If you can make good contact, then a 17" wide by 7" high with 3.5" fins that look thick enough combined with a back plate that is 0.5" thick or more, will be able to dissipate a lot of heat.
Or sell them to an Alaskan.
Or sell them to an Alaskan.
Considering air cooled versions since I have always done fan cooling of these.
The big black sink is 14"x 3"x 9" and 1/2" thick and the gold one is 9"x6"x6" with much thinner mating surface in comparison.
What concerns me is the amount of time the thicker one will take to get up to temp and if any stresses occur during that cycle?
I think Bedini mentioned this at one time and for this reason uses thin stampings for heat sinks instead?
The monos shown have a fan in the bottom and blow into a plenum that forces air up thru the bottom area of the sinks. The fan is used just above the turn on voltage to keep it as quite as possible.
Would that be true or no concern?
Regards
David
The big black sink is 14"x 3"x 9" and 1/2" thick and the gold one is 9"x6"x6" with much thinner mating surface in comparison.
What concerns me is the amount of time the thicker one will take to get up to temp and if any stresses occur during that cycle?
I think Bedini mentioned this at one time and for this reason uses thin stampings for heat sinks instead?
The monos shown have a fan in the bottom and blow into a plenum that forces air up thru the bottom area of the sinks. The fan is used just above the turn on voltage to keep it as quite as possible.
Would that be true or no concern?
Regards
David
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Question - what would be the first component to fail on the KSA-50 when really pushed hard? Like on a pair of 1 ohm Scintillas? Output devices (I have 3 pair of output devices per side) The power supply?
I have a pair of 1 ohm Scinnies that I have had no issues driving with my Pinkmouse KSA-50, but I did not drive them hard, and not for very long (an hour?). Anyway, is this not recommended?
Being Class A, its driving hard all the time, so the Scinnies may not be a big deal... I would think the amp would not get as hot as it as taking more of that power to the Scintillas?
I had a little Accident with my Scinnies and will be doing a repair soon to do my own test.......
I have a pair of 1 ohm Scinnies that I have had no issues driving with my Pinkmouse KSA-50, but I did not drive them hard, and not for very long (an hour?). Anyway, is this not recommended?
Being Class A, its driving hard all the time, so the Scinnies may not be a big deal... I would think the amp would not get as hot as it as taking more of that power to the Scintillas?
I had a little Accident with my Scinnies and will be doing a repair soon to do my own test.......
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I would think that driving nothing would stress them more than driving 1 ohm, since they are Class A all the power is going to the load instead of the heat sinks so long as you are driving a real speaker. Having nothing connected makes the heatsinks dissipate all the watts, which is the worst case. Mine run cooler when playing louder.
It is not strictly accurate to say the amps will not dissipate additional heat or possibly be damaged by a 1ohm load. You are well out of the class A envelope, and as such the current and total power being dropped into the load, output transistors and the heatsink is going to be considerably higher. Depending on the capacity of your transformer(s) you may be able to get the output transistors into trouble, and the drivers will be working hard too.
The quality of all the components in the "supply" path will be tested. In all the accidents my build suffered, nothing in the amp schematic failed, but one of the supply CL30 thermistors de-soldered itself, self limiting in that regard, but obviously if this happened unnoticed, a fire could result...
I've driven my Duettas to clipping and beyond with no ill effects, but they are not 1 ohm loads ;-)
As an owner of Apogee speakers, and with absurd loads in mind, I sized my transformer so it could not trivially supply enough overall power or current to get the output stage (6 pairs of the plastic transistors) into destruction territory, then selected slo-blo fuses that would save my bacon if something catastrophic occurred.
In essence if you have 2kva transformers and an output stage which can only handle half that power, there will be problems under some conditions, and you will pop your house breakers on a regular basis ;-)
Krell seem to have chosen transformers in direct proportion the size of the output stages they used, IIUC the original KSA50 had 400VA for two channels, 2 pairs of TO3 transistors per channel. The KSA100 doubled the transistors, heatsinks and the power supply size, so it seems likely they would not trivially destroy the outputs.
Stuart
The quality of all the components in the "supply" path will be tested. In all the accidents my build suffered, nothing in the amp schematic failed, but one of the supply CL30 thermistors de-soldered itself, self limiting in that regard, but obviously if this happened unnoticed, a fire could result...
I've driven my Duettas to clipping and beyond with no ill effects, but they are not 1 ohm loads ;-)
As an owner of Apogee speakers, and with absurd loads in mind, I sized my transformer so it could not trivially supply enough overall power or current to get the output stage (6 pairs of the plastic transistors) into destruction territory, then selected slo-blo fuses that would save my bacon if something catastrophic occurred.
In essence if you have 2kva transformers and an output stage which can only handle half that power, there will be problems under some conditions, and you will pop your house breakers on a regular basis ;-)
Krell seem to have chosen transformers in direct proportion the size of the output stages they used, IIUC the original KSA50 had 400VA for two channels, 2 pairs of TO3 transistors per channel. The KSA100 doubled the transistors, heatsinks and the power supply size, so it seems likely they would not trivially destroy the outputs.
Stuart
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I have finished my KSA clone
I did it according to the KSA50 schematic but i think it is working under 50w, i supply it with +/-35v dc (2x27v ac 500w transformer) and biased at 1.1A because of the heatsink, in the supply there are 8pcs of 22000uf BHC capacitor.In this mode it must be like 35-40w and up to 25w class a. The heatsink measured at 57deg/C, i think it is in safe mod.
I like the sound of the KSA50, it has very very natural sound and quite good bass performance.Also i drive it with solid state and tube preamplififer but i like it neat (some extra coloration comes with the preamlifier and i dont like it).
It gave me a good excercise and idea in the way how doing KSA100, I have already started to design my KSA100 clone, i think it took some time like a year but i'm sur it will be fun.
Thanks to all DIY Audio members
I did it according to the KSA50 schematic but i think it is working under 50w, i supply it with +/-35v dc (2x27v ac 500w transformer) and biased at 1.1A because of the heatsink, in the supply there are 8pcs of 22000uf BHC capacitor.In this mode it must be like 35-40w and up to 25w class a. The heatsink measured at 57deg/C, i think it is in safe mod.
I like the sound of the KSA50, it has very very natural sound and quite good bass performance.Also i drive it with solid state and tube preamplififer but i like it neat (some extra coloration comes with the preamlifier and i dont like it).
It gave me a good excercise and idea in the way how doing KSA100, I have already started to design my KSA100 clone, i think it took some time like a year but i'm sur it will be fun.
Thanks to all DIY Audio members
Attachments
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hi friends, what you think of these cards refer to the pre-assembled KSA50
Free Shipping! 1pcs KSA50 Class A power amplifier finished board integrated speaker protection-in Other Electronic Components from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
Free Shipping! 1pcs KSA50 Class A power amplifier finished board integrated speaker protection-in Other Electronic Components from Electronic Components & Supplies on Aliexpress.com | Alibaba Group
Asian product and possible fake transistors to go with it
A blank PCB and a schematic first to be sure it's good would be the only way I would touch it.
Regards
David
A blank PCB and a schematic first to be sure it's good would be the only way I would touch it.
Regards
David
If you are planning to run it in class A I would be concerned about the heat on the board. With the outputs soldered to the bottom of the PCB it will be very close to the heatsink. These heatsinks run really hot.
Yes, you need +/- 45 to 48 volts for KSA-50. There must be some one that has boards that never built theirs. We sent out a ton of those boards about 8 years ago. Have you tried a WTB ad in this forum?
BTW: I just rebuilt one of the very first KSA-50 prototypes that a friend has a Few weeks ago. It is all open chassis and somehow got covered in some greasy stuff. I ran some it including the circuit boards in the dishwasher, the rest I cleaned by hand. Bias and balance didn't even need tweaking! But now it looks like new again and is still running perfect.
Mark
BTW: I just rebuilt one of the very first KSA-50 prototypes that a friend has a Few weeks ago. It is all open chassis and somehow got covered in some greasy stuff. I ran some it including the circuit boards in the dishwasher, the rest I cleaned by hand. Bias and balance didn't even need tweaking! But now it looks like new again and is still running perfect.
Mark
@Mark...
WHAT???? You put circuit boards in a dishwasher? That is ballsy dude.. I would have been way to scared to do that fearing the destruction of the components..
WHAT???? You put circuit boards in a dishwasher? That is ballsy dude.. I would have been way to scared to do that fearing the destruction of the components..
You know most manufacturers wash circuit boards after soldering to remove the flux? And yes, water is the preferred solvent for washing...
but is there anyone on this forum who has used the cards that I showed earlier (Wholesale Product Snapshot Product name is Free Shipping! 1pcs KSA50 Class A power amplifier finished board integrated speaker protection),,, watching them closely seem well made with quality components and a layout of the PCB tracks with interesting power oversized gold,, is integrated also the protection circuit board; considering a good wiring in a suitable chassis dissipating, what do you think of these boards pre-assembled and pre-calibrated with a cost of about $ 190;
Another question on the power supply circuit,, according to your opinion a classic CRC consists 47000uF / 0.15 ohm / 47000uF (by branch) with + / 0 / - 50VDC, can be high performance?
Thanks to all and greetings
Another question on the power supply circuit,, according to your opinion a classic CRC consists 47000uF / 0.15 ohm / 47000uF (by branch) with + / 0 / - 50VDC, can be high performance?
Thanks to all and greetings
hey guys,thanks in advance for this awesome thread
i want to build 8 chanels of this clone.
i got los about the output stages how much i will have to build for each channel and also how they should be wired to the main board.
also if you can attach the final pcb layout schematic etc please.
for the power supply im considering 10000uf caps
and Avel Y236852 625VA 35V+35V Toroidal Transformer according to me this shoul drive 2 chnnels perfectly correct me if im wrong
regards
i want to build 8 chanels of this clone.
i got los about the output stages how much i will have to build for each channel and also how they should be wired to the main board.
also if you can attach the final pcb layout schematic etc please.
for the power supply im considering 10000uf caps
and Avel Y236852 625VA 35V+35V Toroidal Transformer according to me this shoul drive 2 chnnels perfectly correct me if im wrong
regards