i'm on a roll... the kgsshv

[spritzer]

+/-400V.  I'd rather run with higher current than go to 450V. 

 

No boards will be sold until the design is finalized.  That could be a while though. 

Edited May 22, 2015 by spritzer

[insanity]

Very interesting. Why did you use ceramic insulators under the SICs? Aren't they in an insulated package?

[spritzer]

Nope. 

[spritzer]

Now with it sitting in my main rack for a couple of hours it's time for some impressions.    The basic concept of this amp came from me wanting to tame the SR-009 artificial top end and doing it in a cool way.  End result is the continued refinement of older circuits but the changes here will no doubt migrate to the older circuits at some point.  As better SiC units became available and the new SR-009 showed up it rendered this amp unnecessary but then it became clear that it could melt together the superb technical nature of the KGSSHV and the musicality of the KGST into one package.  So we basically have a lot of power, with plenty of detail and a tube like sound from a solid state amp. 

 

Now I'm using it with my modified SR-007Mk2 which have pretty much outshone all my other cans.  Nothing can touch the bass these dish out or the sheer control over the entire sound spectrum.  The Carbon just adds to this as the detail they dig out is simply astounding, placing instruments in their own fixed place in the soundstage which the 009 can't really do as well. 

 

Bottom line, I like this amp a lot. 

[Kerry]

 

Congrats!  Really glad to hear that.  Looks like this will go onto my list.

[JimL]

Very cool!  Looks like your build has the single current source rather than the cascode current source, and a mini KGSSHV power supply?

Edited May 23, 2015 by JimL

[Laowei]

Inspiring as always Birgir. And a kick in the pants for me to get soldering my own when I get back home. Wondering what current you have at each SIT?

[spritzer]

They are running at 14mA. 

[nopants]

What size hex nuts/bolts are you using to affix the bracket to the heatsink? I'm currently wrestling with how to do this properly for a BH build.

[Dave R]

Very nice Birgir.

[n_maher]

Indeed, another nice build Birgir.

[JoaMat]

/

Edited November 11, 2015 by JoaMat

[kevin gilmore]

I like this idea, will simulate soon

actually there is a voltage reference, its ground.

looks good.

Edited May 23, 2015 by kevin gilmore

[spritzer]

What size hex nuts/bolts are you using to affix the bracket to the heatsink? I'm currently wrestling with how to do this properly for a BH build.

 

M4 is what I generally use for this.  Locking washers on the bolts so they will never move. 

[gepardcv]

Now I'm using it with my modified SR-007Mk2 which have pretty much outshone all my other cans.

 

How have you modified your SR-007?

[spritzer]

Plugged the ports and played with the springs a bit.  Other than that they are stock. 

[Kerry]

Nice Carbon, Birgir.

 

I've been thinking how to make a servo without a voltage reference and trimmer.

 

Resulting in a daughter board between Mosfets on the bracket.

 

IMG_1417.JPG

 

Schematic below. C1 absolutely necessary. Offset some tenths below zero. Seems to work OK.

 

Offset 3.jpg

That looks like a great idea. I've had concerns about feeding the reference. I've minimized it down to 180uA, but love the idea of removing it and using ground as the reference.

I'll model that later. Might want to drop raise the current a bit for the error amp.

Thanks for pushing this. Awesome work

Edited May 24, 2015 by Kerry

[kevin gilmore]

http://gilmore.chem.northwestern.edu/kgsshvcarbonservo.jpg

[Laowei]

Kevin, is this the first common gate SS Stax amp that you have made public?

Edited May 25, 2015 by Laowei

[kevin gilmore]

lets call it solid state grounded grid.

 

and yes this is the first one with a silicon carbide fet.

[mwl168]

Thanks for tips from sorenb, I tinkered with the VAS on my KGSSHV this morning and after some try and error it appears to be working now. I thought I would share my experience here.

 

I could not find Kevin’s original KGSS article any more (what’s up with the HEADWIZE site?) but going by memory the CCS for the VAS was supposed to source about 3 mA. I am using the ixtp01n100d part, with the drain resistor (R12/R19) at 1.2K as marked on the silkscreen, I got 2.36V voltage drop – only about 2mA of current.

 

I paralleled R12/R19 with a 1K resistor and got it down to 546R and about 2.35V voltage drop - about 4.3mA current.  This change very slightly raised the output device current from 9.7mA to 9.8mA. But two things caught me by surprise:

 

1.     the amps are drawing more current from the PSU, voltage drop on the 15R/3W current-limiting resistors (R2, R3, R13, R14) went from 3.75V to 4.4V.  My, admittedly small, heatsinks are running quite a bit warmer (but not hot).

 

2.     the balance and DC offset are now all over the place. To the point I thought I somehow messed up a working amp (see more below).

 

With the original resistors in the offset chain (R26 = 2K, VR1 = 1K) I could not get the balance and offset to anywhere near 0V. Not only they were all measured well over 200V, it was so bad it almost acted like the amp was not responding to adjustment at all. I had to finally parallel R26 with a 1K resistor and brought the value down to 666R. At that point I was able bring the offset to 0V. Once I was able to get the offset in control the balance adjustment falls in place as well.

 

As it sits playing now, offset VR (VR1) is adjusted to about 235R.

 

I don’t like to describe subjective sound impressions. But I do believe the changes I made to raise the VAS CCS current do improve the sound of the amp. 

Edited May 25, 2015 by mwl168

[spritzer]

Do a double blind test and then report back. 

[wink]

Sound science strikes again.  Find 2 blind audiophiles, and have at it...

[gepardcv]

Just to double-check my sanity (or blindness): the KGSSHV mini stereo board doesn't have servo bypass jumpers, right? I feel like I'm playing Where's Waldo. It's a very pretty board, but super-packed...

Edited May 26, 2015 by gepardcv

[spritzer]

No jumpers on that one.