You mean 2SC and 2SA don't you Terry? Mostvof us used Motorola MJ150XX devices which are easy to get and cheap. I will post the numbers here later.
Mark
Mark
Those will work also. Mouser carries the ksa/ksc versions and they are genuine Fairchild parts.
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The devices I always used in KSA-50 and KSA-100 are MJE15034 and MJE 15035. G suffix. These are 350 volt 4 amp devices in TO-220 package.
Mark
Mark
Mouser has both KSA992 and KSC1845 in T0-92. Mark, where do you find MJE15034-35 G these days?
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Alibear - gorgeous amp man! Please install a perspex cover instead of metal so the inside can be seen 😀
i tested the amp at +- 30vdc wit my lab power supply which can deliver 5a per rail the amp was dawning around 2a per rail is this ok?
First, the original RE value was .68 ohm and you changed it to .22 ohm guessing you have very well matched output transistors at this value, correct?
Check eack Re value and give us a ratio difference for each channel
A 15% difference is acceptable for example
Check eack Re value and give us a ratio difference for each channel
A 15% difference is acceptable for example
ooo i see,i just followed jan scematic with .22, so.68 will make it easier right?
Regardless of the boards used, research current hogging for a better understanding as you lower the resistance values
K-Amps wrote a Class A calculator spreadsheet for this project that is likely somewhere in the first 200 pages of this thread. It works really well! You might also try contacting him to see if he still has it. Tells you class A power out based on rails, number of devices and emitter resisters. Very handy indeed!
Mark
Mark
Post # 8713 wiki shows what most builders were using (499-.68 values)
Play it safe if not sure
Regards David
Play it safe if not sure
Regards David
Except there were a couple of errors in the spreadsheet.
I think one was corrected after I prompted, but I seem to remember that the final version still had an error.
The spreadsheet formulae need to be checked again.
Humm.... its worked fine for all the KSA-50's that I have built. All of them beat factory specs by a long shot and still are in use after all these years.
Mark
Mark
Guys i have a proposal if sll of you agree, ive simulated the original ksa50 in multisim, also jan scematic.
If you agree we can work on a board that uses all the oriiginal vslues and components, also it would be nice if we work on the speardsheet and a kind of building tutorial, video of boards assembly and setup.
I can share the simulation and work on the board
Thanks a ton mark, someone shared me the shert before, according to the sheet i got biased the amp but heat is massive and my heatsinks are huge arround 2.5kg of aluminum each were for industrial use
Yes, well... the heat IS going to be massive! If you think that's bad build the KSA-100! You really have to use forced air cooling on these amps at the minimum. When I biased my amps I used a combination of both the spread sheet and my Sound Technology distortion analyzer to set bias. The distortion correlated petty closely with factory specs at the specified bias on the spread sheet. So I'm still out as to what, if any, mistake there is in the spread sheet itself.
These are true Class A amplifiers unlike the Aleph which has a current mirror to increase efficiency to nearly 50%. I never did any calculations but I'd bet KSA-50 efficiency is down about 20% give or take. Krell even went to a sliding bias scheme in their later amps so they could control the heat and do away with the forced air fans.
Also, we did not follow the original part for part because the addition of two extra outputs has its advantages. It increases reliability becasue it spreads out dissipation better, allows higher power out and into even lower impedance's than the original KSA-50. I compared mine to an original KSA and mine had better bottom end. I also have a 1.2 KVA dual secondary toroid vs. the whimpy toroids Krell used.
Attached is a picture of my daily use KSA-50 that is well over ten years old. Its built on a salvaged AB Systems power amplifier and the heat sinks are relatively small. There are two 4" 120 volt ball bearing fans running at 60 volts in the box at the rear pulling air in from the front and exhausting it out the rear. The fans are only audible if you are right next to the amp. I lubricated both fans bearings with synthetic oil and that quieted them down considerably.
You might also ask Pinkmouse if he'd want to make more boards. He did the design of these boards and wold still have the Gerbers. I still have a number of them left here for future builds. They are very nice boards.
Interestingly I ran into Dan D'Augustino's son on some forums about two years ago and told him about the KSA-50 & 100 Klones we did and he was amazed.
BTW: I have built eight KSA-50's since this thread began and not a one of them has ever so much as hickuped. Its an uber stable long life amp.
Mark
These are true Class A amplifiers unlike the Aleph which has a current mirror to increase efficiency to nearly 50%. I never did any calculations but I'd bet KSA-50 efficiency is down about 20% give or take. Krell even went to a sliding bias scheme in their later amps so they could control the heat and do away with the forced air fans.
Also, we did not follow the original part for part because the addition of two extra outputs has its advantages. It increases reliability becasue it spreads out dissipation better, allows higher power out and into even lower impedance's than the original KSA-50. I compared mine to an original KSA and mine had better bottom end. I also have a 1.2 KVA dual secondary toroid vs. the whimpy toroids Krell used.
Attached is a picture of my daily use KSA-50 that is well over ten years old. Its built on a salvaged AB Systems power amplifier and the heat sinks are relatively small. There are two 4" 120 volt ball bearing fans running at 60 volts in the box at the rear pulling air in from the front and exhausting it out the rear. The fans are only audible if you are right next to the amp. I lubricated both fans bearings with synthetic oil and that quieted them down considerably.
You might also ask Pinkmouse if he'd want to make more boards. He did the design of these boards and wold still have the Gerbers. I still have a number of them left here for future builds. They are very nice boards.
Interestingly I ran into Dan D'Augustino's son on some forums about two years ago and told him about the KSA-50 & 100 Klones we did and he was amazed.
BTW: I have built eight KSA-50's since this thread began and not a one of them has ever so much as hickuped. Its an uber stable long life amp.
Mark
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Transfo and bleeders
I do have Pinkmouse KSA-50 boards and will build this winter. I am out fishing or working on high performance cars.
Mark. May I ask what are your transformer voltage and volt amperage are and what is your Ohm/wattage size of the bleeders on the can capacitors and what capacitance are they? I did build a KSA-100 with 40V/1000VA per channel and they are still running without a hiccup also and mostly never over 41C in temp (120V fans). I rarely bias over .380mA as it really doesn't affect sound and keep temps down. As it is, I can't go over 1/3 of volume control for fear it will blow out my windows but I do need to front the amp with a preamp so it will enhance the lower frequencies (big difference). I just finished diyaudio's Mezmerize B-1 buffer to see which is better, increasing current with the B-1 or voltage with a preamp, to perk up the low frequencies.
I do have Pinkmouse KSA-50 boards and will build this winter. I am out fishing or working on high performance cars.