Citation:
So folks,
too often I heard the rumours about the "fabulous" Korg SDD-3000 preamp which a guitarist used one time.
So I took the SDD-3000 schematic and drew out the relevant part, which can be found here:
Korg SDD-3000 preamplifier schematic
I added a footswitch. This circuit is supplied with +/- 15V in the SDD-3000.
Since this is a horror for battery-junkies, I adapted this circuit for use with a battery. The schematic can be found here:
Analogguru SDD-preamp schematic
There shouldn´t be any difference in sound, only in the maximum headroom is smaller.
Some remarks to the circuit:
R2, D1, D2 are for protecting the TL 072 from static discharge by plugging in the guitar. Marshall omitted them on the valvestate series and had a lot of problems with broken TL072 - they become noisy.
Since the next stage is inverting, D3 and D4 do: simply nothing.
The 3k3 resistor from the +input to Vref is there to minimize offset problems by keeping the input current the same. Since this stage is the second half of the TL072 (high-z FET-opamp) it wouldn´t be necessary to use it.
The coupling capacitor of 10µF (C7) is not necessary to be so high in the "standalone" application. 470n is far enough. With that value you will have a lower corner frequency of -1,5 dB at 20 Hz. For guitar application 100n would do it too, but too keep the original design intact as far as possible I used 470n.
The rest of the adapted values will not have any difference to the original circuit - it´makes it only easier to build.
Since there is a half of a dual op-amp unused I made with it a buffered reference voltage around IC21-1.
I won´t do a pcb or stripboard layout for this, maybe somebody else.
Dirk Hendrik has made a pcb layout (23/08/200
enjoy building and use of this preamp,
analogguru