mwl168

The photo attached is not accessible. And don't forget to change the ballast resistor to 4.7M. I think I used a 1/2W, Mouser part # 594-VR37000004704FR5.

Here is a link to a SRD 7 MK II schematic which has a Pro bias circuit: http://cdn.head-fi.org/5/5d/5d5004f8_srd7mk2diagram.jpeg A couple of modifications are needed( thanks to Birgir! ) which was discussed earlier on this thread and includes information on obsolete parts replacement. I converted my SRD 7 MK I to a MK II based on these information. It worked very well but I have not used it since I built my KGSSHV. Good luck!

Kevin, you are killing me!

A few of us over at another thread started by Blueman2 are contemplating getting SRX Plus PCBs fabricated. See this thread: http://www.head-case.org/forums/topic/12445-plan-to-build-srx-where-to-find-bom-boards/ Discussion of the SRX Plus design can be found here: http://www.head-case.org/forums/topic/11996-srx-revisited/ I've checked with PCBNET and we can get the cost the amp board to $25 if we order at least 15 boards. The board will be 2mm thick with 3 oz copper, the board size is 9.35" x 6.85" ( 2 channels on one board ). Kevin has recently updated the board with teardrops enabled. We have not decided on the PS to use yet. The SRX Plus needs a +/- 340VDC and -20VDC supply in addition to filament supplies for the 12AT7 (x 4) and 6SN7GTB (x 2). JimL is working on a PCB of the shunt regulator he used and published on Audio Xpress. I think a GR HV configured for those voltages will also work. No promise, but if we have enough interest to start a GB, I will run it following similar process and logistics as we did on the Carbon GB earlier this year. Please state the number of boards you like if you are interested as well as your thoughts/preference of the PS. If we cannot reach consensus on the PS to use I am inclined to confine this GB just to the amp board. Thanks and Happy Holidays! EDIT 1/9/2015: Kevin has laid out a PCB for the shunt regulator JimL designed for the SRX Plus and added the 580VDC bias. The PSU board measures 8.9" x 5.05" and requires off-board heatsink. I have also upgraded the boards to 2mm thick and 4 oz copper. The amp board will be $25 each and the PSU board $20 each PSU if we can reach the quantity of 20 boards each. Here are the board counts: MLA: 2 AMP 2 PSU UFN: 1 AMP 1 PSU blueman2: 2 AMP 2 PSU gepardcv: 1 AMP 1 PSU jose: 1 AMP 1 PSU palchiu: 1 AMP 1 PSU charlo89: 2 AMP 2 PSU DefQon: 1 AMP 1 PSU (please let me know if your friend is interested and how many) JimL: 2 AMP 2 PSU sorenb: 2 AMP 2 PSU mwl168: 2 AMP 2 PSU eggill: 1 AMP 1 PSU Samsie: 1 AMP 1 PSU b0bb: 1 AMP 1 PSU GeorgeP: 1 AMP 2 PSU Rodeodave: 1 AMP 1 PSU Bdrew: 1 AMP 1 PSU

Congrats on a great build.

JimL's shunt regulator PSU would be great too. One other thing to consider is the board dimension and its implication to chassis options and layout.

I got quotes back from PCBNET. Basically, we can get per board cost to $25 US plus shipping to each participant if we can get the number up to at least 15. This is with 2mm thick, 3oz copper board. I will start another thread to gauge interest in a day or two. Before I do that we first need to decide if to include PSU board in the GB and, if so, which PSU to use. By looking at the board, we need regulated +/- 340VDC and - 20VDC. I am thinking the GoldenReference HV board with one of the LV configured for - 20VDC is a possible option. What are your thoughts?

My bad, did not send them the Gerber file till later today. Got busy yesterday and did not send it as promised. Hope to hear back tomorrow if people have not already taken off for the Holidays break. Will report back soon as I receive quote.

Apologize for my absence. Have been busy working on a project that's in trouble. I will contact PCBNET Monday and get some quotes. Giving the tubes are mounted on the board, I suggest we go with 2mm thick and 3oz copper PCB. It'll add to the cost but I think it's worth it.

I agree Kevin. After looking at the SRX Plus board I have on hand (thanks MLA). Plus, this is a proven board so I vote to leave it alone. No promise, but if there is enough interest, I'll consider organizing a GB and use PCBNET. I and many others have been very happy with the quality of the boards from the Carbon GB.

No, I have not needed the servo and, although I have populated the parts for both servos, I have not engaged either one yet. The amp is very stable without the servo. In my experience it's more stable than my KGSSHV which uses the IXTP CCS.

I have my Carbon running at 20mA output with the larger heatsinks (10" x 5" x 1.3") I received yesterday. The offset trim pots on both channel are at around 53ohm with 100 ohm tail resistors. So I think 120R tail resistor would work well and allow broader output current adjustment range. I have updated the BOM on the first post accordingly. With the larger heatsinks, the case temperature of the SiC MOSFET is around 58 - 59 Celsius (around 140 F). The heatsinks are quite worm but not hot to the touch (my infrared thermometer gun does not work with the extruded aluminum heatsink).

Thanks Birgir! Good point. i do remember that Kevin has also stated somewhere the we want most of the voltage drop to be on the resistor and not on the trim. When I can comfortably adjust the output current to 20mA with the heatsinks I am expecting, I'll see where the trim pot value ends up and report back with a suggested resistor value.

I can second Birgir's and Soren's point based on my own experience - bad connection either caused by cold solder joints or connectors would be what I look into first.

Hi Kevin; One suggestion, maybe changing the tail resistor of the offset trim pot from 182R to 120R or 100R while you are at it? On my build with the under-size heatsinks, 100R allows me to go to 20mA output current but can not go below 17mA. I believe Steve has similar experience. I am guessing the 120R will provide a broader range of adjustment but cannot confirm till I receive the larger heatsinks I ordered. Thanks!

I have music! Rigged up some rough wiring and pluuged in my Mac and TPA Buffalo DAC, I've been listening to music through my 007 Mk2.9 for the past hour or so. As Soren and John called it, my test heatsinks are too small for the Carbon. I had to dial the output current back to 17mA. Even so, at full warm-up, the heatsinks are very hot to the touch. I may order some larger heatsinks so I can dial them back to 20mA as intended while I decide on a proper chassis. Thanks again to Kevin, Kerry, Jim and many others that make this possible.

Thanks guys! @insanity: the insulation pad is the Aavid 4170G. These are wider and longer than the 4171G but slightly thinner (1.57mm vs 1.77mm). I just happen to have them on hand. These won't work for the 10m90s on the GR HV PS board because they are too wide. For the GR HV PS I use 4171G. The heatsinks are sourced from heatsinkusa. They are the 8.460 width one cut to 4 inch long. I don't know what's their spec (did not find the information on the website). I bought them for testing purposes like what I am doing here. On the hind sight, I wish I had opted for larger ones. @Sorenb and John: yes, the heatsinks are too small for the HV Carbon @ 20mA - after 20 minutes or so of powering on, they got very warm to the touch. I was a bit surprised. I have picked out a few possible chassis for the HV Carbon already but will need to re-evaluate after this empirical experience.

More progress today testing my HV Carbon build (V5 board from the GB). I am running 20mA (1.00VDC measured at test point) and have substituted the 182R tail resistor of the offset VR with a 100R one. No problem zero-out the offset and balance. A few observations at start up (I have all VRs adjusted to mid point of its value before soldering on the board, I also hand measured and picked all passive parts including the LEDs except a few tiny capacitors): 1. the test points measured between 0.71V to 0.76V 2. the balance is around 3.8V 3. the offset is around 38V I also found the following sequence of procedures worked well for me for adjustment: 1. Adjust the two 100R VR next to the test point to read 1VDC - my desired 20mA output current 2. Adjust the 2K balance VR to as close to 0V as possible (it'll drift a bit) 3. adjust 100R offset VR to as close as 0v as possible (it'll drift a bit and also interact with balance adjustment) Next will be to wire up the input and output connectors and see if I'll get music. By the way, this thing runs HOT, much hotter than my KGSSHV. My test heatsink got very warm to the touch. Here are some photos:

I kept losing my sign-in tonight when I switch between forums. Has anyone experienced the same glitch? I did not have this problem ealier today. I am using Safari browser on an iPad.

Right at the heel of kingofsnake, I got my GoldenReference HV Dual up and running an hour or so ago. I don't remember if anyone else has reported successful build of the GR HV Dual board from the GB. I have not hooked up the PSU with load but the initial testing looks good. This particular board is configured for +/- 400VDC output. I hand-measured and picked the resistors and I ended up getting +405.9VDC/-405.6VDC. Close enough. It's been a long time coming and many thanks to sorenb and Jay for the caps GB to make this possible. A word of safety caution; I am using 680uf pre and post regulation filter caps. Without load, 60 seconds after shutting down AC supply to the PSU, the positive rail still measured 262VDC. It took 163 seconds for it to go below 100VDC and 357 seconds to go below 1VDC. At that point, the bias still measured over 300VDC.

What should I rinse with? I've been using a semi-sharp pin to scrap off the hardened flux followed by scrubbing with a tooth brush and high purity isopropyl alcohol (90% IIRC). This cleans the flux well but tends to leave a film of residue that is viible under certain lighting conditions.

Count me in for 20.

I wired up a 25VA toroid with 18v secondaries to the GoldenReference (set up for +/- 18VDC) tonight and as can be expected the heatsink temperature dropped significantly powering the same Susy Dynalo amp. They still run warm but no longer hot to the touch. I guess the take away lesson for me is to allow sufficient headroom choosing the transformer but not to get too overboard. Spent a couple of hours dialing in the offset of the Susy Dynalo, finally sitting down to listen to some music. Happy to report everything appears to be in good working order. I settled on 18VDC rails and 312 ohm for R38/R39 which, after warm-up, results in about 19mA per output device (380mV voltage drop on the 20 ohm emitter resistors). The MPSWx6 output devices run very warm but not hot to the touch.

Here is a pic of my GoldenReference LV PS. The heatsinks in the front are what I originally put on it. As I said, even these large heatsinks get hot - I can only put my fingers on them for a few seconds. I am using a toroid with 22v secondaries regulated to +/- 18VDC. My rough estimate for the current draw by the Susy Dynalo is 190mA per rail.

I'll post a pic when I get home to show the heatsinks I am using - they are quite big but still not up to snuff. If you are running the multiamp around the same current setting I am, I suggest you consider larger heatsink than the one you mentioned in your post Another problem with large heatsink for the GR LV is that they may interfere with the terminal block for the AC wires. When I come to case the amp, I very likely will go with Kevin's suggestion and mount the transistors on the chassis.