Euraudio PSSR2Sc assembly instructions
Welcome to the Euraudio PSSR2Sc assembly instructions. The PSSR2Sc is a symmetrical power supply with two ultra low distortion SPST solid state relays. The PSSR2S has place for two, max. 35 mm diameter filter capacitor pairs. The PSSR2Sc is part of the Euraudio LDA MID ultra low distortion stereo audio amplifier DiY kit, but it may be used for other amplifiers as well. Please find the specifications of the PSSR2S here.
Please read through these instructions before doing anything with the DiY kit.
What the PSSR2Sc DiY kits contains and what it contains not
The kit contains the PSSR2S double-sided, fiberglass-reinforced epoxy PCB (fig. 1) and all the electronic and mechanical components to be mounted on it (fig. 2 and fig. 3), except the filter capacitors, fuses, and cables/wires.
Component list
Please download the PSSR2Sc component list (BOM) from here.
Sizing the filter capacitors and fuses
The filter capacitors and fuses are not part of the DiY kits, 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 LDA17).
The recommended transformer VA value is for heavy duty use, with real musical signals a lower VA rated transformer is often enough.
The LDA MID DiY kits contains the LDA17hc, which is nominally a max. 120 W / 4 ohms power amplifier, so the 1st row of the table applies for this.
You don't have to fill in all the 4 capacitor positions in the PSSR2S PCB, if 2 are 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 LDA17 is excellent, so generally it makes no sense to use bigger filter capacitors with this amplifier.)
|
Amplifier power |
Transformer |
Recommended fuse (4 pcs) |
Recomm. filter caps |
|
2x120
W / 4 ohms |
2x30 VAC, 400 VA |
T5A |
4x
8,200uF / 50V |
|
2x100 W / 4 ohms |
2x27
VAC, 320 VA |
T5A |
4x
7,500uF / 50V |
|
2x75
W / 4 ohms |
2x24
VAC, 240 VA |
T4A |
2x
12,000uF / 50V |
|
2x50
W / 4 ohms |
2x22
VAC, 180 VA |
T4A |
2x
10,000uF / 40V |
|
2x75
W / 8 ohms* |
2x31
VAC, 240 VA |
T3.15A |
2x
8,200uF / 63V |
|
2x50
W / 8 ohms |
2x27
VAC, 180 VA |
T2.5A |
2x
6,800uF / 50V |
* The unloaded power supply voltage should not exceed +/-45V DC, which is the maximum that the PSSR2S can withstand.
Compatibility
PSSR2S is fully compatible with the Euraudio DPB protection board. However, if you have to use PSSR2S with the Euraudio APBF or APBM, then you'll have to reverse diodes D91 and D92 from their original direction shown in the PSSR2S PCB.
General assembly advice
What you'll need and is not in the DiY kit
Solder iron, solder wire, wire cutter, technician's tweezers, 10-conductor ribbon cable (the DPBsc/APBFa/APBMa kit contains it), suitable cables/wires, Phillips 1 (PH1) screwdriver, Phillips 2 (PH2) screwdriver, heatsink compound, drilling machine, 3.5 mm metal drill bit. Anti-static wristband and anti-static (ESD) gloves. A heavier object with solderable surface (e.g. a tin can). 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, so you need knowledge of the electronic component markings. 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.
J103 (LD1) and J95 (LD2)
J103 and J95 are two-pole connectors for 2mA LEDs that show the on/off state of the solid state relays. J103 is for channel 1, J95 is for channel 2. The marking "A" denotes the anode of the LED.
Q94, Q95, Q97 and Q98
Q94, Q95, Q97, and Q98 are electrostatic sensitive devices, which can be damaged unknowingly by electrostatic voltages as low as 20...25 Volts. You MUST use anti-static gloves and an anti-static wristband connected to an earthed point while you handle and solder these components. Such an earthed point can be the metal chassis of an earthed appliance plugged into an earthed wall outlet, e.g. the metal back plate of a desktop PC. The wristband and gloves in themselves do not eliminate all the risks of electrostatic discharge. For complete protection, anti-static desk pad and floor mat, anti-static clothes and anti-static shoes are recommended, but if you don't have them, by all means wear clothes from 100% cotton or other natural fabrics and not synthetic. Touch the packaging of these components (pink or gray anti-static plastic packet) for a few seconds before you take these transistors out of the packaging. Please install Q94, Q95, Q97, and Q98 as the last step of the assembly process and handle the PCB with care afterwards.
You must "straddle" the leads of these transistors to allow soldering them into the PCB.
Assembling the IDC connector
The protection boards are connected through the J92 and J93 ribbon cable connectors (IDC). Observe the polarity: the red colored (marked) side of the ribbon cable should be aligned with the triangle sign on the connector. Please crimp these connectors carefully. If you're unsure how to assemble this type of connector correctly, please google "crimping IDC connectors".
U91 and associated components
U91 can be either FDA217 or VO1263. Some other components depend on which of them is installed in position U91, as follows:
VO1263: Install Q93, Q96, D96, D100; install R108 and R109 (470k or 510k)
FDA217: do not install Q93, Q96, D96, D100; short R108 and R109 (wire link or 0 ohm)
Soldering Q93 and Q96
When component VO1263 is installed in position U91, a small SMD component is needed in positions Q93 and Q96. This tiny SMD can be easily overheated if you are not careful with soldering. However, this component is essential for the reliable operation of the circuit with component VO1263. To solder Q93 and Q96, I recommend to use a controlled temperature solder iron and technician's tweezers. Do not heat the pins for more than 2 second each, and after soldering one lead, let the component cool down before you go on with the other pins. Check the solder joints after soldering.
R97 and R98
If you use the PSSR2S with the Euraudio DPB Protection circuit board, then R97 and R98 are 3.3 kohm resistors.
If you use the PSSR2S with the Euraudio APBF or APBM Protection circuit board, then R97 and R98 are a 5.1 V-os Zener diode each. Install them in the direction shown in the next photo. K is the cathode (marked with the band on the diode).
Solid state relay input and output solder pads
J115 "RLYIN1": input of solid state relay 1; J114 "RLYOUT1": output of solid state relay 1 (loudspeaker hot terminal)
J113 "RLYIN2": input of solid state relay 2; J112 "RLYOUT2": output of solid state relay 2 (loudspeaker hot terminal)
These connections carry high currents. Usually wires with 0.5 mm2 cross section are enough.
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, 1.5 mm2 cross section is usually enough for these 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 spread some heatsink compound (thermal grease) on the back of the bridge rectifier (D93). Then fasten the bridge rectifier to the heatsink and on the other side to the metal corner bracket with the M3x12 screw, washers and nut. Put a flat washer both on the bridge rectifier surface and on the heatsink surface, and then put a spring lock washer on top of one of them. Insert the leads of the rectifier bridge into the corresponding holes in the PCB, and then fasten the whole thing to the PCB with the M4x8 screw, tooth lock washer and nut. Solder the diode bridge into the PCB only after all screws have been fully tightened.
Connecting the grounding points
There is star-like grounding scheme in the PSSR2S 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", "ZGND" and "SPKGND" are all run to the star point, and they all can be used as ground. Connect the loudspeaker grounds to the "SPKGND" points, because they have the thickest PCB traces, allowing them to carry the highest currents. If you use PSSR2S with the LDA17 amplifier, then the ground points in the LDA17 PCB are identically marked as "GND", "PGND" and "ZGND".
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 for "+VCC", "-VCC" and a wire with 0.75 mm2 cross section is enough for "SPKGND".
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 PSSR2S 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 D95 to the metal chassis.
More information on earth grounding can be found at this page: Earthing Your Hi-Fi - Tricks and Techniques.
9V supply voltage connector
The power to the solid state relay and protection circuits is supplied via solder pads J110 and J111. Pad J110 with "+9V" marking is the regulated 9V, and pad J111 with "GND" marking is the ground. The PSSR2S board takes max. 80 mA current from here when two DPB/APBF/APBM protection boards are also connected.
Please click this link, if you don't have a crimp tool suitable for the contacts of the connector.
Suitable wires of 0.25 mm2 cross section with red and black insulation are part of the DiY kit. After you've finished the connector, the two wires should be twisted together (if they are separate).