Euraudio PS1USc assembly instructions
Welcome to the Euraudio PS1USc assembly instructions. The PS1USc is a symmetrical power supply kit with components, and is part of the Euraudio CTA MINI low distortion and the Euraudio LDA MINI ultra low distortion audio amplifier DiY kits, but can be used for other amplifiers as well.
Please find the specifications of the PS1US here.
Please read through these instructions before doing anything with the DiY kit.
What the PS1USc DiY kit contains and what it contains not
The kit contains the PS1US double-sided, fiberglass-reinforced epoxy PCB (fig. 1) and all the electronic and mechanical components to be mandatorily mounted on it (fig. 2), except the filter capacitors and cables/wires.
Note: The PS1USc that comes with the CTA MINI and LDA MINI kits does not include a heatsink, you will have to buy it yourself; a suitable heatsink is a Stonecold RAD-A4755/50. If you intend to use the CTA MINI or LDA MINI only for listening to music at normal volume level, then you can even omit the heatsink.
Sizing the filter capacitors
The filter capacitors are not part of the DiY kit, you must size these components according to the power and allowed load impedance (e.g. 4 ohms or 8 ohms) of the amplifier. The amplifier power and load impedance also largely determines the necessary transformer. The exact sizing procedure is not so simple, so I'd rather help with a table containing a few examples below. These examples are valid for class B or class AB amplifiers that have an output signal that can approach the supply rail voltages within 3-5 Volts (such as the Euraudio LDA14).
IMPORTANT: For the Euraudio CTA12 amplifier, refer to its assembly instructions, not this table, for information on transformer and buffer capacitor sizing.
The recommended transformer VA value is for heavy duty use, with real musical signals a lower VA rated transformer is often enough.
Do not use capacitors with lower capacitance than shown in the table, if you want to exploit the full amplifier power, because the ripple current specification of smaller capacitors may be inadequate. You may choose higher capacitance value, but that translates to higher amplifier power, so that would call for a higher VA rated transformer or for a lower transformer voltage than that shown in the list. (The power supply rejection ratio of the LDA14 is excellent, so generally it makes no sense to use bigger filter capacitors with this amplifier.)
|
Amplifier power |
Transformer |
Recomm. filter cap (2 pcs) |
|
2x75 W / 4 ohms |
2x24 VAC, 240 VA |
12,000uF
/ 50V |
|
2x60
W / 4 ohms |
2x23
VAC, 200 VA |
12,000uF
/ 40V |
|
2x50
W / 4 ohms |
2x22
VAC, 180 VA |
10,000uF
/ 40V |
|
2x100 W / 8 ohms |
2x37
VAC, 320 VA |
8,200uF
/ 82V |
|
2x75
W / 8 ohms |
2x32
VAC, 240 VA |
8,200uF
/ 63V |
|
2x60
W / 8 ohms |
2x29
VAC, 200 VA |
6,800uF
/ 63V |
|
2x50
W / 8 ohms |
2x27
VAC, 180 VA |
6,800uF
/ 50V |
General assembly advice
What you'll need and is not in the DiY kit
Solder iron, solder wire, wire cutter, suitable cables/wires, Phillips 1 (PH1) screwdriver, Phillips 2 (PH2) screwdriver, heatsink compound, drilling machine, 3.5 mm metal drill bit. A PCB holder jig and/or a model-making vice may come handy. Cable insulation stripper is recommended for cables/thick wires. A solder suction pump and/ or desoldering wick may be needed if you make soldering mistakes.
Soldering
Please click this link, if you need soldering tips.
Where polarity matters
There are electronic components which are polarized, these have to be soldered in the right orientation. The polarity is shown in the PCB with appropriate marking. If you solder any of the polarized components not in the correct orientation, that causes trouble when you power up the circuit; either the circuit will malfunction or even some of the components may be damaged.
Detailed help for assembling
Note: I can't help in troubleshooting assembly faults, I can only resend the whole component set on request.
Drilling the fastening holes
It's practical as a first step to drill the holes in the amplifier chassis that will hold the PCB in place. Put the PCB in its intended place within the amplifier enclosure, mark the 4 holes with a marker pen, and then drill the holes with a 3.5 mm drill bit.
Identifying components
The graphical markings and numbers printed on the PCB make it clear where the components belong and in what orientation. Though basic electronic component knowledge is necessary for identification.
In the PS1US PCB the 2 diodes, the 2 filter capacitors, and the bridge rectifier are polarized. The long leg of the bridge rectifier goes into the hole marked with a + sign on the PCB.
JP91 is a wire link realized by a wire with 0.75 mm2 cross section.
The 100nF ceramic capacitor is to be soldered into position C95, the 47 ohm resistor is to be soldered into position R91.
Into positions C93, C94, you may optionally mount foil capacitors of about 1uF, the lead spacing is 7.5mm in the PCB. These are meant to lower the high frequency impedance of the power supply. It's not mandatory to use them, so they are not part of the DiY kit. When you select these components, the proper voltage rating must be observed.
Connecting the transformer
The secondaries of the transformer must be soldered to the points marked "AC", "AC" és "COM". For a center tapped-secondary, as shown in the left of the image below. For a transformer with two separate, identical secondaries, as shown in the right of the image below: Solder together the undotted end of one of the secondaries with the dotted end of the other secondary to make the COM.
Due to high current peaks and subsequent I2R heating, the wire cross section must be big enough to carry about 4 times the max. output current of the amplifier on the "COM" connection, and big enough to carry about 2 times the max. output current of the amplifier on the "AC" connections each. For home audio amplifiers, 0.75 mm2 is usually enough for both wires.
Securing the heatsink of the bridge rectifier
Drill a 3.5 mm diameter through hole into the heatsink, 12 mm from the bottom of it, as shown in the next image, then trim the burr around the hole.
First apply some heatsink compound (thermal grease) to the back of the bridge rectifier (D91). Then fix the bridge rectifier to the heatsink with the M3x12 screw supplied, and to the corner bracket on the other side. To do this, put a flat washer on both the bridge rectifier surface and the corner bracket surface, then a spring lock washer on top of that, and then the nut. Insert the feet of the bridge rectifier into the corresponding holes in the PCB, then secure the whole assembly to the PCB with the M4x8 screw, serrated washer and nut. Solder the bridge rectifier only at the very end, after all screws have been tightened firmly.
Connecting the grounding points
There is star-like grounding scheme in the PS1US PCB to prevent hum resulting from ground loops. Of course, if you have created a ground loop somewhere else in your amplifier, then hum may still appear. Points "GND", "PGND" and "SPKGND" are all run to the star point, and they all can be used as ground. Connect the loudspeaker ground to the "SPKGND" point, because it has the thickest PCB trace, allowing it to carry the highest currents.
If you use PS1US with the CTA12 or LDA14 amplifier, then the ground points in the CTA12 and LDA14 PCBs are identically marked as "GND" and "PGND".
Other high current connections
Besides "COM" and "AC", the supply voltage connections "+VCC", "-VCC" and "SPKGND" also carry high currents. These need thick enough wires that can withstand the maximum amplifier output current. In most cases, wires with 0.5 mm2 cross section are enough.
Connecting the chassis
For protection against electric shock, the metal chassis of the amplifier must be connected to the mains earth ground conductor (or alternatively an equivalently effective protection method against electric shock must be used, which we will not cover here). On amplifiers equipped with protective earthing, it's not recommended to connect the ground of the amplifier to the chassis as well, because hum will develop across the protective earthing conductor. Instead, connect the metal chassis at the same point where the earth ground is connected to the point marked "CHAS" in the PS1US PCB, by soldering the free end of the supplied wire with ring lug to this point. So the effect of this ground loop will be minimized.
DO NOT connect the "CHAS" point to the metal chassis, if the amplifier will be powered off old style fused mains distribution panels that do not feature RCB/RCD (Residual Current Breaker/Residual Current Detector) systems. If in doubt, connect the cathode (K) of D93 to the metal chassis.
More information on earth grounding can be found at this page: Earthing Your Hi-Fi - Tricks and Techniques.