I found this ebay ksa50 clone, I built several amplifiers but this is the first time I seen one that needs 2 voltages. Can anyone explain this? The seller doesnt seem to helpful.
150W Class A KSA50 MONO amplifier board | eBay
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150W Class A KSA50 MONO amplifier board | eBay
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It's quite likely that the input/driver stages require a higher power-supply voltage level in order to allow the input/driver stages to drive the output stages rail-to-rail. See the Nelson Pass A75 design (http://passdiy.com/pdf/a75p1.pdf and http://passdiy.com/pdf/a75p2.pdf), which has a similar requirement for the power-supply design.
If this was a MOSFET output and not a lateral FET output, the higher voltage for the input and driver stage(s) makes sense. But the outputs are bipolar transistors. I guess they want the amp to clip in the output stage with an extra 20 volts (p-p) of headroom for the driver/input stage.
2 oz platinum???
I don't see a bias or offset pot. How is that so??
2 oz platinum???
I don't see a bias or offset pot. How is that so??
A KSA50 at 150 watts?
Did the Original KSA50 go into class AB?
Original output devices were a pair of MJ15003 and MJ15004
I think it is a low bias Class AB KSA50...should still sound nice...
Price is awesome, but can't help but think the transistors could be fake at that price...
I have a KSA50 with a trio of the 2SC5200/2SA1943 and it is my favorite amp by far.
Did the Original KSA50 go into class AB?
Original output devices were a pair of MJ15003 and MJ15004
I think it is a low bias Class AB KSA50...should still sound nice...
Price is awesome, but can't help but think the transistors could be fake at that price...
I have a KSA50 with a trio of the 2SC5200/2SA1943 and it is my favorite amp by far.
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I just built an amp built around two of these
I know, very old thread.
I have just finished connecting two of these and after much time on Google am starting to get somewhere.
I have a very large heat sink, am running +/- 40V to the output stage and +/- 50V to the input stage and have been creeping the quiescent current up. Currently at .5 A per for each output device (8).
One bit that none of the Chinese sellers mention is that the bias transistor needs removed from the board and mounted to the main heat sink.
I see that since I bought these boards that the many sellers are now recommending a 15v spread between input and output stages. I would imagine that that would be a better balance to push the output closer to its max pre-clipping.
Anyway, they are cheap for what you get. I'm not sure if the outputs are fake but they have yet to blow and sound nice.
I have two newbie questions:
1. Although these are symmetrical designed amps with 2 sets of output devices per channel, i cannot get each transistor to match in quiescent current. I have .22 ohm emitter resistors and a voltage drop of .11V so a current of about .5A. The voltage ranges from .08 to .13 depending on which transistor I check. Is that a sign of fake transistors or just standard without using a component matching process?
2. Is there a sweet spot for this type of design with the Toshiba outputs (1943 / 5200) with regards to quiescent current and trying to bais to class A as much as possible?
3. Am I calculating class A power correctly here?
.5 amp * 2 (NPN ans PNP) = 1 AMP per pair peak to peak.
p= I*E so 1A * 38V = 38 Watts??
I am assuming that having multiple pairs of transistors does not increase output if they are not in series (aka Darlington) so I assume that the main reason for multiple pairs is to split the workload and heat dissipation?
Finally, this is a new hobby of mine so please keep this in mind when pondering my questions.
Thanks
I know, very old thread.
I have just finished connecting two of these and after much time on Google am starting to get somewhere.
I have a very large heat sink, am running +/- 40V to the output stage and +/- 50V to the input stage and have been creeping the quiescent current up. Currently at .5 A per for each output device (8).
One bit that none of the Chinese sellers mention is that the bias transistor needs removed from the board and mounted to the main heat sink.
I see that since I bought these boards that the many sellers are now recommending a 15v spread between input and output stages. I would imagine that that would be a better balance to push the output closer to its max pre-clipping.
Anyway, they are cheap for what you get. I'm not sure if the outputs are fake but they have yet to blow and sound nice.
I have two newbie questions:
1. Although these are symmetrical designed amps with 2 sets of output devices per channel, i cannot get each transistor to match in quiescent current. I have .22 ohm emitter resistors and a voltage drop of .11V so a current of about .5A. The voltage ranges from .08 to .13 depending on which transistor I check. Is that a sign of fake transistors or just standard without using a component matching process?
2. Is there a sweet spot for this type of design with the Toshiba outputs (1943 / 5200) with regards to quiescent current and trying to bais to class A as much as possible?
3. Am I calculating class A power correctly here?
.5 amp * 2 (NPN ans PNP) = 1 AMP per pair peak to peak.
p= I*E so 1A * 38V = 38 Watts??
I am assuming that having multiple pairs of transistors does not increase output if they are not in series (aka Darlington) so I assume that the main reason for multiple pairs is to split the workload and heat dissipation?
Finally, this is a new hobby of mine so please keep this in mind when pondering my questions.
Thanks
A combination of variation in transistors and variation in emitter resistors. The emitter resistors are most probably 5% tolerance parts. I would see how it goes, if they are fakes it will probably blow up once pushed a bit.
Make sure you have a DC protection for your speakers!
Multiple pairs increases output by increasing current capability, which in turn spreads the dissipation of load as you say. In series would simply add losses.
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Thanks!
Are my calculations correct regarding class A wattage then or do I add the pairs together as you suggested?
If you don't mind, and I'm sure it has been covered before but I can only allow for so much "hobby time" during a work day
how would I go about calculating class A wattage with this set up?
Two pairs of 2Sc5200 / 2SC1943 each at .5 amps with 38V rails (under load) and with 8 ohm speakers.
My output power supply board has the rectifier and 6 15000 uf 80V capacitors to smooth the AC (big toroidal pulled from Arcam AVR 250) but also has circuits for speaker protection. Just waiting for my upc1237 chip that's in the mail.
Are my calculations correct regarding class A wattage then or do I add the pairs together as you suggested?
If you don't mind, and I'm sure it has been covered before but I can only allow for so much "hobby time" during a work day
how would I go about calculating class A wattage with this set up?Two pairs of 2Sc5200 / 2SC1943 each at .5 amps with 38V rails (under load) and with 8 ohm speakers.
My output power supply board has the rectifier and 6 15000 uf 80V capacitors to smooth the AC (big toroidal pulled from Arcam AVR 250) but also has circuits for speaker protection. Just waiting for my upc1237 chip that's in the mail.
mine was using 35VDC both driver and finals w/ 2A bias over 0.15Ohm emittor resistor.
make sure you didnt get dc offset at the output.
mine using 1 pair MJL3281/1302 and have no problem on the bias.both pnp and npn biased the same .from my studies, this bias difference also caused by dc offset
also try to use lower tolerance emitter resistors.they would makes the measurement more accurate
make sure you didnt get dc offset at the output.
mine using 1 pair MJL3281/1302 and have no problem on the bias.both pnp and npn biased the same
.from my studies, this bias difference also caused by dc offset also try to use lower tolerance emitter resistors.they would makes the measurement more accurate
I think it's a bit more.
The supply is +/- 40V @ 1 A idle current. So idle power is 2x40W = 80W
At a Class A power of just 4 Watts: a lot of heat..
@dihmels : have you already listened to the amp? How does it sound?
It sounds nice. I am comparing it to an Arcam A75 and P75 into Spendor S5Es. It sounds much more effortless at low volumes than the Arcam output stage. But the gain is not great and I see that the board suppliers are now suggesting 15v more for the input stage from the original 10v differential (+45 and +60)
The supply is +/- 40V @ 1 A idle current. So idle power is 2x40W = 80W
At a Class A power of just 4 Watts: a lot of heat..
You are correct. Both upper and lower halves dissipate 40W each.
And I agree on the waste
No, I had accounted for two pairs. The 0.5 amp flows in each pair so 1 amp total.
Having said that, I have seen some claims that a push-pull output stage can deliver double power still class-a. But I'm not sure about that. I only see it as being able to reach a higher max power for a given set of rails.
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I see I've omitted the Idle-current calculation for the KSA-50 (50W class A in 8 Ohms) specification: 3.54 Amps !At a Class A power of just 4 Watts: a lot of heat..
So each channel requires some 285 Watts of energy
Indeed, I would settle for a lesser setting: 1.5 a 2 Amps max. (only if the heatsinks can handle this
)Each channel would require a 500VA tranny (and a soft-start)
I can't imagine achieving that much idle current even if my power supply could handle it. I'm not sure of the va of the toroidal but it's quite large, about 5 by 5 inches, more of a big marshmallow shape than a doughnut. So if I'm fussing this much for 4watts I would rather move from class A to the best class AB possible. Any suggestions?
0.5A bias pr device and 2 pairs in push-pull configuration is 16Wrms at 8ohm.
peak class A current is twice the bias. so 2A peak.
2*0.707=1.414A rms
1.414*1.414*8ohm = 15.99Wrms at 8ohm.
so 80W dissipation is nothing to whine about. besides. the high dissipation is do to the higher power class A/B. you can drop the rails to +/-20V or so. and have 40W dissipation and still 16W class A at 8ohm.
peak class A current is twice the bias. so 2A peak.
2*0.707=1.414A rms
1.414*1.414*8ohm = 15.99Wrms at 8ohm.
so 80W dissipation is nothing to whine about. besides. the high dissipation is do to the higher power class A/B. you can drop the rails to +/-20V or so. and have 40W dissipation and still 16W class A at 8ohm.
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