April 23, 201313 yr Thanks. Maybe I'll pass on the KGSSHV then. ===================================== For the price of this build (and the fun in building it), it is probably still worthwhile even if you are building the DIY T-2. Then you will know how each sounds and which you prefer. As well, it will give you something to listen with while you get your T-2 up and running.
April 24, 201313 yr Turned on the power supply for the first time just now. I got a short "bzzt" and blew a 2A fuse. I couldn't figure out what caused it without touching the board so I put in a new fuse and powered up again. Again, short buzz but it didn't blow the fuse this time and the positive rail is putting out 503V. As far as I can tell though, the negative rail has got nothing. I have a feeling it's arcing under the caps but before I go poking around, I'm going to let it discharge. Already had that bite me once in the past...
April 24, 201313 yr Short under the big caps won't be a buzz. It's more like a BOOM! with very bright flash and burn mark around the cap.. I'm going to guess that something else is causing the problem.
April 24, 201313 yr No backwards caps or visible damage to the board. Tried it again, the sound is more like a quick snap. Positive stays at 503V and keeps a charge after shut-down. Negative fluctuates around 450V and rapidly looses charge after shut-down.
April 24, 201313 yr I just remembered.... when I was having difficultlies with mine, my firend made a LTSpice file for the PSU, and Kevin uploaded it. It's the 500V version and is somewhere in this thread. You can poke around in the LTSpice simulator to find test points and compare that to yours. Also, what I was describing above is a temporary short to the ground. It happens about 5~10 seconds after the startup. The caps get fully charged and instantaneously dump everything into the ground.
April 24, 201313 yr Every time I heard a "bzzt" or a "snap" on my HV, it was one or more transistors meeting it's maker. This was during initial testing, it was my fault slipping with the DMM test probes. So you say originally the neg rail had nothing, then it was fluctuating around 450V?
April 24, 201313 yr The difference seems that it makes the zap noise every time on power-up so far and I haven't got any magic smoke yet. The good thing is my positive rail works so I can compare the two during troubleshooting. Though I'm not too sure how much more I'll be doing during the week.
April 24, 201313 yr well... it doesn't really work that way... I don't really know the specific reason behind it, but the ground for the positive and negative is in different places; so even at the mirrored points, negative rail measures differently from the positive rail... The LTSpice model is fairly accurate. It's what I used as reference to fix my PSU.
April 25, 201313 yr The difference seems that it makes the zap noise every time on power-up so far and I haven't got any magic smoke yet. The good thing is my positive rail works so I can compare the two during troubleshooting. Though I'm not too sure how much more I'll be doing during the week. Did you find the piezo buzzer I installed on the underside of the boards I gave you at MOA?
April 25, 201313 yr As odd as it is.... I got one of those imbalanced Alpha pot.... the left channel is 1.5dB higher than the right. For a long time, I was using the KGSSHV with a pair of imbalanced ESP950. I knew the can had problem.. and oddly it's also the left channel that's louder... I didn't measure the dB of the ESP950 with the KOSS amp, because that broke, so I thought that the imbalance is solely due to the ESP950... Then, I got my first SR-007MK1. The left channel measured 2.5dB higher than the right. To make sure that it's the phone.. I actually swapped the output of the boards (so, the left board into right, the right board into left.) I got values showing that it's still the left that's higher, so I was sure that the phone is imbalanced; however I did not record the difference... And today, I got my second SR-007MK1... and the left channel still measures 1.5dB higher than the right... I freaked out... because either the amp has a problem or that I'm cursed with imbalanced SR-007MK1s. So I opened the amp up and did series of dB test with the pot at varies positions and changed the board output, and clearly, the pot has some problem. Luckily, I got two pots from Birgir, so swapped the other one in. Oddly, the left channel is still higher, but only by 0.3dB this time. All the differences were observed subjectively at first, then tested with a $50 PYLE dB tester. As to the the meter's accuracy, I'm pretty sure it's good enough. With the pot turned to max, the difference between the channels is 0~0.1dB with pink noise(assuming the second SR-007MK1 is balanced.) Just some additional info, 1.5dB difference is very obvious and 0.3dB difference... I don't know yet.. I haven't gotten myself out of the "left channel is louder" feeling... so I still feel that the imaging is a little to the left than I would have liked. I'll test it again tomorrow, and hopefully I'm not hallucinating with the measurements... Also, this means... that I essentialy have had problems with every part of the KGSSHV other than the Transfo.... Thank God that Richard at SumR knows what he is doing... Edited April 25, 201313 yr by jwzhan
April 25, 201313 yr Well my T2 transformers would beg to differ... I've never had imbalance issues with the 100 or so Alpha pots I've used but this could be one of the broken ones. A few of the pots I got in my first shipment had some sections reversed so they wouldn't work correctly. If you can feel a notch when turning it then it would be one of these. I thought I had found them all and returned them to Alpha but I could have missed one. Regardless, just PM me your address and I'll send you a new pot. We can't have an imbalanced amp.
April 26, 201313 yr Just ordered 90% of the stuff (save for the transformer, but with some padding for the mouser parts) from the "BOMv1" document...some of those prices have skyrocketed, particularly the stuff from bdent. If I have a significant surplus I'll try to give it back to people here. I've read somewhere that matching isn't all that important, can anyone confirm this?
April 26, 201313 yr Only the input fets need to be matched, the rest just needs to be from the same class.
April 26, 201313 yr Some news, the new prototype mini boards have shown up. Spent a couple of hours stuffing the amp boards but we'll see what happens when I turn them on... Don't know how we missed the huge mounting holes on the PSU board... The new SMD fet is just a bit too fucking tiny though.
April 27, 201313 yr You guys need to contact Sjöström Audio- we need a credit card sized KGSSHV! Put it in an Altoids tin and be done with it. Maybe whip up some Peltier elements for cooling...
April 27, 201313 yr There was a card sized KGSS back in the day intended for portable use. The circuit is very linear in terms of bias current so it is certainly possible to make it portable. We are working on something else though, an all tube "portable" miniature amp for Stax. Edited April 27, 201313 yr by spritzer
April 27, 201313 yr There was a card sized KGSS back in the day intended for portable use. The circuit is very linear in terms of bias current so it is certainly possible to make it portable. We are working on something else though, an all tube "portable" miniature amp for Stax. Tube, Portable, and Stax are three words that I nvever thought would be in the same sentence. Can't wait to see this one.
April 27, 201313 yr It's all tube so transportable would be a better description. The heaters are hungry...
April 27, 201313 yr I found the LTSpice file that KG is hosting but I got a 404 error. Does anyone still have a copy they can send to me?
Please sign in to comment
You will be able to leave a comment after signing in
Sign In Now