Quote:
Originally Posted by Craig Sawyers
If you are putting an electrolytic from R2 to ground to make an LF roll-off that is the wrong way to go. The tolerance on electrolytics is very wide, and they can introduce harmonic distortion.
Bung another stage on and build a Sallen and Key second or third order filter around it using film capacitors.
Anyhow, the RIAA values in the phoneclone are absolulely fine. Time constants all work out very close to correct.
Craig
|
I wasn't thinking in terms of that being the only reason, but that it is a good idea to put a capacitor there according to advice elsewhere. A quick calculation suggested to me that a 47uF off a 220R resistor got a pole at around 15 hz which was sufficiently low not to affect the LF end.
So would you also say a 1uF at the input is the right value or a bit lower at around 330nF would be more suitable to avoid any excessive LF making it into the circuit.
Its all a bit up in the air until I can get somewhere I can buy some cheap batteries, our village store wants a fiver each for a PP3! And I also want a batch of AA cells.
Ah well maybe I am just making life difficult.
A.