Hi Kmj,
0r68 and 400mV gives Ire=0.4/0.68=0.588A.
Ibias = 3*0.588=1.76A.
The peak (ClassA) current into a load, for a push/pull amplifier, is 2*1.76=3.53Apk
ClassA power = Ipk^2*Rload/2=3.53*3.53*8/2=50W ClassA
Peak voltage at max ClassA power is Ipk*Rload=3.53*8=28.24Vpk=20Vac.
This is worth saving and putting into a text file, or better, into a spread sheet.
Personally I would bias for 1.76+0.1 amps to ensure the very curved knee in the transistor Ic vs Vbe at the near change to ClassB is avoided. I think running into this low Ic region causes an increase in open loop distortion and makes the NFB work very hard. I think that's why ClassAB produces more distortion when biased above optimum.
I would also bias for the minimum impedance presented by the speaker rather than the nominal impedance. These extra levels of Iq will make the output stage run hotter and require larger heatsinks.
0r68 and 400mV gives Ire=0.4/0.68=0.588A.
Ibias = 3*0.588=1.76A.
The peak (ClassA) current into a load, for a push/pull amplifier, is 2*1.76=3.53Apk
ClassA power = Ipk^2*Rload/2=3.53*3.53*8/2=50W ClassA
Peak voltage at max ClassA power is Ipk*Rload=3.53*8=28.24Vpk=20Vac.
This is worth saving and putting into a text file, or better, into a spread sheet.
Personally I would bias for 1.76+0.1 amps to ensure the very curved knee in the transistor Ic vs Vbe at the near change to ClassB is avoided. I think running into this low Ic region causes an increase in open loop distortion and makes the NFB work very hard. I think that's why ClassAB produces more distortion when biased above optimum.
I would also bias for the minimum impedance presented by the speaker rather than the nominal impedance. These extra levels of Iq will make the output stage run hotter and require larger heatsinks.
I have the calculation bookmarked but since it was a while ago I though that I rather ask one extra time and have it confirmed than make a misstake and have the amp unfinished another couple of months
Isn't that the same as 400mV across the resistor? I only meant to lower it if the sinks couldn't handle the needed dissipation.
I thought of a thing, the transistors on the driverboard are the MJE15032/33. I can't find them over here but the MJE15030/31 are available. If I would need to change these on one of the channels, are the compatible or do I need to change them on both channels? I heard that these are virtualy the same models.
I have skipped my KSA-50 project and moved on to the KSA-100 MKII. So now I have two very nice kits left. Troy did a hell of a job making all these kits! Al the electronic parts to stuff the Pinkmouse PCB's to make two channels. Except the output transistors. All quality parts like dale resistors.
I'm asking what I payed for them. 75USD excl. shipment. So if someone is interested, send me a PM.
I'm asking what I payed for them. 75USD excl. shipment. So if someone is interested, send me a PM.
Hi Andrew,
Yes, bi-amping or a an extra amp for another room would be a good idea. Problem is I got way too many projects going on...
So to finish some projects I have to let go of some stuff and generate some cash. Right now I'm putting everything in boxes away for storage. I even took my complete stereo to my parents house for storage. In a few months I have to be out of the place I'm living now.... So have to put all my time in finishing my new house. Sooo much to do.
I could keep the parts, but I know that when the time comes I have enough spare time, I probably have seen dozens of other lovely thingies to build.
These kits are just too nice not to be uses.
Yes, bi-amping or a an extra amp for another room would be a good idea. Problem is I got way too many projects going on...
So to finish some projects I have to let go of some stuff and generate some cash. Right now I'm putting everything in boxes away for storage. I even took my complete stereo to my parents house for storage. In a few months I have to be out of the place I'm living now.... So have to put all my time in finishing my new house. Sooo much to do.
I could keep the parts, but I know that when the time comes I have enough spare time, I probably have seen dozens of other lovely thingies to build.
These kits are just too nice not to be uses.
Krell KAV-250
Guys:
Are we ready for a higher output Krell? If there's interest to work on the KAV-250. I can post schematics and layouts but won't do so for the heck of it.
Here are my conditions :
Al does the Boards.
Mark does the GB.
Troy makes me my kit
Let me know if there is interest in actually doing this.
I own a KAV-250 and love it, As nice as the KSA-100. Mkii sounded, I sold it after I heard the KAV-250. This is one Krell I'd really like to build.
At about 325 watts per channel into 8 ohms (rated 250) and 1000 watts bridged, good enough for almost any application, this is the amp to make !
K-amps
Guys:
Are we ready for a higher output Krell? If there's interest to work on the KAV-250. I can post schematics and layouts but won't do so for the heck of it.
Here are my conditions
:Al does the Boards.
Mark does the GB.
Troy makes me my kit
Let me know if there is interest in actually doing this.
I own a KAV-250 and love it, As nice as the KSA-100. Mkii sounded, I sold it after I heard the KAV-250. This is one Krell I'd really like to build.
At about 325 watts per channel into 8 ohms (rated 250) and 1000 watts bridged, good enough for almost any application, this is the amp to make !
K-amps
Hi,
are your emitter resistors 1r0 or 0r68?
What dissipation are you putting through each pair of sinks?
Those sinks look like 0.5C/W. and a pair with temp de-rating probably come out at near 0.3C/W.
If you keep the sink at 50degC, then the average Tc will be about 55degC and the maximum (for the worst transistor) just under 60degC. The plastic packages should be OK at that or just a little higher.
are your emitter resistors 1r0 or 0r68?
What dissipation are you putting through each pair of sinks?
Those sinks look like 0.5C/W. and a pair with temp de-rating probably come out at near 0.3C/W.
If you keep the sink at 50degC, then the average Tc will be about 55degC and the maximum (for the worst transistor) just under 60degC. The plastic packages should be OK at that or just a little higher.