Pre-Amplifier MKII

As the first version of the Pre-Amplifier was a bit noisy + some other problems changes were needed, which resulted in a MKII wersion of the pre-amplifier.

An active DIY Pre-Amplifier based on the OPA627 and BUF634

The pre-amplifier is based on the op-amp OPA627AP and fast buffer BUF634T, see also the PDF file Audio buffer, which is capable at running in class A mode. The Audio buffer can continuously deliver up to 0.25Watt and can be used with e.g. active interconnects or as an headphone amp.


Figure 1: Second version of my preamp (Changed due to noise problems)

A discussion of the construction and sound can be found here High-end preamp and OPA627 + BUF634 Preamp at www.diyaudio.com.

As far as I know the PCB has been designed by Pavel Macura.

Furthermore kits/components from www.dantimax.dk have been used. Mikkel was very helpful when i came to picking the right kits. The following kits/parts have been used:
- RK27M - An Alps RK27 motor potentiometer, 10kOhm
- Control1 - Remote Control front panel kit
- Input1 - Input selector board kit
- Remote1 - The pcb and driver circuit (used to control the potentiometer)

Everything has been put together in an 19" U2 rack

The Audio Buffer

Well the audio buffer can be seen on figure 2:


Figure 2: The active 2 channel Audio Buffer

The Supply

The supply is nothing special, it utilizing the voltage regulators 7815 and 7915 in order to generate a stable +15VDC and -15VDC. So far the supply is just temporary until I build the final supply

Missing
Figure 3: The +15, 0, -15 Voltage power supply

The back plate

RCA interconnects, AC power plug and main power switch is positioned on the back plate.


Figure 4: The backside of the pre-amplifier, RCA plugs and power inlet.

Control1
Control1 is mounted "outside" the cabinet, isolating the noise generated by the crystal on the circuit.


Figure 5: Control1 (mounted with strips)

Planned future upgrades
Power supply:
Components for a Jung super regulator has been bought. The PCB needs to be designed and produced.

The Sound
So far... Well... I'm satisfied and that's what counts.
A review of the sound of the op-amp OPA627 can be found here OPA627 review (I most definitely agree)

Everything has been put together and is working nicely, there is no noise issues. This preamp combined with my DIY UcD400AD power amp is dead quiet, when no signal is connected or through quiet passages in the music.