18-12-2015, 04:04 PM
The suggested TL081 opamp is hardly an ultra-low input current device. Yes, it's a JFET opamp and the input current will be low enough for any general purpose application but there's plenty that are a lot better. Pinboard (verboard without the copper strips) should be good enough for this sort of device. Otherwise "dead bug" is a quick and dirty way to get low leakage and capacitance. Here's a marvellously untidy dead bug circuit: http://kd1jv.qrpradio.com/ap80/AP_80_ugly.jpg
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
