Krell KSA 100mkII Clone

[pinkmouse]

Grounding is something I paid great attention to in the KSA50 layout, and I judge my efforts as being successful due to the lack of complaints on that topic. However, I would still like to see measurements done with proper equipment.

[PWatts]

Well I do have an Audio Precision SYS2722 (although it cannot do EMI tests), but the spectra I posteda few months ago got precious little attention so I followed a "screw them" policy.

[Zen Mod]

it's a fact that KSA 50 and lookalikes are more than classics in last few decades

one example of this is Oly's bipamp- (Oly is Vangelis here at DIY) ,and he constructed it several years ago; I can't describe his reaction when I send him KSA schematics (somewhere in KSA thread beginning) -he was really surprised how his amp is almost same as KSA.....with few differences ,regarding fewer outputs etc.....

this is one of iterations of pcb for his amp-there you can see his mileage in making demanding pcb applications-this pcb look so simple....but I know that I can't make anything like this....

[Mark A. Gulbrandsen]

I'm definately interested still but lack of time due to lots of work has kept me at bay onthis project. I would front the $$ to get a batch of boards made up from someone's cad work that we can all agree on as I did on the KSA-50 klone. Please make this the MK-2 version as building the earlier versions on the same board will also then be possible ust by adding eom jumpers at unneeded parts locations. Also no planes of any type please... makes parts removal a pain in the butt! Planes are a big fad IMHO.... Not necessary except in RF equipment.

Mark

[PWatts]

Any suggestions so far for the MOSFET's? Preferably something easily available for people all over the world, so if it could be from ONSemi or so it would be great.

As to the layout, I've thought of replicating the original KSA100 Mk2's board in terms of the connector locations, board dimensions and mounting holes. Not only for nostalgic purposes, but also to make it easy to swop around for people with original KSA100's who'd like to do an easy upgrade instead of modding the old boards.

The only issue will be the driver heatsinks - the boltdown type's not going to work as it's going to be too hard for everybody to find the same heatsink. Unfortunately I know from experience that that heatsink on the original KSA100 gets DAMN hot, so it cannot be skimped upon.

[PWatts]

I did a few SPice simulations, and fortunately a few adaptions can easily be made without any penalty. The component variation is actually less than on the KSA50, and all the resistors can be 0.25W except R11-R14 which has to be 0.5W. The output stage's emitter resistors have to be 5W naturally.

Pretty much the same rules as for the KSA50 applies wrt to component tolerance, capacitor quality etc. To stay close to the original, the 62pF caps should be silver mica, and the input shunt an MKP. Polystyrene/polypropylene is a worthy substitution for both, but proper COG ceramics will do fine too. Elna Cerafines will be a good choice for the feedback electrolytic, otherwise a Black Gate NX. For the power supply decoupling Panasonic FC's would be good.

Only the differential amp transistors and zeners should ideally be matched; the rest should be OK without matching.

The following semiconductor substitutions can be made:

Q1,Q2: MPSA42
Q3,Q4: MPSA92
Q5,Q6: IRF610
Q7,Q8: IRF9610
Q9,Q11,Q15,Q17: MJE15031
Q10,Q12,Q13,Q14,Q16: MJE15031
Outputs: MJ(L)21194/3; MJL3281/1302, MJL4281/4302 or any of the popular Sanken or Toshiba types already discussed.

The only part that will be a bit difficult to source is the 1N5309 current regulator. The Vishay CR300 and J509 are viable alternatives, but none of these are easily available. Just to get it working, an 8k2 resistor should do the job, otherwise a JFET can be used. A proper current regulator IC can be used that will also improve performance marginally, but will take up board space. I would suggest that whoever organise the group buy (Mark A?) order a lot of these regulators from Mouser or DigiKey and provide them along with the boards.

A group buy of the resistors and capacitors is a good idea to keep costs down and avoid everybody from placing a special order for only one component.

The trimpots, zeners, transistors, emitter resistors, driver heatsinks, electrolytics etc. are each to his own, but I'd suggest to provide the following as default part of the group buy:

1) All small-signal resistors: Dale
2) 62pF & 680pF caps: silver mica
3) 100nF: Wima MKP

These parts in total will be in the region of $25 for two channels' worth.

[AndrewT]

Hi,
having suggested the adoption of the far faster and more linear and higher gain output devices, I think you should ditch the thought of using mpsa42/92 for the LTP.

A similar upgrade as that applied to the output end would seem more appropriate.

My votes go to
bc546/556b or preferably c grade.
or
2n5551/5401
or
2sa872/c1775, this last probably being best from these three.

Would the locations using MJE15031 benefit from using the slightly better 15034/5? Or something much faster and higher gain.

[Mark A. Gulbrandsen]

Mouser has them
here Quantitiy purcahses don't drop the price very much on these devices.... but I could supply these and the mosfets with the boards. I also have a good working Tektronix 575 curve tracer if we want to match input devices.

I assume you're taling about the MK-2 version of the KSA-100... I don't have the diagrams handy here at work.... With the MK-2 version there is also the need for the mosfets and I had foind a sutable sub for those too. IRF 610 and 9610 will work but these devices are run at extremely low curent and I believe a smaller-higher quality device can safely be used in these positions. Can you check this on your spice program.....?

Mark

[jacco vermeulen]

Originally posted by AndrewT
something much faster and higher gain.

Go nuts in combination with the MJL4302/MJL4281:
2SA1860/2SC4886

Or go completely insane: 2SA1141/2SC2681
(For some obscure reason these are less than $1.50 overhere)

[PWatts]

Yes I am referring to the Mk2.

I have no qualms of using different transistors for the drivers, Mosfets etc, but I was thinking along the lines of what is easily available. MJE1503x and IRFx10 devices are easy and relatively cheap to buy, even at lowly electronics shops. 2Sx transistors and different mosfets are harder to find though, especially in Dark Africa. Going with ONSemi heaven is at hand for only $21
I agree that BC546/556 and the others may be better suited - what about MPS8099/8599?

However, since the stability margin of the KSA is very large, anybody can basically use whatever he/she wants since the package of everything is likely to remain TO220. Likewise switching between TO92 input transistors is also easy.

MJE15034/5 is a perhaps a good idea, I'm already using them in my KSA50 clone. Whether they really perform (audible/measurable) better is debatable.

The original FET's used was spec'd at 100V 3A 2ohms. The IRF610/9610 is easily available but is indeed perhaps not as well suited to a low current duty. A very interesting FET alternative is the IRFD110/9110. These use a nice and small package, and are rated at 100V, 1A, 0.54ohm. They're similarly priced to IRF610, but I don't know how easy they are to get, and their package means that you're stuck with them. Anybody have any suggestions for a better choice available in TO220?

Concerning features I don't think there's much more to add that Al hasn't already incorporated in his boards, any suggestions?

Even though Mouser has the current sources available cheaply, the problem lies with shipping, especially for those overseas. Including components such as these with the board will make it far easier and cheaper for builders.