Hi everyone, I’m new to this diyaudio group and now that I’m retired I have a little more time to explore one of those nostalgic components from the past, although I realise they are still here and fighting, the vacuum tube was a little before my time although it was part of my education back in the early 70’s. I’m interested on everyone’s ideas on some fairly, dare I say, simple projects to start me off in the field of vacuum tubes. I would be most grateful for any help at all. I do have a few books with basic tubes circuits including “Vacuum tube Audio” by Jerry Whitaker which informed me about this website.
What are your feelings about higher voltages? There are some interesting circuits using low voltages.
60V PL504 + ECC82 headphone amp
60V PL504 + ECC82 headphone amp
I don’t have any speakers in mind but I can find some. I currently listen to music using earbuds, headphones or Bluetooth connected sound bar. Why are the speakers important to choosing a project to build?
I’m not necessarily looking for a big amplifier, initially just a fairly simple project to get me started using vacuum tubes so I can get some practical experience. I will look at more technically challenging projects later.
There are lots of easy projects you can build using vacuum tubes. But the question is, what kind of product would you like to have?
You say you listen in headphones now. The suggestion to build a headphone amp is a good one.
1) You can make one as a Single-Ended Triode amp that only makes like half-a-watt or maybe 1 watt (at the most). You could use an output transformer that would make it almost exactly the same as an SET amp meant for speakers, but use a small, inexpensive transformer for headphones.
I was interested in this for listening to 'normal' low impedance headphones like those made by Audio Technica or Sony, but also high impedance headphones like my Sennheiser HD-6XX (300 ohms). The build thread is here -- https://www.diyaudio.com/community/...adphone-amp-i-finally-built-something.324664/ and this is the output transformer I used -- https://edcorusa.com/products/xse10...3&_fid=3476303a8&_ss=c&variant=41117869965499
2) You can make an output-transformer-less ("OTL") headphone amplifier, but these are generally better used with high impedance headphones. There are many designs like this that you can try. They're nice because you don't have to purchase an output transformer, which is a specialty item that may cost a bit of money if you insist on getting a really high quality part.
There are many, many OTL tube headphone designs floating around the web. Too many to list. I think the first one that got popular was the Bottlehead Crack, which is a commercially available kit. https://bottlehead.com/product/crack-1-1-otl-headphone-amplifier-kit/
I'm not saying that's a particularly good design, because I've never seen nor heard one. There's a review of it on ASR, fwiw: https://www.audiosciencereview.com/...d-crack-headphone-amplifier-kit-review.15714/
Here's the schematic (from the ASR review). You can see that this is a super-simple design. Really basic.
Anyway, that's a start, I think.
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You say you listen in headphones now. The suggestion to build a headphone amp is a good one.
1) You can make one as a Single-Ended Triode amp that only makes like half-a-watt or maybe 1 watt (at the most). You could use an output transformer that would make it almost exactly the same as an SET amp meant for speakers, but use a small, inexpensive transformer for headphones.
I was interested in this for listening to 'normal' low impedance headphones like those made by Audio Technica or Sony, but also high impedance headphones like my Sennheiser HD-6XX (300 ohms). The build thread is here -- https://www.diyaudio.com/community/...adphone-amp-i-finally-built-something.324664/ and this is the output transformer I used -- https://edcorusa.com/products/xse10...3&_fid=3476303a8&_ss=c&variant=41117869965499
2) You can make an output-transformer-less ("OTL") headphone amplifier, but these are generally better used with high impedance headphones. There are many designs like this that you can try. They're nice because you don't have to purchase an output transformer, which is a specialty item that may cost a bit of money if you insist on getting a really high quality part.
There are many, many OTL tube headphone designs floating around the web. Too many to list. I think the first one that got popular was the Bottlehead Crack, which is a commercially available kit. https://bottlehead.com/product/crack-1-1-otl-headphone-amplifier-kit/
I'm not saying that's a particularly good design, because I've never seen nor heard one. There's a review of it on ASR, fwiw: https://www.audiosciencereview.com/...d-crack-headphone-amplifier-kit-review.15714/
Here's the schematic (from the ASR review). You can see that this is a super-simple design. Really basic.
Anyway, that's a start, I think.
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I didn't believe till recently that tubes sound better but they do. 12AX7 and 6922 sound great. With that said I use silicon wherever possible with tubes in the power supply , splitter, buffer and filtering.
6922 gives me a 110db s/n so it's working.
6922 gives me a 110db s/n so it's working.
I would not start with tube phono stage. Phono stages are very tricky as I found out.
Oh my, yes. A linestage preamp, a headphone amp, a small SE amp would make much better projects.
I'm not saying it's necessarily the right thing for you, but have a look at the TU-8400 kit that Victor Kung (vkmusic.ca) is selling. Those are nice kits, well engineered and documented, and if your room isn't too big, the few Watt output this produces is perfectly sufficient.
Thanks for this, I have been going the headphone amplifier direction since posting my request. My headphones I believe are 300Ω S
Hi, I have been considering the headphone amplifier direction since posting my request. My headphones are Zennheisser so probably 300Ω which means the OTL route is possible I guess. I think I would want to make it stereo but with maybe left/right volume control or balancing if possible.
Thanks for your highly considered response.
What’s the most sensible way to handle the mechanical aspects of the project - should I buy an off the shelf metal casework?
How comfortable are you with punching and drilling holes in an aluminum chassis?
Do you have good hole punches, like Greenlee or similar?
If you're equipped for that kind of thing, then you could get an aluminum 'Bud' box or Hammond chassis and punch/drill to suit the parts you end up getting.
If you go down that route, I know there are people here who should be willing to help, but you should have experience with that kind of thing before diving in.
If that doesn't sound appealing, perhaps you could get one of those Chinese SE tube amp kits off of ebay and modify it to suit your needs. You may need to replace the electrolytic capacitors with better ones, as these kits are rumored to come with counterfeit parts of dubious quality. However, the cost of the chassis, wooden end pieces, transformers, tube sockets and tubes would easily come to $150, and this chassis is punched for you already. Maybe something like this one for $160 plus shipping, tax, customs, etc:
https://www.ebay.com/itm/251524538404
If you go down the completely built-from-scratch route, make sure you get Greenlee punches in the correct sizes for your holes. See here: https://www.diyaudio.com/community/threads/punch-size-opinion.405532/
I hope this helps.
Do you have good hole punches, like Greenlee or similar?
If you're equipped for that kind of thing, then you could get an aluminum 'Bud' box or Hammond chassis and punch/drill to suit the parts you end up getting.
If you go down that route, I know there are people here who should be willing to help, but you should have experience with that kind of thing before diving in.
If that doesn't sound appealing, perhaps you could get one of those Chinese SE tube amp kits off of ebay and modify it to suit your needs. You may need to replace the electrolytic capacitors with better ones, as these kits are rumored to come with counterfeit parts of dubious quality. However, the cost of the chassis, wooden end pieces, transformers, tube sockets and tubes would easily come to $150, and this chassis is punched for you already. Maybe something like this one for $160 plus shipping, tax, customs, etc:
https://www.ebay.com/itm/251524538404
If you go down the completely built-from-scratch route, make sure you get Greenlee punches in the correct sizes for your holes. See here: https://www.diyaudio.com/community/threads/punch-size-opinion.405532/
I hope this helps.
rfrost: Actually check the impedance spec of your phones. Senn makes high and low imp phones.
The low power, 1~2 watt SE amps are fun to learn on but their usefulness is limited. I suggest you build a Tubelab SPP, forum on this site. It's about 12 wpc. It will run fairly efficient speakers in a normal room, at sensible volumes. In the USA, Antek has decent transformers for cheap. Blank chassis are available on eBay, but you'll have to do a bit of hole drilling and maybe filing. The SPP uses EL84 tubes, which are still fairly cheap. ECL82 and ECL86 tubes are more expensive and will yield a simpler amp but only 5 to 6 wpc.
https://www.diyaudio.com/community/threads/tubelab-simple-p-p.148694/page-46
http://tubelab.com/pc-boards/tubelab-spp/
https://wallofsound.ca/audioreviews/amplification/diy-el84-amp-update/
The low power, 1~2 watt SE amps are fun to learn on but their usefulness is limited. I suggest you build a Tubelab SPP, forum on this site. It's about 12 wpc. It will run fairly efficient speakers in a normal room, at sensible volumes. In the USA, Antek has decent transformers for cheap. Blank chassis are available on eBay, but you'll have to do a bit of hole drilling and maybe filing. The SPP uses EL84 tubes, which are still fairly cheap. ECL82 and ECL86 tubes are more expensive and will yield a simpler amp but only 5 to 6 wpc.
https://www.diyaudio.com/community/threads/tubelab-simple-p-p.148694/page-46
http://tubelab.com/pc-boards/tubelab-spp/
https://wallofsound.ca/audioreviews/amplification/diy-el84-amp-update/
On second thought...
Finding appropriate output transformers for headphone use is not easy. There are a few, but they tend to be expensive. There's a Lundahl available for $109 each. I'm sure that would be very high quality, but being that this is a first project, I don't know if you want to get in that deeply.
There are Chinese-made transformers on ebay that look like they'd do the trick. I really don't know if they're any good at all. The nice part is that they have multiple secondaries, making them suitable for use with pretty much all headphones from low to high impedance. It looks like they'll cost just under $100 a pair, before tax, customs, tariffs, or whatever.
https://www.ebay.com/itm/177073486391
Maybe an output transformer-less design is the best way forward.
The usual design is much like the Bottlehead Crack shown earlier in this thread. That can be modified all sorts of ways to improve performance, but people do seem to like that design.
Years ago, I took some spare parts and made a headphone amp for my brother that I think came out pretty well. It's basically the same idea as the Bottlehead Crack but using all 6DJ8 tubes. It has a relatively low voltage B+ supply (170V) and uses four 6DJ8 twin triode tubes. The first triode in each channel is used as the voltage amp, with a fairly low plate voltage (70V). That stage is DC-coupled to three triodes wired in parallel running as a big cathode follower. Negative feedback is connected from the output after the DC blocking capacitor to the grid of the input triode. The NFB reduces the gain to about 3X (10dB). My brother has a pair of Sennheiser HD580s which work well with this amp. I tried it with standard 32 ohm headphones and it works well enough. A bit dark and warm because of the increased THD from the poor cathode followers struggling to drive that heavy load, but the NFB makes the sound acceptable and loud enough. It sounded pretty good driving my Fostex cans (60 ohms).
The Crack design using a 6AS7 or 6080 for the cathode follower would be easier to wire up (paralleling tubes is a bit of a pain). Here's a redesign of the Crack that I think should work pretty well with Sennheiser headphones. It uses standard guitar amp tubes which you can probably buy at your local Guitar Center, although there are better (and cheaper) sources.
The big cathode follower on the output is a 6V6, but you can sub smaller and cheaper versions like 6P1P (Russian), 6P1 (Chinese version of 6P1P), 6AQ5 (7-pin mini version of 6V6) or 12AQ5 (12-volt heater version of 6AQ5, which costs less).
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Finding appropriate output transformers for headphone use is not easy. There are a few, but they tend to be expensive. There's a Lundahl available for $109 each. I'm sure that would be very high quality, but being that this is a first project, I don't know if you want to get in that deeply.
There are Chinese-made transformers on ebay that look like they'd do the trick. I really don't know if they're any good at all. The nice part is that they have multiple secondaries, making them suitable for use with pretty much all headphones from low to high impedance. It looks like they'll cost just under $100 a pair, before tax, customs, tariffs, or whatever.
https://www.ebay.com/itm/177073486391
Maybe an output transformer-less design is the best way forward.
The usual design is much like the Bottlehead Crack shown earlier in this thread. That can be modified all sorts of ways to improve performance, but people do seem to like that design.
Years ago, I took some spare parts and made a headphone amp for my brother that I think came out pretty well. It's basically the same idea as the Bottlehead Crack but using all 6DJ8 tubes. It has a relatively low voltage B+ supply (170V) and uses four 6DJ8 twin triode tubes. The first triode in each channel is used as the voltage amp, with a fairly low plate voltage (70V). That stage is DC-coupled to three triodes wired in parallel running as a big cathode follower. Negative feedback is connected from the output after the DC blocking capacitor to the grid of the input triode. The NFB reduces the gain to about 3X (10dB). My brother has a pair of Sennheiser HD580s which work well with this amp. I tried it with standard 32 ohm headphones and it works well enough. A bit dark and warm because of the increased THD from the poor cathode followers struggling to drive that heavy load, but the NFB makes the sound acceptable and loud enough. It sounded pretty good driving my Fostex cans (60 ohms).
The Crack design using a 6AS7 or 6080 for the cathode follower would be easier to wire up (paralleling tubes is a bit of a pain). Here's a redesign of the Crack that I think should work pretty well with Sennheiser headphones. It uses standard guitar amp tubes which you can probably buy at your local Guitar Center, although there are better (and cheaper) sources.
The big cathode follower on the output is a 6V6, but you can sub smaller and cheaper versions like 6P1P (Russian), 6P1 (Chinese version of 6P1P), 6AQ5 (7-pin mini version of 6V6) or 12AQ5 (12-volt heater version of 6AQ5, which costs less).
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Both are excellent points.
Sennheiser does make both low and high impedance headphones. Which model do you have?
It's hard to mess up a push-pull EL84 amp. If you want an amp to drive speakers then absolutely, that's the way to go.
Tubelab's PCB is well-tested, well-liked, and a good value too. Building the amp on a PCB makes the wiring easier, but the punching and drilling of holes needs to be done accurately, or things can end up misaligned because the tube sockets and mounting holes on the PCB are where they are; you can't bend and/or stretch them to get them to line up with holes in the chassis. Just measure carefully (measure twice, drill once) and things should be fine.
Good luck with this, and I hope you have fun with whatever you decide to do!
Answering the query, as a starter project either a CC>CF preamp as rongon suggested (cam be done witha ton of dual triodes), an upgrade woulkd be to add CCSes at a later date.
Or a single ended “EL84 amp”. You have to weally hard to make a bad one. Either wired triode (1.5-2 watts) or Schade feedback/RH84 style (4.5-5w). We prefer the latter.Pretty much same number of parts you just put one resistor in a different place.
Next level of complexity would be a PP “EL84”, Depends on what iron you can source easily.
dave
Or a single ended “EL84 amp”. You have to weally hard to make a bad one. Either wired triode (1.5-2 watts) or Schade feedback/RH84 style (4.5-5w). We prefer the latter.Pretty much same number of parts you just put one resistor in a different place.
Next level of complexity would be a PP “EL84”, Depends on what iron you can source easily.
dave