A little piece of advice, don't settle on anything too quickly. You'll get lots of opinions but ultimately it's you who must decide on a first project.
Not necessarily. Here is a simple design using matching transformers which handles both high and low impedance headphones really well.
https://www.cascadetubes.com/the-6dj8-headphone-amp/
Beware of OTLs using large output capacitors. These can have sometime significant DC on the output at startup. Lots of headphones can be damaged by this phenomenon.
Good luck selecting your first project.
Does anyone know anything about the gremlin headphone amp? Sold on APOS. It seems to use a bunch of to-247 stacked I am guessing diodes used for biasing the tubes.
It doesn't use OPT and something like that would be a good diy project.
It doesn't use OPT and something like that would be a good diy project.
Good advice. The field is deep.
But first suggests it will be far from your last. Whatb you learn from your first build, no matter what, will inform you of what comes next.
In all of these, the PS is probably the hardest bit. And a preamp has w less transformers.
Note: i have 2 pair of smallish “EL84” OPTs i’d be happy to send for cost of postage. Just moved fromupstairs and might be a bit tricky to find.
Note2: I consider “EL84” to include 6BQ5, 6AQ6, 6V6, ECL82/86, 6∏15 and variations...
dave
One of the most basic push-pull EL84 amps you can build, no phase splitter neccesary and you may even omit the V1 input tube 6C4, as the EL84 can take an audio signal directly on the grid from f.e. a standalone pre-amp you already have, at the cost of reduced output power. In that case, you should also omit R4, as it is part of the power supply for the input tube and you don't need it anymore. The value of C2 will also be different.
You may also use a fixed R5 resistor of 500kOhm tied between C2 and Earth and the V2 point 2 grid tied to C2 (the 'wiper' of the potmeter to C2), if you have a passive or active pre-amp. Two EL84, that is it. And a power supply with a GZ34/5AR4 rectifier tube and choke or CRC filtering for a nice soft-start. It is advisable to use a good quality cathode resistor with proper dimensions.
You may also use a fixed R5 resistor of 500kOhm tied between C2 and Earth and the V2 point 2 grid tied to C2 (the 'wiper' of the potmeter to C2), if you have a passive or active pre-amp. Two EL84, that is it. And a power supply with a GZ34/5AR4 rectifier tube and choke or CRC filtering for a nice soft-start. It is advisable to use a good quality cathode resistor with proper dimensions.
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Yes, two stereo amps to power my coaxial horn drivers with dsp, without C1 input tube, one with ultralinear OPT and one as pentode connected OPT like in the schematic.
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Okay, thanks again for all the useful information. I’m not tooled up for the metal work at the moment but I do have some experience in handling aluminium chassis work. I’ll have to look into your information and see what might be best for me at this early stage of my project work.
Thanks for your advice which of course I will be taking. I’m a great believer in listening to people who have experience in a particular topic. I am getting a little confused a the moment with all the replies I’ve been getting. Ultimately I need to be happy with the idea and comfortable that I can build it to my personal satisfaction.
Seems right then, no? 43mA of electrons get accelerated by (320V-142V)=178V from cathode to anode, so they deposit 7.7W.
Sorry for asking, but is Hooman a common name? I worked with a student by that name from Iran/Persia in the mid-90s, at a lab in 'the village'.
Sorry for asking, but is Hooman a common name? I worked with a student by that name from Iran/Persia in the mid-90s, at a lab in 'the village'.
My experience after building many tube amplifiers is that the way you put it togheter is as equal or even more important than the schematic. This is because the circuit is simpler than discrete solid state circuits, so less feedback/compensation loops are available, and the impedence is high so unwanted mutual couplings may be a issue.
- when you build a headphone amplifier or a preamp, hum is the main issue. Layout and power supply filtering must be just right. All it takes to get unbearable background hum is a single wire routed in a wrong way.
- when you build a speaker amplifier, you need good transformers and they are the most expensive and difficult part to source, expecially when you want high power output. You need to allocate several hundreds euro/dollars, unless you manage to recover the iron from a old device or settle to a didactic experience rather than true hi-fi level.
I suggest to start with a project with proven printed circuit board available, or a well documented point to point with pictures you can use as reference for component placing.
Hi Pcan, I do have some experience with tracing noise in audio circuits and have refurbished a 1950’s tube radio. I don’t really want to use PCB’s if possible but I may have to for some stages of the project. I will definitely be segregating the mains power circuitry from the input stage and as you point out pay serious attention to the power interconnections to the audio stages.
Not sure what I will do regarding an output stage transformer but will probably hunt around for alternatives and suppliers. Early thoughts have a habit of going by the way side when you start the project so I might start documenting the design & build process.
Thanks for your comments
Not sure what I will do regarding an output stage transformer but will probably hunt around for alternatives and suppliers. Early thoughts have a habit of going by the way side when you start the project so I might start documenting the design & build process.
Thanks for your comments
That's just a note to myself that the power transformer will need to be rated for 100mA if I want to make a stereo amplifier with this circuit. Sorry for the confusion.
Hi Rongon, Is it common to control the volume on a stereo version with a dual log pot or I’m guessing there’s an arrangement that allows for left/right balancing?
No need for PCBs in a simple single -ended amp. P2P builds allow for shorter direct connections and can minimize noise. And you can re-wire any way you see fit, which will happen with your first project.
@Suncalc is modest but his website, Cascade Audio has many projects suitable for beginners in the hobby. I'm partial to the Lakewood 2.0 and the Marblewood is a good beginner amp as well, but the larger Octal sockets on the Lakewood are easier to work with. There's a headphone amp on there too, be aware those amps need big enclosures to isolate all the components to keep the noise floor low.
Tariffs have made everything more expensive. Most parts of an amp are made overseas and are now more pricey, so plan accordingly. I had already turned to US-made transformers from Edcor and Hammond, but even they have Canadian factories subject to tariff.
2nd vote for Elekit. If you're not into fabrication they make some nice kits. The 8900 amp lets you use 300b and 2A3 power triodes, best matches with high-efficiency speakers.
@Suncalc is modest but his website, Cascade Audio has many projects suitable for beginners in the hobby. I'm partial to the Lakewood 2.0 and the Marblewood is a good beginner amp as well, but the larger Octal sockets on the Lakewood are easier to work with. There's a headphone amp on there too, be aware those amps need big enclosures to isolate all the components to keep the noise floor low.
Tariffs have made everything more expensive. Most parts of an amp are made overseas and are now more pricey, so plan accordingly. I had already turned to US-made transformers from Edcor and Hammond, but even they have Canadian factories subject to tariff.
2nd vote for Elekit. If you're not into fabrication they make some nice kits. The 8900 amp lets you use 300b and 2A3 power triodes, best matches with high-efficiency speakers.
You can do two single-deck volume controls, one for Left and one for Right. That would be the simplest, but not the most convenient. Yes, log taper ('audio taper').
The most common arrangement is for a dual-gang volume control to control the volume of both the left and right channels simultaneously, mostly for the convenience of being able to adjust the level of the whole system with a single knob. Add a balance control if you feel you need one.