Ah, my laptop decided to leave me a couple of days ago. The harddrive just broke down left me without datasheets, spreadsheets and saved info...and since I am out of town I only have limited access to internet.
But anyway, everything is coming along great and with only 200mV the heatsinks (tunnels from Steve at Apexjr) doesn't get hot at all. The transistors are mounted on the inside of the tunnel so I can't say what temerature they hold though.
Oh, Ryssen. This one is my friends amp, mine is still in pieces so you still have time to beat me 😉
AndrewT
I/we use 0,68ohms rated to 10W.
No load??? what about the speakers?
Oh, and thanks for the info! 🙂
The output quiescent current and the output offset are set up with the output open circuit and the input short circuit.
Don't try to set up the amplifier any other way.
Iq=0.2/0.68=0.294A
For three pairs all at 0.294A gives total Iq = 0.88A
Class A power is (2*0.88)^2 * 8/2 = 12.4W
NOTE my previous formula omitted the /2 and the result is the peak power at the top of the sinusoidal waveform, The average power is peak power /2.
The dissipation of the output stage is Vrail (+ve to -ve) * total Iq~=0.88*74=65W. I would not expect a sink designed for 141W to run at anything other than cold (to the touch).
Don't try to set up the amplifier any other way.
Iq=0.2/0.68=0.294A
For three pairs all at 0.294A gives total Iq = 0.88A
Class A power is (2*0.88)^2 * 8/2 = 12.4W
NOTE my previous formula omitted the /2 and the result is the peak power at the top of the sinusoidal waveform, The average power is peak power /2.
The dissipation of the output stage is Vrail (+ve to -ve) * total Iq~=0.88*74=65W. I would not expect a sink designed for 141W to run at anything other than cold (to the touch).
So in our case it becomes (after biased to 400mV) :
Iq=0.4/0.68=0.588A
For two pairs all at 0.294A gives total Iq = 1.176A
Class A power is (2*1.176)^2 * 8/2 = 22.1W
And since he uses a 2x30V transformer giving out appr. 42V then the dissipation of the output stage is Vrail (+ve to -ve) * total Iq~=1.176*84=99W.
Iq=0.4/0.68=0.588A
For two pairs all at 0.294A gives total Iq = 1.176A
Class A power is (2*1.176)^2 * 8/2 = 22.1W
And since he uses a 2x30V transformer giving out appr. 42V then the dissipation of the output stage is Vrail (+ve to -ve) * total Iq~=1.176*84=99W.
kmj said:
The maths is correct.
That confirms that you have built a high bias ClassAB amplifier
NOT a ksa50 Klone after you successfully get the bias voltage (Vre) up to 400mV.
For full ClassA of 50W you need 646mV (Iq=1.9A).
If you want full ClassA to the higher output that 30Vac gives then Iq needs to be set even higher (Vre~=750mV). But the output stage would need to be designed for this increased thermal and current loading.
I have a quick question for my fellow-members:
What will happen if you disconnect one of the powersupply-rails from the amplifier-circuit of the ksa ?
With kind regards,
Klaas
What will happen if you disconnect one of the powersupply-rails from the amplifier-circuit of the ksa ?
With kind regards,
Klaas
Hi all, reason i ask is i found a loose screw in my ksa.It should hold down one of the wires carrying the psu-voltage.
The connector was just loosely under the screw.
Tightening the screw btw dramatically increased performance.
with kind regards,
Klaas
The connector was just loosely under the screw.
Tightening the screw btw dramatically increased performance.
with kind regards,
Klaas
It was probabaly intermittent enough to work, but may have been arcing and putting noise on the rail. Glad you got it sorted.
Hello !
If anybode has any spare boards for the KSA50 for sale, I would be interested - og ir anyone knows where they can be bought - I need 4 pcs.
I have mailed Mark G a couple of times without result....?
Cheers !
Buhl
If anybode has any spare boards for the KSA50 for sale, I would be interested - og ir anyone knows where they can be bought - I need 4 pcs.
I have mailed Mark G a couple of times without result....?
Cheers !
Buhl
Buhl said:
you must be patient waiting for Mark's response;
he's more out of home than at home,at least to my knowledge 😉
These are 100% sure from the DIYaudio GB!
These are the "Jan" boards, they were in the GB before the "Pinkmouse" boards were designed.
I build my Krellclone with these boards.
These are the "Jan" boards, they were in the GB before the "Pinkmouse" boards were designed.
I build my Krellclone with these boards.
Wim, sorry bout that, I was to quick on the trigger😉 Totally forgot that Jan Dupont made those boards earlier on.
Steen🙂
Many, many posts ago i posted a couple of photos of 1 finished monoblock. It is tested (with the great help of Loek) and 100% working. The second one is also ready for a while, but with shame i must say that i did not build them in a enclosure at the moment.
Reasons are: time (i divide myself, working on a dozen projects) and i am not a good mechanical worker (do not have the place and engines to make good enclosures).
But, one day.......
Reasons are: time (i divide myself, working on a dozen projects) and i am not a good mechanical worker (do not have the place and engines to make good enclosures).
But, one day.......
I just digged out my KSA Pinkie boards😀 Impelled by this talk. Actually I have all parts to stuff'em put in the box together with the boards. I forgot that too! Thats what you get from stowing away nice projects! I will propably never get around to built the amp anyway...Dooooh.
Steen🙂
Steen🙂