Euraudio PSS701c/PSS702c assembly instructions
Welcome to the Euraudio PSS701c/PSS702c assembly instructions. The PSS701 and PSS702 are symmetrical power supplies with an ultra low distortion SPST solid state relay. The PSS701 has place for one max. 35 mm diameter filter capacitor pair, while the PSS702 has place for two pairs. The PSS701c is part of the Euraudio LDA DMx and LDA MON ultra low distortion audio amplifier DiY kits, but they may be used for other amplifiers as well. The Euraudio LDA MON contains one PSS701c kit, while the LDA DM1 and LDA DM2 contains two. Please find the specifications of the PSS701/PSS702 here.
Please read through these instructions before doing anything with the DiY kit.
What the PSS701c/PSS702c DiY kits contain and what they contain not
Both kits contain the PSS701 or PSS702 double-sided, fiberglass-reinforced epoxy PCB (fig. 1, PSS701 shown) and all the electronic and mechanical components to be mounted on them (fig. 2), except the filter capacitors, fuses, and cables/wires.
Component list
Please download the PSS701c/PSS702c 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 DM1 DiY kits contains the LDA17hc, which is nominally a 120 W power amplifier, so you have to interpolate between the 150 W and 100 W rows of the table.
The LDA MON and the LDA DM2 DiY kits contain the LDA17xc, which is nominally a 200 W power amplifier, so unless you decide to make your amplifier into a lower power unit than that, the 1st row of the table applies.
Only 2 filter capacitors are necessary altogether, so you don't have to fill in all the 4 capacitor positions in the PSS702 PCB. 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 (2 pcs) |
Recomm. filter caps (2 pcs) |
|
200 W / 4 ohms |
2x37
VAC, 300 VA |
T5A |
10,000...12,000uF
/ 63V |
|
150
W / 4 ohms |
2x32
VAC, 240 VA |
T5A |
8,200...10,000uF
/ 63V |
|
100
W / 4 ohms |
2x28
VAC, 180 VA |
T4A |
6,800...8,200uF
/ 63V |
|
150
W / 8 ohms |
2x43 VAC, 250 VA* |
T3.15A |
6,800...8,200uF
/ 80V |
|
100
W / 8 ohms |
2x35 VAC, 190 VA |
T2.5A |
5,600...6,800uF
/ 63V |
* The unloaded power supply voltage should not exceed +/-70V DC in any circumstances, which is the absolute maximum that the PSS701/PSS702 can withstand.
Compatibility
PSS701 and PSS702 are fully compatible with the Euraudio DPB protection board. However, if you have to use PSS701/PSS702 with the Euraudio APBF or APBM, then you'll have to reverse diodes D91 and D92 from their original direction shown in the PSS701 and PSS702 PCBs.
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.
The longer leg of the LED is the anode, this should be connected to the round pad (marked "A" in the image below). The shorter leg is the cathode, that connects to the rectangular pad (marked "K" in the image below).
It's practical to secure the LED onto the front panel of the amplifier, so the on state of relay is visible, then run cables from the LED to the PSS701/PSS702 PCB.
Q92 and Q93
Q92 and Q93 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 Q92 and Q93 (pink or gray anti-static plastic packet) for a few seconds before you take these transistors out of the packaging. Please install Q92 and Q93 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 board is connected through the J92 ribbon cable connector (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 this connector 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 VO1263 or FDA217. Some other components depend on which of them is installed in position U91, as follows:
VO1263: Install Q100 and R102 (470k or 510k); D100 optional.
FDA217: Do not install Q100 and D100; short R102 (wire link or 0R).
Soldering Q100
When component VO1263 is installed in position U91, a small SMD component is needed in position Q100. This tiny SMD can be easily overheated if you are not careful with soldering. However, this component is essential for the reliable operation of this circuit with component VO1263. To solder Q100, 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.
R96
When you use the PSS701/PSS702 with the Euraudio DPB Protection circuit board, then R96 is a 3.3 kohm resistor.
When you use the PSS701/PSS702 with the Euraudio APBF or APBM Protection circuit board, then R96 is a 5.1 V-os Zener diode. Install it in the direction shown in the next photo. K is the cathode (marked with the band on the diode).
D96 and D97
If you intend to use the PSS701/PSS702 for amplifiers with more than 200 W output power, then I recommend using bigger diodes in positions D98 and D99 instead of what is supplied, e.g. use P600M diodes.
Solid state relay input and output (RLYIN and SPKHOT)
Solder pad J102 marked "RLYIN" is the input of the solid state relay, while J101 marked "SPKHOT" is the output of the solid state relay (= loudspeaker hot signal).
These connections carry high currents. Usually wires with 1.0 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 apply some heatsink compound (thermal grease) to the back of the bridge rectifier (D93). 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 PSS701 and PSS702 PCBs 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. It's recommended to 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 PSS701/PSS702 with the LDA17 or LDA172 amplifier, then the ground points in the LDA17 and LDA172 PCBs 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 more than enough for "+VCC", "-VCC" and a wire with 1.0 mm2 cross section is more than 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 PSS701/PSS702 PCBs, 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 D96 to the metal chassis.
More information on earth grounding can be found at this page: Earthing Your Hi-Fi - Tricks and Techniques.
12V supply voltage connector
The power to the solid state relay and protection circuits is supplied via connector J103. The pad next to the "+12V" marking is the regulated 12V, and the other pad is GND. The PSS701/PSS702 board takes max. 40 mA current from connector J103 when a DPB/APBF/APBM protection board is 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).