A crossed wire here, my query on dual vs single rail was aimed at the VSPS circuit that Paul Sherwin originally posted the link to.
http://phonoclone.com/diy-pho5.html
I've got a board on the go with this circuit, having mounted the EQ networks so far after spending a bit of time matching the capacitors and 1% MF resistors.
Heres a thing, the 1% quarter watt Metal films seem to deviate from the nominal value in about the same error as the el cheapo 5% Carbon films I Use in non critical stuff. i.e. the 5% jobs are remarkably close to their nominal value which is remarkable I think.
OK so right now I'm looking at a value of capacitor from R2 to ground, assume that I am using 220R here for the full 50dB, rather than 680R for 40dB. if there's no issues at 50 dB then that's what I shall use. 220R suggests a 220uF capacitor, but if I want to roll off at around 15Hz I think 100 or even 47uF might be more appropriate?
I accept a higher gain means I have to use a higher voltage power supply, currently a 15V AA cell battery pack, and I have another one I can use to make a 15 0 15 V dual supply for now.
But I was doodling around with the circuits and I could see no reason why adapting that simple circuit to work off a single rail shouldn't work.
I was looking to bias the op amp up with a pair of 180k resistors, bearing in mind the noise filter on the inputs there.
The coupling capacitor would then have a 100k across the input side to earth across the cartridge output which would give an overall 47.3k load which isn't a country mile off. that assumes I get a combination of resistors on the top leg of the biasing and noise filter that equals 180k.
Or I forget the 100k which isn't really necessary but nice as mark points out if hot swapping headshells. That's not something I can do anyway but who knows in the future., in that case its fudge around to get 47k load across the input/bias resistors as I like symmetry and seems good practice to reduce DC offsets as much as practically possible and easily achieved using E24 resistors.
I also will put something like 200 to 470uF across the supply to ground whichever stratagem I decide on. And should I put a 0.1uf ceramic or other across the supply pins of the op amps? That seems to be omitted on the circuit and I thought a small value cap across the supply pins as close as possible helped prevent instability?
People new to this thread may be wondering why I am trying another simple chip circuit when the first one seems to work so well. I'm curious, this is nothing more than me discovering stuff for myself.
With masses of help from others here.
Andy