KSA 100 Mk2 Boards
Gentlemen
I think Pierre Watts needs to be congratulated for his excellent PCB layout. I have great confidence in this fellow South African expertise who lives a stone's throw from me.
I am convinced that this project is going to be a greater success than the KSA50 clone.
Apart from being a true audiophile he is also a serious home theatre enthusiast.
Jozua
Gentlemen
I think Pierre Watts needs to be congratulated for his excellent PCB layout. I have great confidence in this fellow South African expertise who lives a stone's throw from me.
I am convinced that this project is going to be a greater success than the KSA50 clone.
Apart from being a true audiophile he is also a serious home theatre enthusiast.
Jozua
Home theater is not my thing, yet.
But anyone who offers to do a PCB layout, especially without the intention of using it himself, i take my hat off for.
If the gent is a pro designer as well, i'll do the deepest Japanese bow i still manage.
I'll go along with the first two lines of Jozua's post, i have spare KSA50 boards but stage 3 looks even better.
Thanks, Pierre.
btw: what does the finishing stage of the kitchen table KSA50 look like ?
But anyone who offers to do a PCB layout, especially without the intention of using it himself, i take my hat off for.
If the gent is a pro designer as well, i'll do the deepest Japanese bow i still manage.
I'll go along with the first two lines of Jozua's post, i have spare KSA50 boards but stage 3 looks even better.
Thanks, Pierre.
btw: what does the finishing stage of the kitchen table KSA50 look like ?
Hi,
I went back to post11 for the mk2 schematic. Have I found the right one?
Is c7 the cap across the Vbe multiplier?
The bias current through the drivers is about 1.1v controlled by the 75r emitter resistors. Have I got the right values? This comes out at about 14mA?
Driver dissipation is about 51V * 14mA = 750mW not 3.3W.
Can someone confirm the numbers or the calculation?
I went back to post11 for the mk2 schematic. Have I found the right one?
Is c7 the cap across the Vbe multiplier?
The bias current through the drivers is about 1.1v controlled by the 75r emitter resistors. Have I got the right values? This comes out at about 14mA?
Driver dissipation is about 51V * 14mA = 750mW not 3.3W.
Can someone confirm the numbers or the calculation?
AndrewT,
Your calculating is right but you forget the milliamps for to drive 1.3Amps thru the CE in the output pair (a pair to each driver). If counting with worth Hfe value in output (ca 25) the driver (each of them) must also supply the output base with ca 52mA (0.052A). Total thru each driver is: 14+52mA=66mA
Total dissipation will then be of the order: 0.066x51V=3.37W(each driver)
hope this make sense.
Regards
Your calculating is right but you forget the milliamps for to drive 1.3Amps thru the CE in the output pair (a pair to each driver). If counting with worth Hfe value in output (ca 25) the driver (each of them) must also supply the output base with ca 52mA (0.052A). Total thru each driver is: 14+52mA=66mA
Total dissipation will then be of the order: 0.066x51V=3.37W(each driver)
hope this make sense.
Regards
Thanks for the flattering comments
I'll check the simulations tonight and post some disspation figures according to supply rails, bias and load. If memory serves, at 52V rails and 100W bias into 8ohms, the drivers dissipate somewhere in the 2-3W region, the predrivers 800mW and 30mW for the two sections and the others almost nothing. All the resistors can be 0.25W except the 1k feeding the LTP's and 12k1's that should ideally be 0.5W since they dissipate over 100mW each. Simulated THD at 1kHz under these conditions is about 0.01%.
I'll check the simulations tonight and post some disspation figures according to supply rails, bias and load. If memory serves, at 52V rails and 100W bias into 8ohms, the drivers dissipate somewhere in the 2-3W region, the predrivers 800mW and 30mW for the two sections and the others almost nothing. All the resistors can be 0.25W except the 1k feeding the LTP's and 12k1's that should ideally be 0.5W since they dissipate over 100mW each. Simulated THD at 1kHz under these conditions is about 0.01%.
Hi,
I see what you're getting at. I had overlooked the quiescent bias requirement. Thanks.
I had better go back and check my 50 Klone calculations.
What if one uses modern output devices with a minimum gain of 80? That would reduce the driver dissipation to about 1.5W.
Selected devices have hFE>=100
Now, do we design the layout for low gain (guaranteed to be 25 or better) or selected higher gain at Iq=430ma, or 50 or 80?
I see what you're getting at. I had overlooked the quiescent bias requirement. Thanks.
I had better go back and check my 50 Klone calculations.
What if one uses modern output devices with a minimum gain of 80? That would reduce the driver dissipation to about 1.5W.
Selected devices have hFE>=100
Now, do we design the layout for low gain (guaranteed to be 25 or better) or selected higher gain at Iq=430ma, or 50 or 80?
Hi,
ideas for extra dissipation capability for the drivers.
could a large aluminium angle be bolted across all 5 devices and then a computer CPU cooler or two be bolted on top and run at low revs (low voltage) and thus low noise?
Is there sufficient head height/room?
What if the drivers were soldered from the underside and bolted tight to the PCB but with the hot face away from the PCB.
CPU coolers could then be bolted direct to the drivers?
Would this release more room?
ideas for extra dissipation capability for the drivers.
could a large aluminium angle be bolted across all 5 devices and then a computer CPU cooler or two be bolted on top and run at low revs (low voltage) and thus low noise?
Is there sufficient head height/room?
What if the drivers were soldered from the underside and bolted tight to the PCB but with the hot face away from the PCB.
CPU coolers could then be bolted direct to the drivers?
Would this release more room?
output stage gain...
...will diminish as more current is delivered to low impedance loads, so even if the quiescent gain can be guaranteed to be high enough, we are unlikely to be able to predict the hFE under more extreme conditions...
More output transistors will help their collective gain remain at the upper end of the range, but IMHO it would be unwise to design heatsinking for drivers that is sized for anything but the lowest gain...and of course in the spirit of excess capacity the heatsinks should be at least twice the required size...
Just my 2c
Stuart
...will diminish as more current is delivered to low impedance loads, so even if the quiescent gain can be guaranteed to be high enough, we are unlikely to be able to predict the hFE under more extreme conditions...
More output transistors will help their collective gain remain at the upper end of the range, but IMHO it would be unwise to design heatsinking for drivers that is sized for anything but the lowest gain...and of course in the spirit of excess capacity the heatsinks should be at least twice the required size...
Just my 2c
Stuart
Hi Stuart,
I hear you, but let's take your numbers on a bit farther.
Many modern devices maintain excellent gain upto 5A and some beyond 7A.
In the KSA100 Klone we will be dealing with two sets of 3pair of output devices (from the 2pairs of drivers) or even more for a few builders who like to go that bit further.
Assuming a gain of 80 upto 5A per device, that equates to 30Apk of output current into 1r5 and requires 45Vpk of output voltage (=675W into1r5). This must be pretty near the maximum that the Klone (on 6pair) can manage into that kind of load. The base current will be about 62.5mA and the emitter current of each driver half will be about 188mA. The drivers have long ago left ClassA bias. The drivers will now be dissipating about (52-45) * 0.188 = 1.3W into a resistive load. Their dissipation into a reactive load could easily exceed many times that, but only for very short periods. During these short periods a massive driver sink should absorb a considerable amount of heat for a small rise in sink temperature.
It transpires that the worst condition is high quiescent current and low gain. Just as Flod identified before he needed to correct my error.
ps. I have now committed to twin drivers into 6pair for my 50 Klone (just as the 100 does), but using hFE>=80 for all output currents and driver gain>=120 (2sa649/c669)for all output currents and loads down to 3ohm but with heatsink designed to match the required dissipation and projected temperatures (not doubled in size).
I hear you, but let's take your numbers on a bit farther.
Many modern devices maintain excellent gain upto 5A and some beyond 7A.
In the KSA100 Klone we will be dealing with two sets of 3pair of output devices (from the 2pairs of drivers) or even more for a few builders who like to go that bit further.
Assuming a gain of 80 upto 5A per device, that equates to 30Apk of output current into 1r5 and requires 45Vpk of output voltage (=675W into1r5). This must be pretty near the maximum that the Klone (on 6pair) can manage into that kind of load. The base current will be about 62.5mA and the emitter current of each driver half will be about 188mA. The drivers have long ago left ClassA bias. The drivers will now be dissipating about (52-45) * 0.188 = 1.3W into a resistive load. Their dissipation into a reactive load could easily exceed many times that, but only for very short periods. During these short periods a massive driver sink should absorb a considerable amount of heat for a small rise in sink temperature.
It transpires that the worst condition is high quiescent current and low gain. Just as Flod identified before he needed to correct my error.
ps. I have now committed to twin drivers into 6pair for my 50 Klone (just as the 100 does), but using hFE>=80 for all output currents and driver gain>=120 (2sa649/c669)for all output currents and loads down to 3ohm but with heatsink designed to match the required dissipation and projected temperatures (not doubled in size).
I also thought about the CPU cooler idea; it will also help for some airflow over the predrivers incase they get hot. Small AC fans will be better as they generate less noise than DC - even with a separate transformer and regulation for DC fans some of their noise still creep into the rest. Unfortunately many ideas will not be useable for those wanting to place it into the original's chassis, but no problem for others. Just tap a few holes, modify a piece of angle iron to support the fan and bolt all that to the sink. Even non-directed airflow will help a lot.
To get concencus over a few components; especially the drivers and predrivers: I thought of using the MJE15034/5 for all, and MJE15030 for the bias transistor since it gives a better gain range than the others. Of course changing the series resistor to a smaller value; say 820ohms instead of 1k5 will also help and reducing the 5k pot to a smaller one. For the LTP's the BC546/556e's are cheap and fast, and for the MOSFET's (depending on the prototype results anyway), I like the SOT-23 package because it will have the best heat dissipation without any heatsink since it has a large copper area with lots of vias to fill with solder. That way you can sink a lot of heat, easily 2W that's far more than'd ever be needed. The nice thing about the IRFD's is that they're in DIP-4 packages so if placed in a socket they're easy to replace.
To get concencus over a few components; especially the drivers and predrivers: I thought of using the MJE15034/5 for all, and MJE15030 for the bias transistor since it gives a better gain range than the others. Of course changing the series resistor to a smaller value; say 820ohms instead of 1k5 will also help and reducing the 5k pot to a smaller one. For the LTP's the BC546/556e's are cheap and fast, and for the MOSFET's (depending on the prototype results anyway), I like the SOT-23 package because it will have the best heat dissipation without any heatsink since it has a large copper area with lots of vias to fill with solder. That way you can sink a lot of heat, easily 2W that's far more than'd ever be needed. The nice thing about the IRFD's is that they're in DIP-4 packages so if placed in a socket they're easy to replace.
well...
...I was being somewhat facetious with the doubling comment, but in any case, I'd be designing for the worst case scenario...
Presumably the worst scenario is if the output ends up shorted, in which case the dissipation in the drivers and the outputs will be instantaneously very high. They all have to survive the few millisecs needed to open the protection relay...bigger heatsinks that are not already at the upper end of the temperature range will help this...
Good airflow in the case will make a big difference to the required size of the driver heatsinks...not necessarily fans, but just basic good airflow...lots of vents etc.
HTH
Stuart
...I was being somewhat facetious with the doubling comment, but in any case, I'd be designing for the worst case scenario...
Presumably the worst scenario is if the output ends up shorted, in which case the dissipation in the drivers and the outputs will be instantaneously very high. They all have to survive the few millisecs needed to open the protection relay...bigger heatsinks that are not already at the upper end of the temperature range will help this...
Good airflow in the case will make a big difference to the required size of the driver heatsinks...not necessarily fans, but just basic good airflow...lots of vents etc.
HTH
Stuart
hi..
yes this is my first post
i just findout from the pictures that you guys post here, my krell is ksa 100 mk1 (with the blue wire inside) ok.. ok.. i m really new here .. we opened my krell with my friend to fix the fan ,krell ask me to send them but it was really heavy ,and they ask $170 for the fan.. we just cleaned with the vacuum cleaner and it worked my question is ; can i upgrade my mk1 to mk2 ? yea maybe its stupid question but i have to ask 
regards
yes this is my first post
i just findout from the pictures that you guys post here, my krell is ksa 100 mk1 (with the blue wire inside)
ok.. ok.. i m really new here .. we opened my krell with my friend to fix the fan ,krell ask me to send them but it was really heavy ,and they ask $170 for the fan.. we just cleaned with the vacuum cleaner and it worked my question is ; can i upgrade my mk1 to mk2 ? yea maybe its stupid question but i have to ask regards
selcuksiyoni said:hi..
yes this is my first post
i just findout from the pictures that you guys post here, my krell is ksa 100 mk1 (with the blue wire inside)
regards
you must participate in this group project with photographs,measuring etc.
after that -you can freely send KSA100 to me,and I'll make every needed upgrade,and I'll never return it to ya
selcuksiyoni: The short answer is yes. That was one of the design motivations of the board, to make it interchangeable with both the original Mk1 and Mk2's. Of course it does not include the soft-start and protection circuitry of the Mk2, but that's not so difficult to cobble together.
All you need to do for the upgrade is to participate in the group buy, which will provide you with the boards, driver heatsink and resistors. Then you have to buy and solder another few basic components, take out the old boards (just desolder 10 wires in total and unscrew the boards), replace them with the new ones that will fit exactly into the old one's place, set the trimpots and you're done.
If you use components of similar quality of the original Krell you can get away for less than $60 in total for two channels. Of course if you're already doing the swopout you can also splash out a few extra $$ for some better quality components here and there.
If you're hesitant or uncertain I'm sure somebody here will be willing to assemble and test a full board for you at a small cost - in that case all you need to do is the straight swop. I'll do the board fo you if you'd be willing to cover the shipping.
PS - As always with Krell, $170 for a fan is a total ripoff. They used standard Papst AC fans, which can be bought for less than $40.
All you need to do for the upgrade is to participate in the group buy, which will provide you with the boards, driver heatsink and resistors. Then you have to buy and solder another few basic components, take out the old boards (just desolder 10 wires in total and unscrew the boards), replace them with the new ones that will fit exactly into the old one's place, set the trimpots and you're done.
If you use components of similar quality of the original Krell you can get away for less than $60 in total for two channels. Of course if you're already doing the swopout you can also splash out a few extra $$ for some better quality components here and there.
If you're hesitant or uncertain I'm sure somebody here will be willing to assemble and test a full board for you at a small cost - in that case all you need to do is the straight swop. I'll do the board fo you if you'd be willing to cover the shipping.
PS - As always with Krell, $170 for a fan is a total ripoff. They used standard Papst AC fans, which can be bought for less than $40.
i couldnt see any adress in your post ohh i forgot , i have to post pictures first
http://web.mac.com/selchuk/iWeb/Site/my listening room_files/slideshow.html thats all picture i have from krell but if you guys need, i can make and post more..
ok again my question, is it worth to upgrade mk1 to mk2? another question im using them with audio research sp11 + link lp12 turntable +rotel 850 ,everythink its just fine with turntable but with rotel in high volume (like half volume) 1 side-right of the speakers not working(allison one) any idea? let me know about the ksa100 pictures maybe i can help ,they put lots of screw on it but i have good screwdriver
thank you..
ohh i forgot , i have to post pictures firsthttp://web.mac.com/selchuk/iWeb/Site/my listening room_files/slideshow.html thats all picture i have from krell but if you guys need, i can make and post more..
ok again my question, is it worth to upgrade mk1 to mk2? another question
im using them with audio research sp11 + link lp12 turntable +rotel 850 ,everythink its just fine with turntable but with rotel in high volume (like half volume) 1 side-right of the speakers not working(allison one) any idea? let me know about the ksa100 pictures maybe i can help ,they put lots of screw on it but i have good screwdriver thank you..OK, here's another refined version. Once again cosmetic changes, added a proper copper pour for both power and power ground, added 4 extra power electrolytics (7.5mm lead spacing) and two axial caps e.g. Solen. That brings the total PSU decoupling to:
6x 7.5mm pitch electro's
2x 5mm pitch electro's
2x 5/7.5/10mm MKP's
2x 25mm axials
Of course not all or even none has to be used, but it gives ample playroom for those wanting to experiment with different amounts and types of capacitance.
I suspect this to be pretty much the final version (unless there's a gross problem with the prototype's performance), and the only changes from now on may be small silkscreen ones and slight shifting of the wire pads, mounting holes and board size when I have the exact parameters.
6x 7.5mm pitch electro's
2x 5mm pitch electro's
2x 5/7.5/10mm MKP's
2x 25mm axials
Of course not all or even none has to be used, but it gives ample playroom for those wanting to experiment with different amounts and types of capacitance.
I suspect this to be pretty much the final version (unless there's a gross problem with the prototype's performance), and the only changes from now on may be small silkscreen ones and slight shifting of the wire pads, mounting holes and board size when I have the exact parameters.