Newbie with headphone amp questions:

Hello all!
I have a few beginner's questions about the construction of a basic headphone practice amp circuit found here:

**broken link removed**

a) the circuit diagram has three connections (two at the input stages and one near the battery) laballed B. Are these connected together?

b) at pin 8 of IC1 is C8. This is not covered in the legend. Safe value?

c) Q1 and Q2 are presumably input boosting npn transistors. I can't find any BC-549's locally. Any recommended equivalents?

d) I'm guessing from the diagram that P1 is what I would label VR1 and is a 50kohm audio taper pot. Okay to use a 100Kohm if I can't find a 50k?

e) The capacitor values are all in microfarads with the exception of C7? And the designation x16 would be the operating voltage? (i.e. 2.2x16 would be 2.2 microfarads at 16volts?)

Thanks!
Cheers
Chris

emotepix said:

Hello all!
I have a few beginner's questions about the construction of a basic headphone practice amp circuit found here:

**broken link removed**

a) the circuit diagram has three connections (two at the input stages and one near the battery) laballed B. Are these connected together?

Click to expand...

Yes, R8/9 create a 4.5V (half power rail) supply.

b) at pin 8 of IC1 is C8. This is not covered in the legend. Safe value?

Click to expand...

It's to give a treble boost, try different values to find what you like, or just leave it out (it's switched in and out by a switch anyway) - or try anything from 1000pF to 0.47uF, and see what effect it gives. But it's clearly marked as 0.1uF in the parts list.

c) Q1 and Q2 are presumably input boosting npn transistors. I can't find any BC-549's locally. Any recommended equivalents?

Click to expand...

They are common NPN low noise audio transistors, any small NPN would be fine.

d) I'm guessing from the diagram that P1 is what I would label VR1 and is a 50kohm audio taper pot. Okay to use a 100Kohm if I can't find a 50k?

Click to expand...

Yes, a log pot, and 100K or 47K would be fine.

e) The capacitor values are all in microfarads with the exception of C7? And the designation x16 would be the operating voltage? (i.e. 2.2x16 would be 2.2 microfarads at 16volts?)

Click to expand...

Yes, it's only got a 9V supply, so anything over that would be OK.

My goodness, that was fast!
Thanks, Nigel, you are your legend!
Cheers
Chris