The emitter resistor values for those amps are 1 Ohm, not 0.5 Ohm.
325mA quiescent current per output device in the KSA-80 sums up to 3.9A peak class A output current (2 banks of 6 output devices).
3.9A is ~120W peak class A or some 60W continuous Class A power.
Neither value really fits the bill for a nominal 80W Class A power amp.
Reality is that the bias level is determined by the power handling capability of the Krell design heatsink in the KSA/KMA series.
Still today a very efficient heatsink for it's cubic volume and mounting footprint imo, but bottomline remains that it can handle no more than 80W at an acceptable temperature limit.
REAL Class A power amps are biased to the nominal level for both 8 and 4 Ohm operation.
1.8A bias for the KSA50 means that it not only does 50W Class A in 8 Ohm, but also in 4 Ohm loads (as in : 3.6 x 3.6 x 4 = 50W without entering the cross-over area)
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Got mine too 😎
Guys the Class-A calculations have been vetted by a host of experts on the forum including the one and only himself. PC walley... as far as sonics go, thats a debate that will not be settled anytime soon. I can tell you this, it is not merely about only eliminating x-over distortion... (though that is one of the benefits) heavy Bias has many other effects on the system.
One last thing, when I joined the forum a few years ago, to my own detriment I did not sometimes give everyone the respect they deserved. The amount of collective knowledge that the forum has; is simply astounding, consider yourself blessed.
oops.
The maximum ClassA current for a 1.9A bias is ~3.7Apk.
This will result in a maximum ClassA power into 8r0 of 3.7 * 3.7 * 8 / 2 = 54W.
The maximum ClassA power into 4r0 is 3.7 *3.7 * 4 / 2 = 27W
The KSA50 is biased for maximum ClassA power into 8r0 not 4r0, nor 6r0.
Hi,
I finished may KSA50 but I'm not really happy. The sound isn't I expected. I feel something like fog. Trebles are not very good and i think that there are to few details in music. Do you think it'll change?
Bias 1A/transistor
2xMJ15003 & 2xMJ15004 per channel
Power supply 2x47000uF Rifa & 2x45V per channel
Everything is like in an original schematic of ksa50.
I finished may KSA50 but I'm not really happy. The sound isn't I expected. I feel something like fog. Trebles are not very good and i think that there are to few details in music. Do you think it'll change?
Bias 1A/transistor
2xMJ15003 & 2xMJ15004 per channel
Power supply 2x47000uF Rifa & 2x45V per channel
Everything is like in an original schematic of ksa50.
KSA-50 runs warmer (soundwise) than other amps thats why people like them. So if you are used to more HF then an adjustment needs to happen... (and not necessarily to the KSA-50 😉 ).
What drivers do you have? The MJ1503x are warmer sounding than Japanese trannies in my experience e.g. d669 b649s sound very clear but at high bias levels they may be inadequate...
I've got drivers MJ15032/33. So, should I use 2sd669 & 2sb649s to have clear sound? How high bias can I use with this drivers? And the last question: where can I buy original sd669 & 2sb649s? I can't find any shop selling 2sb649s.
Make sure your grounding on input is correct. Mine sounded totally bland until I realized the signal ground was not correctly connected...also check the neg signal input is connected to ground too...unless your running balanced...
How do you make grounding on input right?
I connected chassis with RCA using wire but it's a very slim wire - a leg from rezistor 0,6W. Maybe I have to use solid cable.
I connected chassis with RCA using wire but it's a very slim wire - a leg from rezistor 0,6W. Maybe I have to use solid cable.
I think the grounding is ok.
I wonder what bias will be perfect for 2x47V? I have 2x450VA transformers and big heat-sinks.
I wonder what bias will be perfect for 2x47V? I have 2x450VA transformers and big heat-sinks.
Original had only 500 mA per device, total 2 A bias. The sound character changes with bias setup, so try to reduce bias amount 😉
Lets say you have infinite heatsinking and keep increasing bias (but within SOAR), at any point does beta droop in outputs or drivers begin to surface as remarkable?
The RCA input ground to board input ground (assuming your using the Pimkmouse boards?) and no where else. The signal input ground should not terminate into chassis.
Also a jumper on board from neg signal input to ground since you indicated RCA input (Single ended) and not balanced (XLR).
What I can't remember if your supposed to have continuity (zero resistance) from RCA barrel ground to power supply ground ....I think so...
Also, as Neychi says, check your bias. Too much or little will affect sound - although can't see too much being bad if your sinks can take teh heat.
Also a jumper on board from neg signal input to ground since you indicated RCA input (Single ended) and not balanced (XLR).
What I can't remember if your supposed to have continuity (zero resistance) from RCA barrel ground to power supply ground ....I think so...
Also, as Neychi says, check your bias. Too much or little will affect sound - although can't see too much being bad if your sinks can take teh heat.
1A bias on +-48Vdc will dissipate ~96W, or about 24W per device.
1A bias will allow upto 16W of ClassA output, very much short of the 50W of ClassA that the KSA50 gives.
Yes, but obviously there is a reason for that. KSA 50 Mark II had two editions, with and without mosfets. Mark I had also two editions, with 36,5 V rails (1,8 A bias) and later with 48 V rails (1 A bias). That, later edition of Mark I, had same layout as earlier Mark II but with cooling fan on the botom.
I wrote mistake - I have (1A / 1 transistor) so I have bias = 2A because I've got 2 pairs of transistors. Yesterday i set bias 2,2A and sound is better. Today I try set 1,2A and I'll see. How much power in class A will I have with 48V and 2,4A bias?
Where should I wire ground with chassis?
I've got another PCb than Pikmouse. My PCB is from forum audiostereo.pl from Poland.
Of course ground from RCA is connected with ground on PCB. I also connected RCA ground with chassis. And you say it's wrong...How should I do this?
Where should I wire ground with chassis?
I've got another PCb than Pikmouse. My PCB is from forum audiostereo.pl from Poland.
Of course ground from RCA is connected with ground on PCB. I also connected RCA ground with chassis. And you say it's wrong...How should I do this?