $45.00 JimL 2 2 $90.00 sorenb 2 2 $90.00 eggill 1 1 $45.00 Samsie 1 1 $45.00 b0bb 1 1 $45.00 GeorgeP 1 2 $65.00 Rodeodave 1 1 $45.00 bdrew 1 1 $45.00 mwl168 2 2 $90.00

FWIW, I did a bit of testing; the drop out voltage of the GR HV PS is about 9 VDC for my build which is configured for 400 VDC output.

Just in time. Added to the list. I will finalize the GB tomorrow and start collecting payments.

You can just get the heatsinks too; http://world.taobao.com/item/39029827416.htm?spm=a312a.7728556.2014080708.7.Q9YXwK They look cool but I wonder how effective they are at dissipating heat.

Thanks joehpj for your response. I did a little bit of search after reading your previous post and found unmatched 6S4 for less than $5 US each at a couple US vendors. I share your view points of tube matching and for that reason have always been skeptical of the claims. I have bought tubes from Upscale Audio because I like their 72 hours burn in process for power tubes and I trust them. They do come at a higher price and I don't know if they'll match the desired tubes under specified operating points. For that matter, one has to wonder what happens to those tubes that are excluded from the QC and matching process especially dual-section tubes! I've always fantacized about building a simple tube testing and matching circuit for my own purpose ( I use a lot of 6SN7 and 6AS7 in my gears) But I have not done the homework to learn how to do it right.

Yes, that makes total sense. The shop I inquired about the matched 6S4 told me they'll have to weed out many tubes to find a matched quad thus the high asking price. The JJ EL34 is an interesting case, most of the stuff I read on the web either praise their sound or condemn their reliability. Unfortunately I did not pay enough attention to plot the data points and see if there is a correlation with time/period of production. I've read good things about the re-issue Gold Lion KT77. Anyone has experience with them?

I just spent the past few weeks researching EL34 options. Winged C EL34 price from reliable sources are actually pretty close to that of the RFT/Siemens EL34. Matched quad of NOS Mullard EL34 are on a complete different price bracket. Can you share where you find 6S4 for $10? Last time I look, a matched quad would set me back about $90 US.

I moved the board count to the first post for ease of access. Also, there are requests on the other thread to not have to order the AMP and PSU board in sets. That's no problem with me. We just need to keep in mind board cost is affected by quantities fabricated. Those that like to order different quantities of AMP and PSU boards please state your request on this thread. I plan to close the GB in the next few days and start collecting payment toward the end of the week of Monday 1/11.

Winged C EL34 from reliable vendors like Upscale Audio is around $70 US each.

No problem for me if people prefer to order amp and PS board separately. We just have to keep in mind that small quantity will drive the cost high. I plan to finalze the GB next week.

Thanks Kevin!

Kevin and JimL: Any particular reason why the shunt regulator PS board is set up for center tapped secondary? Thanks!

Check page 384 or discussions in early March of 2015 of this thread about changes to the 007 which is basically what happened to the 009 as well.

I received quote for the PSU and response to an upgrade inquiry yesterday. We'll be able to get one set of amp + PSU boards cost at $45 US with 2 mm thick PCB and 4 oz copper. I have visually traced the PSU board against the schematic JimL provided. It looks good to me but additional pairs of eyes to verify will be great and much appreciated.

My bad, I mssed your entry.

Thanks Birgir and Kevin.

Thanks Kevin! No sure if this is a sensible question to ask, but what are the likely amp operation scenarios that can damage a Stax headphone?

Here is the count of sets of boards so far. Please correct or update. Looks like we have enough for a GB. I will get quote for the PSU board and report back with cost. Each set will be one amp board and one of JimL's shunt regulator board with bias circuit added. I will also change the title of this thread to indicate that we are moving forward with a GB. EDIT 1/10/2015: List of GB participant and board count moved to first post.

Thanks Birgir! If I understand you correctly, the headphone should be safe to be plugged into the amp at all time as long as the amp is functioning properly. The exception would be the amps that use tubes as output devices and without a HV delay. The headphone should function properly as long as the offset is below 20 VDC which, in my observation, usually occurs after 15 minutes of power on.

I have a few general operating questions (balance and offset) that apply to all KG ES amps and have not been able to find definitive answers on the threads. So pardon me if these topics have already been discussed before. Before I ask the questions, here are some baseline information from my own observations (all without servo engaged): after adjusting the balance and offset to below 1VDC when the amp is fully warmed up (after more than 60 minutes of powering on), from a cold start, I usually observe the balance to be around 10VDC and offset to be around 35 VDC. It then takes about 20 minutes for the balance and 60 minutes for the offset to settle to below 1VDC. They'll drift a bit afterwards. Here are the questions (for headphones operating at 580VDC bias): 1) what's the highest balance and offset voltage to safely operate the headphone without concern of damage? 2) what's the balance and offset voltage where the headphone's performance starts to be impaired? 3) relevant to question 1, is it advisable to keep the headphone plugged into the amp at all time including power-on and power-off or is it better to unplug the headphone from the amp during power-on and power-off? Thanks!

Thans JimL for the explanation.

Pardon my ignorance, but if the 22uF/450V caps are for bypassing purpose, wouldn't they ideally be located on the amp board where they are closest to the load?