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i'm on a roll... the kgsshv


kevin gilmore
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Thanks.  Maybe I'll pass on the KGSSHV  then.

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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.

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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...

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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.

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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.

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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.

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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?

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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.... :palm: Thank God that Richard at SumR knows what he is doing...

Edited by jwzhan
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Well my T2 transformers would beg to differ...  :laugh:

 

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.  :)

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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?

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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... 

 

3oAphu1h.jpg

Ii4bOmah.jpg

 

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. 

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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.  :D

Edited by spritzer
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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.  :D

Tube, Portable, and Stax are three words that I nvever thought would be in the same sentence.  Can't wait to see this one.

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