Now I know that best practice would be to use a 2 gain stage circuit but the purpose of this exercise was to see if I could get an ACCEPTABLE result for a less demanding application, such as perhaps replacing a ceramic cartridge for a magnetic in an older Gramophone that had a deck up to using a heavy ish tracking mag cartridge, (Some DJ stuff is good for 5g tracking weights).Īnyway, first impressions have been very favourable and I am getting a nice sound via my reasonably decent stereo system, certainly good enough for many people.

So after a bit of advice and thought, I altered the feedback resistors R8 and R9 to roughly 770 ohms by the expedient of a 1k in parallel with the existing 3.3k.

In fact it was struggling to drive the old Leak Stereo20 and that only needs 125mV. And 150pF across the input to give a bit of capacitive loading for my mag cartridge.Īs built it was a bit weedy for my power amps that need over half a volt to drive to full power (I use either a 'passive' volume control or a unity gain cathode follower buffer, or a rega preamp set to unity gain.) The only mods i made were to use polypropylene capacitors on the EQ instead of ceramics (ugh!) and polyesters instead of electrolytics for the 1uF DC blockers on input and output. What started this off was building up one of the velleman kit magnetic cartridge preamps based on a TL072 with the EQ in the feedback network.Įverything seemed fine on the initial build. Until today I had more or less thought that these audio op amps were more or less interchangeable.

Download tl072 pinout for free