Euraudio LDA14uc, LDA14mc, and LDA14hc assembly instructions
Welcome to the Euraudio LDA14uc, LDA14mc, and LDA14hc assembly instructions page.
The LDA14uc, LDA14mc, and LDA14hc are high performance, ultra low distortion, mono DiY audio power amplifier kits. You need two kits for dual mono or stereo configurations. They are part of the Euraudio LDA MINI, LDA MIN+, LDA MID-M, LDA MID-H, and LDA DM DiY kits. Please find the LDA14 specifications here.
Please read through these instructions before doing anything with the DiY kit.
Differences among LDA14uc, LDA14mc, and LDA14hc
The PCB is the same for LDA14uc, LDA14mc, and LDA14hc, only the component set differs. The main difference lies in the permissible power dissipation of the end stage transistors: the hc is the high power, the mc is the medium power, while the uc is the low power version.
The recommended transformer and filter capacitor parameters for two LDA14uc's in a stereo configuration (e.g. LDA MINI kit) can be found in the assembly instructions of the PS1US Power Supply board.
The recommended transformer and filter capacitor parameters for two LDA14mc's in a stereo configuration (e.g. LDA MIN+ kit) can be found in the assembly instructions of the PS1S Power Supply board.
If you use two LDA14mc's or two LDA14hc's with the PSSR2S/PSS2S Power Supply & Solid State Relay board (e.g. LDA MID-M or LDA MID-H kits), then the you'll find the recommended transformer and filter capacitor parameters in the assembly instructions of the PSSR2S/PSS2S Power Supply & Relay board.
The recommended transformer and filter capacitor parameters for one LDA14hc in a mono configuration can be found in the assembly instructions of the PSS701/PSS702 Power Supply & Relay board. Two of this power supply are needed for dual mono configuration (e.g. LDA DM kit).
The uc, mc, and hc versions can all safely drive a 4-ohm load if the supply voltage is low enough, see specifications.
What the LDA14uc, LDA14mc, and LDA14hc DiY kits contain and what they contain not
The kits contain the LDA14 double-sided, fiberglass-reinforced epoxy PCB and all the electronic and mechanical components to be mounted on it, except the wires and the heat sink.
Component list
Please download the LDA14uc and LDA14mc component list (BOM) from here.
Note that a single spreadsheet file contains the BOM's for the uc and mc versions.
General assembly advice
What you'll need and is not in the DiY kit
Solder iron, solder wire, wire cutter, shielded cable for the input signal, suitable wires, Phillips 1 (PH1) screwdriver, Phillips 2 (PH2) screwdriver, miniature flat screwdriver (for setting the trimpot), thermal grease, drilling machine, 2.4 mm and 3.2 mm metal drill bits, digital multimeter (DMM). An AAA battery and a utility knife for making the L1 coil. 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 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 install 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.
Recommended assembly order
(1) Start with soldering the "collector wire links", see below. (2) Continue with soldering the smaller components, i.e. small resistors and small diodes first. (3) Solder bigger components. (4) Mount output transistors and bias setting transistor onto the main heat sink and solder them. (5) Solder the wires into the PCB.
Note: I can't help in troubleshooting assembly faults, I can only resend the whole component set on request.
Before installing the RV1 trimmer potentiometer
Adjust the RV1 preset turning it counter clockwise until its wiper hits the limit.
Soldering the collector wire links
Use the supplied 0.6-0.7 mm diameter solid copper wire to make the JW1 and JW2 links.
Polarity issues
In the LDA14 PCB you have to observe the polarity of the following components: diodes (including the LED), transistors, polarized electrolytic capacitors.
Note: The orientation of transistors in TO-126 package (Q8, Q9) is not easy to identify on the PCB. The leads on a TO-126 package are not in the center-line of the plastic case of the transistor, they are displaced toward the front of the case. This is how you can determine the proper orientation.
D2 is an LED. 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).
Paralleled emitter resistors
Two resistors are paralleled to make up a double power emitter resistor for each installed output transistor. This is why there are twin holes in the PCB, and the two resistors are stacked on each other.
Winding the L1 coil
Please use the supplied enameled copper wire and wind 15 turns close to each other on an AAA size battery. Scrape off the insulation with a utility knife and spread solder over the wire ends. The result looks like this figure.
Heat sink
Heat sinks can be external on the chassis sides or can be internal. In any case it should be assured that air move freely around the heat sink. If you use an internal heat sink, ventilation holes must be drilled or cut in the chassis top and bottom: that is below and above the heat sink(s), and the chassis should have tall enough feet. In case you want to use fan cooling, then the main heat sink is allowed to be much smaller than specified below. How small it can be depends on many factors including the fan parameters, so I can't provide heat sink data for fan cooled versions of the LDA14. The Euraudio APBF and DPB protection boards have heat sink overtemperature protection as well as fan control capability.
Sizing the heat sink
The heat sink parameter that will be specified below is the thermal resistance to ambient air in K/W, where 25 °C air temperature is assumed. Refer to manufacturer data of the actual heat sink profile to determine or calculate the K/W value.
For a mono LDA14uc, the main heat sink should have 1.6 K/W or somewhat lower thermal resistance to allow exploiting the full 60W power. For dual mono or stereo, use 2 of this heat sink or use a single heat sink with 0.8 K/W or lower thermal resistance.
For a mono LDA14mc, the main heat sink should have 1.2 K/W or somewhat lower thermal resistance to allow exploiting the full 90W power. For dual mono or stereo, use 2 of this heat sink or use a single heat sink with 0.6 K/W or lower thermal resistance.
For a mono LDA14hc, the main heat sink should have 0.8 K/W thermal resistance to allow exploiting the full 120W power. For dual mono or stereo, use 2 of this heat sink or use a single heat sink with 0.4 K/W or lower thermal resistance.
The Dissipante 2U or 3U (e.g. with deluxe-style faceplate) can be a suitable chassis that includes big enough side facing heat sinks for a dual mono or stereo amplifier. They can be ordered from diyaudiostore.com or modushop.biz.
Mounting driver and output transistors and bias setting transistor to heat sink
The driver and output transistors and biasing transistor must be tightened onto the heat sink(s) with screws. We supply three DIN7981F ST2,9x13 and one ST2,9x16 self-tapping sheet metal screws. These screws don't need a pre-made thread, they cut the thread for themselves in an aluminum heat sink. The important thing is to drill just the right diameter hole (it is 2.4 mm for the ST2,9 screws) so that the transistors can be screwed tightly and securely to the heat sink. Alternatively, you may use M3 screws, but in this case you should cut an M3 thread into the heat sink material, so you'll need a thread cutter. Please use the supplied flat washer and spring lock washer to prevent the screw getting loose by the repeated warming and cooling of the transistor. If a power transistor gets loose, then it will be damaged, causing risk to the amplifier and loudspeaker.
Drill the holes into the heat sink according to the pattern below (dimensions in mm). Trim any burr around the holes and clean off all metal chips.
Driver transistors
You will need two ST2,9x13 screws with spring washer and flat washer. If drive transistors with an exposed metal tab were supplied, then use the plastic ring to insulate the screw from the metal part of the TO-220 case, and place the silicone thermal washers between the transistors and the heat sink.
Output transistors
For the LDA14mc and LDA14hc, the supplied high-efficiency thermal pads should be placed between the output transistors and the heat sink. This is a phase-change thermal interface, its surface material will melt when the transistor heats up the first time, so it fills the surface imperfections and drives out air voids. Therefore no thermal compound or grease is needed, and you mustn't use thermal compound or grease with this product!
If an output transistor ever needs to be replaced or removed from the heat sink, then its thermal pad also needs to be changed. Suitable thermal pads can be ordered from Mouser, and here are the order codes: CD-02-05-247 (for LDA14mc), and CD-02-05-264 (for LDA14hc). If you can't purchase this Wakefield-Vette product, you may replace it with a mica washer plus a thermal compound or grease, but the thermal conductivity will be inferior.
For the LDA14uc, use the supplied mica insulator by applying thermal paste on both sides.
Bias setting transistor
The bias setting transistor Q10 should be mounted on top of one of the output transistor cases applying some thermal grease between the two transistors. Please use the tiny 6-hole PCB for the biasing transistor, and solder the supplied 3-wire colored ribbon cable onto the tiny PCB then solder the other end to the three Q10 solder pads in the LDA14 PCB.
Important: the Q10 (BD139-16 transistor) pinout from left to right is E-C-B. Note "B C E" indicated in the LDA14 PCB, so the 3-wire ribbon cable should be twisted half a turn for proper orientation.
For appropriate heat transfer, if possible, mount the power transistors directly to the heat sink (not through an L-profile).
Soldering the driver and output transistors is usually the last step of the installing of components. The recommended procedure: (1) Drill the mounting holes into heat sink. Trim any burr around the holes and clean off all metal chips. (2) Screw the transistors to the heat sink, but do not tighten the screws yet. (3) Insert all transistor leads into the holes in the PCB. (4) Tighten the screws first and then solder the transistors. (5) Check with a DMM that there is no short circuit between the heat sink and the transistor collectors (collector is the middle pin).
Ground points and ground wires
There are 2 ground points in the LDA14 PCB: "GND" and "PGND". Both should be connected to the star ground point in the power supply via independent wires. It's recommended to hold the 2 ground wires together with cable ties. If you use one of Euraudio's power supply PCB's, then there are grounding pads marked with the same name on the power supply PCB. The recommended wire cross sections are as follows: GND=0.35 mm2, PGND=0.5 mm2. Wires longer than 30 cm may require thicker cross sections than these.
Power supply wiring
The +VCC and -VCC points connect to the +/- power supply. Use insulated wires of at least 0.75 mm2 conductor. Important: Twist the +VCC and -VCC wires together.
High current connections
The current carrying copper foils of the +VCC, -VCC, and AOUT high current connections all run on the bottom of the PCB. Therefore, if you push the wires of +VCC, -VCC, or AOUT into the PCB from the top downwards, then everything will be alright. However, if you mount any of them from the bottom upwards (which may be more esthetic or more to the purpose in some cases), then you must ensure that the solder around the wire spills over to the bottom side of the PCB. It's because the galvanic plating of through-holes is not as sturdy and does not conduct as well as the copper foil on the PCB surface; at high currents, this may lead to overheating and the plating of the hole may crack and open.
Input connection
Shielded cable should be used to connect the input signal to the input connector J1. Do not connect the cable shield to the chassis or to system ground separately! It will be grounded via the LDA14 PCB.
If you build a stereo amplifier using two LDA14 PCB's, do not connect the shields (grounds) of the 2 input channels at the input connector or at any other point, they both will be grounded via the two LDA14 PCB's.
Assembling the input connector
If you don't have a crimp tool suitable for the contacts of the input connector, you can always solder them, please click this link. You need 2 contacts. We supply 3, just in case you spoil one of them.
Input live and ground point
The pinout of J1 is the following ("live" is the internal core and "gnd" is the shield of the input cable):
Volume pot
Ideally, the LDA14 amplifier should be driven from a low impedance source (e.g. active preamplifier), so it has no volume pot connection. However, if need be, you may fit a logarithmic volume control pot on your own, through which you can feed the input of the amplifier. For more information, see the "Volume control" section later in this page.
R3 resistor
R3=short is recommended in mono or dual mono amplifier; the short should be realized not with a 0R resistor, but with a piece of wire. R3=10 ohm is recommended in stereo amplifier; the 10R is damping the hum introduced by the ground loop formed around the shields of the 2 shielded cables running into the stereo amplifier.
Connecting to the APBF/APBM/DPB overcurrent protection
If you use the Euraudio APBF, APBM, or DPB protection board, they need the voltage across the emitter resistors for their overcurrent protection. There are two emitter resistor (ER) test points in the LDA14 PCB. You'll have to connect these points (+ and - point) to the ERV connector in the APBF/APBM/DPB board with correct polarity. Caution: Reverse polarity (+ and - points exchanged by mistake) renders the overcurrent protection ineffective and may damage the protection board as soon as the output current of the LDA14 gets high enough.
How to avoid increased distortion?
The distortion of this amplifier is remarkably low, and it can easily be compromised by incorrect grounding scheme, incorrectly routing cables/wires or incorrectly positioning the amplifier board within the chassis. For the advises below, I assume a conventional power supply with rectifier bridge and filter capacitors. The amplifier wasn't tested with switch mode power supply.
Regarding grounding: I recommend you use one of the power supply boards that I designed. If you use your own power supply board, the grounding reference should be a star-point, and route the critical ground points of every subassembly into the star point with separate wires.
Regarding cable/wire routing: (1) The most important is to avoid running any wire or cable, including wire from the amplifier output (AOUT) near the L1 output coil. (2) Avoid running the input cable (a) near the output wire, (b) near the +/-VCC wires, (c) near the cable/wires going to the bridge rectifier or (d) in the vicinity of the main transformer. (3) Avoid running the wire from the amplifier output (AOUT) (a) near the +/-VCC wire, (b) near the cable/wires going to the bridge rectifier or (c) near the main transformer. If you can't altogether ensure a large distance between these cables/wires, then at least don't run them parallel, rather just let them cross at a single point at right angle.
Regarding board positioning: Avoid placing the input connector side of the LDA14 board near the transformer(s), near the area of the bridge rectifier on the power supply board, or near the cable running to the bridge rectifier.
Assembled PCB look
This is how an assembled LDA14 looks like without the wiring.
Powering up the first time and setting idling current
1. CAUTION! Before powering up for the first time, the RV1 preset should be turned counter clockwise until its wiper hits the limit. As a verification, the resistance between the two extreme legs (Emitter-Base) of the Q10 bias setting transistor should be about 2 kohms.
2. Check that every wire is connected.
3. Do not connect anything to the input and output. Turn on the power supplies to the amplifier.
4. Check the DC voltage at the output, it should be less than 30mV, if it is not, then you've made a mistake.
5. Adjust the voltage between the +ER and -ER point. Be careful not to short-circuit the +ER or -ER point to any other point by accident, because the amplifier will be damaged. If you've already connected the wires to the APBF/APBM/DPB overcurrent protection and so the +ER and -ER points are not freely accessible, then you can measure the +ER and -ER voltage at the leads of the emitter resistors, as shown below:
When the output transistors are cool (20...25 °C) and immediately after the power is switched on, set potentiometer RV1 (idling current increases clockwise) extremely slowly until the measured DC voltage between the +ER and -ER points reaches 13mV ±2mV. The correct setting should be around the middle position of the wiper. With the amplifier as it will be used (e.g. close the top of the chassis), wait 20 minutes for the transistors to warm up. Adjust the potentiometer again if necessary so that the voltage is 20mV ±2mV.
Volume control
It's challenging to find an active preamplifier that meets the low distortion of the LDA14, yet this amplifier is best used with an active preamplifier that has low output resistance (e.g. 50...300 ohms). High serial resistances at the input of the LDA14, such that are presented by passive preamplifiers or volume pots have their disadvantages.
Disadvantages of passive preamplifiers and volume pots
High resistance seen at the input of the LDA14 will impair (1) the very low noise and (2) the excellent PSRR of this amplifier, and (3) will create a wiper position dependent high frequency roll-off, because the resistance forms a low-pass filter with the RF input filter capacitor of the LDA14.
Using a passive preamplifier
If you use a passive preamplifier with the LDA14, then consult the specifications or the schematic of the preamplifier to ensure that the output impedance of the preamplifier is lower than 2.5k ohms at all positions of the preamlifier controls. (If the passive preamplifier is a single volume pot, then the resistance of the pot should be 10k ohms or lower, this ensures that the resulting output impedance of the pot remains below 2.5k ohms at all positions of the wiper.)
Volume pot
If you don't have a preamplifier and want volume control on the LDA14, then you may install a logarithmic volume pot between the input connector on the chassis (e.g. RCA) and the J1 input connector on the LDA14 PCB. You must make the little PCB yourself for the volume pot. In a stereo (or dual mono) system, do not short the cable shields of the left and right channels at the volume pot PCB or at the input connector (e.g. RCA), because the shields will be grounded through the LDA14 boards. The volume pot should be 10k ohms or lower.
The connection of the potentiometer:
Never use a pot higher than 10k ohms, because it will create a low pass cut-off with C1 and may affect audible frequencies. For lower noise and higher PSRR, I recommend a 5k ohm volume pot, as long as your source equipment can drive a 5k ohm load without increase in distortion. Use only quality potentiometer.
Selecting the frequency compensation
The J3 jumper lets you select between TPC and Miller frequency compensation. Miller compensation results in somewhat increased distortion above 1kHz. I think the difference is not audible, but you can try for yourself. You may need a tweezer to remove or install the jumper.
Now only one thing remains: enjoy the music!