Hello and happy New Year!
I wanted to post something for the forum on the first day of 2008 in the hope that we all have happy and enjoyable new year, and hopefully some of you can use it in your audio pursuits.
I have designed a discrete operational amp/headphone amp I have named "Diamante" mostly because it has a diamond buffer type output stage.
The design is pretty simple and not at all expensive to build. The cost/performance ratio is very high. The prototype was made with all BC550 and BC560 transistors but others with the same pin configuration can also be used. I chose BC550/BC560 because of their low noise and high gain. Many transistors have reverse pin configurations and they can also be used but you will need to put them in reversed of course.
The basic schematic as shown is configured as a 6db voltage gain headphone amp. But you can configure the board any way you like. The amp is unity gain stable with 10pf at C5. Choose RF and RG so as not to overly load the output stage.
The output R (R26) is a 3W type with magnet wire wrapped around it (15-20 turns is fine) to form an output inductor. This will prevent ringing into capacitive loads, but it is not required. The amp is stable without it. if you wish to omit it you can jumper it with wire or take your output at the resistor pad.
Rbias sets the bias for all stages. I should be a 1K pot, when initially setting up the amp set it to full 1K resistance. Then slowly adjust it downward until you get about 25mv across the emitter resistors (R1-R6). This is a safe bias point.
Once you have the bias properly set, then adjust Roffset to get 0V offset from output to GND.
Wait around 5 minutes and re-check bias and offset.
This amp is pretty simple to scale. As it is presented it should be about to do 100ma or so without much problem. If you change the output devices you could get even more output.
It drives headphones with ease and that's really the purpose I had in mind. I will easily drive even 32ohm cans. 300ohm types such as HD650s are cake for this amp.
Noise floor is very low with the transistors specified. I can't hear any noise through the cans - nada.
Distortion is very very low, though I don't have any pretty graphs to show you yet.
So happy new year to all. I am providing PDFs and the Schematic for those who want to etch boards for DIY use only. The amp can actually be built pretty easily on prototyping board too.
Here is a picture of a prototype (slightly different CCS) in use. Special thanks to Brian Donegan who etched stuffed the first boards and encouraged me to finish the project.
Cheers!
Russ
I wanted to post something for the forum on the first day of 2008 in the hope that we all have happy and enjoyable new year, and hopefully some of you can use it in your audio pursuits.
I have designed a discrete operational amp/headphone amp I have named "Diamante" mostly because it has a diamond buffer type output stage.
The design is pretty simple and not at all expensive to build. The cost/performance ratio is very high. The prototype was made with all BC550 and BC560 transistors but others with the same pin configuration can also be used. I chose BC550/BC560 because of their low noise and high gain. Many transistors have reverse pin configurations and they can also be used but you will need to put them in reversed of course.
The basic schematic as shown is configured as a 6db voltage gain headphone amp. But you can configure the board any way you like. The amp is unity gain stable with 10pf at C5. Choose RF and RG so as not to overly load the output stage.
The output R (R26) is a 3W type with magnet wire wrapped around it (15-20 turns is fine) to form an output inductor. This will prevent ringing into capacitive loads, but it is not required. The amp is stable without it. if you wish to omit it you can jumper it with wire or take your output at the resistor pad.
Rbias sets the bias for all stages. I should be a 1K pot, when initially setting up the amp set it to full 1K resistance. Then slowly adjust it downward until you get about 25mv across the emitter resistors (R1-R6). This is a safe bias point.
Once you have the bias properly set, then adjust Roffset to get 0V offset from output to GND.
Wait around 5 minutes and re-check bias and offset.
This amp is pretty simple to scale. As it is presented it should be about to do 100ma or so without much problem. If you change the output devices you could get even more output.
It drives headphones with ease and that's really the purpose I had in mind. I will easily drive even 32ohm cans. 300ohm types such as HD650s are cake for this amp.
Noise floor is very low with the transistors specified. I can't hear any noise through the cans - nada.
Distortion is very very low, though I don't have any pretty graphs to show you yet.
So happy new year to all. I am providing PDFs and the Schematic for those who want to etch boards for DIY use only. The amp can actually be built pretty easily on prototyping board too.
Here is a picture of a prototype (slightly different CCS) in use. Special thanks to Brian Donegan who etched stuffed the first boards and encouraged me to finish the project.
Cheers!
Russ
