Dual Inverting Pre-amp, so named as it have dual output, and it
uses inverting schematic.
Some time ago, after I completed my gainclone, I decided to make
a Pre-amp. A search reveals that OPA627 and AD8610 are the most
favored opamps for pre-amp. Since I cannot decide which opamp to
use, I decided to use both, so that I can compare between them.
I follow nearly the same schematic as the gainclone, but uses 2.7x
gain instead of 22x. The configuration is again inverting (how much
I like the simplicity of inverting!) There are very few components,
and I knew I could never go wrong with simple schematic.
The resistors and caps values are chosen because the shop I got
the resistor from only have a few selected values for Holco resistor.
Again, R4 is selected to balance the resistance seen at both input
ports - to make sure the output offset voltage remains low.
C1 is the decoupling cap, even though the power supply cap is very
close to the IC.
I got this nice box from a 2nd hand shop. The cover looks and feels
like plastic, but it is in fact aluminum!
I will be using 1000uF MUSE, 1uF stacked film, Holco resistors
and MUR860. I got the Noble pot from a friend, and the Elma 3 way
switch from Farnell. I have 2 AD8610 and 2 OPA627 on hand at that
time. The transformer is dual 0-15v, but since I run the primaries
in series, the voltage is cut by half.
I use coupler to place the pot and switch as near to the rear as
possible. I do not like the idea of running the signal cable too
I etched a PCB so that it is easy for me to solder, as well as
I can make it as compact as I like. Also I can use very minimum
jumper and the orientation of the components can be controlled.
Cat 5 Teflon cable is use to connect the signals between the PCB,
input, switch, pot and output.
Finally, the DI-Pre is completed after 3 months of planning and
You can see more pictures here.
After listening to the DI-Pre, we concluded that the AD8610 sounds
nearly like the Bridge of Zen. The AD8610 have a wider sound stage,
better highs. The OPA627 have better transparency and better mids.
However, it is very hard to decide which sounds better; as different
music have different impact on each opamp - on some music the AD8610
sounds better, while on some the OPA627 sounds better.