Krell KSA 50 PCB

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#3,941
Hi guys,

Thanks for the info on the KSA100. I guess I have some decisions to make. I may just try a Mono-block setup as a KSA50.

Heat is the enemy. My cooling fan is already starting to get noisy. I placed it between the heatsink and the case, blowing out. I was afraid that having the heated air passing through it may be hard on it but some folks told me not to worry about it that the fans were designed to run like that. Well, maybe I got a faulty fan but it was nice and quiet when I first installed it. It is beginning to develop a whine. I will have to move things around if I have to place it in front of the heatsink. I don't think it would be a good idea to reverse it and have it blowing into the case. I would lose the cooling on the drivers that I now have.
Which way did the fans blow on the originals?

Thanks, Terry
 
#3,943
Hi Guys,

I've got a question as I begin to prepare for the new boards

Is there any advantage/disadvantage to using 6 pair of outputs per channel as opposed to the three pair planned with these boards?

I have some large flat heatsinks that I would like to use since I don't have another tunnel. I also have extra output boards. Would the amp run any cooler if I use more outputs per channel?

Thanks, Terry
 
#3,944
Assuming both sets are run within the SOAR, From what I have heard, that unless devices are micro-matched, the set with fewer outputs will sound a little more open and soft. The set with twice the outputs will have a little tigher bass but may sound slightly veiled... However it would take a good pair of ears to hear the difference, I am not sure I am as "gold" ear'ed.

The obvious is that the one with 6 will be more forgiving of any abuse and more power capable.
 
#3,945
Attention Group Board Purchasers!

The KSA-50 boards have been shipped and will be here Wednesday morning.... I cain't believe it myself but they are actually on the way! My plan is to first send boards out to buyers of just the amp boards. These boards will all go out Saturday morning as this is the only large amount of time I have to spend at the Post Office. The boards from Brian should be here early next week and those that purchased both boards will have theirs sent out later that next week.

I am also in the process of moving in the middle of all this...:xeye: :cannotbe: was supposed to move last week.... lazy real estate people:devilr: ! Fortunately its not a very far move..... less than 1000 feet to be exact. I will have a huge listening room there, large enough for a 5.1 setup of Kleinhorns and intend to have several more amp shoot outs there before winter sets in.

There will be EXTRA KSA-50 and Power Supply boards but they will not be available until after I get unpacked and I will announce when they will be made available. Don't write to me now requesting one as I will just delete your mail, no time to keep track of it :hypno2: ! So keep an eye on this thread for that announcement, besides eveyone wants to be part of the largest thread on DIY Audio and dive in and wade through all of the 400 plus pages of posts:smash: that have been made by this wonderful bunch of people. It should be turned into a book :yes: .

Mark

P.S. guys... please hurry and post those 5 pages... I hinted that it was 400 plus pages long :yikes:!!!!
 
#3,946
Mark A. Gulbrandsen said:
P.S. guys... please hurry and post those 5 pages... I hinted that it was 400 plus pages long :yikes:!!!!
Click to expand...

I'll try to contribute 😎

Thats great news Mark, thanks for all your efforts!

Troy - What do you need to finalize the parts order?

I think the conversation last drifted off into alternatives for the out of stock or unobtainable quantity Dale resistors. So for everyone getting in on the parts GB lets get this straightened out.


~Brad
 
#3,948
still4given said:
Would the amp run any cooler if I use more outputs per channel?
Click to expand...

The temperature of the amplifier is determined by the heatsink alone.
Without forced cooling the static cooling factor of the heatsink needs to be at least twice as high for the same temperature level.
On top of that there is no reversed linearity between size and thermal resistance of a heatsink : a heatsink twice as big handles less than twice the number of watts for the same temperature.

And then there is economics :
a combination of a number of output devices and a specific type of heatsink results in a number of dissipation watts per invested dollar. There's an optimum number of output devices for a heatsink that has the lowest price tag for each watt of heat the combo is able to handle. Putting more output devices on the sink adds more dollars than the increase of heat capability is worth.

imo, for a 6 pair output stage, select the output devices on Vbe and Hfe and use base resistors, Terry.
 
#3,951
still4given said:
I just saw this on ebay. Nice

Blessings, Terry
Click to expand...


Very nice, but I think it is more fun "rolling your own"...

As for the GB on parts, we still do not have sources for all of them and I do NOT have time to research them now. I listed the parts that were MIA from Mouser, if we find a new source that has all, or one additional source that has what Mouser can't supply...

Anyone can find the parts, and get a price for 50 kits. Then we can add the 3% paypal, the shipping, and a few cents per order for envelopes and waa la the kit price. I will then collect the money, order the parts, kit out the parts and mail.
 
#3,952
Hi Andrew,

No, no, no, I'm not bidding on that. I just thought those who follow this thread would enjoy seeing it. I agree with Troy. It's more fun to roll your own. Cheaper too.

The temperature of the amplifier is determined by the heatsink alone.
Without forced cooling the static cooling factor of the heatsink needs to be at least twice as high for the same temperature level.
On top of that there is no reversed linearity between size and thermal resistance of a heatsink : a heatsink twice as big handles less than twice the number of watts for the same temperature.

And then there is economics :
a combination of a number of output devices and a specific type of heatsink results in a number of dissipation watts per invested dollar. There's an optimum number of output devices for a heatsink that has the lowest price tag for each watt of heat the combo is able to handle. Putting more output devices on the sink adds more dollars than the increase of heat capability is worth.

imo, for a 6 pair output stage, select the output devices on Vbe and Hfe and use base resistors, Terry.
Click to expand...

Hi jacco,

Here's where I'm at. I have gobs of transistors. At least 20 each of MJL4281/4203 as well as 20 each MJL3281/1302 and even 20 each of MJL21193/21194, so cost per device is not a worry for me right now. I am more concerned about the heatsinks I would like to use. They measure 8" x 12" x 1 3/4" with 5/16" thick back plate and 18 fins. Do I understand that while more devices lower the current per device that there’s still the same amount of heat to be dissipated? I wanted to not use a fan if possible after the hassle I’m having with the one I just used. It is making so much noise. I could mount them face to face and put some fans on them but I would rather not. It would make a huge tunnel that would make the case larger than I would like.

Also, my meter measures Hfe but how do you measure for Vbe?

By the way, I am really enjoying the way this Krell sounds now that I've got the right caps in there. Just lovely. Now if I can just find a quiet fan that can live in there.

Now one answered my question about the fan in the original Krell. Did it draw air in from the bottom and exhaust into the case or did it exhaust out the bottom?

Thanks, Terry
 
#3,953
still4given said:
Now one answered my question about the fan in the original Krell. Did it draw air in from the bottom and exhaust into the case or did it exhaust out the bottom?

Thanks, Terry
Click to expand...


I'm pretty sure the fan would not blow down. It was most likely designed so that convection will still occur should the fan fail.
 
#3,954
The KSA-100 Mk.II I had (same as the ksa-50 but twice of everything) sucked air from the bottom and pushed it up into the case via the heatsink. The case was ventilated well enough that you could feel a quiet draft 4 feet above the case. The fan was rather quiet.
 
#3,955
still4given said:
Do I understand that while more devices lower the current per device that there’s still the same amount of heat to be dissipated?
Did it draw air in from the bottom and exhaust into the case or did it exhaust out the bottom?
Click to expand...

1st question : correct.
2nd question:
the fans on the Krell sucked air through the duct and blew it out on the top.
A: i know
B: you can see it on the pictures of the Krell, the Papst on the Krell blows in the direction of the label
2 reasons:
fans are better at that than blowing air through a heatsink because of pressure differences.
hot air goes up by itself, pushing it down means lower efficiency.
 
#3,957
jacco vermeulen said:


the fans on the Krell sucked air through the duct and blew it out on the top.
A: i know
B: you can see it on the pictures of the Krell, the Papst on the Krell blows in the direction of the label
2 reasons:
fans are better at that than blowing air through a heatsink because of pressure differences.
hot air goes up by itself, pushing it down means lower efficiency.
Click to expand...


The pictures of the Krells I've seen seem to show the fan at the bottom of of the tunnel. Are you saying that the fan is drawing the air down through the tunnel or blowing it up through the tunnel? Your wording is confusing to me.
 
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