mwl168

Looks like there is a built-in delay and it uses SMD, other than that, what's the difference between this one and the GoldenReference HV PS?

On the Carbon V5 board, the jumpers/pins are for engaging the two optional offset servos. you should be able to find some discussion on this thread.

Thanks JimL. An additional data point to add; while I was testing and using the SRX Plus, I also measured the tube temperatures using an infrared gun pointing at the plate of the tubes. As perhaps a testimony to JimL's point; both the 12AT7 and 6SN7GTB were running at surprisingly (to me) low temperature. IIRC, the 12AT7 was at around 65C and the 6SN7GTB at around 120C. These temperatures measured the same after I accidentally left it on for 14 + hours. EDIT: corrected the temperature unit of measure

Accidentally left the SRX Plus running overnight. So as it sits now it's been running continuously for more than 14 hours. Happy to report that it appears to be very stable, the offset and balance all measured as expected and all the heatsink temperatures are steady as well. No, it does not sound better than say, after a couple hours of warming up but it's very good to know that the amps is very stable and my ignorance did not set the house on fire.

I built a SuSy Dynalo and I really like it with my LCD-2.

A quick update on the buzz. I finally traced the buzz to noisy 12AT7 tubes. Once I replaced the noisy tubes the amp is silent without input signal. As JimL advised, I twisted the AC filament wires tight, keep them away from the input stage as far as possible and also arrange them so they are perpendicular to the signal traces.

Hi Kerry: I got them from eBay: http://www.ebay.com/itm/130301072783?_trksid=p2045573.m570.l5999&_trkparms=gh1g%3DI130301072783.N36.S1.R2.TR11 They are bakelite material. Good price and works great so far

Not possible on the current PCB to install the 10M90S resistors on the other side. As is, the heatsinks do not get too warm running 330VDC rail and 7mA output current in open air. I measure about 51 degree Celsius (about 123 F) after 4+ hours of continuous running. It'll obviously run warmer once cased. I am using 38.1mm tall heatsink (Mouser part # 532-529801B25G) and there are taller ones available.

Now that the SRX Plus has been running for a few days and seems stable, I thought I would share some information that others may find helpful for initial testing. Congo5 was kind enough to share similar information with me that really made my testing much straightforward. As I mentioned in earlier post, I adjusted the value of the fixed resistors in series with the source pin of the DN2540 and the trim pots based on the recommendation from both Congo5 and MLA. So for the 7mA output current source, 17mA output current sink and 1.1mA (based on 300K 12AT7 plate resistors) input current sink as JimL recommended, here are the approximate mean of the trim pot values I end up with: Output current source (100 ohm): 35 ohm (200 ohm fixed resistor) Output current sink (20 ohm): 12.5 ohm (75 ohm fixed resistor) Input current sink (500 ohm): 410 ohm (1.2K fixed resistor) To adjust for balance of the input stage, I put the DVM probes on the two .22uf/1000V coupling caps where they are connected with the plates of the upper 12AT7 then adjust the 5K trim pot until the meter reads approximately 0 VDC which sets both the plates of the 12AT7 at the same voltage relative to ground. I then re-adjust the 500 ohm pot as needed so the 12AT7 plate voltage sits at mid point of the B+ and ground (167 VDC for my SRX Plus which runs on 330 VDC rails). As to how does it sound? It's a different sound signature than all other KG ES amps I have built (I don't have a Megatron or DIY T2). I am guessing it's the nature of an all-tube circuit. It's surprisingly spacious and punchy sounding to me for such a minimalistic circuit. I think the cascoded CCS is really doing its job. I like it very much. I hope more people will build it.

Thanks JimL! What you advised were the first things I tried. After some experiment, it seems to come down to one of the 12AT7 tubes after I started swapping tubes around. Once I knew the amp is working, I did rearrange and tidy up the wiring up a bit in my testing setup. I am still not 100% sure though but happy to report it seems to be buzz-free at the moment. As is customary, here are some pics of my build. As you can see I put the trim pots and the 100R resistors on the top to make it easier for testing and tuning. The gizmo next to the amp board is something I rigged up to lower the AC filament voltage. I am really liking the sound of this amp even with the cheapo tubes I am running with at the moment.

I forgot to mention that I am using 4 made in China Golden Dragon 12AT7 and 2 GE 6SN7GTB I randomly took from my parts bin for this initial testing. I don't know if they were matched or not. But simply by adjusting and balancing the upper 12AT7 plate voltage (they were off by roughly 15VDC with the 5K pot set in its mid-point) and leaving the output current source and sink at their pre-dialed current setting, the output balance are within 2 VDC and the offset under 4 VDC once the amp is warmed up and that's where I left it. Maybe I got really lucky with the tubes I use.

I have been listening to my newly built SRX Plus for the past 2 hours or so. I am using a reconfigured KGSSHV PSU to supply the HV (+/- 330 VDC) and a -15VDC for input stage current sink. The build was pretty straight forward. I did change the value of the resistors in series with the trim pot of all the cascoded CCS as advised by both Congo5 and MLA. Specifically: Output current source: 200R in place of 250R Output current sink: 75R in place of 102R Input current sink: 1.2K in place of 1.43K The DN2540 has quite a bit of variance from sample to sample even from the same batch so be prepared to adjust these value for your build. I am running 7mA output plate current, 17mA for output current sink and adjust the input current sink (the 500R trim pot) so the upper 12AT7 plate voltage is half way between ground and B+ (167VDC for my build) and adjust the 5K trim pot so both the plates of the upper 12AT7 sit on the same voltage. I do have a very slight buzz on one of the channels that is not attenuated with volume. I need to trouble shoot it. It happens to be the channel where my AC heater supply wires pass below but there could be many other causes. Thanks to JimL for coming up with this modified SRX circuit, Kevin for laying out the PCB and JimL, Congo5 and MLA for helping me along my build.

I may be stating the obvious but the TL081 is rated at +/-18VDC max supply voltage. The OP27 is rated +/- 22VDC, OPA445 is rated up to +/- 45 VDC.

I have a dumb question. How do you supply the power needed?

I bought a few aluminum chassises from VT4C before. The QC is non-exisitent. One of the chassis is impossible to put together due to serious misalignment. One of the chassis cover was not even rectangular. Don't have experience with their other products.

For more than a week now, I have not been able to save edit to a post or PM using iPad/Safari. No problem submitting new post or sending PM. Anyone else experienced similar issue?

Thanks JimL.

Many thanks for the detailed explanation JimL. Very much appreciated. I should have read your posts more carefully. One more point of clarification; based on you post on May 22, 2015 on the SRX Revisited thread where you explained the input stage in detail, do I understand correctly, that the "lower tube" refers to the 12AT7 that accepts the input and the "upper tube" is the 12AT7 that drives the output stage? Thanks!

Hi JimL: I am building the SRX Plus and have been thinking about how to adjust the completed amplifier for optimal operating condition. I compiled the following procedure by reading and parsing through the information in your earlier posts on the SRX Revisited thread. Can you verify and advise if it’s correct? Set input stage current source to about 1.1 mA by adjusting the 500R pot and measure the voltage drop of the 100R resistor in series between the -20V input and the 500R pot. (Assuming 300K plate resistor for the upper 12AT7 as marked on the board. If you use 250K plate resistor then it should be 1.3mA) Set the output current load for 7 mA by adjusting the 100R pot and measure the voltage drop of the 100R resistor in series between the 5.1K output resistor and the 100R pot. Set the output current sink for about 17 mA by adjusting the 20R pot and measure the voltage drop of the 100R resistor in series between B- and the 20R pot. Set output balance close to 0 VDC by adjusting the 5K pot. Set the INPUT balance to 0 VDC by adjusting the 5k pot. You are trying to get the upper 12AT7 plate voltages to be the same. An easy way to do this is to connect your meter leads between the "bottom" of the two 12AT7 plate resistors and adjust the 5k pot to zero volts. Set output offset close to 0 VDC by adjusting the output current sink pot (20R). Also, below is a quote from your post on May 6, 2015. Can you advise where and how this fine-tuning fit in? Thanks! “…the published schematic has adjustments in the output current loads, this can in fact be used to vary the cathode-to-plate voltage individually for each output section by slightly altering the current running through each section. The concept is, start with the output current loads fixed, adjust the cathode current sink to approximately zero the output plates, then vary the current loads to adjust the offset between + and - voltages for each channel. The three adjustments are interactive, so, it would probably be best to adjust one of the current loads to partially decrease the offset, the adjust the other in the opposite direction to further decrease the offset until that is balanced, then adjust the current sink to zero both plates…” EDIT: procedure corrected based on JimL's response in the next post where he also explains how to adjust for output balance if necessary.

I do know there is heaven in DIY.

I am fairly certain I used kgdynalobal5.zip from Kevin's site back in January 2015. On the silkscreen it says version 1.02. However, the current kgdynalobal5.zip on Kevin's site has a June 2015 date and the version is 1.1. IIRC, Kevin fixed an issue of the board on this version - this information is somewhere in this thread.

The last board run I did was the TO92 version and sorry I don't have any spare boards available. The boards I had were from SeeedStudio, 1.6mm/2oz. As Pars said, they work fine and the cost was reasonable.

Too early to tell. Need to spend more time with the SR-009 and run it through the different KG ES amplifiers for me to get a good handle of its sound. I was just surprised by the margin of difference between the two - wider than I have expected.

Just received a pair of SR-009 tonight. Serial No. SZ9-34xx. Running it through my HV Carbon. This thing sounds different than my 007 MK 2.9.

Thanks Kevin. I experimented with the opto server tonight (this time with the OP27 in place) and here are my observations: Without the servo jumpers in, I first adjusted the offset of both boards to be about +18 VDC at cold start, measured between the + output and ground (this applies to all subsequent measurement). I then inserted the jumpers and powered on the Carbon with opto servo now engaged. The offset on one board measured -2.5 VDC right from the start, it dropped to about -1 VDC after 5 - 6 minutes, from there it hovers around -0.9 VDC, drifting about 0.5 VDC or so up and down. I measured again at 20 minutes and then at one hour marks with same results. At the one hour mark, I adjusted the balance from around 2 VDC to within 0.5 VDC (absolute value). This brought the offset to hover around -0.1 VDC. The other board exhibited similar behaviors but started with and ended at lower offset voltage. (Without servo, this board has always had lower offset and balance compares to the other one.) It appears to me that the opto servo is working and it's effective from the very start although it does take about 5 minutes or longer to reach the lowest possible offset voltage. As I have mentioned in the past, the Carbon, without the servo, is very stable to start with. It seems to me the main advantage of the opto servo is to keep the offset at a low voltage from the start and settle it down faster. Without the servo, my Carbon typically takes between 15 - 20 minutes for the offset to settle.