We've all been there.
I've probably got half a dozen of the very same hats floating around, if only I can remember where i left one......
I've probably got half a dozen of the very same hats floating around, if only I can remember where i left one......
hi, i had also done this project but i put 8 ohm load resistor instead of 15r. what should be the right midpoint voltage in order to get maximum output swing out the ckt with an 8 ohm speaker? will it be 8volts too?
My current set up is at 12v midpoint voltage. Also planning to use automotive head lamp 12v 90w..will it be possible as load?
Hi Junm.
You should be about right with 12V for 8R resistor. Best way to check is to feed a sine wave in and up the volume until you get clipping then adjust the volts set pot for equal clipping as seen on a 'scope.
Don't use a headlamp bulb as the resistance changes dramatically depending on temperature (intensity of illumination), and you may well blow the FET when switched on cold.
Regards
Henry
PS do let us know how it works out.
You should be about right with 12V for 8R resistor. Best way to check is to feed a sine wave in and up the volume until you get clipping then adjust the volts set pot for equal clipping as seen on a 'scope.
Don't use a headlamp bulb as the resistance changes dramatically depending on temperature (intensity of illumination), and you may well blow the FET when switched on cold.
Regards
Henry
PS do let us know how it works out.
I've thought about this a bit more and it could be that even with 8R the output should be at 8V, and with 15R possibly even lower.
I might even have to knock up this circuit quickly to test the guess.
Probably won't be able to do that until next week as I'm busy getting myself organised for the Big Audiojumble at Bracknell this Sunday (Stallholder)
I might even have to knock up this circuit quickly to test the guess.
Probably won't be able to do that until next week as I'm busy getting myself organised for the Big Audiojumble at Bracknell this Sunday (Stallholder)
Teoretical, and my SPICE simulation test shows, it should be +8V to +9V for a 8R resistor.
This means like 2A current. This gives maximal outputt.
Okay thanks henry for the info....one more thing how about 2 pcs // 20w 12 volts (40W total) bulb which i also have..will it suite the requirement?
thanks lineup, i try to play with this soon and even test it with other kind of load.
If you make this amp balanced then you've also made it bridged. The major difference, other than power, is that the relatively high distortion of such a simple circuit is going to change in character quite a bit between single-ended and differential mode. Maybe someone running simulations of these circuits can post some FFTs of the same circuit in both modes.
Hi Lineup, thanks there for the confirmation, around 8V will be correct for 8R resistor.
Junm, don't use light bulbs here, they are very non linear as are highly temperature dependent.
Junm, don't use light bulbs here, they are very non linear as are highly temperature dependent.
Guys: A good friend of mine eluded me to this thread. I have just read all the posts and would like to point out a few things about my ZCA. Firstly there are hundreds of these amps in the wild and I get regular mail from those who are building them. The ZCA seems to impress most who do build them. If you stay very close to my original cct. and specs I’m sure you also will be pleased with the results. For such a simple amp it works extremely well.
Note these points: The amp verges on instability but thanks to FET’s having a negative temp. coefficient this is OK. If you drop the load to 8omhs you must lower the B+. Because the amp is pure class A the PS must deliver very clean DC power or your amp will hum. A choked PS in both SS and tube gear generally sounds better than a non-choked PS and in this case provides clean DC. Choke the PS.
The amp gets very hot. Use a large heatsink with good ventilation and an over specced power tranni. The amp inverts the signal so swap the speaker connections around inside the amp. In the first week you will need to adjust the bias initially hourly then once a day and after a week of play check it twice a year. The FETs and other components settle due to the heat generated. I always divide the PS across load and FET.
Build and enjoy.
Note these points: The amp verges on instability but thanks to FET’s having a negative temp. coefficient this is OK. If you drop the load to 8omhs you must lower the B+. Because the amp is pure class A the PS must deliver very clean DC power or your amp will hum. A choked PS in both SS and tube gear generally sounds better than a non-choked PS and in this case provides clean DC. Choke the PS.
The amp gets very hot. Use a large heatsink with good ventilation and an over specced power tranni. The amp inverts the signal so swap the speaker connections around inside the amp. In the first week you will need to adjust the bias initially hourly then once a day and after a week of play check it twice a year. The FETs and other components settle due to the heat generated. I always divide the PS across load and FET.
Build and enjoy.
I would try 8.5V. (8V is only a teoretical value).
In practice the value can be 8.5V or even 9V.
As markhouston himself says,
- a clean supply and a rather big transformer is a must - otherwise ripple hum
- a larger heatsink (than for 15R)
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A test I remember Nico Ras suggesting is to us a big capacitor in series with some headphones and put it on the power rail - if you can hear hum, it isn't good.
The challenge with such a basic SS Class A design is having low rail voltages compared with tube amps, using a resistor (or a light bulb as Nelson Pass has demonstrated) as a load to approximate a constant current source doesn't work nearly as well (technically that is, not sound-wise) with these lower rail voltages as lower value resistors are needed - which more or less couple the supply rail hum straight to the output. But I like this design - when the school text books on common source amplifiers say this simple ciruit can't be used for high power it's good to see somebody proving it can be done !
The challenge with such a basic SS Class A design is having low rail voltages compared with tube amps, using a resistor (or a light bulb as Nelson Pass has demonstrated) as a load to approximate a constant current source doesn't work nearly as well (technically that is, not sound-wise) with these lower rail voltages as lower value resistors are needed - which more or less couple the supply rail hum straight to the output. But I like this design - when the school text books on common source amplifiers say this simple ciruit can't be used for high power it's good to see somebody proving it can be done !
I just used cerammic encased resistors for my load (4 x 10W). The heatsink I refere to is for the FETs.
Mark,
Is there a more detailed article describing this very interesting looking amp?
Cheers,
Keith Arnold
blakkshepeaudio
Is there a more detailed article describing this very interesting looking amp?
Cheers,
Keith Arnold
blakkshepeaudio
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and a higher voltage variant :
High voltage version of Mark Houston's ZCA single mosfet amp • DIY Audio Projects Forum
High voltage version of Mark Houston's ZCA single mosfet amp • DIY Audio Projects Forum
What would be the output power if I use this amp to drive 4 OHm speakers (two pieces of 8 Ohm speaker in parallel). Please advice.
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