I picked up a pair of ksa50/ksa100mk2 boards off ebay from Jim's audio in hopes of building a ksa50mk2. In reading a few of the very long threads on this amplifier, I think I'm more confused as to which schematic jim's audio is following. Is this his own rendition? There seems to be many variations of this circuit, his seems to use mosfets before the drivers. To the people who have used his boards, did you build it exactly to his BOM?
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@MEGA-amp: Jim's audio use exactly the same circuit as original ksa50/100mk2. There was several variations in production since 1980 to 1987 when production stops. The first versions of ksa50/100 were without mosfets, later version use them. Don't worry, amp works perfectly.
Btw., some of the components are obsolete so you have to find substitutions for them. Read this thread carfully and you will find all the answers
@Michael: this looks much better
Btw., some of the components are obsolete so you have to find substitutions for them. Read this thread carfully and you will find all the answers
@Michael: this looks much better
I see. I've found this: 1N5309 - AMERICAN POWER DEVICES - CURRENT REGULATOR DIODE, 600mW | Newark. A bit pricey, any cheaper alternatives?
In Jims BOM, his alternative is to replace D5/6 with 33R, and there are two positions to install LM334 adjustable current source. My thinking is that the LM334 would provide a less noisy regulation than using the crd option. I'm trying to get as close to original as possible, but if the crd option provides better performace, i'm all for it.
Hi all, I am building a version of the KSA50 clone using Jans boards as described in the thread started by Bra in March 2004. Although the amplifier is still not completed in it's final form I have had it running for quite some time. I am interested in the PCB that is available from Jim's Audio for the KSA50 / 100 Mk2 but I do not know the differences to the boards I am using already. Has anyone a circuit of Jims board that they could post, so I could compare. Any views as to which is best board to use for my final version of this amp.
many thanks
Alan
many thanks
Alan
I found these fan type heatsinks on ebay although they seem to be a little too small lengthwise? ebay's starting bid is $99.00.
Aluminum Transistor Heat Sink Assembly | eBay The fans they use are Mouser Part #: 433-BP1202524H which are 120mm x 25mm x 120mm.
Aluminum Transistor Heat Sink Assembly | eBay The fans they use are Mouser Part #: 433-BP1202524H which are 120mm x 25mm x 120mm.
Thanks necdetyetisgen! :-D Maybe I will buy them too. I really like them.
Thanks Jozua and Dean!! :-D I will consider adding a base. Hope I can find the metals over here.
Hi David!
I would say they are indeed a bit too small to cope with the large amounth of heat generated by the KSA. I would say you will need at least 120 X 120 X 110 (=4.3 inch lenght) mm per channel, but I think even that is too small, unless you want to 1) dial bias down or 2) run the fans at full RPM. You will need a lot of metal for sufficient cooling. You could stack two of them onto each other per channel. I would also recommend 120 x 120 x 38 mm fans. They have larger blades and are capable of generating more static pressure (higher static air pressure is favorable since you need to push a lot of air through the tunnel coolers), so they can run more silent. You can also, with a fan adapter (120 mm to 140 mm), use 140 mm2 fans, like I do. They can run even more silent, while maintaining the same air flow. I am currently using tunnel coolers that are 120 X 120 X 150 mm. Have not tried them yet. I am overhauling my Audio Analyse A9 at the moment. But I will post some updates soon! Hope the new config will do.
Thanks Jozua and Dean!! :-D I will consider adding a base. Hope I can find the metals over here.
Hi David!
I would say they are indeed a bit too small to cope with the large amounth of heat generated by the KSA. I would say you will need at least 120 X 120 X 110 (=4.3 inch lenght) mm per channel, but I think even that is too small, unless you want to 1) dial bias down or 2) run the fans at full RPM. You will need a lot of metal for sufficient cooling. You could stack two of them onto each other per channel. I would also recommend 120 x 120 x 38 mm fans. They have larger blades and are capable of generating more static pressure (higher static air pressure is favorable since you need to push a lot of air through the tunnel coolers), so they can run more silent. You can also, with a fan adapter (120 mm to 140 mm), use 140 mm2 fans, like I do. They can run even more silent, while maintaining the same air flow. I am currently using tunnel coolers that are 120 X 120 X 150 mm. Have not tried them yet. I am overhauling my Audio Analyse A9 at the moment. But I will post some updates soon
! Hope the new config will do.
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I hope you are not referring to the tunnel coolers on Ebay Andrew. If so... good luck with keeping this beast beneath 55 degrees C using the tunnel coolers from Ebay going fully biassed ;-). In the old thread one can find that Fix used tunnel coolers that were even a bit larger and thicker. But even Fix experienced cooling problems. I faced the same problems (using even larger tunnels), but my configuration was not optimal. So that is maybe not representative.
Anyway the one on eBay is a poor copy of a proper tunnel cooler David. A waste of (a lot of) money if you would ask me. If you want to use tunnel coolers, you can contact Seifert in Germany. They offer very nice tunnel coolers, that are far more usable. But I am afraid shipping to the USA will be expensive :-(. See:
http://q04.digtion.de/qanportal/Uploads/seifert_punkte/pdfs/25[0].pdf
By the way, David, why not using the heatsinks from Adcom? They seem larger than the ones pointed out on Ebay, and would probaly do better. Just give it a try.
Anyway the one on eBay is a poor copy of a proper tunnel cooler David. A waste of (a lot of) money if you would ask me. If you want to use tunnel coolers, you can contact Seifert in Germany. They offer very nice tunnel coolers, that are far more usable. But I am afraid shipping to the USA will be expensive :-(. See:
http://q04.digtion.de/qanportal/Uploads/seifert_punkte/pdfs/25[0].pdf
By the way, David, why not using the heatsinks from Adcom? They seem larger than the ones pointed out on Ebay, and would probaly do better. Just give it a try
.
Ai Andrew, I would say that is a bad advice (no offence). I honestly think those are not capable to offer enough cooling capacity. Even when running the fans at full speed. The internal aluminum blades from the ones on eBay are realy thin, from what I can see in the protograph. Let alone the length which is rather small.
For example, I am working at this amplifier right now:
An externally hosted image should be here but it was not working when we last tested it.
It is an commercial class A amplifier (Audio Analyse A9). The designers choose to bias it at 30W class A (@ 8ohm). Not without a reason, it gets pretty hot (about 40 degrees Celsius). Although it is cooled passively, the heatsinks give a good impression about the amounth of cooling needed (realy, this amp is huge). Offcourse, every man needs to make his own decisions, but in al honesty, and from my 'experience' I would say buying these heatsinks would result in dissapointment.
Whise choise David. Indeed they seem huge
I am very curious to your build. Please keep us informed!
Hi Spurite, thanks for your reply in the other Krell thread.
I have seen the boards from JIMS audio and also asked on this thread about their performance and how the finished amplifiers sound.I would really like to know builders opinions on finished articles.
The reason I enquired about P Watts boards was that an awful lot were built with mostly good results.
Any information would be great fully recieved.
Thanks
Alan.
I have seen the boards from JIMS audio and also asked on this thread about their performance and how the finished amplifiers sound.I would really like to know builders opinions on finished articles.
The reason I enquired about P Watts boards was that an awful lot were built with mostly good results.
Any information would be great fully recieved.
Thanks
Alan.
Nice Boards
I just cut the holes in my base board for the cooling fan system. The Jim's Audio had a few problems that was covered in this thread, thanks to Kaplaars's hawk eyes, such as a few misprints and one open route that was corrected with a very small jumper. Then there is caution about connecting the MJE15s's heat shinks to the soldering rings/connections. There isn't too many completed Jim's Audio mainly, I would suspect, is the cost of this project and some hard to find transistors. But I have heard nothing but praise for the BEAST. I read somewhere that Krell KSA 100 MKII can handle down to 1/2ohm speakers. I believe they went for $24,000 at the time. I am not an ardent audiophile, but do enjoy clean air pressure and can't wait to see what all this current (1000VA in transformers) will do for me in class A. So, yes these board are really the only one out there and they are strongly built and 70 bucks for the two setups, the price isn't bad either. Now here is something that should perk your ears up. Some of those guys who have build the KSA 100 much earlier are considering building the newer setup--I believe one of the original KSA 100 diyaudio member, FIX, had mentioned interest not to long ago.
Simplicity
That is about the most simply built amplifier I have ever seen but built like a Sherman Tank.Ai Andrew, I would say that is a bad advice (no offence). I honestly think those are not capable to offer enough cooling capacity. Even when running the fans at full speed. The internal aluminum blades from the ones on eBay are realy thin, from what I can see in the protograph. Let alone the length which is rather small.
For example, I am working at this amplifier right now:
.JPG)
It is an commercial class A amplifier (Audio Analyse A9). The designers choose to bias it at 30W class A (@ 8ohm). Not without a reason, it gets pretty hot (about 40 degrees Celsius). Although it is cooled passively, the heatsinks give a good impression about the amounth of cooling needed (realy, this amp is huge). Offcourse, every man needs to make his own decisions, but in al honesty, and from my 'experience' I would say buying these heatsinks would result in dissapointment.
Whise choise David. Indeed they seem huge
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