DefQon
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An update, the SRA-12S that had a dead transformer has been replaced with one from another 12S.
Now I haven't touched anything on the two output boards except replace the 50kohm resistors.
I powered on the amp and all measures were fine and plugged in a spare SR-3 to test. Left channel works, right channel does not.
So it could be a bad HV transistor or trimpot balance going off, swapped the output boards and issue still persisted with right channel.
Made a measure for dc offset and balance.
Measure the working left side first and it was floating around 0.4-7vdc. Measured the right side and holy shit 195-225vdc, measured the dc offset on right channel (-/+R) and it stabilised at about 380-400vdc. What the fuck is going on?
Checked the underboard wiring and all is correct, tried turning the trimpots and no values changed.
Any ideas?
I have a feeling the trimpot has gone bad, as I did clean the boards last time, one is 50kohm and other is 500ohm. Which is dc offset and which is for balance?
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You mean the black caps? They are 100uf 400v rated caps, looks to be from factory and identical to the ones in my stock SRM1 MK2 Pro C series based serial number batch.
I'll disconnect the amplifier board completely from the power supply to rule out any short on the amp board preventing the amp turning on.
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One for spritzer:
I'm a bit stumped with trying to fix a borked SRM-3 (half populated Xh board on output stage only piggy backed by a separate power supply for those that don't know), this one came to me with one of the resistors R19 (other channel R19 measured 270ohms) blown apart with scorch marks in the heatsink and next to it a missing 2SA1156 (regular Xh board's use 2SA1091 and R19 is 400ohms). This one has been sitting here for a quite a while now because it became a PITA to source the HV output devices and I needed 8 (Sanyo 2SC4630's). I already had a few left over 2SA1156 so I did do some quick troubleshooting the last time I tested the amp with a new A1156 and 270ohm resistor populated where missing.
The 270ohm resistor started burning and the onboard LED for each channel never lit up. So I left it till today.
I tested all the transistors (8 2SC4630, 8 2SC2705, 4 2SA1413, 4 2SA1156 and the dual JFET pairs 2SJ109GR's, also tested all the diodes and resistors for shorts and all were fine. They all tested fine except for the 2SC4630, while diode testing the BCE connectors all gave relevant results, when I did a DC current gain hFe test it read 0 on my meter. My new 2SC4630's read between 39-45 (datasheet states a minimum of 30 so it's all good). I replaced all the 4630's with the new ones and put in what I had the closest 287ohm resistors in place of both R19 (only had Panny 240 and 47ohm's at hand to give a closer result to 270). Powering it up the amp doesn't power on, front LED doesn't light up, no smoke, no burns, onboard LED's doesn't light, 1.5A fuse still intact, odd readings from 100uf 400v filter caps in the PS on the offboard pcb connected to the transformer. I even did a diode test on the LED's to be sure they work, and sure enough they do emit when connected from DMM.
There is a multi-tap voltage jumper selector on the side of the PCB, currently wired for 100v.
To rewire for 240v, I'm assuming 120v - 0 and other one is 120 - 0? Currently for 100v its as seen in the picture, 100 to 100 and 0 to 0
SRM-Xh
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so you think this is a headphone forum
Booze and guns forum obviously.
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Good to see this one moving forward........
RE: Cases and enclosures? Who needs em, have em built Don Garber style, open frame and easy to touch.
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The circlotron sounds scary from what I've read serious HV territory. Soon Kevin will be releasing designs that can power your house. Or seriously make the lights dim when powered on.
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Guess I'll need to check out my boards for anomalies. Will report back.
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I think there are some minor differences but not worth seeking out 1968s for the prices they command
Good thing I'm sitting on about 200 pieces of 1968's.
I know Birgir is sitting on few thousand or so, he depleted pretty much all the 1968's in Japan.
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the output stage costs less and uses in production parts
Any difference in sound vs 1968 or IXYS part output devices?
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Indeed it is, very reliable and long shelf life (10 years no problem). I still have some of the older PEH165 and 169 series.
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Going to be broke from buying all these boards, is this any less expensive to build compared to the other kgsshv's?
Might have to skip this one out.
I'm still waiting for a Megatron and DIYT2 PCB gb Mike.
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Did you fix the problem?
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What? Troubleshooting is the fun part.
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I was going to suggest switching the boards to see if the problem goes to the other side. Have checked the solder joints? The 5 watt Riken 50kohm resistors get stinking hot and on my unit the solder was completely fractured and broken which gave the amp (before restoration) a wishy washy static noise. A solder reflow fixed the problem.
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I prefer the 1540 more to the recent heard pm3. Former less boomy.
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Kgst boards came. So small compared to my new and old kgsshv offboards.
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In that case fuck that haha. Have my KGST boards on the way to me so no point if thats the case.
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Wonder how it sounds. Looks simple enough for a quick p2p build. Wonder if it can be improved.
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OK, so, who's up for this little beauty...?
Must be a reeeeeel bargain.
You're a bit far behind wink:
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Build the kgst if you want tubes. The parts for it isn`t high compared to the kgsshv or megatron. I`ve got 3 sets of kgsshv to get through and my kgst boards is on the way have done a quick BOM calculation for the kgst and its much less then my kgsshv.
I think JimL and Kevin are still working n ways of improving the SRX circuit in the other thread.
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No love and mention for the Megatron?
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I missed out his last set of posts calling out nopants. Gold.
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Though speaker taps? by the way what is the impedance of these things?
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Oh wait for Michael to do a gb run of the T2 boards I suggested to him.
Repair and restoration of my STAX SRA-12S
in Headphone Amplification
Posted
Measured the trimpots, both are fine.
It's quite odd why I'm seeing raw 200vdc+ when measuring the balance via red probe in +R and black probe in -R and dc offset measure by black probe on ground post almost floating at 400vdc. But when I test the HV output 2sc1167's they are all fine. Measured all resistors and values within spec range. Swapping the boards doesn't flip the bad channel.
Any ideas spritzer?