Sort of stompbox related DC power question?

[chumbox]

Hey All

Looking at putting together this phono preamp:

http://www.paulinthelab.com/2014/05/riaa-phono-preamp-stripboard-layout.html

However the power section of the circuit is shown as Vin and Vin-.  Are these just referring to the + and GND (-) connections as usual or is there something else I should be considering here?  I have worked out (I think) that the ground symbol in this pic is the audio ground from work back from the vero in the link.



Thanks in advance.

[amptramp]

Since you have no connection to ground from the power input, the ground will move around a bit - enough that the result may not be what you want.  If you want to retain the single supply, you may want to use an amplified  ground that you can make from an op amp section connected as a unity gain follower to where the junction of R10 and R11 are now and use the output of the op amp as ground.  I believe you can do a simple rail splitter with an LM386 as well.

[PRR]

Use a dedicated (un-shared) power supply, at least 15V (else clipping will spoil your fine vinyl sounds), and LOW hum/ripple.

Personally I would use 30V-36V total, and 2-stage R-C ripple filtering before the opamp.

Don't even try to put the power supply in the same box as the preamp.

Two (or four) 9V batteries is an excellent phono preamp supply. If you remember to turn it off, battery cost will be less than stylus replacement cost. Then you can avoid the rail-splitter, though I do not think it is a real issue.

[merlinb]

However the power section of the circuit is shown as Vin and Vin-. 

That circuit requires a floating power source (not a problem). What he has labelled Vin is actually the positive supply input e.g. battery + terminal, and what he has labelled GND is actually the negative supply input, e.g. battery - terminal.

[chumbox]

Thanks all for the advice, it's all a lot clearer now.  Thanks Merlinb for clearing up the connections and  I'll get started on this over the next week or so and let you know how I go.  I'll be sure to use 15V or above as you suggest PRR.  Once I get this circuit running on a breadboard amptramp I'll see if I can get the amplified ground idea working as well, that really tweaked my interest. 

[ashcat_lt]

However the power section of the circuit is shown as Vin and Vin-. 

That circuit requires a floating power source (not a problem). What he has labelled Vin is actually the positive supply input e.g. battery + terminal, and what he has labelled GND is actually the negative supply input, e.g. battery - terminal.

NO!!!  So completely no.  It may not blow anything up to connect it like that, but it sure ain't gonna work right.

The Vin+ is the most positive wire from the power supply and the Vin- is the most negative.  The ground is "virtual", situated halfway between the two.  You do have to be careful about where you reference the enclosure and how that voltage relates to those of the other things you might connect this to.

[davent]

I've used the TLE2426 in a bunch of headphone amps to create the virtual ground in a bunch of headphone amps, powered by a series pair of 9v. Also had  battery packs for ten 'AA's that i could use.

For a phono preamp built a discrete circuit with a complimentary pair of BJT's that did the job fine.

http://ca.mouser.com/ProductDetail/Texas-Instruments/TLE2426CLP/?qs=sGAEpiMZZMuBck1X%252b7j9fIoDfAon0vCg%2fkby7j1fvE4%3d

[chumbox]

For a phono preamp built a discrete circuit with a complimentary pair of BJT's that did the job fine.

Do you have a preferred discrete circuit you used for the phono purpose?

[davent]

This is what i used.