Powering the preamp from power amp PSU

[Fredde79]

Hi,

I would like to integrate a simple phono preamp into my lm3886 power amp. The psu for the power amp supplies +/-26 VDC, and the phono preamp (a TL072-design) needs max +/-15VDC.

Is it possible/recommendable to use the same power supply for this? Would for example this ESP "Simple Pre-Regulator" Pre-Regulator be a possible solution?

I hope you have time for this basic question!

Best regards,

Fredde

[BobEllis]

With 26 volt amp rails you can just use a three pin regulator such as LM317 and LM337 to get your preamp rails. Most integrated regulators can easily handle your rails without need for a pre-regulator to drop the voltage.

With an appropriate zener diode string to get you 12-15V you can use the ESP circuit you linked to as your regulator if you add a 100-200 uf cap at the output, but I suspect you will get better performance from the LM3xx regulators. Powering a couple of TL072s you wouldn't need TO-220 pass transistors, as the dissipation would be less than .25W. You could save some space and substitute MPSA42 and MPSA92 or if you want a little more margin, MJE340 and MJE350.

You might also consider substituting OPA2134 for the TL072 in your preamp. A bit cleaner sound, just be sure to put the 100nf power bypass caps right at the chip.

[Fredde79]

So it's even simpler

Space is rather essential here, so I'll be glad to skip unnecessary components. I read in the datasheet that LM317/37 can take 40V which is more than enough.

And yes OPA2134 would probably be a better choice. I have some NE5532 at home so I might go for those. The author of this schematic: Hi-Fi RIAA Phono Preamp also suggests substituting TL072 with either OPA or NE.

Thanks a lot for your info!

/Fredde

[BobEllis]

Glad to help.

FWIW, I prefer the sound of the OPA2134 in my active crossovers to NE5532. For very little money you can add sockets for the opamps and try both. With the distance to the rail bypass caps on Rod's boards, I don't think I'd try anything faster.

[Fredde79]

Yes I usually use sockets anyway, it's easier to correct possible mistakes.

I will not use Rod's board since I don't have room for it in my amp chassis, and, so I'll probably make a tight little veroboard design (as usual).

I don't like using premade PCB:s as you can't make modifications or additions very easily, and IMO it simply takes away part of the fun with DIY! My first electronics-project was a velleman-kit phono preamp (the one I'm now about to replace) and when I was finished I asked myself why I just spent much more time and money putting a kit together (bad sounding and with low grade components) than buying a cheap and good sounding factory made preamp. Then I started to read and modify schematics, buying components, breadboarding and veroboarding. Built a couple of synths of variable weirdness, a few guitar effects and finally a chip amp. So much more fun, and a great feeling of success when something works!

And of course, this forum has been, and will continue to be a great resource! Thanks again!

I don't really know what this refection has to do with anything, but I'll let it stand

Regards,
/Fredde

[Atilla]

If you want to save space/components, get 2 fixed-voltage 15V regulators from the same family and you're good to go.

[Fredde79]

Good idea, I'll see if I can find any in my local store!

Takk for din hjelp!

Edit: 7915 & 7815 (TO220 1,5A) seem to be available, they should do the trick!