Hello
My first post on this site, the site looks great so much information, I would still like to ask a question, my diy solid state 15w class a power amp is sounding fantastic, but it is running very hot you can keep your hand on the heatsinks but only just, the seperate regulated power supply does not get as hot, is this temp normal, and should I not worry about it or is there anyway to disipate the heat further. I am using the amp with a bottlehead pre that has quite a lot of gain would this make any difference, also the weather has been very hot for the last couple of days that may have made a difference. Thank you in advance
Regards from Western Australia
Roger
My first post on this site, the site looks great so much information, I would still like to ask a question, my diy solid state 15w class a power amp is sounding fantastic, but it is running very hot you can keep your hand on the heatsinks but only just, the seperate regulated power supply does not get as hot, is this temp normal, and should I not worry about it or is there anyway to disipate the heat further. I am using the amp with a bottlehead pre that has quite a lot of gain would this make any difference, also the weather has been very hot for the last couple of days that may have made a difference. Thank you in advance
Regards from Western Australia
Roger
Hi Rojer,
What amp is it?
Your description sounds about right to me. If the temperature remains stable after an extended period of use, especailly in hot weather, then it should be OK.
You can increase the size of your heatsink or add a fan if you are worried about temperature of the transistors. The cooler they are, the longer they will last.
Did you follow the advice of the amp designer?
What amp is it?
Your description sounds about right to me. If the temperature remains stable after an extended period of use, especailly in hot weather, then it should be OK.
You can increase the size of your heatsink or add a fan if you are worried about temperature of the transistors. The cooler they are, the longer they will last.
Did you follow the advice of the amp designer?
Hi Roger,
Yes Australia's having it's hottest weather on record and it's catching up with Perth ( and freo). Could be all those Class A amps?
Have to ask the same question as Greg #1. What is it?
Possibly, if it's unusually hot over the heatsink, that the temp comp is not adequate so when the ambient temp rises, so does the standing current in the output stage, compounding the rise.
Need to see a schema...
Cheers,
greg
Yes Australia's having it's hottest weather on record and it's catching up with Perth ( and freo). Could be all those Class A amps?
Have to ask the same question as Greg #1. What is it?
Possibly, if it's unusually hot over the heatsink, that the temp comp is not adequate so when the ambient temp rises, so does the standing current in the output stage, compounding the rise.
Need to see a schema...
Cheers,
greg
As Greg say
a Class A can get very hot.
Same amount of current runs in supply regulator as in amplifier.
But heat = power.
And power is Current x Voltage.
Across regulator maybe 6+6 Volt.
Across amplifier maybe 24+24 Volt.
This makes power ( and heat ) 4 times more in amp than in regulator heatsink.
Power = Current x Voltage
Watt = Ampere x Volt
P = I x U
Class A often requires large heatsinks.
This lowers the temperature.
Nelson Pass extreme Class A amplifiers, uses enourmously overdimensioned heatsinks.
This gives much lower temperature. Maybe only 40-60 degrees Celsius.
And he says transistors, MOSFETS, will work better.
This picture shows a Pass DIY, Zen Amplifier, version 2
a Class A can get very hot.
Same amount of current runs in supply regulator as in amplifier.
But heat = power.
And power is Current x Voltage.
Across regulator maybe 6+6 Volt.
Across amplifier maybe 24+24 Volt.
This makes power ( and heat ) 4 times more in amp than in regulator heatsink.
Power = Current x Voltage
Watt = Ampere x Volt
P = I x U
Class A often requires large heatsinks.
This lowers the temperature.
Nelson Pass extreme Class A amplifiers, uses enourmously overdimensioned heatsinks.
This gives much lower temperature. Maybe only 40-60 degrees Celsius.
And he says transistors, MOSFETS, will work better.
This picture shows a Pass DIY, Zen Amplifier, version 2
An externally hosted image should be here but it was not working when we last tested it.
You should find out how much current is flowing in output.
You can measure across a know resistor in output stage.
To produce 15 Watt Class A into 4 ohm you need:
2.74 A for single end (constant current source)
1.37 A for push-push output stage
adding 20% gives:
1.6 Ampere and 3.2 Ampere
For 15 Watt into 8 Ohm
1.2 Ampere and 2.4 Ampere
Setting bias to more current than this, is a waste of current and heat.
You can measure across a know resistor in output stage.
To produce 15 Watt Class A into 4 ohm you need:
2.74 A for single end (constant current source)
1.37 A for push-push output stage
adding 20% gives:
1.6 Ampere and 3.2 Ampere
For 15 Watt into 8 Ohm
1.2 Ampere and 2.4 Ampere
Setting bias to more current than this, is a waste of current and heat.
Wow what great replies
Thanks for all the advice, the amp is an altronics kit, I think it is from silicone chip and it is a really sweet sounding amp it can be found on the altronics web site under kits, the instructions are pretty vague but it was worth it. I can send photos of internals by email if anyone is interested, the amp does reach a stable temp but it has been hotter the last few days, following the air temp I hope. Picked up a great cd Harry Manx Mantras for madmen really worth a listen (blues with a little eastern flavour)
Regards Roger
Thanks for all the advice, the amp is an altronics kit, I think it is from silicone chip and it is a really sweet sounding amp it can be found on the altronics web site under kits, the instructions are pretty vague but it was worth it. I can send photos of internals by email if anyone is interested, the amp does reach a stable temp but it has been hotter the last few days, following the air temp I hope. Picked up a great cd Harry Manx Mantras for madmen really worth a listen (blues with a little eastern flavour)
Regards Roger
Hi freo,
You might find that's all it is - just the heatsinks tracking the rise in ambient temp. Just check the small black transistor (going from the catalogue pic) between the large flat output devices to make sure it is in intimate contact with the heatsink to sense variations.
Cheers,
greg
You might find that's all it is - just the heatsinks tracking the rise in ambient temp. Just check the small black transistor (going from the catalogue pic) between the large flat output devices to make sure it is in intimate contact with the heatsink to sense variations.
Cheers,
greg
Hi freo,
I think this amp is known as the SC ULD Class-A (or the Silicon Chip Ultra Low Distortion Class-A in long hand). I believe I have heard a slightly modified one of these a few years back and you are right it was a sweet little amp.
Did you use the regulated power supply kit? I have one of these amps in my "to be completed in 2006" list.
I guess a picture is worth a thousand words so I would appreciate if you could send me a PM.
Hey 'guru,
If we are looking at the same amp, I noticed it is a CFP amp (I have the schematics) so I was wondering why they mount the Vbias transistor with the output devices and not the drivers?
regards
I think this amp is known as the SC ULD Class-A (or the Silicon Chip Ultra Low Distortion Class-A in long hand). I believe I have heard a slightly modified one of these a few years back and you are right it was a sweet little amp.
Did you use the regulated power supply kit? I have one of these amps in my "to be completed in 2006" list.
I guess a picture is worth a thousand words so I would appreciate if you could send me a PM.
Hey 'guru,
If we are looking at the same amp, I noticed it is a CFP amp (I have the schematics) so I was wondering why they mount the Vbias transistor with the output devices and not the drivers?
regards
Hi Greg #1,
You have the schema... i was just going from the pic. And you're absolutely right, a CFP amp does not need the bias sense BJT in intimate contact with the heatsink. If the drivers (can't spot those unless they're TO92's) don't have a heatsink, it's quite customary to arrange the bias BJT in 'semi-intimate' contact so it doesn't over-compensate and back the bias off too much. Of course with a Class A, it could be a extra measure against severe overheating to overcompensate as it's really only going to cut back at the full power end.
Cheers,
Greg
You have the schema... i was just going from the pic. And you're absolutely right, a CFP amp does not need the bias sense BJT in intimate contact with the heatsink. If the drivers (can't spot those unless they're TO92's) don't have a heatsink, it's quite customary to arrange the bias BJT in 'semi-intimate' contact so it doesn't over-compensate and back the bias off too much. Of course with a Class A, it could be a extra measure against severe overheating to overcompensate as it's really only going to cut back at the full power end.
Cheers,
Greg
15w class a
Hi Freo,
I was wondering if you have persisted with these little beauties as it has been extremely hot around your way jusy recently.
I had the same problem in Brisbane until I used twice the heatsinking capacity as shown by Silicon Chip, ie, one 300mm heat sink per module plus one 300mm for the dual power supplies(dual mono) and this proved most satisfactory
Hi Freo,I was wondering if you have persisted with these little beauties as it has been extremely hot around your way jusy recently.
I had the same problem in Brisbane until I used twice the heatsinking capacity as shown by Silicon Chip, ie, one 300mm heat sink per module plus one 300mm for the dual power supplies(dual mono) and this proved most satisfactory
15 w class a power amp
Hello
My name is Nick from the UK and i have been making power amps for the last 20 years, this is my 1st response to this forum. Most of my amps have been designed by JLH. I was thinking of making the SC magazine 15w class a as described in this post. Any chance some of you could send me the CCT diagram and pics of your amps if you have constructed the amp in question ?
best regards
Nick
Hello
My name is Nick from the UK and i have been making power amps for the last 20 years, this is my 1st response to this forum. Most of my amps have been designed by JLH. I was thinking of making the SC magazine 15w class a as described in this post. Any chance some of you could send me the CCT diagram and pics of your amps if you have constructed the amp in question ?
best regards
Nick
15w class a
Hello Nick,
I am new to all this as well so I will do my best. I built a few of these a couple years ago and was very happy with them and are available as a kit from Altronics in Perth or bare circuit boards in several guises from RCS Radio in Sydney. I think thay are better run as mono blocks utilising separate power supplies as the single power supply runs very hot , unless you use a large heatsink, powering dual channels. I will see if I can find a circuit diag but have moved house twice so hang in there.
PS They are very east to implement and mine powered a pair of 2 way Cabasses and B&W dm4s
Hello Nick,
I am new to all this as well so I will do my best. I built a few of these a couple years ago and was very happy with them and are available as a kit from Altronics in Perth or bare circuit boards in several guises from RCS Radio in Sydney. I think thay are better run as mono blocks utilising separate power supplies as the single power supply runs very hot , unless you use a large heatsink, powering dual channels. I will see if I can find a circuit diag but have moved house twice so hang in there.
PS They are very east to implement and mine powered a pair of 2 way Cabasses and B&W dm4s
Hi Nick,
I hope you enjoy listening to these 15 watters once they are up and running. They have sufficient sensitivity to run without a preamp so a volume control can be added if your source does not have the same and do take care to keep the power supply well away from {12 feet at least} from the amp to keep hum at bay. Should you run into trouble Silicon Chip do have a fault diag service via email for kits they devised.
Cheers
Wayne
I hope you enjoy listening to these 15 watters once they are up and running. They have sufficient sensitivity to run without a preamp so a volume control can be added if your source does not have the same and do take care to keep the power supply well away from {12 feet at least} from the amp to keep hum at bay. Should you run into trouble Silicon Chip do have a fault diag service via email for kits they devised.
Cheers
Wayne
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