12AX7 stereo tube preamp only 12 volts
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- เผยแพร่เมื่อ 28 ก.ย. 2024
- Low voltage tube / valve preamp with gain about 20db. Schematic and music samples included after description. TH-cam's audio compression does harm the sound somewhat, but the amp sounds good to me direct through my power amp.
the music recorded through preamp sound phenomenal
I am trying to learn about tubes and basic electronics again. A low-voltage tube amp is IDEAL for what I want! Thanks for providing a schematic! It will really help me get the basics down.
Thanks for watching. Using a 24 volt supply should work better for a preamp. My tube was worn, just good enough to use, so you have to tweak the bias for best performance with a new tube and 24v supply.
JohnAudioTech Seriously, thanks for uploading, but I need your help. I am really pulling out at the basics from way back. I know what components are supposed to do, but I'm still learning how they effect a circuit overall. Bias effects and tweaking are unknown to me but I'm guessing you mean something about how to maximize the electron transfer in the tubes. I would learn a lot if you could let me see a clear pic of the schematic, as I can't see the upper left. What I can see I'm not certain where the power supply fits in here completely and where the "ground" for the in/out connections would be. I'm also guessing that there is a separate simple circuit for the tube heat element. I hate to be a pain but can you help a "newbie" out? Cheers....and thanks for any help!
*****
The components in the upper left are not needed. They were for supplying the tube from an automotive electrical system. The biasing (called class A in this amp) sets the quiescent (no signal point) on the plate to around 1/2 the supply voltage which allows room for the voltage to swing up and below this halfway point as it amplifies the signal. The output, input and power negative go to the same point which is called ground and not necessarily grounded to earth. All this might not make sense to you now. I really can't give a lesson in a few words where book chapters of reading and soldering iron in hand are needed.
JohnAudioTech Hello. I understnad basic schematics and what the ground of the circuit could be, but I don't know exactly where the negative/ground of the circuit would be with certainty. So the upper left is power supply....OK. Understood. However, I don't know for certain where the ground or negative terminal would be indicated here...but I'm assuming it is the "bottom" of your schematic as it's all connected in one line opposite the many resistors? Yes?
***** Yes, you are correct. It is the bottom horizontal line that represents the negative side or common point of the circuit.
Great work John. Been watching your great content for a week now. Have learned a lot! I think tubes are great to play around with. Please do more stuff like this.
Just a couple of suggestions: Reduce the value of the pull-up grid resistor, and connect it to the plate. While it will slightly reduce gain, and input impedance, it will also reduce the output impedance, by introducing an element of negative feedback in the amplifier. I will guarantee, it will greatly reduce harmonic distortion. It will also improve frequency response. Another thing might be to connect another output capacitor to the plate, and connect a high value of resistance in series with it, to the control grid. That will allow negative feedback of the AC component, without affecting the DC bias. you can adjust the value of the feedback resistor, to find the happy medium between gain and distortion. Larger coupling capacitors help with the low frequency response.
It actually sounds pretty good, but it's interesting to note, that most of the harmonics you hear are artifacts in the speaker caused by resonance, rather than the amplifier. You can't hear the difference between 3% and .03% Harmonic distortion in the amplifier, because speakers typically have THD of ~20% or worse. Headphones are typically much better than speakers, but even with them, it's hard to hear differences between amplifiers.
That is surprisingly good for a tube not known for working well at low B+. You ought to play around with 12AT7 and 12AU7 and see what you can get You may even be able to use a more standard biasing on those tubes. Too bad plate chokes are so expensive. Would help a lot.
It would be interesting to drive it from a line level source. Your headphone output is a small power amp and so probably is more capable of supplying grid current to drive the forward biased grid.
Dude, could you please share the schematic with us pls? I wanna build this piece of art.
Very nice little circuit actually. And btw that special tube ur using seems to be a NOS Telefunken 12ax7, so I'd check this if I were you as they can be CRAZY expensive nowadays
Completely unbelievable !!! ........ AWESOME !!!!I would pay what little I have right now for one !!!!!
@JohnAudioTech
I enjoy watching your videos and i love your icon picture of the chip man.
Always reminds me of Germany and their flag,same colours,red,black and yellow
Would you be interested in running a similar experiment with spectral analysis again with a 12AE7 tube if I sent it to you?
I would really like to see if there is a similar "low order harmonics" effect like with this one.
Was a great experiment and the preamp works amazingly well!
+MAN CAVE NO.1 You would find that about any amplifier with a single active element whether transistor or tube will produce low order harmonics due to the nonlinear gain structure of the devices. If tubes or transistors has a perfectly linear gain structure, amplifiers would be a lot simpler to make!
I notice that on some guitar pedals built for distortion they use the same valve but with a current of only 9volts. I have guitar valve amplifiers and my main stereo amplifier is also valve . You can feel the heat from them. The guitar pedal I have barely lights the valve. I find it hard to believe that such a low voltage has an effect but it most definately does.
Thanks for the great video. The guitar sounds wonderful. Could you please share with us in the description what mic and recorder you used to record the sound?
Hi John!
How are you doing the spectral analysis, can you write a few words on that?
Did you calculate THD, I suspect it's not that great for "warm sounding" tube amps?
i love it buddy well done
Also may I ask what software you're using for the analysis ?
Thank you
Cool, whether the scheme is suitable for alteration in a tube microphone?
Awesome circuit & sound! , the tube looks like the monster from war of the world, how does it stay up with just few wires?
+Tennisplayer21Kim Solid core wire is stiff enough to hold it up.
Actually, a 12AE7 or a 12U7 double-triode would work MUCH better than a 12AX7. The specs are waaay off. If you want to use 12volts a tube that is made for 12 volts should work much better than a 12AX7.
***** I'm aware of better tubes for the purpose. This was an experiment to see if the scavenged tube I had laying around would work. I didn't want to spend anything on new tubes. I might try it with other tubes if I can scavenge some up someday.
Right on. Understood. Sorry, I didn't intend to be critical. I totally didn't understand at first anyway. It was a great idea, actually. I think there are even some websites dedicated to the use of HV tubes at way below their intended voltage with interesting results.
Good info.
Actually, the 12AX7 is designed for use on both 6 and 12 volts. There are 3 heater pins on the tube, allowing it to be driven directly from a 12 volt battery. This type of tube was used in early car radios, and was expected to run right off the 12 volt battery. For use on 6 volt filament supplies in Hi Fi and guitar amps, the center tap pin becomes one, and the other two are connected in parallel, allowing the heaters to draw twice the current at half the voltage, making it compatible with the 6 volt power tubes supplied from the same transformer winding.
@@vincentrobinette1507 Well sure the HEATER works on a 6 or 12 volt circuit but that has nothing to do with the plate current at that same voltage. 12AX7 may be able to operate it's plate at that low voltage but a tube designed for it would work better...if one must have tubes. A 30 volt design works particularly well and is still somewhat low voltage.
excellent!
Planning to build this for bass guitar as a preamp in chain - bass guitar - tube preamp - TDA chip power amp,how do you think,this might work out as a instrument to line level boost?For now I am trying to get valvecaster do this,but in clean it actually dont boost my signal,but when I apply gain it is too much overdriven for a bass guitar.
do you have an schematic, please? i wanna build one to, but i have no experience with tubes :)
+Marian B 2:37 you see the schematic. But why not design your own? From that point your experience starts. You can use any triode tube from the junk box, that's part of the fun.
I'd like to see the full schematic too please!
I have a question. I saw a similar schematic, but am needing some help with an understanding of it.
www.cyclone-radio.com/preamp.png
If I just give this circuit 12V, I get no noise out of the other end of this. I am guessing it is because I need to bias the input? If so, what resistor value should I pull up to 12V and what should I pull down to ground? I see you used a 47K to 12V and a 470K to ground on your example. Now, assuming I go to the 30V the schematic has it labelled at, then what should I use for the bias resistors? And the last question is on the 12V rail, or in my possible case, the 30V rail, how much current do I need to source? Like, if I made a switching boost power supply to 30V, how much current would it need to be able to deliver? Are we talking a couple of milli-amps, 100's of milliamps? 1000's of milliamps? Sorry for being such a noob!
hi fellas, I'm noob in DIY world, but I have an 12ax7 and i wanna build one of these amp, but I didn't understand what pole of the tube that used because there no number in schematic. Regards,,
Google "12AX7 datasheet" to get the tube pinout.
thanks John, I'll search it, did you have an e-mail, so I can sent my trial result :)
Great!! But... I can't find the schematics :/ could you give me the schematics?
Javier Peña Did you watch the whole video? Schematic shown and explained starting at 2:40.
I'm sorry, I thought you forgot some components :c
Javier Peña Actually, my schematic is only for one channel of the stereo preamp. The other channel would be identical. That is why there are more components on the board vs. the schematic.
I understand, well, thank you so much, one last question... What did you do with the pins 4, 5 and 9?
Javier Peña I have connected pin 4 to GND and pin 5 to +12V
I'm seeing B+ on the grid 47k or is it part of the circuit 470k ohms grid bias is right.
That's not a mistake. With the plate voltage that low, it is actually necessary to pull the grid slightly positive of the cathode, much like the screen grid on a tetrode or pentode. As the plate voltage increases, the grid needs to go further and further negative, to maintain plate current. At high voltage, the grid is indeed pulled below the cathode, weather it's accomplished by a cathode follower resistor, or, negative bias voltage on the cathode. A typical set-up in a guitar amplifier is a 1k resistor from the cathode to ground, and a 100k resistor from the plate to positive. That does a pretty good job of splitting the voltage between the tube and load resistor, to give maximum headroom. The gain is ~100:1, and the grid can be referenced to ground,(usually 100k) without any need for input capacitor. The guitar can be connected straight to the grid. The 100 K resistor to ground is just to maintain bias when the guitar is unplugged, and the jack doesn't ground.
@@vincentrobinette1507 I remember in my 20s I would do experiments like this with 12ax7 12au7s after I got stoned I remember pins 2 and 7 are the inputs pins i and 6 plates and 3 and 8 cathode and a small negative charge in respect to ground to pins 2 and 7 like 750K ohms. I used raytheon and rca 12ax7s off an old baldwin organ good ole days.
@@TheWarped45 I got my start the same way! I used to get tubes and other passive components from old RCA television chassis, and old radios. My interest has always been amplifiers. I salvaged a tube amplifier out of an old Magnavox console, and that became my power supply for experimenting with tubes.
@@vincentrobinette1507 that is very cool right now I have 807s nos I think I will make a stereo amplifier one day I have 6l6s but 807s look cool maybe a 6cg7 6fq7 for the phase inverter ef86 in the preamp.
Good evening my friend, can you tell me the values of the capacitors? I was very interested to carry out your project.
the capacitor's values are one the schematic itself...
1 uF?
wenderson eliecio Yes. You can use unpolarised electrolytic. If you don't have one, you can make one from two polarised ones, like this:
----)|---|(---- Make sure they're both 2uF because in series, that would equal to 1uF.
Thanks a lot, I do not know how to read capacitors, only resistors.
wenderson eliecio Even if they are marked, they are sometimes wrong. Your best bet is to take the multimeter, and set it to capacitance, and measure every cap you will use. Be sure to discharge them before you measure them!
If you had gain to spare, you might be able to lower the THD by removing the cathode bye pass capacitor giving a degree of negative feedback. Just a thought!
It's in the video I am drawing my own and I'm going to beef up the plate voltage by using ac and use a voltage multiplier for the B+ 96 vdc. I may use a 24 volt transformer because they are available, they are used in heating and air conditioning. There are power adapters that are AC as well. If you want the true tube sound you will need some iron on the output. A 70 volt line transformer will work, the kind used in PA systems. 73
can you share the diagram of this proyect please?
When I get my bench restored, I'd love to tinker around with unusual tubes used in place of traditionally standard ones. Say, instead of a 12AX7, use something odd like a 6AJ8 (www.mif.pg.gda.pl/homepages/frank/sheets/020/e/ECH81.pdf)
Or one of those nuvistors... www.thevalvepage.com/valvetek/Nuvistor/nuvistor.htm
What a lovely project this looks like! I would like to use this preamp in conjunction with a solid-sate amp shown here: www.adafruit.com/products/1752
As a friend of mine pointed out, the amp can only take 3Vpp line-level input, would I be able to run this preamp with the same 12V SLA battery used to power the class D amp?
Also, how hot does that tube get with a 6V heater?
Thanks!
12vAC ? how much current does it draw ?
Is 12v dc man..not ac
thats unusual for vacuum tube to be on dc. but pretty cool. so how much amps does it draw ?
Vadim Martynyuk it draws about 210mA.
Brooooooooo... First song title?
Hey do you have the schematic for it
Rolly Praise
yes
hi do you have the schematic for the pre amp
You will only notice the warmer tube sound if you have a tube amplifier, not just 1 tube. And for you to really notice the difference you have to have very good speakers that can handle those frequency responses that only tubes can deliver, but off course you will notice nothing with only a pre-amp tube and some sheety speakers of plastic...
"but off course you will notice nothing with only a pre-amp tube "
You are talking out of your ass man. You are very wrong. You can get a dramatic difference in sound simply by tube rolling a pre-amp. Although the difference is not as much as a tube power amp, a tube pre-amp VERY MUCH colors the sound.
you're not supposed to get those harmonics until near saturation though. must be very nonlinear
+nikotwenty Those harmonics are quite mild and equate to 0.4% THD. Not hifi, but not bad for a single element amp.
+JohnAudioTech interesting though 48db down, I think you are right I don't think that could even be heard
Harmonic distortion is what gives tubes that "warm" sound. Stereo manufacturers use THD as a performance indicator as though it were a bad thing. That's a little misleading. Intermodulation distortion is the "bad" distortion that makes an amp sound unpleasant.
Intermodulation distortion is what matters most, a two-tone test is the simplest way to see it. All distortion both generates harmonics and intermodulation products, but the latter are usually far more audible.
@Diggy Dude, not wanting to sound elitist or audio snob but, any (hearable) distortion is bad distortion in a hi-fi system, a system that is meant to accurately reproduce a signal instead of coloring it.
Sure there more important factors than THD but ideally a hifi amp should have as little THD as possible.
I build these starved tube preamps and get better results with 12AU7's
Considering the limitations it's not bad. Tubes are high impedance devices so some distortion (including harmonics) are introduced matching low input/output devices to the amp. As hinted you had to adjust the bias to get the tube to work as a class A amp, without boosting the grid voltage it will be class B only. You have no frequency bias compensation so the natural RC filter will set the response curve. I worked with tubes since the 60's and still love the way they sound. In my opinion what I noticed is that tube amps are "warm" and solid state amps are "brilliant" sounding. Tubes can't be coupled together the same way transistors can and a different strategy is used in each case.
Kimberly Buck id love to pick your brain as im at the drawing board designing a hybrid.
Why you dont need an output transformer to adapt Z?
What hardware and software are you using to do the spectral analysis. I assume just a sound card would do it?
From the looks on the icon on the task bar hi is using www.audacityteam.org
I think hi might just have played the 1K test signal and then taken the output and put that on the line in on teh sound card and recorded it, and THEN done a spectrum analysis on the recording.
Hey JAT, I hope you are doing good. Nice pre-amp, love the tube/valve, a dual Triode. I'm gathering parts to build a simple Fender 5F1 " Champ-amp", 5 watts = -. 5Y3, 6V6, and the 12AX7 pre-amp tube. As you may know, GT refers to 'Glass' tube. Check out Uncle Doug on TH-cam. He made one from an old signal generator, awesome job. Still check you out as am able, love your channel. Happy Year End and Holidays, all the best in 2016. C.
An ECC82 will perform better (and actually exhibit more gain) at such a low plate voltage. I was playing around with similar circuits several years ago, but for guitar pre-amp purposes. I kept wondering why I got less gain when going from an '82 to an '83. I initially thought the '83s I had were dud. Good thing I didn't throw 'em out! lol
If your primary purpose is to level match the output of an Mp3 player into a hifi amp, a transformer will do the trick nicely. Those headphone outs don't have much voltage, but they can drive into quite low impedance loads so a step-up transformer can work well with them.
I am working on a project whereby I only want to light up the tube filament with DC current. I am putting 6.3 through them and they light up. Not very bright though. When I put 7 to 10 volts they glow real pretty!! I only did it for a few seconds. How much current can I safely use? What happens if too much? Do they just burn up or is it dangerous?
for as far as i know , the ECC81-82-83 tubes are designed for 6,3V +- 5% heater voltage , so putting more voltage will destroy the tube over time.
According to the specifications, the heaters use 6.3 volts, 150 Milliamps each. For 6 volts, use the center tap pin, and connect the other two in parallel. The tube will draw .3 amps. for 12 volts, leave the center tap pin open, and connect each of the other pins to the battery. it will draw .15 amps at 12 volts. Running the voltages higher will make the tube work better at these low voltages, but will shorten the life of the tube.(not recommended!)
What many people don't know about the tube sound is that not only has the added harmonic content, but, those harmonics are also distorted, just in the same way as if you put a distortion pedal to your electric guitar.
Also, so you know, tubes distort the even and odd harmonics, but tape saturation has exactly the same behaviour, only, the odd harmonics are the ones distorted.
This harmonic distortion is low level as you can see on your oscilloscope, but, for some reason they add some richness to the sound.
They have tried to duplicate this digitally on some extent, and there are many VST plugins for music production in the market for that, some better than others, but the key is to make those low order harmonics distort, and, in real tubes, those harmonics levels change randomly over time, same as tape, which makes it more difficult to replicate.
I can tell that some warm is added just by listening the first song of your demo at 6:44.
Thank you for posting this, Im making me one of those soon, Cheers.
a good tube amp has 0.003 thd!
Its because a tube is volt amplifier,like mosfets(transistor )
A normal transistor amplifies by current,
Thats why tube s,and good mosfets sound so natural.
Best is to use tube as pre amp,and mosfet end power.
Thats the way i build now,
Active with 6 litle amps,class a single ended. distortion only sounds great in gitar amps,in audio its callt clipping,or over modulation.
Did you know the 12AX7 tube was introduced in 1945 by RCA? And we still use it. But this is amazing. I didn't know you could feed the plates a mere 12 volts and get it to work.
My guitar preamp runs off 4 AA batteries (6volts) and is a cold cathode 12ax7 impedance (probably a
darlington dc configuration?) "transformer" to a high impedance bridge piezo. it is referred to as "a cool tube"
preamp..works good and really provides a warm sound for the guitar.
The tube heater runs off 6 volts. Don't know what the plate voltage would be but
I expect that it may have a doubler working off the 6 volt batteries for 12 volts.
The o/p of the preamp tube goes into so solid state circutry and being proprietary,
I don't have a schematic for it.
The music sample sounds very clean, similar to mine.
The tube filaments would normally be wired in parallel, to properly heat the tube on 6 volts, but, the heaters require .3 amps. In that configuration, the batteries would only last 8~10 hours. Running as "cool tube", the filaments are likely connected without the center tap pin, causing the heaters to run at only .08 amps, receiving 3 volts each. A tube can operate in this condition, but the circuitry around the tube must be very high impedance. Most likely, JFET op amps. The tube should last a lifetime.
You pointed out something I have never seen anyone else do. You pointed out that in "normal" operation, a tube acts like a JFET (where a negative gate voltage, relative to the 'source', is needed to control the current flow by limiting what would otherwise be runaway current), as opposed to operating the tube in a low voltage situation, where it behaves more like a MOSFET, where a 'gate' voltage that is positive, relative to the 'source', is needed to entice current to flow and so control the current flow. Congratulations! It's about time someone brought that fact to light.
Well, it's not like a mosfet in that the voltage isn't actually backed by much current, so its output needs to be buffered. It's only purpose in the circuit is to add 'good' distortion to the signal.
So this circuit acts like a buffer? Im only beginnin to learn electronics. But this circuit reminds me of a ce transistor amp..
@@Axelvad That's not off the mark, but a tube ran on low voltage can't really supply much current, so it's output is then buffered by an op amp, usually with close to 1 gain, sometimes 1.25 gain.
Having the cathode follower resistor helps with thermal drift. It serves EXACTLY the same purpose as an emitter follower, or source follower.(bipolar junction transistor, field effect transistor) Besides, at this reduced voltage, it's hard to pass enough current to get the tube anywhere near it's rating.
You all make excellent points. and I mistyped when I said MOSFET - I should have said BJT. And while it is true that the current would be extremely low, that does not change the fact that when the grid has to be positive to entice the current off the cathode, it is behaving like a BJT. Even so much that there will be a small grid current analogous to the base current of a BJT.
I built a class a headphone amp from one of ljohn linsley hood design and it sound excellent better than a tube headphone amplifier lent to me by a friend.
I just watched your video and im thinking about making a guitar preamp with this tube, as it is a double triode tube can it be used so one triode makes the clean sound and the other does the overdrive? Then the sound goes into a class D amplifier (because I like efficiency) also I have read the previous com about the input impedance (i know it's 4 months old) and it's usually fixed with a 22k resistor (at least on transistor amps) I need to study again how to wire a triode and then I think I will be able to make some cheap and gread sounding amps
Also most people put on a plate voltage about 200V and you don't, what do you do instead?
But maybe im saying something insane because it's 1am
Hi, this low voltage tube amp was more of an experiment. The gain is fairly low so you should experiment with additional stages for distortion driving. Input impedance can be low or high depending on the amplifier topology.
JohnAudioTech but 12volts as plate voltage works? (well it should, or I don't know where you get sound in the video)
I think a little chip or transistor as a pre-preamp should do the work to get enough gain (and if gain is still too low, maybe take the output signal of one triode and put it in the other triode of the tube)
A better way would be to cascade the two haves. Connect the signal to one, connect it's output to the input of the other. This amplifier inverts the signal, so running into the next stage will put it back in phase. The gain will be multiplied, making it much more sensitive. For distortion, you can delete the 10 uF capacitor that's in parallel with the cathode follower resistor. That will give a much cleaner, less distortion sound, than even this amplifier in the video. When you WANT distortion, putting the capacitor back in circuit will give enough gain, that it won't be hard at all, to get the "overdrive" or "tube stack" sound.
Can i use this as a preamplifier in front of a dedicated subwoofer in order to hear the tube sound???
I! Can you send to my email the schematic of this peramplifier? I'm curious about it!
Thanks for this great video. The sound seems very good. I designed a theremin with 12AU7s that uses a B+ of 50 volts.
thank you for this great content! I've learned so much! Your Preamp Sounds Fantastic! Do you mind if I use it and put an OPA2134 at the output with Unity Gain? I Love way it sounds as-is.
Here's the "complete" schematic...still just one chan but boosted by both sides of the triode this time. I will be happy with any improvement. If I figure this out I may dust off some Type 30s up in the attic! Power amps...the next frontier.
This is your schematic but showing both sides of the valve the way I set them up 2nd time around:
i51.photobucket.com/albums/f396/czechrite/W-AMP1-contrast_zpsbd58742a.jpg
I'm curious if the resistors should stay the same on the "end" of the circuit of if the other half of the tube should have the same resistors applied to it.
Hey! I know this was a long time ago, but did this schematic work for you? I see you used a 6N2P-EV. I have a 6N2 (chinese) here, and was wondering if I could build a reasonable preamp with the schematic you drew.
The WALLDORF - the site will not let you on any more...
470k 4k7 (neg 10uf) and 100k is connecting to ground?
This is incredible!
I found a similar model I'll gonna build, a guitar distortion like ehx lbp-2. I'll put that thing into a guitar. A guitar with two ecc83 glowing in the dark yeeehaaa!
That's gonna go through batteries like a glowing hot sword through margarine.
@@Abandonedmachine it'll get a stereo cable where one channel is the power
Sample music ... played on my solid state laptop... sounds great solid state !
Sound samples online are pointless, and yet, we still listen. LOL.
Valve amps still really produce warm, detailed sounds...thanks for very vivid video
ficou legal .... melhor porque não trabalhando com tensões maiores , fica mais fácil de ligar em uma fonte só ... menos componente e dor de cabeça também ... =)
good evening very good work well done.
I would like if it is an easy design or a pcb with its accessories because I like it and I would like to make it and I thank you very much
Here's my attempt to copy your amp project here. I only half-succeeded. Now that I am actually looking at the video again, I'm seeing about twice the components on yours compared to mine (and I am not including the power circuit). It seems that you have joined the twin triodes together somehow. All I did was copy your schematic and "double" the plate/surface size of the anode/cathode by connecting them in parallel. I guess the effect is not "double gain" but rather I've turned this 6N2P-EV into a 6N1P or something like it (a single triode rather than a double or twin).
My "video reply" to this vid is here:
th-cam.com/video/zqErVXI3d_4/w-d-xo.html
If you have time to watch and comment, I'd be grateful.
Thanks.
MAN CAVE NO.1
If you only use one triode of a 12AX7, you can install the tube backwards to use the other triode. It was designed this way, the pins line up perfectly in both orientations, as long as you drive the heater at 6.3v instead of 12.6v.
This is a great thing to design in as it will double the life of your tubes, or if you are picky, double your chance of finding perfectly matched triode pairs.
I wish I understood why you have a 47K resistor and a 470K in series. Is that where you're splitting the power supply?
He made a voltage divider with those two resistors
Whats software is that???
Beautiful "tube" sound created in a simple way with a 2 triode tube, well done.
Wonderful video. Damn wonderful video.
Cheers from Indonesia
Binging on this channel.. :) I have a dac thats just too loud for my tube 6j1 preamp. how can i make this kind of preamp that still buffers controlling just the gain and not the input voltage? like 2v input to tube buffer to 0.9V output 100ohm impedance?
btw im using a 15v DC power supply
I am not an expert, I have read about it but don't have much listening experience, but part of the so called tube sound is that the clipping is not as harsh as a transistor amp. Of I don't know if this applies to preamps the same as power amps. Of course tube power amps that with big iron core output transformers get expensive.
***** I think a lot of "tube sound" is born out of musical instrument amplifiers that are supposed to distort like those for electric guitars. This (some how) carried over to audio amplifiers where you really don't want clipping or distortion. Still, very good tube audio amplifiers sound great, but are somewhat impractical to me as they are costly and consume a lot of power, even at idle. Solid state is just as good or better to me. Perhaps not as good for guitar amps but I'm not a musician.
JohnAudioTech What you get with a tube guitar amp is that seamless transition from clean to distortion. Plus the distortion itself just plainly sounds alot better. As for clean sound, the difference is not that great in my opinion.
Bogy Wan Kenobi was right, salute to JAT
I'm a guitarist and I live for those harmonics
A simple boost converter with a good filter capacitor can yield a higher voltage for that 12AX7
+Kevin Roosa The entire point was to explore NOT doing that.
did know if the 12v was possible, but you showed me how. Thanks
Before transistors....all car radios were tube based and none of them had "100-150 volts on the plate."....and they ran on 6volts and 12volts...
Tubes produce more distortion than SS/Digital That's it! That's why people say tubes produce a warmer sound. Scientists did lab controlled experiment and discovered that humans prefer the distortion in tone that a tube amp produces naturally over the clean, somewhat sterile SS/Digital tones. So simple. I hope you can grasp what I have explained and from now on you will not use the phrase "people say tubes sound warmer", without clarification that tubes produce a pleasing distortion which humans prefer over the clean steril SS tones.
I kinda wanna build 4 of these and sling them into series to build a gain stage for laughs... would be interesting to see how it breaks up on a 12v circuit... Might be like a less hot version of a JCM-800 lol
This is how so many manufacturers got away with selling "tube" amps for years. By avoiding having to build expensive high-voltage power supplies to make these tubes operate where they actually work, they put cheap, shitty IC/transistor amps on the output to kick up the gain...
Very nice preamp. Im very new to Vacuum Tubes and I would love to build a small headphone amp. I would have a question: would this circuit also work with a ECC81? That's currently the only tube I have (except for two EL95's)
Hoka me pasarias los planos que has utilizado saludos
Hi John this is really cool. Thank you so much for sharing it! I"m going to build it.
An interesting circuit which I may knock up. The audio sounds fine on youtube but as I have smashed up my hearing by shooting over the years all audio sounds good. Well not horribly distorted stuff but anything subtle just does not matter. Makes for a much cheaper listening experience.
Is there any chance to get a better schematic?
Thank you in advance!
yes, i would ask the same question
Yes, a good schematic. I would like to build one for my self.
Sounds good, would you do a revisit on how to design a "flawless" distortion free power supply for the heaters?
As I understand it, the different between tubes sounding sweeter than solid state is in WHICH harmonics are being emphasized. As you go up through the harmonic series of a sound, some harmonics blend better than others with the fundamental pitch.
I have a question about the 1µF capacitor : Must they be "film" capacitor or can the be ceramic or electrolythic ?
If you're just playing around on a breadboard, you can use any capacitor type, however, I'd recommend film if you're building a finished amp.
JohnAudioTech I tried the schematic in your video, but it doesn't give a louder sound, it gives a much dimmer sound. Can you help me please?
JohnAudioTech Ok after some experimentings withe the circuit, I found a solution !! I've added a buffer circuit with an LM386 and it works really well !!!
What's the maximum gain you can get from these at 12V? I'm struggling to get more than 30dB
+Jack Holden Not a lot of headroom to work with at such low voltage. 30dB is not bad. You might want additional stages for higher gain.
...does that mean you can basically 'bolt on' additional stages for more gain?
yes. Up to a total output voltage of 10-12V, assuming you get the grid bias correct.
it's hard though and you might need transformers between stages.
Sorry to say this, but your tube circuit does not operate, as you only hear the sound from the path formed by this: input cap ->47k -> 22k -> output cap. That the path the signal goes. The tube is just switched off. Disconnect or omit the 47k resistor and you´ll see what i mean;)
If you want to use low voltage, the former battery tubes are what you need. european DCxx ol DLxx types or some ECH84 alike, intended to use in former car audio, will do as well....
The amplifier has a measured 20db of voltage gain. The path you say has the signal passing through the positive supply. The 12v battery has too low of impedance and would effectively short the signal to ground before it gets to the 22K resistor. Removing the battery, the amplifier goes silent, also no signal until the filament warms the cathode. The signal path is through the tube.
To be honest, this was my first guess, just for the looks of your wiring....I never run tubes at low voltages, but i´ll do a test of your design, to see if it works ;)
As i have to do a basic tube amplifier setup anyway.
So i´ll do a 12AX7 (=ECC83) design and show how to pick the needed components for 250V and then run this and your design as well on 12V....
TubiCal A circuit designed for 250V B+ probably would not work at 12V B+ (among other things, the bias would be totally wrong, as pointed out in the video). It's not unheard of to build low-voltage pre-amps out of tubes that normally run at high voltage. I've built a guitar overdrive stomp box with dual-12AU7s that runs on 12V B+ (and actually runs fine on 9V B+ and 9V heater supply).
Is my drawing correct?
Regarding the pinout of the tube :
www.dropbox.com/s/729191q6gloyln0/TubePre.png
I didn't see where the negative supply terminal connects. I assume it's the bottom rail, correct?
I always understoof that odd harmonics produced an unpleasant sound/timbre
PUSHPULL AND TRANSISTORS
Intermodulation distortion contributes a lot more harshness to the sound than harmonic distortion.
What's the plate voltage on that? I didn't think 12V was enough to get any gain out of a tube like that.
I was hoping to hear it off compared to on .That could have been just all player.
hello, how about such an excellent project, could not you give us the schematic? thank you very much
When you say the gain is poor are you implying the waveform couldn’t compress and distort like a preamp tube can do in a conventional guitar amplifier? I am asking this because I own a Vox Cooltron guitar effects pedal with a 12au7 tube in the circuit being run at low voltage, 20 volts I believe. And in some literature Vox admitted it wasn’t doing much more than some amplication and any distortion effects were coming from silicon elements earlier in the circuit. And I wonder if this has to be true?
It will still compress when driven hard, it just lacks much gain.
The positive voltage on the grid is interesting. I tried some 12ax7 tubes in 12au7 headphone amp and one worked well but the other two didn't. I tried a 1 meg resistor from grid to 12 volts and that improved things greatly. Thanks for your help. It looks like the tube wasn't passing enough current to get a decent positive cathode in relation to the grid.
Plate voltage is so important to get proper tone from the tube🤦♂️
I bet the harmonics would reduce a lot if it was run on 3-4 times the voltage
6.3 volts per element. 12.6 volts, if you're running the heater filaments in series. Traditionally, tubes were rated for 6.3 volts, because that's the actual terminal voltage of a 3-cell Lead Acid storage battery, which were used to run heaters in old portable radios. Using a 12 volt Lead Acid battery is absolutely perfect, for running the filaments in series. The heater filaments require 150 milliamps each, so that's .15 amps @ 12 volts, or, .3 amps @ 6 volts.
You neglected the lower harmonic....
Hi John! I'm currently working on a low distortion tube input amplifier. The circuit topology requires grounded input DC operation with dual rail supply. As I noticed at high voltage grid is lower voltage than cathode. At 12V grid is much high than cathode also higher than half voltage of plate from cathode. What's the supply voltage that have the grid biased at mid point? What type of tubes are good for this? I'm looking at 12ax7 as it has higher gain. Thanks!
Wow. This was only a week ago? I achieved 0.0003% THD minimum. And 0.001% THD+N.
Im new to electronics, can someone explain why there is a 100k?
do you happen to have this project with schematics and all somewhere on the internet ? would like to try it out myself
It's not the tube that gives the harmonics Odd or Even. It's the architecture of the preamplifier. Use a NPN or PNP transistor in the same configuration (class A) and you will have the same Harmonic Products
You can get the miniature wire-ended valves from the CCCP if your know where to look or try EBAY, It is like being in the KRONUS HIFI factory showroom in DUNGANNON Northern Ireland.
David, do you have a model in mind that is known (by experimental designs or otherwise) to create good sound? And do any of them come with a datasheet that quotes IV characteristics with a low supply voltage?
i have a pc type tube socket coming so i can mount the tube right on the board
Great job! I am a novice and know very little regarding this, but willing to try to build the circuit by realizing the circuit is low voltage and safe to work with. Is the circuit your priority or can you share your schematic? I will understand if you tell me you wish not to do so. Thank you for a great video.
+Carl Philistine Hi, The schematic is shown in the video. You may need to tweak the biasing resistor values as my tube was worn.