+T, thanks for the drawing!
So, do you think the LT1469 is going to be better than the LT6233 I'm using? The LT1469 has better specs (and comes in a DIP package!) but takes 3.5mA vs. 1.2mA for each amp. I might build around the 1469 if it is better. Also, can you PM a source for LT1469? I checked Digikey but they don't have any in stock.
Another note is the gain. I like a gain switch instead of a pot, but that is personal preference.
Good luck, and please bring back photos when you're done!
Richard
Hi again
It's difficult to say whether the 1469 will be better than the 6233 - it's a bit of a gamble until you listen to it, although either op-amp is probably better than the mics. I wanted something that was unity gain stable, and I wasn't all that worried about the current draw. I doubt I'll need more than about 25hrs between recharges! I preferred it to the 6233 because of lower input bias current and better supply rejection. The noise is a little higher, but I believe that the mic noise will the dominant factor. I also liked the circuit topology from the data sheet - looks like the kind of thing I might design
One small issue is that it is not guaranteed to work within spec below 9V (it will typically work at 5V, but 9V is the worst case). Most PP3 rechargeables are actually 8.4V, but I managed to find one that is 9.6V (and still 220mAh).
I considered a gain switch but decided on a pot because this may sometimes be used into a minidisc (Hi-MD) recorder. On that, you can't adjust the record level without pausing the recording. Pretty daft, I think.
I'm afraid I'm in the UK, so I doubt my sources would be of use to you...
I'll post some pics when it's done. I've just worked out a layout that lets me use the box I wanted, but it only just squeezes in. It's a good job that I could only source the LT1469 in surface mount format, I guess
Any thoughts on the values of the bass cut frequencies? I still don't know why it's needed - if the bass level is so high, surely the gig would sound awful? Still, I've put them on there just in case, at frequencies mostly decided by the capacitors I had available.