Here are a couple simple preamps I drew for protoyping. It is built on the protoboard you can get from futurlec.
These two designed work great for me.
The power supply is not shown, but any decent power supply from +/-10V to +/-18V should work fine.
I build mine with a regulated +/- 12V supply.
Only one channel is shown. You can build two channels per side of the board, which if you are doing a stereo preamp allows you to use the entire other side for the power supply which is what I did.
I can send a drawing of the PS and photos if you wish.
Drawing #1 is the opa627/637 + buf634 version.
Drawing #2 is a LT1015 + LT1010 version with 2 channels shown. This version may benefit from a 5-100pf cap soldered direct between the negative input and the output of the LT1015 if you see any instability. The biasing for the LT1010 will make it run pretty hot. You can safely omit the biasing resistor, or use a high value like 1K.
Both also make excellent headphone amps.
Humbly submitted in the hope you have some fun.
These two designed work great for me.
The power supply is not shown, but any decent power supply from +/-10V to +/-18V should work fine.
I build mine with a regulated +/- 12V supply.
Only one channel is shown. You can build two channels per side of the board, which if you are doing a stereo preamp allows you to use the entire other side for the power supply which is what I did.
I can send a drawing of the PS and photos if you wish.
Drawing #1 is the opa627/637 + buf634 version.
Drawing #2 is a LT1015 + LT1010 version with 2 channels shown. This version may benefit from a 5-100pf cap soldered direct between the negative input and the output of the LT1015 if you see any instability. The biasing for the LT1010 will make it run pretty hot. You can safely omit the biasing resistor, or use a high value like 1K.
Both also make excellent headphone amps.
Humbly submitted in the hope you have some fun.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I forgot to mention that I used a simple 10K stereo pot for volume control.
Also note that I did not use input capacitors since I know that I have no DC coming from my source. If you think you might you should add at least a .2uf capacitor either before or after the pot (I have seen people do both).
Also note that I did not use input capacitors since I know that I have no DC coming from my source. If you think you might you should add at least a .2uf capacitor either before or after the pot (I have seen people do both).
pics of finished preamp
Here is the LT1115 version finished.
Here is the LT1115 version finished.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
The trafo is 2amp 25VCT it actually puts out closer to 30V idle.
After full bridge rectifier I have ~ +/-16V which is then regulated to +/- 12.
Of these two designs I really like the 1115 and 1010 combo best so far. But really I think I like AD8610/8620 best (different pre).
The circuit draws very little idle (a few ma), but it could drive about 150ma per channel.
One thing I am changing tonight is I will make the input impedance 100K instead of 1M. I am getting too much line noise.
After full bridge rectifier I have ~ +/-16V which is then regulated to +/- 12.
Of these two designs I really like the 1115 and 1010 combo best so far. But really I think I like AD8610/8620 best (different pre).
The circuit draws very little idle (a few ma), but it could drive about 150ma per channel.
One thing I am changing tonight is I will make the input impedance 100K instead of 1M. I am getting too much line noise.
Well actually it is not 100% efficient, and that is 150ma per channel. So i would say it could actually draw 400-500ma at its full potential. But still the trafo I have is certainly overkill. I got it cheap a while back at an estate sale. Plus I know it to be a very quiet well built trafo with next to no EMI.
You could probably use a 400-500ma trafo fine with either of these circuits.
I have 1,500uf on each rail prior to the regulators, then there is 1000uf per rail after the regulators.
The output capactitor can be as large as you like or even omitted (mine is 1000uf) you only need the small input cap if your regulators are not close to the power supply(filter) caps. Mine are about 3/4" from the 1500uf filter caps. So I do not need the additional filter cap on the input to the regulators.
It did improve the sound. Funny thing though. The regs are running cooler, but the trafo warmer now... wild.
In any case I got great input from Jan, Mauro, macboy, and peranders in no particular order.
The pre-amp sounds great.
For all those who have not thought about it the LT1115 and the LT1110 are quite a combo.
I will next try the opa637/buf634 in the same circuit.
I will also try the opa637/LT1010 as well as the LT1115/buf634.
Thanks to all who helped me. I am sure I forgot a few.
In any case I got great input from Jan, Mauro, macboy, and peranders in no particular order.
The pre-amp sounds great.
For all those who have not thought about it the LT1115 and the LT1110 are quite a combo.
I will next try the opa637/buf634 in the same circuit.
I will also try the opa637/LT1010 as well as the LT1115/buf634.
Thanks to all who helped me. I am sure I forgot a few.
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