Krell KSA 100mkII Clone

[Mark A. Gulbrandsen]

Stuart,

Its good to have you back here!

I am aware of your high power adaption to the 50 but there has to be a very good reason that Dan The Man did what he did in the MK-2 version of the 100.... and I suspect that it has more to do with its ability to drive very low impedances than any other factor. I remember a post about driver current way back in the thread and the lack of ability of the present driver to supply adaquate drive current to the KSA-50 OP stage.

Please compare the older pre 1983 KSA-100 versions with the MK-2 version and let me know what your take is on it and why he went the route he did... perhaps Andrrew would also chime in on this?

Mark

[AndrewT]

Hi,
it's a while since I last looked at the KSA Klone driver stage, so I'll sumarise from memory.
The MJE1503x pairs will take loads down to 1ohm easily.
2sa649/c669 will take loads down to 2ohm from +-40V rails.
At 1ohm loading they are being stretched to beyond MY limits but only just beyond.

If you want to go to higher voltages then the driver and output stages may (will) need to be beefed up. I would keep the drivers cooler than the outputs if designing for very low loads. CPU cooler with slow fan or copy Still4given's cool inlet over passive sink.

I suggest that if the output stage NEEDS 6pairs then the driver stage probably needs 2 pair to give the current capacity demanded by the multi outputs.

1pair MJE1503x to <5pair 2sa1943/c5200 (2ohm upwards)
2pair MJE 1503x to 6pair 2sa1943/c5200 (1ohm upwards)
1pair 2sb649/c669 to <4pair 2sa1943/c5200 (3ohm upwards)
2pair 2sb649/c669 to 4pair or 6pair 2sa1943/c5200 (1.5ohm upwards)

If you substitute higher power devices than 150W then proportion the number of devices to suit. i.e. 5pair @150W = 3pair @250W

[Flodstroem]

Mark:

Since you are almost doing the entire KSA-100 MK-2 with the exception of some of the preceeding stages might I suggest that we just do an actual board for the KSA-100 MK-2 including both TO-3 and TO-247 OP boards instead. I'm not sure that the preceeding stages of the KSA-50 can supply enough drive current for 2 pairs of drivers when operating at low impedances. Take a look at the actual schematic of the 100 MK-2 and I think you will agree that Dan went to great lengths to be sure that each preceeding stage was able to make its mark. Also those obsolete VN0210N5 and VPO210N5 devices only operate at about 3 mils so good subs are Zetex ZVP3310 and ZVN3310 and they are readily available and dirt cheap. The 1N5309 current limiter diodes are still made by MicroSemi Corp and in stock at Mouser.

Yes Im with you, but I have already payed for KSA -50 boards (as you now) and also I have bought components for the KSA-50 (but, I could surely sell those at the Trading Post or in this post)

My first Krell-project will be one of (eg. four of) either the KSA 50 (100W), or the KSA 100 mk-2. I should prefer the KSA-100 mk-2 if there will be boards available.

I have the software needed to make everything for a PCB design including the Gerber generator, drill table, solder masks etc..... (one ore multi layer boards), but I havnt the component needed for to dimensioning the board etc.. and Im not a very skilled designer of Audio-boards.

But I have the experiences for to build Class-A amps (Pass) and thats good. Also I have useful ideas for the design of the driver-output boards. I have ordered Conrads heat sinks for this building project and they will be pre-toled for my output device block (+ OP boards). I could post some drawings of my ideas if need be if this is going to be a new building project.

Mark, what will be the first steps for to design this 100W mk-2 Agreement for a chematics ? or do we already have come to the next stage?

I have design a toroidal custom transformer (at Avel) for this project (for mono-blocks) and it could be used for either the KSA 50 (for 100W) or the KSA 100 mk-2 (76V CT @ 8-9 Amps 6-700VA).

I think your idea for to build this amp was an excellent innovation, especially when thinking of there is not so many building projects for a Class-A amp of 100W+ out there like this one.

Im looking forward to follow this "new" tread. Any more interested out there?

Regards

[pinkmouse]

Mark, what PCB package does your friend use? I have Eagle, Osmond and Protel99SE, and if he uses one of those we could perhaps do it as a collaboration.

[ROVSING]

And here we go again...
I am sure that KSA100MkII would suit my PCB collection perfect
Any bets on the date of reply no. 1000 ?

[dr.strangelove3]

Would there be an advantage if these possibly upcoming ksa-100 MK2 boards were used with the dissipation of the ksa-50?

I have most of the parts for a nice ksa-50, but the ksa-100 mk2 appeals strongly to me.

A lot of parts I have for the ksa-50 can be used for the ksa-100, what I can't use I can always sell.
But I don't want to go for a new case, and the case I have can only dissipate the heat of a ksa-50.

[AndrewT]

Hi,
can someone post specs for the various KSA/KMA outputs, bias & Vrail? possibly even Xpairs of devices & driver types.

Then we can see which are full ClassA (if any) and what dissipation/voltage we are talking about.

[acenovelty]

This would be the board to clone?

[Flodstroem]

This is perfect.
acenovelty:

This would be the board to clone?

Yes, it looks very nice, also I liked the mountings of the input stage on same heat sink (same temp on all transistors)

But I would prefer to mount the driver stage on same heat sink as for the output devices (as where the bias device should be mounted)

I would like to post some drawings for my output boards soon so you could se what is my solution for this arrangement.

BTW, I work on the McCAD software from Vamp Inc.

Regards

[Mark A. Gulbrandsen]

Pinky, Thanks for creating this new thread!

Everyone,
My original desire was to ultimately build a KSA-80 but the KSA-100 Mk-2 circuit has had me greatly intreguied since the links to Mr. Macleans site was posted. kloning the KSA-80 would also involve aquireing ALOT of even harder to get parts and ALOT of device matching. The KSA-100 MK-2 version will require some matching but not to the extent that a fully balanced amp like the KSA-80 would. On the other hand a PCB design for the KSA-80 board already exists in these threads at DIY!!

Note that there also existed the KMA-100 Monoblock Krell amp that had the addition of regulated supplies for the front end and driver stages, similar to the regulated supplies done in the KSA-80. This additional supply could be a future addition to this amp and one could build a huge stereo amp or Monoblocks. I'd love to see a 6 channel version..... it would probably be the size of a refrigerator.

Al,

I know that at GE he uses Pads which is a very expensive program. I know he also has the full version of Eagle but not sure which release version. The good thing is that he is very up to date on all the industry standard design codes and such and he does alot of high voltage-high current stuff at GE. Allhe does there is PCB design. Anyway I have e-mailed Dave so we'll see if he is interested and has the time.

Getting to the Board.... Itt would be good to make it exactly as the Pinkmouse KSA-50 boards were done, just expanded a bit. Al's boards make bulding the KSA-50 VERY EASY! This would entail expanding the present driver board to accomodate the 2 extra driver devices and expanding the main board to accomodate the current source(?) MOSFETS and extra cascoded(?) predrivers. I would much prefer to see O.P. boards designed for both TO-3 and TO-247 devices done this time around and these should be done as seperate boards completely. Mk21193/94 devices are readily available in both TO-3 and TO-247P packages and are dirt cheap. This will serve to make the whole thing alot more universal and anyone wanting to purchase boards could literally go any route he desired... or could change his mind at a later date as per the O.P. device. So basically it should be the main board and driver board done together and routed to snap apart if desired. Then larger sheets of O.P. boards could be done up to just snap apart into the desired quantuty someone wanted to order. With the KSA-50 some folks didn't want the O.P. boards at all and some wanted extras...... So some board sets had to be sacrificed in order to get the extra O.P. boards. Hopefully they will sell some day.


Andrew,

I believe the rails of the KSA-100 are at +/- 48 to 50 volts. I am also pretty sure that its clip point is around 160 WRMS into 8 ohms... so the 100 watts class A might be valid as the 50 watts was in the KSA-50. Below are links to the schematics of both the main board and the output stage. Let me know why you think the driver and pre driver stages were greatly expanded upon as compared to the Post 1983 version which a link to is also below. There had to be a good reason he went to all the trouble of designing the Mk-2 version other than just plain marketing!! To me the post 1983 version IS nothing more than an expanded KSA-50! It could probably be built on the present KSA-50 board with some minor trace changes.

KSA-100 Mk-2 Main Board

KSA-100 Mk-2 Output Stage

Pre 1983 KSA-100

Every one else please jump in with your ideas and thoughts... perhaps then we can have boards on hand in about 60 days or so.

Thanks!

Mark