I am not going to argue either way as I don't have the experience but this is how I was putting it together in my head. I was summing the quiescent current of each output device. So IF I could idle the outputs at .75amp I would have 3A across the 80V peak to peak or 3*.707 = 2.12A rms
2.12*2.12*8= 35.9Wrms at 8ohms?
Is this accurate?
2.12*2.12*8= 35.9Wrms at 8ohms?
Is this accurate?
Good. Just bought a bigger fan and more heat transfer compound. I would imagine if I ran analog amp meters on the outputs I should see 3 amps at idle and during class. If the meters start to dance I will know that we are leaving class a. Too simple?
no. you will only see 1.5A at idle. 3A is peak class a current.
and that is enough for 2 output pairs🙂 0.75A*40V=30W dissipation pr output device. and a total dissipation of 120W pr ch at idle.
and that is enough for 2 output pairs🙂 0.75A*40V=30W dissipation pr output device. and a total dissipation of 120W pr ch at idle.
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Thanks for your help guys. If I put the ammeters before the outputs in line with the common rail ground I think I should see the sum of all the current draw, or 3 amps at .75a per output device times 4 devices per channel.
you will never see 3A at idle. 3A are peak current. with 0.75A pr device you will see 1.5A at idle. N ch devices are -40V at 1.5A. P ch devices are +40V at 1.5A.
Idle current does not flow into ground, it flows from +ve rail to -ve rail. A meter in the +ve rail will show idle and jump up on +ve swings above idle, but would be idle on -ve swings above idle.
Then that's what I'll do 🙂 I cleaned, re-greased, and reset the transistors. Mounted a 5 inch 12v DC fan and running it at 5v. Idling at .165v a at .22 ohm emitter resistor so .75A per device.
All is barely warm to the touch with the transistors not being too hot to keep you finger on.
Pulling 4 amps per channel off the secondary winding or the toroidal and 2.3 A at 155V out of the wall.
Not sure if i need a soft start as there did not seem to be too much effort in the cold charge when firing it up. (90,000 uf).
Next, put in ammeters for fun and connect a source and speakers.
I am sharing a power supply for both channels so i will run the gauges at + and - total for both channels.
All is barely warm to the touch with the transistors not being too hot to keep you finger on.
Pulling 4 amps per channel off the secondary winding or the toroidal and 2.3 A at 155V out of the wall.
Not sure if i need a soft start as there did not seem to be too much effort in the cold charge when firing it up. (90,000 uf).
Next, put in ammeters for fun and connect a source and speakers.
I am sharing a power supply for both channels so i will run the gauges at + and - total for both channels.
Photo and update
Here is is so far. More of an experiment than an amp. It does sound nice so far. Very effortless. Problem is that the Arcam A75+ that i am using for a pre-amp kicks out before my meters even move from 3 amps. I Think the output may be too low for the amp's input stage. Just guessing there though.
Toroidal heats up some. If I am drawing 8A across 80V does that equate to a 640VA?
the toroid is good and warm but not what I would call hot by any means. How would I calculate the max VA of the transformer?
Thanks
Here is is so far. More of an experiment than an amp. It does sound nice so far. Very effortless. Problem is that the Arcam A75+ that i am using for a pre-amp kicks out before my meters even move from 3 amps. I Think the output may be too low for the amp's input stage. Just guessing there though.
Toroidal heats up some. If I am drawing 8A across 80V does that equate to a 640VA?
the toroid is good and warm but not what I would call hot by any means. How would I calculate the max VA of the transformer?
Thanks
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I have to put some load on the speaker terminals of my Arcam A75+ or it trips at mid volume. I don't think a low watt resistor would last too long. What else is 4 to 8 ohms that would make a good dummy speaker?
Need a real pre-amp.
Need a real pre-amp.
I think you have a fault with the Arcam amp, I wonder if the zobel network has gone open circuit. Open the box up and look for a burnt resistor.
I have had both the A75+ and P75+ apart and they are both clean without burnt components. Actually neither amp can be pushed at all with no load or the small load of the tweeter in my bi-amped configuration. Both amps perform the same and have since new when I bought them. Oddly, when I bi-wire to iether of the two the problem goes away and I can get a lot more volume from just one amp. Low sensitivity Spendors but still an apples to apples experiment.
output vs. input line voltage
Folks. Here are the schematics and CAD drawing for the KSA50 boards I am using. If I drop the resistance of R22 (1K) will I increase the gain based on a higher voltage in? I don't think that the voltage line out from my Arcam is as high as it should be for the input on this board.
Does that make sense? 😕
Folks. Here are the schematics and CAD drawing for the KSA50 boards I am using. If I drop the resistance of R22 (1K) will I increase the gain based on a higher voltage in? I don't think that the voltage line out from my Arcam is as high as it should be for the input on this board.
Does that make sense? 😕
Any takers on the input resistor question. If I piggy back another 1k resistor on the existing one will the 500 ohm result in a increase gain across the voltage increase end of the amplifier?
Reducing the value of R22 will only make negligible audible difference. You could try reducing R13 to 750 ohm which will double the gain, but I'm surprised that the output from a CD player (via your Arcam) cannot drive the amp enough.
The Arcam has a nominal output of 540mv. I need to find out from the board manufacturer what the input sensitivity is on the amplifier board. I'm not sure if 540mv is higher or lower than avaerage.
Nice to see some posts about these. I bought a pair but I think I am out of my depth with them. I honestly dont see the point of building them if I cant get them running to original spec without blowing up. I can get 16 watts out of a 845 with less trouble.
When I bought them I thought all I had to do was buy the right trans and some caps and heatsinks and fire them up. I bought a lower power zen maybe that might be a less chantsy option though I will follow this post with fingers crossed.
dont forget the cheap naim boards. They could be a cooler running option. cheers
When I bought them I thought all I had to do was buy the right trans and some caps and heatsinks and fire them up. I bought a lower power zen maybe that might be a less chantsy option though I will follow this post with fingers crossed.
dont forget the cheap naim boards. They could be a cooler running option. cheers
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