Peter Daniel moving magnet
 
Phono Preamp

Built 4/22/09

 

This preamp design was published by Peter Daniel on DIYAudio.com, in his AudioSector thread (in Vendor's Bazaar forum in the marketplace section) on DIYAudio.com, here.  Peter's website is AudioSector.com.  Like many of Peter's designs, this one uses a low parts count circuit with short signal paths and high quality parts.

 

Above: Peter Daniel's schematic, click to enlarge.  This circuit is similar to the VSPS project, by RJM Audio, here.   That project is also supported by a diyAudio thread, here.  Peter however, has optimized parts values and types.  The PCB designed for the VSPS project appeared to fit this project well except that it lacks spots for the rectifiers and the first set of pre-regulator caps.  However, I found a small PCB that fits the bill perfectly...

 

Above: The rectifier PCB I used, from Chipamp.com as part of their LM1875 amp project. 

 

Above: The populated rectifier PCB, with MUR860 diodes and blackgate 100uf/25V caps.  Note that to inlcude the 10 ohm dropping resistors on this PCB, I had to cut a trace on the bottom of the PCB (not shown here).

 

Above: The main PCB including power supply regulators, is shown above.  It was designed by for the VSPS project, and purchased on ebay from seller akita.skycoral.  Note that this PCB is designed for 2 channels, and normally uses a dual op-amp (such as the OPA2134).  Peter's circuit calls for the OPA627, which is only available in mono configuration, so I used a Browndog adapter (here) to mount two OPA627's where one dual IC would go on the PCB, as shown below. 

 

Above: PCB populated.  I used parts values suggested by Peter, and mostly his suggested brands as well, with the primary exception being the use of Resista and Dale resistors instead of his recommended Caddock MK132s.   These include LM2937 and LM2990 regulators and Blackgate 1000uf/25V PS caps, and Blackgate Type N's as output couplers and as local PS decouplers located at the ICs.  I also used RelCap RT Polystyrene and WIMA FKP-2 RIAA caps, both selected to 1% of the target values.   I've read that the OPA627's sometimes oscillate if mounted in sockets, so there are no sockets between the chips and the Browndog adapter or between the adapter and the PCB.

 

Above: another view of the completed PCB.  I also decided to mount the input RCAs directly to the PCB.  I used Vampire PCB2F/S connectors.

 

Above: The classis used was also sourced on ebay, from seller fan_computer.  Its a nice extruded two piece aluminum box that is held together by the endcaps.  This shows the main PCB installed, along with the IEC jack and fuseholder.

Above: Fully assembled unit without faceplate.  I added a divider around the main PCB to isolate it from any AC in the chassis, otherwise a pretty simple setup.  AC input at the IEC on the top right, to the power transformer, to the regulator PCB, which feed unregulated DC to the main board.  All audio signals are in a very short distance from the input/output jacks.

 

Above: Rear view showing back panel.  I used dry transfer lettering for the labels.

 

Above: completed unit, with front panel from Frontpanelexpress.com.  The front panel contains simply the power switch and an LED.

 

Above: Completed unit, rear view.

 

When I tested the frequency response of the preamp, it was within the tolerance of my Hagerman inverse RIAA (0.25db).

Upon listening with my Dynavector 10x4 cartridge (a high output moving coil, 2.0mV), the gain was a bit low, so I added a 100ohm resistor in parallel with the 220ohm to ground, increasing the gain from 40 to 50dB.

Its still breaking in, but already sounds great!

 

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