HEADPHONE PRACTICE AMP

I needed a headphone practice amp with the following requirements:

1. Mono bass/guitar input.
2. Stereo CD input.
3. Stereo headphone out.
4. Individual control of stereo and mono inputs.

This is based on a design by PAiA. The 5532 opamps where chosen for their high output. TL072 or 4552 opamps will not work here.

I borrowed an idea from Johan Blomdahl, and used the free opamp to provide the reference ground. Not only does this give a very stable reference, it makes it much easier to provide the input voltage since it does not need to be split.

I show two batteries in the schematic, but I have successfully run the effect off one 9V battery. It runs even better from a 12V supply.

Notes

• For the 5532, pin 8 goes to Vcc and pin 4 goes to -Vcc.
• The two 500k pots shown should be dual ganged. 250k pots where specified in the original, but I only had a 500k on hand.
• I have very efficient headphones (Audio-Technica ATH-M40fs) and I found that the original amp had way too much gain. I changed the opamp feedback resistor and cap from 100k/47pF to 10k/470pF. You may need to change them back.
• A cab simulator would probably help the sound from the bass/guitar.

Credits

• PAiA for the basic stereo headphone amp.
• Johan Blomdahl for the opamp voltage reference idea.

Back to the stompboxes.

Contact Sean MacLennan
Last modified: Sat May 14 23:10:11 EDT 2005