Tube headphone amp schematic

Transcription

1 Tube headphone amp schematic headphones, so no negative feedback was employed in the execution. 125mA plate current. There are no plate curves in my RCA manual for the 6AS7G, second-order harmonics with virtually no odd harmonics. Also, a cathode follower. Build your own Accurate LC Meter (Capacitance Inductance Meter) and start making your own coils and inductors. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors. LC Meter can measure inductances starting from 10nH nH, 1uH uH, 1mH - 100mH and capacitances from 0.1pF up to 900nF. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings. I observed 84dB rarely on peaks. I raised the volume to get an average 84dB. This was probably for AM tabletop radios. I wanted the frequency response. There is no battery charge monitoring built in, so you will have to monitor battery voltage with a meter or just wait until things start sounding funny to know the battery is dead. Or, just develop a standard charging cycle of overnight every 2 days or something. for the 6AS7G. R4 drops the rectified voltage to 120V DC. R4 also provides. The power supply provides direct current (DC) for the tube heaters and a well filtered B+. I believe that using alternating current (AC) on the tube heaters would also be just fine, but since I have the PCBs and components to get the DC, that is what I used. Since the plate load is a 0.56mA constant-current diode, moving the bias point around does not affect the plate current. If you substitute a resistor for the constant-current diode, you can still adjust the bias in the same manner, but the plate current will vary with the bias setting. I looked at common voltage gain tubes such as 12AT7 and 6SN7, but their gains. may have different results if you use different diodes or transformer, but. and is self-biased using an un-bypassed cathode resistor. The input stage is direct coupled to a 6CA7 that is used as a. There are several such tubes that you can use; I tried the 12AE6 (or 12AE6A) and the 12FM6. Other tubes that may work, and all with the same pinout, include the 12AJ6, 12EL6, 12FK6, and 12FT6. Since the diode sections are unused, they are simply tied to ground. Bias for the tube

2 stage is developed across an adjustable resistor (R2, R6), which is paralleled by both an electrolytic capacitor and a film capacitor. The exact value of these caps is not critical, but it does set the low-frequency response limit of the amplifier. For most headphones, anything over 47µF is adequate. The output side of the capacitors then connects to both the headphone jack (J1) and an RCA line output jack (J3). but I needed to utilize some interpolation of the data between 180V and 300V. of 250-ohm which I tried, but found it a little low for my application. the 6SL7G input stage. I had a 250V plate sup ply transformer I wanted to use, (7.64V = +18dB above 102dB, or 120dB for maximum CD output. 2.0V RMS equals. Check for DC Offset at the Output Photograph 15: Check for DC Offset at the Output. After a few years the circuit has been modified from my original 12AU7 Tube / IRF612 MOSFET Hybrid Headphone Amplifier build to fit on a single layer printed circuit board (PCB). Although it can easily be constructed point-to-point on a 750 hole proto board, a PCB is a cost effective upgrade. There are several sites that give in depth instructions on etching a PCB at home, and the whole process can be very rewarding. Just know that etching utilizes some very caustic and nasty chemicals, so proper ventilation and use of personal protective equipment (PPE) will make the process easy, fun and safe. Muriatic acid and hydrogen peroxide yielded the best results and also is much cheaper than ferric chloride. If you measure the voltage at the output of the BUF634 with no audio applied (which is the same DC voltage as on the plate of the tube), you can set the operating point of the tube by adjusting the bias trimpot. Measuring at the output of the BUF634 guarantees that the voltmeter won't load the voltage on the high-impedance plate. First, the schematic calls for a 117 volt/12.6 volt transformer across what I think is the output, I can only find a 115 volt/12.6 volt 2.5 amp transformer. Will this work? Another question is about the numbering of tube pins on the 12AU7A, there's two sets of numbers. Which ones am I supposed to read? Last question is regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks for your help. * Tested with several headphone models of different impedance: 32, 100, 245, 300, 600 & 2000 Ohm. Photograph 4: 9-pin vacuum tube / valve socket on PCB. Solder the MOSFETS, LM317voltage regulators, and the remaining components. When printing the enclosure, I realized just how awesome 3D printers are. When they are working. The printer in the Imagnieering lab is a Makerbot Replicator. (the day I typed this they unboxed a 2x) It works great, minus the small issues with clogged ejectors, unlevel build plates, random glitches when slicing but those are usually few and far between. The major problem I kept having was the

3 piece warping while printing. The build plate temperature was adjusted, the ejector temp adjusted, infill adjusted, print speed.. Eventually I got most of the parts straight enough that it worked. The corners of the enclosure itself on the bottom were still a little warped, but they are concealed by the base, which printed straight. Overall, I am not disappointed with the final result, though relieved that it is done and I don't have to worry about printing anymore. As another note, don't get thrown off by the heat of the circuit. The MOSFETs and LM317s will get hot to the touch but not dangerously so. Also, the tube needs heat to operate properly so don't panic about it either if its warm. First, the schematic calls for a 117 volt/12.6 volt transformer across what I think is the output, I can only find a 115 volt/12.6 volt 2.5 amp transformer. Will this work? Another question is about the numbering of tube pins on the 12AU7A, there's two sets of numbers. Which ones am I supposed to read? Last question is regarding the 12AU7A itself, will I regular 12AU7 work here? Thanks for your help. The bias is set by adjusting the 50k trim potemtiometer (P1) until the output side of the MOSFET (Source) is at one-half of the supply voltage (Drain). Adjusting the two trim potemtiometers to one-half of your supply voltage, 6 volts since we are using a 12v supply. You will want to check and reset the bias a few times in the first few hours of use as it will drift while everything settles in. Sich posted Oct 1, 2018 at 6:56 PM. Photograph 6: Tube / Mosfet Hybrid Headphone Amplifier Measurements - Tube / MOSFET Hybrid Headphone Amp Here are a few scope shots of the 10 Hz sine wave response, as well as the square wave response at 100 Hz. The performance was very consistent and the voltage stayed the same over the most of the sweep. The TINA curve shows approx 19dB of gain over the spectrum of the audible range. The sound from my Grado SR125 headphones is crisp with a tight lower end. This amp is very nice considering the low voltage and low component count. It may not be true audiophile quality, but the average cost is only $40 USD or less. -- Tim Wescott Control systems and communications consulting. Hello, Can I replace the headphones with a normal speaker and if yes, what power would the speaker need to be?. The two numbers refer to the first and second sections of the tube. Use the first set of numbers for one channel and the second set for the other channel. The schematic above shows only one channel, you will have to wire the the tube for both channels using different pins. The only wiring that is common for the 12AU7 tube between the two channels is the heater. * B1, SW1, J1 & C3 are common to both channels. Navigation: DIY Audio Projects / DIY Vacuum Tube Projects / DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project. The

4 MOSFET is biased into class-a operation and will be constantly conducting at approximately 125 ma. The LM317 regulator is configured as a constant current source and regulates at 125 ma in the given configuration. You can use the online LM317 current regulator calculator to determine the current through the regulator by adjusting the program resistor. It is suggested that a 10 ohm 1/2W program resistors is used for R4 (you can use two 1/4W 20 ohm resistors in parallel). Note that the regulator and MOSFET devices will heat up and radiate heat. There are some real in depth calculations for heat, but know that the MOSFET can dissipate at least 1.6 Watts and the LM317 voltage regulator IC 2 Watts to air, at room temp. I tested a prototype over a continuous 24 hours period in a 150 cubic-centimeter (about 9 cubic-inch) enclosure and there were no thermal stability issues. You can add heatsinks to the devices, just ensure that if you gang the FETs together to use mica and silicone washers to prevent the 12V supply from transferring to the heat sinks. 1Hz - 2MHz XR2206 Function Generator produces high quality sine, square and triangle waveforms of high-stability and accuracy. The output waveforms can be both amplitude and frequency modulated. Output of 1Hz - 2MHz XR2206 Function Generator can be connected directly to 60MHz Counter for setting precise frequency output. The gain device in the original Zen amplifier is biased by fixed current source. For this amp, I employed an active current source described in Pass' patent no. 5,710,522 (see Zen Variations Part 2). The benefits of an active source include higher output current, lower distortion and 50% theoretical operating efficiency (compared to the 25% efficiency from a fixed source). This type of current source is featured in the Aleph power amplifiers from Pass Labs. Photograph 8: 100 Hz Square Wave Response This amp is perfect for the novice builder and the components are available at mouser, digikey. You can substitute other Mosfets as long as the resistance is similar and the internal capacitance does not effect the response curve. It is best to use TINA-TI to build the schematic and make any changes, this way you can check the ac output before building. This will save you much time. Lastly, make sure that your headphones are not plugged into the jack while powering up or down, this amp as well as other DIY builds have a large rush of current at power up and down and damage can occur to you headphones if you are not careful. I am sure you will be pleased with the sound of this little amp and better yet the price. UPDATE 28 August 2008: I have built another version of this amplifier which is smaller, has less parts and runs off of a 12V battery. For full details, see the 12AU7 Tube / IRF612 MOSFET Hybrid Headphone Amplifier update on the DIY Audio Projects

5 Forum. After many modifications the PCB was reduced to a 2-1/4" x 4-3/4" and then down to 2" x 4" (50 x 100 mm) with thicker traces. The build is demonstrated on the first version (slightly larger PCB). DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier. Bend Resistor Leads to Fit on PCB Photograph 5: Bend Resistor Leads to Fit on PCB. R1 R2 R3 R4 R5 U1 C1 C2 C3 Q1 Socket V1 P1 Case Mica Heatsink Jack Battery. - 8 channel microphone splitter which can inject phantom power to microphone, product datasheet with circuit diagram in pdf format. JT- 10KB-D Isolates and Converts Speaker Drive to Line Level. DIY 12AU7 (ECC82) Tube / IRF510 MOSFET Headphone Amplifier. - less wasted power than true class A but not as good sound. HEATSINKS - As previously noted, it is completely fine to run the MOSFETS and LM317 regulators to air, I did the math from the datasheets and the current is low enough to keep them stable. However, please do note that they do get hot. The metal tabs will sizzle water from your finger tip, like checking a clothes iron, but have not had a failure yet. There is not too much radiant heat though. If you are worried about heat you can use a small heat sink on the devices. - The TDA7294 is a monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications (Home Stereo, self powered loudspeakers,topclass TV). This IC datasheet gives example circuit for up to 100W amplifier using this IC. - This is a simple RIAA preamplifier that can be plugged to a PC soundcard. The text of this document is in Finnish. Check that 12AU7 Tube Heaters are Working Photograph 13: Check that 12AU7 Tube Heaters are Working Setting the Bias. - This is a very simple tube based line stage. In case you're wondering, yes, it's OK to put audio on the tube heaters. Think about it - normally they run on 19V RMS AC. In this case they're running on 19V DC, with a little bit of audio superimposed (rarely more than 1V or so). There could (theoretically) be a little coupling from the filament to the cathode - the cathode resistor is un-bypassed - but it would be negative feedback, and the capacitance from heater to cathode is so low compared to the cathode resistor it would probably only be measurable at RF frequencies. JT-10KB-D & JT-DB-E Provide "J-Box" Consumer to Studio Interfaces. Photograph 9: Dry fit the PCB into the enclosure. - This is a builging plan for an audio amplifier with 2 x 220W output power. Text is in Finnish. JT-11-BM High Level High Current Differential Output Stage with DC Servo. A Bipolar Junction Transistor (BJT) can be used in place of the MOSFET, but MOSFETs tend to be more stable with temperature and current shifts. Use caution when handling MOSFETs as they are very static sensitive. The schematic above shows only one channel, you will

6 have to wire the the tube for both channels using different pins. The only wiring that is common for the 12AU7 tube between the two channels is the heater. Photograph 13: Check that 12AU7 Tube Heaters are Working. The circuit consists of two stages: 1. a common cathode tube volt amp stage (gain), 2. a MOSFET source follower for current gain (with a LM317 voltage regulator IC configured as a constant current source ). Since most headphones are less than 50 ohms a little current is necessary to run them efficiently. JT-DB-E Converts Consumer Stereo Inputs to Mono Balanced Mic Output.