Krell KSA 50 PCB

Aaron,

I am a software guy not an engineer so I cannot give you all the scientific reasons why it is so. However I have been toying with power amps/ building kits etc for 20 years. I know through experience that amps with lower rails (same topology) almost always sound better. Specifically they are less fatiguing. Higher rail amps sound hard, thin and piercing. No black magic... I have consistently seen this result.

Case in point the Adcom 535II is considered Adcom's finest sounding amp (arguable but large consensus) it is topologically identical to the larger 545II with the exception of 2 things, the 545II has an extra pair of OP devices and has a larger PSU with higher rails. Even the PCB's are the same part numbers, yet people say the 535II is their favorite. Same is the case with the Krell KSA-50 and KSA-100, the KSA-50 makes many critic's list as top ten amps of all time not the KSA-100.

I have no scientific basis for what I am about to say (so don't laugh) it's pure practical experience.

1) Small amps with a single OP pair sound softer, more detail and lush. As you add more OP devices, the sound gets slightly fatiguing, though bass seems to get a little better controlled. This is assuming both are biased proportionally i.e. at a device level they see same bias in both scenarios. I do not know the reason but perhaps it has to do with micro level interations between devices (even if matched well which might alleviate the effect to some extent).

2) Bridge balance OP stage seem to have less grain than the same amp non-bridged HOWEVER in hi rail scenarios, it will have have more glare, so this one is tricky to implement. In my experience, bridging the KSA-50 would be the best combinition because of lower rails and already good sounding front end. I conducted an experiment with 2 Adcom 555II's, one running a bridged OP stage / with reduced rails ( I connected the Trafo's primaries in series to reduce rails to 41vdc from 82vdc), the other was a straight up vanilla 555II. Both clipped between 250 to 280 watts into 8 ohms depending on my home AC line. Yet in listening tests the low rail/ bridged version seemed like a different animal altogether, it just blew the vanilla 555II away. I cannot explain the scientific reasons but I know what I heard. ;-) I have used this trick many times on several amps and like it better this way. The obvious disadvantage is the additional cost and effort of bulding a balanced design but I personally like it sounding that way.

If you see the Krells/ Thresholds/ Nak 200 watt amps compared to Sony/Kenwood/Pioneer etc amps also of 200 watts (radically different topologies ofcourse) you will see that the higher end amps use rails between 68 to 75 vdc, the Japanese amps use 80 to 92 vdc for the same power.... guess which ones sound more fatiguing. (granted there are several variables at play but still... )

I will let the experts explain or debunk what my humble observations have been. :angel:

Hope this did not make it even more confusing.
 
NUTTTR said:


How come that is the case? (sounding better) is there something to it, or just black magic? Seriously interested because lower rails actually make it EASIER for me rather than harder, just wondering if there's a reason? i could go with 28vac or something instead.. :)
Aaron


26-0-26vac to 28-0-28vac (35-38vdc) sounds just about right to me. It also allows you to set the bias a tad higher than the 30-0-30 scenario.

With lower rails. I'd use more capacitance, also use bypass caps and add smaller lytics near the OP devices. If you are unhappy with the power you's get, you can always bi-amp ;-).
 
Thanks for the ideas :)
I don't always agree with "theory" because in "theory" a lot of things are good that in practise they aren't!!!

I go for listening, and experience!
I will be running 4 ohm from it 90% of the time, so i guess 28vac (even though it is only a LITTLE lower) might be the best bet....
Do you really think more capacitance would be needed? Trying to justify extra expense now ;)

I have massive (470mmx470mm) heatsink area (per channel!!!) and i am using a few more outputs to allow for greater biasing... I want as much class A as i can get, but am still stuck with the power point limit (i now need a 15amp 240v line installed!)... I might as well do "everything" well....

If i ultimately need more capacitance, i will put it onto the main speaker channels not the centre (3 channels) - i'd have to double (so 224,000uf) per channel - i think that might be overkill? Especially when the toroids will be largely underused with 14 amp @ 28vac per channel... yes?

I'm up to "final" design specs, etc, etc, etc and toroids being wound are the final step so these can be customised totally...
:)
Aaron
 
I have several MJ21195/96's I got from from an ONSEMI distributor (AVNET to be exact) . I can let them go much cheaper than digikey. I may have 100 pairs or so but I will have to check. Onsemi sells in 100's, I can give you whatever qty you want.

The 95/96 has better SOAR's than the 93/94. Also As I will hand select them from the same tray, they are likely to be well matched. (Sorry no gain matching service available ;) )
 
Some Questions seeking basic guidance/answers

Hi,

I just discovered this thread adn what appears to be a group buy for some boards that may still be current. I have not had time to read this entire thread. I have only got to the 4 set of 50 postings, and at that a lot of skimming. So if you be so kinds to help me a bit with a few simple questions I appreciate it:

1) Can one still get boards if one wants at the $10.00US a board?
2) If one oders more boards how does that affect or not shipping costs?
3) I do not use paypay or otehr such things. Call me parnoid. Can I send the $$ in well hidden manner to the party? No need for deatils how to yet, just yes/no is all looking for.
4) What is the rated pwoer output of this Krell 50 close in 8/4/2 ohms? I like to have safety so I like to have stability to 2 ohms for odd moments that happens in some drivers. So I liek amp to be able to be cope well with 2 ohm loads. I fully udnerstand power supply, heatsinling and all are factors. Just need to knwo if the design as is can handle down to 2 ohms and if not if can what in summary needs changing, i.e. values, PSU operating voltage/VA, etc. Agan no need for details just yet, just if dable and if theare any major considerations.
5) This is big question here so please keep the answers simple if you can and wish as I am not looking for large details haere and I am aware that personal tastes, and such are a large factor here. Pros, cons differences and such and any major points of consideration are all I need. THE BIGGY is what are the differences between this Krell 50 clone, the ACD LYNX and delta-audio.com Leach clone of amps? I believe they are all bipolar from the little I know so far of amp design and such.

I am asking as a few time I missed out (I did not know about this site until few months ago, let alone time takes to learn adn dig about things) on some excellent boards made in group buys which neither the artwork or gerber files are available for me to even have made later if I wished or hand made in my own unique manner. I know the gerber files for this are available, just if this is an amp that suits my needs I like to get in and not miss a group buy.


Regards,

John L. Males
Willowdale, Ontario
Canada
07 January 2005 17:31
 
Re: Some Questions seeking basic guidance/answers

keypunch said:


1) Can one still get boards if one wants at the $10.00US a board?

Yes.


2) If one oders more boards how does that affect or not shipping costs?

Does not unless you order over 10 boards.


3) I do not use paypay or otehr such things. Call me parnoid. Can I send the $$ in well hidden manner to the party? No need for deatils how to yet, just yes/no is all looking for.

Mail check or money order to me. I suggest you use track able method.


4) What is the rated pwoer output of this Krell 50 close in 8/4/2 ohms? I like to have safety so I like to have stability to 2 ohms for odd moments that happens in some drivers. So I liek amp to be able to be cope well with 2 ohm loads. I fully udnerstand power supply, heatsinling and all are factors. Just need to knwo if the design as is can handle down to 2 ohms and if not if can what in summary needs changing, i.e. values, PSU operating voltage/VA, etc. Agan no need for details just yet, just if dable and if theare any major considerations.

I'll leave the technical questions for the edumacated people.


5) This is big question here so please keep the answers simple if you can and wish as I am not looking for large details haere and I am aware that personal tastes, and such are a large factor here. Pros, cons differences and such and any major points of consideration are all I need. THE BIGGY is what are the differences between this Krell 50 clone, the ACD LYNX and delta-audio.com Leach clone of amps? I believe they are all bipolar from the little I know so far of amp design and such.

KSA-50 is a class A design, Leach is AB.
KSA-50 was a comercial design that received great reviews and will not disapoint if executed correctly.

Regards,
John







NUTTTR said:
Again: To clarify - board shipping is (for "other countries") $7us for ALL the boards, not each, yes?
Thanks
Aaron



Aaron-

Yes $7US is for shipment of a package outside the US.

Now if you order more than 10 and the package becomes overly heavy I may request the difference be reimbursed.
 
acenovelty said:
lgreen,
MJ15003/4 were the original transistors in the KSA 50 and they are also still available as free samples from:

http://www.onsemi.com/site/MyON

Prosit :drink:

Do they give samples to non-professional users?

I occasionally get samples at work, and they follow up with a phone call asking what they're for, how many will we be buying this year and can they send a rep round to help with anything...can't see them being amused at being told 'they're for a fat amplifier for my living room, and I'll hopefully never need to buy any more'