Euraudio LDA17(mk2/mk3)mc, LDA17(mk2/mk3)hc, and LDA17(mk2/mk3)xc assembly instructions
Welcome to the Euraudio LDA17mc, LDA17hc and LDA17xc assembly instructions page. The assembly of the mk2 and mk3 PCB versions are practically the same as the original version, so it is only mentioned where it differs.
The LDA17mc, LDA17hc and LDA17xc are high performance, ultra low distortion and low noise, mono DiY audio power amplifier kits. You need two kits for dual mono or stereo configurations. They are part of the Euraudio LDA MIN, LDA MID, LDA DM1, LDA DM2, and LDA MON DiY kits. Please find the LDA17 specifications here.
Please read through these instructions before doing anything with the DiY kit.
Differences among LDA17mc, LDA17hc, and LDA17xc
The PCB is the same for LDA17mc, LDA17hc, and LDA17xc, only the component set differs. The main difference is that the xc is the "extra high power" (max. 200 Watts / 4 ohms) version utilizing both output transistor pairs in the PCB, while the mc (max. 80 Watts / 4 ohms) and hc (max. 120 Watts / 4 ohms) versions need only a single output transistor pair installed. The other difference is that in the xc version some components are more heavy-duty and some component values slightly differ. The only significant difference between the mc and hc versions is that in the hc version the output transistors are of higher power.
The recommended transformer and filter capacitor parameters for two LDA17mc's or two LDA17hc's in a stereo configuration can be found in the assembly instructions of the PS1S Power Supply board.
If you use two LDA17hc's with the PSSR2S Power Supply & Relay board, then the you'll find the recommended transformer and filter capacitor parameters in the assembly instructions of the PSSR2S Power Supply & Relay board.
The recommended transformer and filter capacitor parameters for one LDA17hc or one LDA17xc 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.
The mc, hc, and xc versions can all safely drive a 4-ohm load if the supply voltage is low enough, see specifications.
What the LDA17mc, LDA17hc, and LDA17xc DiY kits contain and what they contain not
The kits contain the LDA17 or LDA17 mk2 or LDA17 mk3 double-sided, fiberglass-reinforced epoxy PCB and all the electronic and mechanical components to be mounted on it, except the wires and the main heatsink.
Component list
The component lists are different for the LDA17, LDA17 mk2 and LDA17 mk3 PCB versions.
Please download the LDA17mc, LDA17hc, and LDA17xc component list (BOM) from here.
Please download the LDA17mk2(mk3)mc, LDA17mk2(mk3)hc, and LDA17mk2(mk3)xc component list (BOM) from here.
Note that a single spreadsheet file contains the BOM's for the mc, hc, and xc 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, 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 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.
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 heatsink and solder them. (5) Assemble the driver heatsink and solder its transistors. (6) Solder the wires to 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, if necessary, turning it counter clockwise until its resistance between the two legs shown below is 1.5 kohms or more.
Soldering the "collector wire links"
Solder first the components marked R200 through R203. In the mk2 and mk3 PCB versions they are marked JW1 through JW4. In the LDA17 and LDA17 mk2 they should be made up of two parallel solid copper wires of at least 0.6 mm diameter. Do not use zero ohm (0R) resistors here. You can make use of the cut-off excess leads of the supplied 0.6 Watt resistors.
In the LDA17 mk3 use the supplied 0.95 mm diameter solid copper wire to make the links.
Important:
JW3 (R202) must always be installed, even if Q16 is not used.
Polarity issues
In the LDA17 PCB you have to observe the polarity of the following components: diodes (including LEDs), transistors, polarized electrolytic capacitors. C3 is different, its polarity doesn't matter. The polarity of C2 in the LDA17mc kit doesn't matter either.
Note: The orientation of transistors in TO-126 package (Q8, Q9, Q11) 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.
D4 and D6 are LEDs. 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).
Hard to read capacitor values
There are a few capacitors that may be supplied with the LDA17mc, LDA17hc, or LDA17xc kit, on which the marking is hardly visible. See image below for identification.
Paralleled emitter resistors
Two 3-Watt resistors are paralleled to make up a 6-Watt 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, as shown below.
Winding the L1 coil
Please use the supplied enameled copper wire and wind 16 turns close to each other on an AAA size battery. Scrape off the insulation with a utility knife and solder over the wire ends. The result looks something like this (fig. 1). Or you can make the coil like in fig. 2, and solder it with its axis upright.
Main heatsink
Heatsinks can be external on the chassis sides or can be internal. In any case it should be assured that air move freely around the heatsink. If you use an internal heatsink, ventilation holes must be drilled or cut in the chassis top and bottom: that is below and above the heatsink(s), and the chassis should have tall enough feet. In case you want to use fan cooling, then the main heatsink 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 heatsink data for fan cooled versions of the LDA. The Euraudio APBF and DPB protection boards have heatsink overtemperature protection as well as fan control capability.
Sizing the main heatsink
The heatsink 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 heatsink profile to determine or calculate the K/W value.
LDA17mc and LDA17hc
Mount the 2 output transistors so that the transistors are evenly distributed on the heasink(s) and have plenty of space between them. I recommend installing Q14 and Q17 because my LDA17mc and LDA17hc tests and measurements were done with these ones installed.
For a mono LDA17mc, the main heatsink should have 1.2 K/W or somewhat lower thermal resistance to allow exploiting the full 80W power. For dual mono or stereo, use 2 of this heatsink or use a single heatsink with 0.6 K/W or lower thermal resistance.
For a mono LDA17hc, the main heatsink should have 0.8 K/W or somewhat lower thermal resistance to allow exploiting the full 120W power. For dual mono or stereo, use 2 of this heatsink or use a single heatsink 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 heatsinks for a dual mono or stereo amplifier. They can be ordered from diyaudiostore.com or modushop.biz.
LDA17xc
Since the 4 output transistors are quite close to each other, the heatsink base should be at least 5 mm thick. This is to facilitate better heat conduction toward the remote parts of the heatsink. For a mono LDA17xc, the main heatsink should have 0.5 K/W or somewhat lower thermal resistance to allow exploiting the full 200W power. For dual mono or stereo, use 2 of this heatsink or use a single heatsink with 0.25 K/W or lower thermal resistance.
The Dissipante 4U (e.g. with deluxe-style faceplate) or Deluxe 4U can be a suitable chassis that include big enough side facing heatsinks for a dual mono or stereo amplifier. They can be ordered from diyaudiostore.com or modushop.biz.
The single output transistor pair for LDA17mc and LDA17hc
Since only one of two output transistor (OPT) pairs is installed for the LDA17mc and LDA17hc, you decide which transistors you wish to mount onto the PCB. You should install one of the positive side OPTs, and one of the negative side OPTs:
Base and emitter resistors that belong to output transistors (LDA17mc and LDA17hc)
For the two output transistors installed in the LDA17mc and LDA17hc, two sets of emitter and base resistors are supplied. With the OPT's you also need to mount the base and emitter resistors that belong to them. So you should install
either ( Q14 + R29 + R31 ) or ( Q16 + R33 + R35 )
plus
either ( Q15 + R30 + R32 ) or ( Q17 + R34 + R36 ).
Note: I recommend installing Q14 (green) and Q17 (red) and their resistors because the LDA17mc and LDA17hc tests and measurements were done with these ones installed.
Mounting output transistors and bias setting transistor to main heatsink
The output transistors must be tightened onto the main heatsink(s) with screws. We supply one DIN7981F ST2,9x13 and one ST2,9x16 self-tapping sheet metal screws for LDA17mc and LDA17hc. We supply three DIN7981F ST2,9x13 and one ST2,9x16 self-tapping sheet metal screws for LDA17xc. These screws don't need a pre-made thread, they cut the thread for themselves in an aluminum heatsink. The important thing is to drill just the right diameter hole (it is 2.4 mm for the ST2,9 screws) so that the output transistors can be screwed tightly and securely to the heatsink. Alternatively, you may use M3 screws, but in this case you should cut an M3 thread into the heatsink 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 the power transistor gets loose, then it will be damaged, causing risk to the amplifier and loudspeaker.
For the LDA17hc and LDA17xc, the supplied high-efficiency thermal pads should be placed between the output transistors and the heatsink. 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 the output transistor ever needs to be replaced or removed from the heatsink, then its thermal pad also needs to be changed. I order this product from Mouser, and here is the order code: CD-02-05-264. 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 with the latter.
For the LDA17mc, use the supplied mica insulator by applying thermal paste on both sides.
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. If all 4 output transistors are in use, then mount the biasing transistor on one of the inside transistors (Q14 or Q15). 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 LDA17 PCB.
Important: the Q10 (BD139-16 transistor) pinout from left to right is E-C-B. Note "B C E" indicated in the LDA17 PCB, so the 3-wire ribbon cable should be twisted half a turn for proper orientation. Note: Make sure the ribbon cable is kept away from the immediate vicinity of the driver heatsink that can get very hot and might melt off the cable insulation.
For appropriate heat transfer, if possible, mount the power transistors directly to the main heatsink (not through an L-profile).
Soldering the OPTs is usually the last but one step of the intalling of components. The recommended procedure: (1) Drill the mounting holes into heatsink. The transistor midpoints are 26 mm apart. Trim any burr around the holes and clean off all metal chips. (2) Screw the OPTs to the heatsink, 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 heatsink and the transistor collectors (collector is the middle pin).
Ensuring the two OPTs are from the same manufacturing batch (LDA17xc)
For the LDA17xc, both output transistor pairs are installed. To ensure better current sharing between OPTs, I supply the two NPN and the two PNP OPTs from the same manufacturing batch. If you order more than one amplifier kit, then it is not sure that all of the NPN and PNP output transistors will be from the same batch. Therefore always pick two NPN transistors with the same batch code and two PNP transistors with the same batch code for use within an LDA17xc amplifier channel. The batch code is usually etched below the type of the transistor.
Auxiliary heatsinks
Q8 and Q9 heatsinks
When the supply voltage is higher than +/-50V, small heatsinks are recommended on Q8 and Q9. These 2 small heatsinks are not supplied with the LDA17mc and LDA17hc kits, only with the LDA17xc. You must drill the hole yourself, as shown here:
Apply a bit of thermal grease between the transistor case and the heatsink, and screw the transistor to the heatsink using an M3x10mm screw, flat washer, spring lock washer and nut.
Driver heatsink
The 2 output driver transistors and a temperature sensing transistor sits on a separate aluminum heatsink in the middle of the PCB. Installing these 3 transistors and mounting the small heatsink to the PCB is usually the last step, comes just after mounting the output transistors. You must drill the holes yourself according to the following pattern:
Trim any burr around the holes and clean off all metal chips.
Before soldering in the three transistors, first mount the transistors onto the heatsink, but do not tighten the screws yet. You'll need three M3x10mm screws with flat washer, spring lock washer and nut. Put silicon pads between the transistors and heatsink to isolate their exposed metal part from the heatsink. In some cases, you may get the middle transistor (Q11) in a TO-126 package totally encapsulated in plastic. Then Q11 doesn't need a silicon pad, you just have to put some heatsink compound beneath the transistor. The two transistors at the side need the plastic ring that isolates the M3 screw from the metal tab of the TO-220 package.
Now get the steel corner bracket, and screw it to heatsink using the M3x8mm countersunk head type screw, flat washer, spring lock washer and nut. Then align and push the transistor leads into their corresponding holes in the PCB, and screw the steel bracket to the PCB using the M4 screw with M4 tooth lock washer and M4 nut. Tighten all screws first on the steel bracket then on the transistors, and when all is tightened, solder the 3 transistors to the PCB. Check with a DMM that there is no short circuit between the heatsink and the transistor collectors (collector is the middle pin on all of these transistors).
By no means let the driver heatsink touch the PCB surface, because it may short circuit the output to ground.
Ground points and ground wires
There are 3 ground points in the LDA17 PCB: "GND", "ZGND", and "PGND". These all should be connected to the star ground point in the power supply via independent wires. It's recommended to hold the 3 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, ZGND=0.35 mm2, PGND=0.5 mm2. Wires longer than 25 cm may require thicker cross sections than these.
Power supply wiring
The +VCC and -VCC points connect to the +/- power supply. Use wires of at least 0.75 mm2 cross section. 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 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 break away.
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 LDA17 PCB.
If you build a stereo amplifier using two LDA17 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 LDA17 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, I 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 LDA17 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 4 emitter resistor (ER) test points in the LDA17 PCB. You'll have to connect two of these points (one + and one - 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 LDA17 gets high enough.
All the 4 ER test points (2 +ER and 2 -ER) are active in the LDA17xc, and you should select one of the + and one of the - points for connection (I recommend the J5, J6 points around the middle that are close to each other).
Only 2 ER test points are active in the LDA17mc and in the LDA17hc, where you should select the points that belong to the installed output transistors. The following listing and image helps you identify them.
J5: +ER, belongs to Q14; J6: -ER, belongs to Q15; J7: +ER, belongs to Q16; J8: -ER, belongs to Q17.
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 LDA17 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 LDA17hc looks like without the wiring. The recommended Q14 and Q17 output transistors were mounted.
Powering up the first time and setting idling current
1. CAUTION! Before powering up for the first time, the resistance between the two legs of the RV1 preset shown below should be 1.5 kohms or more.
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. Measure the voltage between the +ER and -ER points that belong to installed OPTs. 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 installed emitter resistors, as shown below:
6. When the output transistors are cool (20...25 °C) and immediately after the power is switched on, set potentiometer RV1 (idling current increases clockwise) until the measured DC voltage reaches the Initial bias setting shown in the table below. Initially, several turns may be needed until the voltage moves away from near zero. 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 equals the Final bias setting shown in the table below. Don't turn the pot back and forth a lot, as it may fail or loose accuracy.
|
|
Professional use |
Home use |
|
Initial bias |
9mV -1/+2mV |
12mV -1/+2mV |
|
Final bias |
14mV -1/+2mV |
19mV -1/+2mV |
Volume control
It's challenging to find an active preamplifier that meets the low distortion and low noise of the LDA17, 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 LDA17, 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 LDA17 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 LDA17.
Using a passive preamplifier
If you use a passive preamplifier with the LDA17, 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 LDA17, 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 LDA17 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 LDA17 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 J4 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.
The tube-like distortion tweak
It is possible to spoil the very low distortion of the LDA amplifier in a way that the spectrum of distortion harmonics will look similar to those of quality tube amplifiers, that is, stronger low order, mostly 2nd and 3rd order harmonic distortion will be generated. With this modification the total harmonic distortion will become about 20 times higher in the low and mid frequency range.
To achieve this "tube-like distortion profile",
On LDA17 and LDA17mk2, remove R13 and also change the value of R14 (originally 910 ohms) to something between 2.2k...3k ohms (this resistor is not supplied with the kit).
On LDA17mk3, disconnect (cut or desolder) the collector of Q6 while its base and emitter remains connected to the PCB and also change the value of R14 (originally 910R) to something between 2.2k...3k ohms (this resistor is not supplied with the kit).
I'm interested whether you can hear any difference in how the amplifier sounds with this modification.
Now only one thing remains: enjoy the music!