KGSSHV Carbon Build Thread

[Blueman2]

Pars, there is a replacement/alternative for the C2M that I found and used successfully in my build.  Let me find that part number.  

EDIT:

Here is a link to my post:

Here is the part:

755-SCT2H12NZGC11

Unfortunately, it also appears out of stock, but it is an alternative that worked for me in my Blue Hawaii and is still going strong, if you can find it elsewhere.    

EDIT2:

I just checked my supply of parts and have none of the SiCs.  Sorry.  

EDIT3: TTI appears to have some of the ones I used:

https://www.tti.com/content/ttiinc/en/apps/part-detail.html?partsNumber=SCT2H12NZGC11&mfgShortname=ROH&utm=ECIA

 

Edited November 11, 2020 by Blueman2

[JoaMat]

9 hours ago, Pars said:

does anyone have a couple of the Crees that I could buy?

I might. Give me a ping.

[Pars]

12 hours ago, Blueman2 said:

EDIT3: TTI appears to have some of the ones I used:

https://www.tti.com/content/ttiinc/en/apps/part-detail.html?partsNumber=SCT2H12NZGC11&mfgShortname=ROH&utm=ECIA

 

You have to order 30 from TTI.

5 hours ago, JoaMat said:

I might. Give me a ping.

Thanks! I'll send you a pm.

[Blueman2]

Doh, sorry Pars. I did not see the min order quantity.  The only part that appears in stock at Mouser that might be compatible is 

https://www.mouser.com/ProductDetail/?qs=vHuUswq2%2Bsy%2BS7yfkaWaCA%3D%3D

Item on left is the one that is in stock but has not been tested.  Item to the right is the alternative that I successfully used.  Middle is the standard part.  

Edited November 11, 2020 by Blueman2

[Pflugshaupt]

On 11/5/2020 at 10:49 PM, waltzingbear said:

I would get the LV 15V supplies working next after you get -400V regulation back.

I have no idea which transistor maybe bad, but most likely one is. Once you get the supplies working correctly you should measure the voltages on both channels, that may point to the problem.  The observation that it passes audio while turning on or off leads me to think that is happening when it passes thru working bias points. And stabilizes with everything biased off.

Brace for newcomer problems.. sorry.

After a lot of struggle I managed to fix my power supply. It had a multitude of issues, but now it finally produces all the right voltages again. So now here I am again with one working and one broken kgsshv carbon channel and not much of an idea how to fix it. In the meantime I received spare parts for most things.

I inspected my faulty channel at length and resoldered some stuff to be sure and then decided to fire it up with the +-15V rails. This appears to work fine. I voltage-compared all the test points between the two channels and they were very similar.

Then I tried to compare resistances between the high-voltage parts of the channels. I saw some differences here, which most likely means at least one part is broken. F.I. the resistance between B+ and the via next to the terminal block is only 250 kohm on the broken channel, while is is over 1.5 mohm on the good channel. I did replace the PZTA42 next to that. 

Foolishly and because I didn't know how to go on, I decided to fire up the full voltages. aaaand.. magic smoke. At least I know one thing that's broken now. It came from the 20k resistor connected to B- and I guess that's really a bad sign. I fear what is broken is at least one of my c2m1000170D. Of course the part that is the hardest to desolder for testing and has also became unavailable recently :(. If the 20k burns.. could anything else than the c2m1000170Ds be the problem? They look so sturdy.. but do they break easily?

Update: in the meantime I replaced a couple both PZTA42 and two PZTA06, but resistances do not check out. I measure 51.7kohm between B- and B+(1.3 mohm on the healthy side) and turning it on would produce smoke again.

[Pars]

Looking at the schematic, you are probably correct that it is one of the c2m1000170ds. I would replace the 20K resistor, then ohm out the c2m pins to each other (G-D, G-S, etc.). Compare to the good channel. I believe that MOSFETs will often fail as a short (could be misremembering though). I don't know if the UnitedSiC part that Blueman posted above would work. Kevin or Birgir might be able to comment on that.

Edited November 16, 2020 by Pars

[Pflugshaupt]

Thanks, I did that already and one c2m1000170d measured very low. I then managed to remove that one. Unconnected, resistances are much higher and appear to be correct. Even with one removed I still measure only 50k between B- and B+... so I'm beginning to think there's just a short somewhere on the board or in the board itself but I have no luck finding the issue. I did triple check below the center terminal and applied generous amounts of nail lacquer as I read about shorts in that location somewhere on this thread.

I already ordered the UnitedSIC part, but now I don't think the problem is the mosfets. 

As there are many test points on the board, is there a guide somewhere how to use those? 

Edit: I guess I confused k & M on my meter late at night . measuring again I'm quite sure the part I removed was indeed broken. G to S resistance is 2.6 kOhm 🤨. But now I'm wondering how much it should be on a healthy one? The other one on my broken channel measures 0.4 mOhm, while the two on the "good" side measure 5 mOhm and 9 mOhm. I'm kinda scared my broken psu might have destroyed all four of them and theoretically it should be infinite.. right?

[Pflugshaupt]

I received new c2m1000170d I bought on eBay from Honk Kong for $7.50 per piece. The eBay images looked a bit strange, but the parts that arrived looked and felt absolutely identical to my broken ones. They measure infinite resistance between G & S on my meter and so I built them in and now my amp is working again! Will post some images tomorrow.

[Pars]

I was also going to ask where you buy your parts from. Ebay and aliexpress, etc. are known bastions of fakes.

BTW, Richardson RFPD (a division of Arrow) has the c2m1000170d (for $4.66 each) and ships from Hong Kong (at least mine did).

[Pflugshaupt]

The ones I broke I had ordered from mouser when they still were available - like everything else in the build. However my psu was not made by me and I have no idea where those parts came from. I still don't understand how the mosfets could break down completely. I read up on mosfet failures and what I got seems to come from overvoltage. However I have a 400V psu that became unregulated on the negative voltage and it never surpassed -460V... anyway very happy it works again. 

I realize ebay is known for fake parts and I would never buy truly rare parts from there like those K170. But I took my chance with the c2m as it just became hard to order recently and isn't obsolete yet.

I also received the UnitedSIC parts from mouser, but without more opinions I didn't want to try putting them on my board.

 

Here are some images. I cnc'd a front panel from future carbon (acazia wood). The extra boards are a 3-stage dc filter and a relay/resistor-based inrush limiter. My old house with strange wiring has quite some dc and it made the transformer hum constantly. The PSU is the standard BH-mini-psu circuit. I increased the cap size when I replaced almost everything on the board.

[Blueman2]

@Pflugshaupt, thanks for sharing pics!  Love the old school volume knob.  And the woodwork looks wonderful.  

There is something different about your SR-007's.  Is that a custom yolk?    

Edited November 20, 2020 by Blueman2

[Pflugshaupt]

Not sure what you mean by yolk.. part of an egg? Sorry.. I'm not a native english speaker. Do you mean the color? It's a very early SR-007 mk1, so maybe it has seen many more hours of sunlight than most. The ear cushions and the headstrap had the same color - creamy brown, but I replaced those due to previous owner perfume smell ;). 

I added a few dampers to combat the ringing when the headphones are touched.

[Rodeodave]

He probably meant yoke, the springy part connecting the two drivers. Looks like you added some clamps to the springs, maybe in order to damp out some resonances?

[Pflugshaupt]

Yes it's to get rid of resonances while handling the headphones or tapping them - or moving your head. These are 3d printed parts with a layer of sorbothane sandwitched in between. They were inspired by a thread on another forum, can't remember where - but google can find it if you look for stax 007 sorbothane damper.

[Blueman2]

[embarrassed]  Yes, yoke.  [/embarrassed]  Sigh. 

 

 

Edited November 21, 2020 by Blueman2

[Rodeodave]

Want impedance volume pot is everyone using?

And those of you who aren't using a volume pot in their amp, are you terminating your inputs to ground with a resistors other than the 500k on the circuit board?

[UFN]

10k pots is sort of the standard for Kevin's amps

[Rodeodave]

 

Thanks, I'll be adding 10k resistors at the inputs then.

I'm making good progress with my build after it lay dormant for over a year:

[dingding123]

I think a 10k pot a bit too low and it is more suitable for amps with bjt input. With the jfet input on carbon you can use a 50k or 100k pot.

[Pars]

10K pot on that amp, even with the JFET input, is fine. With JFET, yes you could go higher, though I would never use 100K.

As for bypassing the pot, I would just jumper it and leave it alone. No need for the 10K resistors in place of the pot.

[Rodeodave]

Here are some more build pics:

[Pars]

What Phoenix connectors are those you are using? They look nice (though I'm still not a fan of the screw down terminal blocks). However, what is the voltage rating on those?

[Rodeodave]

If I recall correctly, they are Molex Eurostyle Terminal Blocks UL certified for 300VAC, which would mean 425V DC peak. I'm not sure if there are terminal blocks rated for 600V with a 5.08mm pitch.

 

Since I'm using the amplifier boards with a ground plane, i used a couple of layers of Kapton tape at the bottom of the terminals and used very little solder in order to avoid the arching that's been reported with these boards.

 

Edit: I just realized that the terminal blocks aren't the Molex that I thought I had installed. I guess I should replace them, which is not going to be easy 😕

Mouser has some phoenix 5.08mm pitch terminals rated for 400V.

What would be a good alternative to the screw terminals? I'm not their biggest fan either.

[Rodeodave]

Okay, moving on.

Here's how I wired up the transformer:

And here we see the unloaded secondary voltages:

Here the PSU boards are mounted to the front plate for heatsinking. The power resistors (500R and 16k) will be used to load the PSU for testing:

And finally, the moment of truth:

One more view from above:

So far, so good.

[Rodeodave]

The amplifier boards are now fully populated, including the front end Jfets, for which I picked pairs of 2sk170bl from the same batch with an Idss of 7.3 and 7.4mA.

Using a benchtop PSU supplying 20.00V DC I then set the constant current sources to 17.00mA:

It's going to be interesting to see how much this will go up with the full B+.