From: "Saved by Internet Explorer 11" Subject: NP-100v12: DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier Date: Thu, 23 Jan 2014 14:02:47 -0800 MIME-Version: 1.0 Content-Type: multipart/related; type="text/html"; boundary="----=_NextPart_000_0000_01CF1843.CBA9EBE0" X-MimeOLE: Produced By Microsoft MimeOLE V6.1.7601.17609 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01CF1843.CBA9EBE0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://diyaudioprojects.com/Solid/12AU7-IRF510-LM317-Headamp/
Rogers Gomez |
=20 | =20 |
The NP-100v12 is a simple headphone amplifier that allows an entry = level=20 builder to experience assembling and listening to their own creation. I = use the=20 term builder as electronic experience combined with innovation which = allows the=20 creation of a device, rather than simple board stuffing. This amplifier = can take=20 on many shapes and sizes; I especially like when builders reuse older = devices as=20 cases and even recycle some components from various discarded power = supplies. I=20 try to keep price at a minimum because this amplifier is very basic and = allows=20 the builder to seek out theory, and actually "listen" to their music, = and grow=20 to build more complex projects in the future.
There are plenty of wonderful websites out there that can explain = tube=20 theory, I learned from the US Navy NEETS module 6. I will = not go to in=20 depth into the theory, but will introduce you to the 12AU7 (known in = Europe as=20 ECC82).
The 12AU7 (ECC82) is a Twin Triode vacuum tube, it is very popular in = the=20 audio world because it is rather rugged and can be operated at lower = voltages.=20 You will find these tubes in vintage amplifiers and organs. They are = even used=20 in older vacuum tube volt meters and their life span can reach into = decades. =20 The 12AU7 has an amplification factor (=B5) of about 17, this is = moderate as=20 compared to its cousin the 12AX7 that comes in at 100. For purpose of = the=20 NP-100v12 the 12AU7 tube will be used in a common cathode configuration, = and the=20 incoming signal will be amplified by approximately 10dB. The 12AU7 is = usually=20 operated at plate voltages of over 120 volts, but fortunately it can be = operated=20 at lower voltages with decent results.
As you see in the load lone graph below, we will operate in the 6 = volt=20 region. 6 volts allows enough "swing" for the signal to reach 12 volts = and down=20 to the 0 volt line. Since this amplifier is single-ended we will not be = applying=20 an external negative voltage, but due to grid leak bias the voltage does = sit=20 above common.
The tube has 9 pins and follows the EIA 9A pin out configuration. = Remember=20 that pin out diagrams are always read from the bottom of the tube, this = little=20 detail may save you much rework in the future.
The great thing about this tube - it is basically two tubes in one. = The other=20 plus is that the heaters (filaments) can be powered by 6.3 or 12.6 volts = AC or=20 DC. In lower voltage amps, using DC for the heaters is preferred to = reduce hum.=20 For the NP-100v12 we will be using a 12 volt sealed lead acid (SLA) = battery as=20 the power supply (hence v12). The two filaments are pinned 4 to 9 and 9 = to 5,=20 with pin 9 as a center tap. One can apply 12.6 volts across pins 4 and = 5, or 6.3=20 volts to pins 4 and 5 with pin 9 used for common (negative), or 6.3 = volts can be=20 applied to pin 9 with pins 4 and 5 used as common.
The power supply is rather simple and straightforward, a 12v SLA = battery. The=20 battery is rated at 1.3 ampere-hour (Ah) and the total amplifier draw is = about=20 400 mA, so we can expect some hours of playback between charges. A = battery is=20 the perfect source for voltage as there is no ripple or noise that will = be=20 injected into the signal, this is very important with headphone = applications. =20
An alternate is a regulated switch mode power supply. I use a Cannon = K30120 =20 13v 1.8A portable printer power supply. The voltage is kept constant, = great=20 filtering, and most of all there is a built in over current protect. = These power=20 supplies can easily be found in thrift stores, the cost is miniscule to = building=20 a similar supply. It is important that the power supply be regulated to = keep=20 the unwanted noise levels low.
The circuit consists of two stages: 1. a common cathode tube volt amp = stage=20 (gain), 2. a MOSFET source follower for current gain (with a LM317=20 voltage regulator IC configured as a constan= t=20 current source). Since most headphones are less than 50 ohms a = little=20 current is necessary to run them efficiently.
A Bipolar Junction Transistor (BJT) can be used in place of the = MOSFET, but=20 MOSFETs tend to be more stable with temperature and current shifts. Use = caution=20 when handling MOSFETs as they are very static sensitive.
The signal enters the grid via a coupling capacitor, it leaves the = plate=20 (anode) amplified and 180 degrees out of phase, it is then directly = coupled to=20 the gate of the MOSFET and leaves the source. The signal is then coupled = to the=20 headphones via a electrolytic capacitor, which blocks the DC from your=20 headphones. Since the sleeve of your headphones is common it completes = the=20 circuit.
The MOSFET is biased into class-A operation and will be constantly = conducting=20 at approximately 125 mA. The LM317 regulator is configured as a constant = current=20 source and regulates at 125 mA in the given configuration. You can use = the online = LM317=20 current regulator calculator to determine the current through the = regulator=20 by adjusting the program resistor. It is suggested that a 10 ohm 1/2W = program=20 resistors is used for R4 (you can use two 1/4W 20 ohm resistors in = parallel). =20 Note that the regulator and MOSFET devices will heat up and radiate = heat. There=20 are some real in depth calculations for heat, but know that the MOSFET = can=20 dissipate at least 1.6 Watts and the LM317=20 voltage regulator IC 2 Watts to air, at room temp. I tested a = prototype over=20 a continuous 24 hours period in a 150 cubic-centimeter (about 9 = cubic-inch)=20 enclosure and there were no thermal stability issues. You can add = heatsinks to=20 the devices, just ensure that if you gang the FETs together to use mica = and=20 silicone washers to prevent the 12V supply from transferring to the heat = sinks. =20
The schematic above shows only one channel, you will have to wire the = the=20 tube for both channels using different pins. The only wiring that is = common for=20 the 12AU7 tube between the two channels is the heater.
With any project there are specialized tools that are required; in = this=20 project you will need some basic electronic test equipment and tools. =
Ohm's=20 Law deals with three basic measurements, Voltage, Resistance and = Current.=20 Knowing at least two of the variables, we can extrapolate a multitude of = others.=20 To make good readings, one must use a digital multimeter (DMM or DVOM). = There=20 are hundreds of DMMs on the market and you do not need to spend $200 on = a DMM if=20 you are only doing hobby work, but try to stay away from the very cheap = $10=20 knock offs. One should use a meter that reads all three parameters and = have=20 probes that are safe up to 1000 volts.
The second most important tool is the soldering iron. You can use a = soldering=20 pencil, but for best results, a soldering station equivalent to the Weller WLC100 will save you = headaches down=20 the line. Nothing like leaving your soldering pencil on the table and = finding it=20 with your arm, or burning your laptop, etc.. Rosin core 60/40 solder is = the=20 best for new builders, there are others who swear by silver solder and = other=20 fancy solder, but for this application, the 60/40 flows well and will = last=20 years. Lastly purchase some liquid flux in a needle type applicator. Flux = helps to=20 transfer the heat to the joint, and will make the job so much easier. = The solder=20 has a flux core, but again the job will go much better with flux. = Cleaning of=20 the flux can be done with an acid brush and 99% isopropyl alcohol; you = do not=20 have to go crazy with cleaning, as the low voltage will not be an issue. = Stay=20 away from plumbing flux, it is conductive and can destroy your project. =
Purchase some cheap headphones for troubleshooting. Similar to the = ones you=20 use on the airplane, nothing like frying your $300 Sennheiser headphones = to make=20 a project go upside down.
The bill of materials (BOM) is pretty straightforward, I selected = readily=20 available parts, 90% of them can be purchased at Radio Shack. If you = have access=20 to similar components, or you want to buy higher quality components, you = can use=20 Nichicon FG, KZ or Elna electrolytic capacitors and maybe Solen = polypropylene=20 film for C1. The only issue is shipping charges can make the project = expensive,=20 if you use a local Guitar Center and Radio Shack you can cut out = shipping costs=20 completely. The BOM for this 12AU7 (ECC82) / IRF510 Headphone Amp is = provided=20 in Table 1.
Component | Value | QTY | Mouser | Radio=20 Shack | TubeDepot | Guitar=20 Center | Parts Express |
R1 R2 R3 R4 R5 U1 C1 C2 C3 Q1 Socket V1 P1 Case Mica Heatsink Jack Battery |
100k, 1/4W 150, 1/4W 4.7k, 1/4W 10, 1/4W 1k,=20 1/4W LM317 2.2uF, 16V 100uF, 16V 470uF, = 16V IRF510 9pin=20 = PCB 12AU7 50k Optional Optional Optional Optional 12= V=20 1.3Ah |
=
2 2 2 2 2 2 2 2 2 2 2 1 2 1 4 4 1 1 |
=
660-MF1/4DCT52R1003F 660-MF1/4D52R1500F 660-MF1/4LCT52R472J = 660-MF1/4DC10R0F=20 = 660-MF1/4LCT52R102G 512LM317AHVT 505-MKS42.2/63/10P15 647-UF= G1C101MPM=20 =20 = 647-UFG1E471MHM 844-IRFI510GPBF N/A N/A 3299W-1-503LF = N/A N/A N/A N/A N/A |
=
* * * * * 276-1778 272-997 272-1028 272-1030<= BR>276-2072 N/A N/A * 270-1802 276-1373 276-1363 274= -0249 23-9080 |
=
** ** ** ** ** N/A N/A N/A N/A N/A 9pin PC 12AU7/ECC82 N/A N/A N/A N/A N/A N/= A |
=
N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A ST-12AU7-C N/A N/A N/A N/A N/A N/A |
=
*** *** *** *** *** LM317T 027-324 020-1664 0= 20-1710 N/A 055-502 055-508 N/A N/A N/A N/A ***N/A |
N/A - Not Avalailable
* - 50-Piece 1/4-Watt Metal-Film Resistor=20
Assortment, Radio Shack Part # 271-309
** - Misc Resistors at TubeDepot, it is =
suggested you=20
use a 1/2W 10 ohm resistor for R4
*** - Misc 1/2W Resistors and Jacks =
available from Parts Express
R3 - A fixed resistor (R3) may be used in place of the 50k = potentiometer=20 (P1). 4k7 worked for many 12AU7 tube types, but you should pick a value = to get=20 half the supply voltage (see setting the bias Photograph 14).
Q1 - The MOSFET (Q1) can be replaced by an IRF610, IRF611 or IRF612, = all of=20 which will work as well. Stay away from IRF530 or IRF540 types (commonly = found=20 in power supplies) as there will be terrible roll-off of the highs.
C1 - Non-polarized electrolytic or film type capacitors may be used = for C1=20 (2.2uF or greater). Most will find that a film type capacitor will = sound best. =20 Generic Polyester or Polypropylene types work well.
HEATSINKS - As previously noted, it is completely fine to run the = MOSFETS and=20 LM317 regulators to air, I did the math from the datasheets and the = current is=20 low enough to keep them stable. However, please do note that they do = get hot. =20 The metal tabs will sizzle water from your finger tip, like checking a = clothes=20 iron, but have not had a failure yet. There is not too much radiant heat = though.=20 If you are worried about heat you can use a small heat sink on the = devices.=20
After a few years the circuit has been modified from my original 12AU7 Tube / IRF612 MOSFET Hybrid Headphone = Amplifier build=20 to fit on a single layer printed circuit board (PCB). Although it can = easily be=20 constructed point-to-point on a 750 hole proto board, a PCB is a cost = effective=20 upgrade. There are several sites that give in depth instructions on = etching a=20 PCB at home, and the whole process can be very rewarding. Just know = that=20 etching utilizes some very caustic and nasty chemicals, so proper = ventilation=20 and use of personal protective equipment (PPE) will make the process = easy, fun=20 and safe. Muriatic acid and hydrogen peroxide yielded the best results = and also=20 is much cheaper than ferric chloride.
The board layouts are included in the attachments; you can print them = out and=20 etch them using the toner transfer method.
I used the free version of the CADSOFT Eagle program to = construct the=20 board on a single plane. The process is done with a standard Toner = Transfer=20 method. Basically print the trace design onto cheap glossy photo paper. = You must=20 use a laser printer, or a Xerox copier on the darkest setting possible. = The dark=20 setting will allow the most toner to build up on the paper. Follow one = of the=20 many instruction set found online, I found the glossy magazine transfer method the best and = easiest. You=20 will have a transfer, just touch up and then finish the etching process. = =20 Another key note is to have a dremel press, or use two hands when = drilling=20 holes. Use the smallest bit possible then move up in size. If you remove = too=20 much copper, it will make the process of soldering cumbersome.
After many modifications the PCB was reduced to a 2-1/4" x 4-3/4" and = then=20 down to 2" x 4" (50 x 100 mm) with thicker traces. The build is = demonstrated on=20 the first version (slightly larger PCB).
The components are fed through the top of the PCB and soldered onto = the=20 bottom (copper side). There are several types of 9 pin sockets, some = will fit=20 better than others, but with a little diligence either socket will work = fine. =20
Solder in the tube socket, the pins will fit in the hole pattern, = just use=20 caution not to overstress the pins or they will break.
Solder the resistors next, the PCB spacing is for 1/4 watt metal film = types,=20 if you only have 1/2 watt or higher resistors, you will have to bend the = leads=20 to fit the PCB.
After populating resistors, solder in the capacitors. The C1 = capacitors are=20 polyester film types (non-polar) and can be placed in either direction. = The=20 remaining capacitors are electrolytic, and must follow proper polarity. = C2 has=20 the ground pin facing the tube, and C3 have the ground pin facing back. =
Solder the MOSFETS, LM317voltage regulators, and the remaining = components. =20
Solder in the power jack, which in this case is a terminal block. If = you=20 prefer, you can run wires to a jack on the enclosure.
Test fit the PCB into the enclosure and trim the sides as necessary. =
With the board complete, prepare the case for the sockets and volume=20 potentiometer. A stepped drill bit works great for drilling the holes = into the=20 enclosure.
The input signal is fed into the right side of the enclosure via a = set of RCA=20 jack or can use a 3.5 mm stereo jack if you prefer. The signal comes in = through=20 the jack and to the potentiometer which allows level control and then to = the=20 circuit for amplification. The output exits the amplifier via the output = jack. =20 If your signal source allows you to control the signal level, you can = omit the=20 potentiometer. The Radio Shack potentiometer can be used, but the fit = will be=20 tight so to prevent a short, you may want to use a smaller Alps 10k = audio pot=20 (part number RK0971221Z05)
I have drafted a routing PCB (see the previous PCB section), but = three small=20 gauge wires will work fine too. Solder all connections before mounting. = Mount=20 the jacks and potentiometer and leave the amp board free for testing. =
The positive lead from C3 is the same potential as the MOSFET source = pin. It=20 is best to check voltage at the capacitor, because the MOSFET can be = damaged if=20 the pins are shorted. Also, check that both heaters glow.
The bias is set by adjusting the 50k trim potemtiometer (P1) until = the output=20 side of the MOSFET (Source) is at one-half of the supply voltage = (Drain). =20 Adjusting the two trim potemtiometers to one-half of your supply = voltage, 6=20 volts since we are using a 12v supply. You will want to check and reset = the=20 bias a few times in the first few hours of use as it will drift while = everything=20 settles in.
Next check for DC offset at the headphone output using a DMM. The DC = offset=20 should be less than 10 mV. After a number of prototypes I measured 8 mV = max and=20 typically about 3 mV.
Now its time to hook up the cheap phones for a quick listen.
If all is good, secure the amp to the case, one more check with the = cheap=20 headphones, then try out your new amp.
Now its time for tube rolling. Enjoy!
If you have any questions, feel free to ask them in the 12AU7 / IRF510 HeadAmp Support Thread in the = message forum. =20
=20=20 |