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krell ksa5 klone

kevin gilmore

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Dear Pars,

Thank you for your quick reply, and constructive comments. As i have not look all of the post before i do, so i don't know the 2SK389/LSK389 or 2x2SK170BL can instead of it.

The 2SK389/LSK389 or 2x2SK170BL are very difficult to order from RS, Digikey etc, i can find some of its in Tabao, but i can't sure that they are genuine.

I know the 2sk366-BL gm is not same as 2N5546 or 389/170, but the value are nearly,  and i had done the 1% device matching of it, so maybe it is OK but not sure.

The MPSA06/56, MJF15030/31 are genuine and the MPSA06/56 had done the 1% device matching. so i have not worries .

The machine run is not hot when i use sigma22 PSU, just can said warm.  I don't know why, it is out of my expectation (i think it run hot so).

I will try KG PSU with 22VAC after i finish sigma22 and KSA5 chassis mounting.


Dear Jose,

Thx for your reminder.


I will mount the sigma22 on chassis  the coming few day.

This is sony R type transformer(from Sony audio machine).27-0-27



This is customer make E type transformer. 28-0-28


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  • 2 weeks later...

I solved the Hummmmm sound issue after made grounding correctly.

As i checked my volume control have problem, so i have not install it now. and next time i will change the signal cable to OCC copper and the 2SK366 to 2N5564, hope this changing will get positive effect. 

The amp's sound are petty good, high resolution  and very clear, but the sound hearing cold. Maybe the R-type transformer or 2SK366 input transistor affected the sound, so i don't know why. Anyone have idea for this issue, i want the sound warn.

About the sigma22 PSU information, as i asked the seller and got that the circuit is same as AMB sigma22 but the PCB layout is not. So it is not a factor to caused the Hummmmm sound. But i Thank you very much for your concern and gave me idea.


Revise, the transformer is dual 25.4vac, not 27vac. the PSU  voltage regulation are from 25.4vac to 22.0vdc. I think it have a little bit high after understand your comment.






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  • 3 weeks later...

I replaced the input transistor to 5N5564 (second hand) then got the the amazing result. Beside, i replaced the volume control to step volume control.

The sound hearing clear, warmth and have good feeling of spaciousness, the dynamic very high and strong.

The treble are very smooth and bright, the bass are taut and rich, the alto are got high transparency and clarity.   

The cables looks in disarray, next time try to tidy it up.




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  • 3 months later...

I'm finally about to build my KSA-5 Klone. I shelved the boards for like 5 years - can't believe I waited that long. Thus far with eBay and a cart full of goodies from Mouser I've gotten the price down to a reasonable ≈$215 including I/O jacks, standoffs, etc. The kits offered on eBay are cheaper. I've been tempted to buy the kits, but fear the parts are cheap and cheerful.

After reading through most of the thread... a question or two...

For the 2Ω resistors - can I use this? - 667-ERX-3SJ2R0

Or are 1% resistors necessary throughout amp?




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Toroidal transformers are not completely symmetrical, because of the wire exits. The usual way of reducing hum induced by the asymmetry is to leave the leads long (or solder on temporary extension wires), loosen the chassis fixing and rotate the transformer to minimise or reduce below audibility the hum. Then tighten up the fixing bolt and tidy up the wiring.

Also make sure that the primary, and secondary wires are twisted. Open wire loops can induce hum and buzz in signal circuits through simple transformer action.

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these cover are mostly cosmetic but i like to use them, the only shield a tad vs grain orientated metal or mu metal.

place the trafo near the big transistors with heatsink and you have a silent amp like in this pic (the 3th i made).

my first version had some inducted hum because the trafo was on the other side near the small transistors.

good luck with your build :-).




Edited by rumina
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I happen to have some KSA5 alternative supply. I wonder what parts need to be changed to get it output +/-18v (Dynalo) and +/-30v (Dynahi) respectively? Would the 2x18V and 2x30V transformers work here? I tried to find a link to the schematics but all seem to be dead now.



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Usually the Stax topic is where you find the links (since Kevin retired from Northwestern University).

docs:  https://drive.google.com/drive/folders/0B7egryukiT7_TFlEQlBRejdVdDQ

gerbers (for PCBs): https://drive.google.com/drive/folders/0B_iJFfZStuVhSE5nOHBVdTByR1k

The TO-3 transistors used for that might be problematic to find. This might help: https://www.diyaudio.com/forums/solid-state/106973-krell-484081-484002-output-transistors-remplaces-codes-help.html

Not sure if there is a BOM floating around anywhere for that version of the PSU.

EDIT: Ahhh, right above, Rumina is using that PSU version for his KSA clone. Looks like MJ15024 and MJ15025.

Edited by Pars
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So I ended up figuring out what my hum issue was after moving trafo orientation. BTW this is for an EHHA Rev A. It turns out that my RK27 was going bad. After readjusting everything, I noticed that I was still getting leakage even though my pot was fully turned down. I could hear a small amount of audio coming through. I replaced the pot and now we're back in business.

With regard to my Klone, are those silicone / mica insulator kits for all the F15030/1 parts required? I'm counting 10 on the main amp board and possibly 2 on the alt. psu board.

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For the alternate power supply shown a few posts above, what hardware is requiered for the TO-3 transistors? I'm looking at kits on eBay and they come with more parts than I think I'd need. I'm thinking all that is needed is: 2x plastic washers, 2x screws, and 2x nuts. The kits come with 2 sets of metal washers and a metal tab for soldering. I'm thinking I wouldn't need these extra parts. See attached picture.

TO-3 hardware.jpg

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