Krell KSA 100mkII Clone

Mark A. Gulbrandsen said:
I was quoted about $130.00 to $150.00 for a simple dual secondary toroid. Extra windings will add to the cost.
If the big audio tranformer with all the extras is getting too expensive, then maybe we shouuld look at a simple twin secondary 1kVA with screen and guass band vac impregnated.
And add a supplementary transformer/s for the extra voltages required. Could even be one or two EI types to help reduce mains borne artifacts and keep the control back emf out of the pure audio circuits.
9+9@2A=36VA and 14+14@1A=28VA. these are fairly cheap whether toroid or EI.
 
I third that vote

It is the price that is keeping me from committing to the xformer buy. I'm all for the version Andrew and Mark suggested. I have a couple of VM transformers and they are beautiful. I'd like to see this, and particularly this version, happen.

Just my two cents.

Cheers,
Ryan
 
I would be in for a couple at a fair price. The suggestion of extra low voltage full power windings or taps makes sense for those of us that will move on to other projects. I would pay considerably more for a transformer I could move from an Aleph to a KSA50 to a KSA100 to "the next project". Maybe mount it in an external box with a bridge and caps, with a huge cable and connector. By switching taps it could power all our projects and reduce build time. It also may have wider DIY appeal and a higher quantity order.

Bob G.
 
Hi folks.
The original Krell KSA-100 transformer from Avel was quoted for approx. $295 (each unit if buying more than 5) This meant a total costs of $ 590 which is a lot of money. If we could reach a price level of say, $150 for e single unit including all extra Aux windings then it might be a GB. But I think if much higher a price it would not be a GB, Its my qualified guessing.

Folks, You should be aware of this: if buying an extra Aux-transformer you must calculate an extra cost for that. If looking at transformer supplier here in Norway, the cost for one unit (25-50VA, 2-3 secondary windings) would be as calculated:

transformer: 180NOK + VAT: 45NOK + shipping/handling: approx 65NOK would yield a totals of 290NOK which is approx. $53.20. :xeye:
But this is only applicable for us in Norway, and if you dont live right besides an electronic shop.

I cant see any benefits at all (for me) if going for a smaller (and probably a bad audio) aux transformer. Also, the whole amplifiers mains circuit will be more complicated (H.V. circuits, Fuses etc) and an extra transformer also do need a chassis area to be mounted at. :cannotbe:

I believe, if going for only one transformer unit (1kVA) included all extra aux-windings, such a unit wont be more expensive compared to a simpler mains + extra Aux transformer. :rolleyes: (of course, more expensive for those already sitting on a bunch of small transformers)

Regards :cool:
 
Some feedback

Gentlemen

This weekend the following changes were done to my 100.2

a) Pierre replaced the 16 gauge Van Den Hul wire between the output transistors on my 100.2 with a 12 gauge version.
b) A second Black Gate ( I literally had to hold a gun against Pierre head to add the 2nd cap) was also added to each PCB.
c) An additional power crosswire was added as suggested some time back and;
d) The floating earth on the VDH 103 mk1 internal interconnect was terminated to ground on the PCB.

The sonic impact is as follows:

1. The high frequency respone is now possibly the best I have ever heard.
2. Much more inner detail and a 30 % iimprovement in the image and soundstage.
3. The midrange is still not as transparent as the 50.2 but it could be the BG still needs to burn in.
4. Globally the sound can be desribed as very natural but just lacking in that sense of absolute control on the bass end.

When I removed the extra crosswire on one channel the sound mmediately became thinner with a slight emphasis on the high frequencies. The extra cable concept was definitely a good idea.

The next step is to double up the remaining 16 gauge cable feeding the output stage with the same cable as I now suspect that the 16 gauge might be too thin and the possible cause of the lack of extreme bass tightness.

My subjective impression is:

1. Be VERY careful with your cable selection.
2. To my ears adding the second BG cap was a good idea.



Jozua
 
My comments and description of the changes:

- The floating earth of the coax was since the upgraded coax was a balanced type. The normal method of using balanced cable for unbalanced applications is to use the two conductors for signal and ground respectively, and tie the shield to ground at one side only. This doesn't provide very good shielding though, so I grounded the shield.

- The crosswire Jozua refers to was due to my suggestion of hardwiring a thick wire from the NPN's output to the PNP's, so that the current has a shorter path to the speaker terminals and the connection at the PCB is now only for the feedback reference and not to carry the full current. Ideally speaking the speaker output should be taken from a cut in the centre of this wire for perfect symmetry.

- A shorter & more symmetrical wiring scheme than the original's 15cm for one output NPN's emitter and 2cm for a PNP will have a more profound effect - no cable is after all the best cable

- Using two non-polar BG NX's in series merely for the sake of having it look the same as the original's polarised ones is senseless in any possible aspect. The improvements in sound can rather be attributed to the other mods as it wasn't individually evaluated and can hardly be considered as an accurate assessment.
 
KSA100 Questions

Hello folks,

I¡¯ve been low profile on the DIY audio projects but things are heating up again. I¡¯ve stuffed most of the parts in my KSA100MK II boards and I have a few questions.

A) Regarding C4 (0.1uF) & the C2/C3 pair (AKA 470uF bipolar) they seem to be floating and not terminated to ground via a missing resistor R16 (825R). Looks like a simple fix to run R16 to the ground on the underside of the board?

B) R37 (7K50) and R36 (1K50) from the schematic do not have ¡°homes¡± on the MK II boards but there are some mysterious pad/via¡¯s that line up with the layout images. The layout image file seems to be different from the actual PCB¡¯s that were manufactured. It looks like the resistors do have positions to be soldered into but some slicing and dicing would be required on the actual traces to make them work, possibly?

Or was the design changed to eliminate these parts?

Hope all is well,

Shawn.
 

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General comments KSA100 MK II

I used the SOT-223 package options for Q5, 6, 7 and 8 and it was very easy to solder these surface-mount parts on the underside of the board. I was hasty on my components purchase last spring so now I have the extra substitutes for these devices if anybody wants them; I have 4 pieces each :

IRFD110PBF-ND
IRFD9110PBF-ND
ZVP2110A-ND
ZVN2110A-ND (Obviously you would use one set or the other)

I also deployed the use of some of the extra capacitor positions provided, using 4 pcs on each board of 100v 680uF FC type electrolytic. I now have 4 extra pcs if anybody wants those too.

I purchased 100 each of 2SC2240 & 2SA970 and found perfect matches for all of my Q1~Q4¡¯s and I was lucky because there were only 4 pcs of the A970¡¯s to match the large bunch that came from C2240¡¯s.

I¡¯ll be using my 1000VA 44-0-44 VAC transformers, one for each channel so my rail voltages should be just under -+60 VDC so I decided to use 100V electrolytic caps. I picked up the cap bank for the main supply from Steve @ Apex as I purchased 4 pcs Hitachi 47,000uF 80 VDC but just recently I picked up 4 pcs of Panasonic 68,000uF 100 VDC. I think it makes sense to use the 68¡¯s on the Krell KSA100 and the 47¡¯s on the KSA50 (which is almost ready to go into the enclosure).

Mr. Watts has placed jumper positions J4 and J5 to connect the front end power supply to the driver stage power supply and has indicated a value of 0R to 10R. Regarding my power supply rails, I was wondering what you think would be an ideal value to place here for best RC filter performance vs. voltage drop on the front end? Again my rails should be just under 60VDC by a few volts depending on the level of bias current that is set.

I have not 100% decided how many output transistors I want to use but think a total of 12 per channel would be plenty. I have some samples of the MJW21196 and MJW21195 and I can easily get more. Any thoughts using these devices versus others from On Semi?

The -+60VDC will obviously sag but is it too high to operate this thing at 55~57VDC?

See pics of my stuffed KSA100 MK II's
 

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PWatts said:
These three components were routed on the bottom of the board; the bottom silkscreen was merely left out to save costs. R37 can just as well be placed on the top, I put it on the bottom to prevent it from possibly interfering with Q9-11's heatsinks.

Cheers PWatts!

I guess you folks have already discussed all this stuff? Sorry I have'nt been around to catch it all. I'll make the adjustments and post some more pics.

Have you dropped your boards into your friends Krell yet? How many of you people are listening to this baby nowadays?

Shawn.