Construction Guide
Hints and tips for the VSPS and Phonoclone projects.
First, what cartridge do you plan on using? Low output moving coil, you'll be building a Phonoclone. For everything else, there's the VSPS. Next, choose which circuit board to use. There are a selection of boards available for each project, differing mainly in the complexity and quality of the voltage regulator circuitry. The simple fixed-voltage LM7812-based boards are small and cheap, while the Xreg versions are larger and more expensive. The phono stage, voltage regulators, and filter capacitors are all present on the board layout but you'll need a power supply as well as the chassis and hardware. The power supply is simply a power transformer and rectifier diodes as everything else is on the main circuit board. The supply is usually placed in a separate case. More about the power supply in the next section!
Completed Phonoclone B.E. boards fitted in a Hammond 1590D aluminum project box.
The VSPS Power Supply
Although an external supply is recommended, the power supply and phono stage can share a common chassis if desired.
The same external power supply consisting of a transformer and rectifying diodes can be used for all the VSPS and Phonoclone varients, and actually just about any op amp based audio circuit you might come up with, be it a line stage, mixer, active crossover, headphone amp, or mic preamp as long as the filtering and regulation circuitry is on the other end so to speak. Two power supplies can be used with the dual-mono VSPS and Phonoclone varients. The "VSPS Power Supply" is therefore an extremely versatile module, I recommend building a bunch and keeping a couple of spares around.
The transformer should have two 12 VAC secondary windings. A good basic choice is a 35 VA toroid, e.g. Talema 62072. (25 VA and 50 VA models are also fine.) Large toroidal or R-core transformers 100 VA or more are recommended for improved performance, e.g. Plitron. Much of the quality of the sound depends on the power transformer, so don't skimp on this part just because the current demands are only a few milliamps. Rectifying diodes (200 V / 3 A or larger, e.g. Vishay GBPC 602-E4/51GI) and a 250 mA, slow-blow (T-type in Europe) fuse rounds out the required componentry. A switch and power indicator LED are strictly optional.
Voltage Regulation and Filter Capacitors
All the circuit boards have these circuit elements build in, so you don't need to include them in the power supply. The description is included for your information, and for anyone building the circuits from scratch. The simplest versions of the VSPS and Phonoclone projects use fixed voltage 3-pin regulators, e.g. LM7812 and LM7912, with electrolytic filter and bypass capacitors on the inputs and outputs, respectively. The input capacitors C_in are typically 1000 µF, while the output capacitors C_out should be smaller, typically 100 µF or less. Make sure the voltage rating is 25 V or higher.
The high performance versions use the Xreg circuit.
Sourcing the Parts
All components can be bought from Digikey, Mouser, or similar online suppliers. Audio specific parts are be obtained from specialty retailers like Parts Connexion.
The circuit boards are designed for 7 mm, 0.25 W resistors.
Nichicon Muse (FW or KW) 1000 µF and 100 µF can be used in all current boards as filter and bypass capacitors. Most standard low impedance types like Nichicon KMG, Panasonic FC etc. may be substituted. The larger capacitors on the boards are 10 mm diameter, 5 mm lead spacing. The smaller ones are 6 mm diameter, 2.5 mm lead spacing. The brand or value is not critical, just note that some special audio types are larger than normal and may not fit.
For the RIAA capacitors C1 and C2, all boards excpet for the stereo VSPS will accept Cornell Dubilier silver mica 100 V or 500 V rated models in the outer set of pads. Alternatively Wima FKP2 capacitors (5 mm lead spacing) can be fitted in the inner set. If possible hand-pick matched values that are as close as possible to those listed on the project page. The stereo VSPS board can accept any slim-bodied metallized film capacitor having a lead spacing of between 5 mm to 10 mm.
There are various options for the output coupling capacitor C3 depending on the board. The default is a small Nichicon audio grade bipolar electrolytic. The VSPS 300 and Phonoclone 3 will also accept Wima MKP4 series with 27 mm lean spacing. Large axial film capacitors can be used with two VSPS boards. The value should be around 2.2 µF.
There is also a worksheet with Mouser part numbers for all current boards which you can download.
Soldering the Circuit Board
A couple of tips for stuffing the PCB: Soldering components to a PCB is a little harder than doing point-to-point. Since the components are usually snug to the PCB that leaves precious little lead length between the component on one side and you soldering on the other. Smoking the components is a real risk. I found the following recipe works for me: place the component snug to the PCB, and bend the leads on the opposite side of the board out slightly to hold it in place. Place the soldering iron tip on the pad first for a second or two to heat that up before moving the tip slightly so it contacts both the pad and the lead wire. Wait a further couple of seconds to get the wire locally hot before applying the solder. Of course getting the timing right is, well, a matter of practice.
All the components can be placed on the top, print, side of the PCB.
The op-amps can be used with sockets or soldered directly to the pcb. The order in which to solder in the components are,
- Sockets and pins. Here, sockets if using.
- Resistors. Low power ones first, these are snug to the board. High power ones second, these are positionned with 2 mm - 3 mm of clearance above the PCB. No high power resistors are used on the VSPS PCB.
- Capacitors. Film types first, electrolytics second, smallest to biggest. Check and double check polarity.
- Op-amps and regulators. Check and double check polarity. If the op-amps are socketed, leave putting them in until last.
- Connection wires.
Hooking Things Up
Mounting: There are mounting holes at each corner of the board, 3.3 mm in diameter. The board is attached to the case by standoffs and either M3 or 4-40 machine screws.
Connections: IN+ and IN- go directly to insulated input RCA jacks. OUT+ and OUT- connect to insulated output RCA jacks. V++, V--, and COM go to the power supply. The GND pad of each board is connected to the case usually at the nut used to connect the turntable ground wire.
Example connection diagrams for stereo and single channel boards, having either shared and independent power supplies:
Connection schematic for a single stereo board.
Connection schematic for two single channel boards with a shared power supply.
Connection schematic for two single channel boards with separate power supplies.
Finally, here are some components and part numbers you might find useful:
- Transformer 35VA 2x12VAC (M4 mounting hole) / Digikey TE62072-ND
- Diodes 200V 3A (M3.5 mounting hole) / Digikey GBPC 602-E4/51GI-ND
- Hammond 1590 series aluminum case (one for the power supply, one for the phono stage) / Digikey 1590DBK-ND
- XLR 3 pin female socket for power umbilical / Digikey SC1001-ND
- XLR 3 pin male receptacle for power umbilical / Digikey SC1010-ND
- 5mm standoffs / Digikey 24390K-ND
- IEC power cord receptacle / Digikey CCM1401-ND
Please consult the VSPS and Phonoclone Help Desk at diyaudio.com for additional help and discussion, together with many photos of completed projects.
rjm003.geo at yahoo.com
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