Krell KSA 50 PCB

Ok, maybe I misread that...which makes this project more intersting...is there a clear bipolar preference ? Seem to be different versions out there...

Hi I am also collecting parts to build a krell ksa 50.
What I have read from others early version was full class A
Mk11 version higher rail voltage is not full class A but sounds best.
you can also check this guide out.
bhttps://www.diyaudio.com/forums/diyaudio-com-wiki/152448-krell-ksa-50-clone-building-guide.htmlut sounds best.
 
Ok, maybe I misread that...which makes this project more intersting...is there a clear bipolar preference ? Seem to be different versions out there...

These were some we used to build the clones:

https://www.onsemi.com/pub/Collateral/MJL21193-D.PDF

https://www.onsemi.com/pub/Collateral/MJL3281A-D.PDF

You can also get them in the TO-3P packaging as

https://www.onsemi.com/pub/Collateral/NJW3281-D.PDF

https://www.onsemi.com/pub/Collateral/NJW21193-D.PDF

Some of us could still source these in the older TO-3 packaging, but I doubt you will still get them now. Those on eBay is almost guaranteed to be fake. Rather use the modern packaged units from a guaranteed source like Mouser, Farnell and Digikey.
 
Well, what is the recommended board version ?

Attached is the version most people built (including me).

The KSA50 is very dynamic and fast, but most of all "listenable". It has an extremely wide bandwidth (200kHz at 1 watt), low distortion and low noise.

Even though is is an "old design", I believe it is a benchmark even today. It is a very forgiving design and a lot of parts (many different transistors can be used) are not critical.

The design is tried and true as built by many DIYers.
 

Attachments

  • KSA50 Schematic.jpg
    KSA50 Schematic.jpg
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Starting on post #8883 I showed pictures of the 10th anniversary makeover of my KSA-50 mono blocks. I used PCBs designed by member Pinkmouse and created long output PCBs to better use the length of my heat sinks.
I have an unused set of the Pinkmouse PCBs and can also provide long output boards. If anybody is interested in building the Krell clone using those proven PCBs, contact me through private message.
 
Well, some people says that the latest version sounds best, some people prefers first mk2. I had no opportunity to listen every version of original ksa50 (just first mk2) but I can tell you that higher rail voltage do things better. I've finished two clones, one with Delta boards, and 37V DC rails (1.8 A bias, 3 pair of output devices, 300mV per device), and one with mosfet-ccs, 48 V DC rails (1,3 A bias, 2 pair of output devices, 325mV per device). The difference between this two amps is so obvious. The later has more punch, more authority but still has smooth silky highs which is exactly what I remember from listening original KSA50.

Dean

neychi, may I ask which boards did you use for your version with 48V and mosfet ccs ?

I can find some versions on aliexpress, but more for KSA100 if I get it right:

HTB1qS9Xor1YBuNjSszhq6AUsFXav.jpg


from this offer:
KRELL KSA100 improved BA15MKII power amplifier kit Class A power amplifier board-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

Are these the Mosfet-Versions you talked about ?

medisinmannen, I got the schematics of your boards, they seem to be the early Mk2 version without mosfet ccs. They as well have some changes compares to the schematic from THD+N...(not sure how I can attach a pdf here)
 
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May I ask those who built it and compared it with other builds like Pass F5 or other class A SS power amps: Is it still worth it to build it or are other models superior...given that this was invented in the 80s...and yes, I wanted one of them as well when I was a student and could not afford them...so it is easy to convince me to build one, but really...should I ?

I built an F5 several years ago and I must say I didn't like it, this is just a personal opinion, and I am sure there are a great many who think differently.
I have a passively cooled KSA50 that is modified for 25 W output that I enjoy a lot. Also currently building another KSA50 that will be biased to at least 50W with fan cooled heatsinks.
Also worth considering is the Aksa Lender Alpha class A . I have built this and although not yet installed in a chassis is a very listenable amplifier that to my ears is very nice.
Best Regards
Alan
 
And you would recommend this version of the PCB ? I see that this one has the LM339 CCS on board, while the green ones above do not have them on board and I guess the ones of ounkmouse neither ?

I am asking if you think which version to pick as Jim is charging a hefty margin on the red board (80$ for a stereo set)...you could get for that money a fully stuffed set of boards incl. speaker protection from aliexpress.
 
And you would recommend this version of the PCB ? I see that this one has the LM339 CCS on board, while the green ones above do not have them on board and I guess the ones of ounkmouse neither ?

I am asking if you think which version to pick as Jim is charging a hefty margin on the red board (80$ for a stereo set)...you could get for that money a fully stuffed set of boards incl. speaker protection from aliexpress.

I got the green boards from ebay item number 112435193237 £18.50
They seem to be good quality boards and look similar to original krell ksa50 mk2.
I personally would components separately from mouser, RS components, hifi collective, airlink transformers or digikey.
 
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Ok, Guys you got me believe in this, thanks for bringing me on speed...

...as I have many (too many) projects going on at the same time, I ask myself: Should I order a set of these assembled boards:

YJ KSA50 Class A Krell 50W+50W 2SA1943/2SC5200 MJE15034/MJE15035 Completed Amplifier board in YJ KSA50 Class A Krell 50W+50W 2SA1943/2SC5200 MJE15034/MJE15035 Completed Amplifier board aus Verstarker auf AliExpress.com | Alibaba Group

or its sister

YJ KSA50 Class A Krell 50W+50W MJ15024G/MJ15025G MJE15034/MJE15035 Completed Amplifier board in YJ KSA50 Class A Krell 50W+50W MJ15024G/MJ15025G MJE15034/MJE15035 Completed Amplifier board aus Verstarker auf AliExpress.com | Alibaba Group

...and have a playing amplifier rather fast. If it is good and I could imagine it could become great with more careful parts selection etc.: Wonderful. Lets invest more time and money. If it is soso: Lets move on...100 Euro for two stuffed boards are hard to beat...enclosure, transformer and caps I do always have from previous projects

Makes sense ? Any preference for one or the other version above ?
 
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And you would recommend this version of the PCB ? I see that this one has the LM339 CCS on board, while the green ones above do not have them on board and I guess the ones of ounkmouse neither ?

I am asking if you think which version to pick as Jim is charging a hefty margin on the red board (80$ for a stereo set)...you could get for that money a fully stuffed set of boards incl. speaker protection from aliexpress.

LM334

I can't give you a recommendation for other boards that you mentioned, but I can tell you my experience with boards that i have and they are very positive.
If you want to go a simpler way then buy green boards without mosfet-ccs, but if you want the option of upgrading to ksa100mk2 some day then buy Jims boards.
 
Damned...you know how to convince...Ok, will do. I was not sure, how much the CCS is needed or not.

By the way: I understand that most of you guys do not use speaker protection, correct ?

I have two big 800VA toroids with 30V*2 on the shelf from a former project...may not give me the 48V you proposed, I would guess more like 43V...but I guess a good start.

I always wonderd if 22K input impedance has any particular reason ? Why not 100K ? My line-stage would like that. Can anything go south when taking a different value ?
 
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Damned...you know how to convince...Ok, will do. I was not sure, how much the CCS is needed or not.

By the way: I understand that most of you guys do not use speaker protection, correct ?

I have two big 800VA toroids with 30V*2 on the shelf from a former project...may not give me the 48V you proposed, I would guess more like 43V...but I guess a good start.

I always wonderd if 22K input impedance has any particular reason ? Why not 100K ? My line-stage would like that. Can anything go south when taking a different value ?

You will change the characteristics of the input filter somewhat.
And you will find there is somewhat less noise with 22k than 100k.

I would be surprised if a line stage can't deal with 22k ?
Is it a special configuration?

-Dan
 
Yes, it is...its a DHT tube outputstage with OPTs, output impedqnce approx. 1K. Lots of current, but that is at the moment what it is...depending on the sensitivity of the KSA, I could bring output impedance down to 250ohm. Nevertheless I tested the sound of the OPT with different impedances of the input side of my power amp (300B) and you can hear quiet a bit of differnces...funny enough with the grid choke of 7000H/1.2kohm being the best...maybe a grid choke as well for the KSA ? This may drive its DC path to 1.2k and its AC impedance into the megaohm area...
 
[QUOTE=Blitz

By the way: I understand that most of you guys do not use speaker protection, correct ?

Never used protection on any of my 6 monoblocks ( 50-100-150 watt versions)
And never had an issue except on my 150 pair that started to give me signs and was shut down quickly ( power supply caps age )

Torture testing and living with it on the bench for an extended time should cover most bets before putting it on your favorite speaks

Dont like the signal output path and willing to live dangerously yes

Regards
David
 
I have the same philosophy.

I do not want anything in the signal path which does not have to be there. In my tube equipment, I found even gridstopper resistor sound bad, destroy the micro-dynamics/ musical energy...a small HF bread which has around 1k impedance at 10Mhz sounds much, much better...not sure I want the 1k series resistor in the input section. What is the purpose ? HF filter ? I have a natural HF filter in my line stage (output transformer).