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Topic: First adventure into DIY: making my own headphone amp based on the A47 (Read 13139 times) previous topic - next topic
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First adventure into DIY: making my own headphone amp based on the A47

So, I've been thinking a lot about making my own headphone amp based on the A47 design I've seen around the net for a while. I've got a pair of Grado SR80's, which is why I'm looking at the A47 design, since it has the buffer capable of delivering the current.

I'm an electrical engineering student, but my program concentrates more on hydro power, motors etc. rather than electronics or audio (there's no audio stuff at all).

I don't want to just build a basic A47 though, I'd like to build something completely custom, partly for the experience in design, and partly because I want to possibly improve upon the classic A47 design. I was thinking I might like to add in some tubes and make a hybrid design (inspired in part by http://www.pmillett.com/starving.htm), because I'm really not concerned with making the amp ultra-portable, and more concerned about making it sound as good as I can for as little money as I can manage (I'm not exactly rich, considering I'm a college student.)

Of course, I know almost nothing about vacuum tubes, other than the absolute basics, so I was wondering if you guys knew of anywhere that talks about the basics of using tubes in an amplifier, without getting too technical and into stuff that doesn't matter. I might be an EE student, but I'd much rather get practical information first, and technical details later.

I've been wondering about the supply voltage I should be using as well, I've seen people mention being able to run amps on anything between about 3 volts per channel to using 2 9V batteries with a rail splitter to get 9 volts per channel...

I'm a bit confused about why such a huge difference in voltages is present, considering how much of an impact it would have on the volume in a headphone...

First adventure into DIY: making my own headphone amp based on the A47

Reply #1 –
First off, if you're making a tube amp, you will need more than 3 or 9 volts.  The schematic for that amp you referenced says 48 volts.

The best sound for the least money will likely be something like the A47.  Conceptually it is easier to deal with an amplifier chip where you have inputs and outputs and just have to manage the feedback to get the gain you want.

If you want to design with discrete components then you have to consider operating points.  That is, your components have some substantial DC voltage across their pins (bias) plus a relatively small signal voltage.  You have to isolate that DC bias so it doesn't appear on your input and output jacks.  The DC voltages can be in the 3-9 volt range for a transistor amp, or 50-100 volts for a tube amp.  That's for a headphone amp.  For a moderate power amp driving speakers, you might have 50 volts for a transistor amp.

First adventure into DIY: making my own headphone amp based on the A47

Reply #2 –
Ok, I wasn't quite being so clear there. I'm aware that the hybrid amp has a 48v supply voltage.

I meant that in various A47 or similar amps (small semiconductor amps) I've seen mention of voltages lower than the 18v supply with a splitter set up to create a virtual ground at +9 volts seen in this schematic: http://benfeist.com/a47/images/a47_assembl...d_schematic.pdf Sometimes 15v, sometimes less. 3v was a number I remember reading somewhere as an absolute low limit on what their amp would seem to operate on, but I'm not sure if that was the actual supply voltage or not.

I've actually been wondering what voltage levels my headphones generally see from a supply.

I'm relatively clueless about audio electronics, but I have some decent understanding of electrical theory, as well as digital theory (much of which is self taught, since my program concentrates much more heavily on the high power stuff).

I can afford to make something a little more substantial than a A47, which is why I'm looking at making something a bit more complex than that, but I'm really not sure what to look for, or how much it would cost to go beyond the basic A47 design.

First adventure into DIY: making my own headphone amp based on the A47

Reply #3 –
First the tube idea...  A lot of audiophiles are fascinated with this 1950's technology.  But, I don't believe there are any real advantages.    The main advantage is that vacuum tubes typically clip (distort) more softly than solid state electronics, but in a high-fidelity application, there should be no clipping.    (Guitar players like the sound of overdriven tubes, and some recording engineers might like a little soft-clipping "warmth" in their microphone preamps.)    But, soft clipping can be done with solid state circuits too (or in software).

Tubes are inefficient.  They require heater power and high operating voltage, which makes battery operation impractical.  And they are high impedance,  which means you need an audio-output transformer if you are going to drive speakers.  Of course, you can make a hybrid device with solid state output-circuits.  (I'm not sure if you can drive headphones directly with tubes.)    It's very difficult to make a transformer that's flat over the full audio bandwidth...  But, it's easy to build a solid-state amplifier that's flat from DC to over 100kHz.  (I'm not saying you need to go to 100kHz...  I'm just saying it's a LOT cheaper & easier to make good audio circuits with op-amps than with tubes & transformers.)

-----------

The A47 circuit looks fine.    The high negative feedback of any (proper) op-amp design virtually guaranties low distortion and flat frequency response.  Noise might be a concern, but probably not.  So, you just need enough voltage & current.  And, you want low output source-impedance, so that headphone impedance variations over the frequency range don't cause frequency response variations.  You don't want to "match" the impedance... The headphone amp can have an output impedance of 1 ohm, even though it can't drive a 1 ohm load.

Quote
I can afford to make something a little more substantial than a A47, which is why I'm looking at making something a bit more complex than that, but I'm really not sure what to look for, or how much it would cost to go beyond the basic A47 design.
I don't see any obvious "weakness" in that design, but you might want to put it in a better box, and you might want to build an AC power supply.

Since you're an engineering student, I'll let you make the Ohms Law & power calculations.    The Grado Labs website says that the SR60i has sensitivity of 98dB SPL at 1mW.  If you double the power, volume goes up by 3dB, and if you double the voltage you get 4 times the power (+6dB). And, it has an impedance of 32 ohms. 

The output needs to swing positive and negative, so with an "ideal" amplifier than can swing "rail-to-rail", you could theoretically get about 3V RMS from a 9V battery.  You can check device specs to see how close the output can actually get to the power supply, and if there are series output resistors (as with the A47),  you have to allow for voltage drop across those resistors.

I haven't really studied the A47 circuit in detail...  But the power supply looks like it creates a virtual ground in order to supply positive & negative voltages from a single-polarity source.  Some chips require dual power supplies, and with a dual power supply you can eliminate the output capacitors.  Output capacitors can limit low-frequency response (and they take-up space if you are trying to build  something small).    Eliminating the output capacitor isn't a requirement...  I've got a 100W power amp with a single supply and output capacitors....  With a large enough capacitor you can go below 20Hz...  But, if you can eliminate the input & output capacitors you can go to DC (zero Hz).    You might not want to go to DC... The A47 does have an input capacitor...  The input capacitor is operating into a higher inpedance, so you can use a smaller-value capacitor without loosing bass.

I like the fact that the feedback in the A47 circuit is connected to the output-side of the 47 Ohm current-limiting resistors.  This will give you the desired low output-source impedance.  (Feedback does all kinds of amazing things!  )

Before you go ahead with the A47 design, take a look at National Semiconductor's website[/color][/b] They've got lot's of specialized audio chips and helpful application notes.    I'm pretty sure you can find a chip & circuit that's simpler than the A47, and just as good.  You may still decide to build the A47, but check-out what else is available first.

If you are building a power supply, National also makes lots of voltage regulators.  You don't really need "regulation", but the regulators will knock-out any AC hum that's not filtered-out by the power supplies capacitors.

I'm not trying to "push" National...  I just have some old National application books with lots of audio circuits, and many of those designs seem to now be on their website.

For my DIY projects, I generally use this kind[/u] of solderless prototyping board.  They are a somewhat more bulky and more costly than perfboard or wire-wrap, but very convenient.  I built a microcontroller-based car alarm on one (or two?) of these prototype boards and it's been running in my van constantly for over 10 years with no trouble.  (The program runs even with the alarm is "off".)

Or, if your school has a lab that makes PC boards, that's better.  When I was in school, my school had a PC Board lab where students could order PC boards for a few dollars...  I didn't realize what a good deal that was 'till I got a job and found out that it costs several hundred dollars to get a few prototype-quantity boards made!      (If you can get a board made, you can use surface-mount if you wish.)

First adventure into DIY: making my own headphone amp based on the A47

Reply #4 –
First off, thanks for the reply.

Well, I can tell you my school doesn't have a PC board lab... The electronics side of things there is pretty much absolute garbage. About all we learn about electronics is a fair bit about transistors (which was over a year ago now, and it wasn't really much in the way of practical knowledge, it was mostly just basic theory, nothing about how they work with AC or anything), and some basic stuff about binary, boolean logic, and flip-flops... And the teacher we had basically couldn't teach (I think more than a third of students likely failed that class first time around).

You've got a point about tubes being inefficient... I might want to wait and make a less portable headphone amp later on that uses tubes, because I would like to learn about how they work in more detail.

I'm familiar with solderless breadboard... I'm using it in my final project for college right now actually (using an arduino to control stepper motors for an old robot arm). I hear that it's really not good for hi-fi audio though, because of the parasitic capacitance between the conductors.

It looks like a lot of the National chips are surface mount, which would be a problem for me since I won't likely be etching a board for this (you never know though... I might feel up to trying to toner transfer method), and certainly won't be ordering one from one of those sites that lets you do that (just plain expensive, and not really necessary for this).

I did do some digging at the national site and they do have what looks like an excellent high-end audio setup. I found a link to this article, which outlines a couple different amplifier topologies, and another article on that site talks about one of the chips mentioned in the high-end topology mentioned in the first, the LME49600 Bufer, which is apparently generally used with the LM4562 OpAmp. From the looks of things these would be an excellent choice for my headphone amp, and I'm thinking I might go with them, but I figure I'll do a bit more digging first...

So, If my math is correct, if I wanted 3mw of power, I should be getting 104dB SPL, and the voltage required should be 309.8mV drawing about 9.682mA... (assuming that my headphons are a 32 ohm load)...

The datasheet for the LME49600 outlines a headphone amp circuit on page 11 using the LME4972 (which as far as I can tell is completely identical to the LM4562), and it looks like it might be a nice design to put into practice. Can I get away with just using normal capacitors without worrying about getting high-quality expensive caps for that design?

Also, apparently that amp setup is capable of driving a 32ohm headphone set to up to 500mw of power.... That is so absurdly overpowered, lol.

First adventure into DIY: making my own headphone amp based on the A47

Reply #5 –
Quote from: Bobbias on
Ok, I wasn't quite being so clear there. I'm aware that the hybrid amp has a 48v supply voltage.


I don't know if you are aware that a tube amp stage with a B+ voltage of just 48 volts is just a EFX box  in disguise.

In this day and age there are only two reasons to put tubes running off voltages that low into headphone amps:

(1) Looks cool

(2) Adds audible nonlinear disstortion

If you want to build EFX boxes for playback and inundate yourself with audible distrotion, you are kinda sorta violating the basic tenets of high fidelity. Is that your big idea?

First adventure into DIY: making my own headphone amp based on the A47

Reply #6 –
Quote from: Arnold B. Krueger on
Quote from: Bobbias on
Ok, I wasn't quite being so clear there. I'm aware that the hybrid amp has a 48v supply voltage.


I don't know if you are aware that a tube amp stage with a B+ voltage of just 48 volts is just a EFX box  in disguise.

In this day and age there are only two reasons to put tubes running off voltages that low into headphone amps:

(1) Looks cool

(2) Adds audible nonlinear disstortion

If you want to build EFX boxes for playback and inundate yourself with audible distrotion, you are kinda sorta violating the basic tenets of high fidelity. Is that your big idea?



I should point out that I'm still not exactly at the level of knowledge that most audiophiles here likely are... I'm aware of lossy vs lossless, and some aspects of high-fidelity in equipment, but I'm really still pretty clueless about hardware overall...

From what I understood those tubes were designed to run properly at that low of a voltage, and from my understanding "properly" meant in the linear operation... I thought it would possibly sound good, and would also teach me a bit about tubes, since I know essentially zip about actually using tubes. I might yet make something with tubes in it, but my first priority is definitely a good headphone amp, that doesn't cost me an arm and a leg to put together... The parts for the amp I talked about in my last post are about $3.05 and $10.50 at digikey, which is extremely cheap, and getting capacitors, if I don't actually need audio-grade ones, is also dirt-cheap. All in all if I can make an amp based on the one linked above in the National datasheet, it would probably only cost me $30 or $40 and from what I've been reading from the datasheets, should have almost no noise etc.

I'm also curious about low frequency crossover... Do audiophiles really use that sort of thing in their headphone amps? I thought that something like that would directly go against the idea of hearing exactly what was recorded in your headphones....

And what sort of effect does not having enough current cause in low impedance headphones like the Grados? I've heard that it degrades sound quality, but in what way?

First adventure into DIY: making my own headphone amp based on the A47

Reply #7 –
Quote from: Bobbias on
And what sort of effect does not having enough current cause in low impedance headphones like the Grados? I've heard that it degrades sound quality, but in what way?

If the amp cannot provide either sufficient current or sufficient voltage then that produces clipping.

First adventure into DIY: making my own headphone amp based on the A47

Reply #8 –
Quote from: Bobbias on
From what I understood those tubes were designed to run properly at that low of a voltage, and from my understanding "properly" meant in the linear operation...


Tubes can't hold a candle to SS and parcicularly appropriate ICs when it comes to sounding clean and accurate and like a duplicate of the source only louder.


Quote
I thought it would possibly sound good, and would also teach me a bit about tubes, since I know essentially zip about actually using tubes. I might yet make something with tubes in it, but my first priority is definitely a good headphone amp, that doesn't cost me an arm and a leg to put together...


For most people learning about tubes is about as useful as studying buggy whips with the intent of being a NASCAR champion. ;-)

Learn the basics well forst.


Quote
The parts for the amp I talked about in my last post are about $3.05 and $10.50 at digikey, which is extremely cheap, and getting capacitors, if I don't actually need audio-grade ones, is also dirt-cheap.


Audiophile grade capacitors are sales hype.


Quote
All in all if I can make an amp based on the one linked above in the National datasheet, it would probably only cost me $30 or $40 and from what I've been reading from the datasheets, should have almost no noise etc.



Or, you could buy a Fiio E3 for less than $20 and move on to something really interesting...

Quote
I'm also curious about low frequency crossover... Do audiophiles really use that sort of thing in their headphone amps? I thought that something like that would directly go against the idea of hearing exactly what was recorded in your headphones....


You mean low frequency equalization?  Crossovers only relate to speakers with multiple drivers for each channel and the drivers working at different frequencies.

Intersting that you mention that. The FIIO E3 has a low frequency eq switch and it is basically there to make things sound better at low volumes or with earphones/headphones that are short on bass.

Quote
And what sort of effect does not having enough current cause in low impedance headphones like the Grados?


Clipping. A little might not be heard, but a lot makes things sound trashy and garbled.


Quote
I've heard that it degrades sound quality, but in what way?



Clipping when strong enough makes things sound grundgy and with an artificial sound. Most of us go way out of our way to avoid it.

First adventure into DIY: making my own headphone amp based on the A47

Reply #9 –
Quote
I'm also curious about low frequency crossover... Do audiophiles really use that sort of thing in their headphone amps? I thought that something like that would directly go against the idea of hearing exactly what was recorded in your headphones....
I think you're talking about crossfeed, where some left-channel signal is feed-into the right headphone and vice-versa.  I think the idea is that when you listen to speakers or a live performance sound from both speakers (or both sides of the stage) goes to both ears.  So with some recordings, crossfeed can apparently create a more realistic headphone experience. 

Since you are building your own amp, it might be a nice "fun" feature to add.  (Oh...  If you're not sure, you can experiment by doing this with software, or with an audio editor first.)

I've never owned an amp with crossfeed.  I mostly listen to speakers, so it's not a really big deal for me.  I kind-of like to hear the left-right separation.  And, I mostly listen to rock...  If you want to re-create the experience of a live classical orchestra...  maybe crossfeed helps???

Special binaural recordings[/u][/url], which are recorded with a pair of microphones in "ear position" are designed for headphone listening and don't need crossfeed.


Quote
Also, apparently that amp setup is capable of driving a 32ohm headphone set to up to 500mwof power.... That is so absurdly overpowered, lol.

And what sort of effect does not having enough current cause in low impedance headphones like the Grados? I've heard that it degrades sound quality, but in what way?
The "average" op-amp probably can't power headphones,  But, there are plenty of chips that can do it easily!  I've only built a headphone amp once, and I used a chip that was designed to drive speakers...  I think it was capable of 2W into 8 ohms.


Quote
I'm familiar with solderless breadboard... I'm using it in my final project for college right now actually (using an arduino to control stepper motors for an old robot arm).  I hear that it's really not good for hi-fi audio though, because of the parasitic capacitance between the conductors.
It's up to you...  There may be some other "layout concerns", but I wouldn't worry about capacitance...  If you've studied AC theory, you understand the relationship between capacitance, resistance, and frequency.  A few picoFarads(?) at ~10k ohms and 20kHz shouldn't be an issue.

First adventure into DIY: making my own headphone amp based on the A47

Reply #10 –
Arnold B. Krueger, sorry to say, but your posts have been somewhat less than useful so far, other than explaining the effect of not having enough current. if I wanted to buy a headphone amp, I'd have said I was looking to buy one. I am an electrical engineering student, and happen to enjoy building circuits, and learning, and when I can combine that with making something that I'd actually have a use for, then I've got a pretty good reason to favor building over buying.

DVDdoug, I was thinking of crossfeed, just got the wrong word. The article I read about it in mentioned that often bass of one sort or another can end up being panned in a recording, and when listening on headphones, it can cause a fairly different experience than on speakers. When you listen to bass frequencies coming out of speakers, panned or not, they generally feel like they're coming from the center, but panned bass on headphones, due to the fact that headphones are directly beside you ear, will not feel centered. I've heard that effect myself before in various recordings (I do like my bass) through my headphones, and was wondering if that was something that was seriously considered in some high-quality headphone amps, or whether I should just ignore it and leave things be.

I think the reason I'd most not want to use breadboard like that is simply that I'd be lugging this thing around with me all over the place (I take my laptop and headphones everywhere) and would like my connections soldered... I might even take the opportunity to try my hand at home etching anyway.

First adventure into DIY: making my own headphone amp based on the A47

Reply #12 –
From your first post:
Quote
[snip]more concerned about making it sound as good as I can for as little money as I can manage[/snip]


If you just want to make an accurate, inexpensive, and portable (battery powered) amp, stick with solid state parts.

A vacuum tube headphone amp is really only good for looks and/or nostalgia, and the looks part only counts when using larger glass tubes which let you see the glowing tubes, which probably isn't what you want in a portable amp.

You're not going to learn much about using tubes in the modern world with tiny low powered tubes that you'd find in a portable amp as pretty much the only modern uses of tubes are in are in high power high frequency situations like microwave ovens, radar, and radio transmitters.

First adventure into DIY: making my own headphone amp based on the A47

Reply #13 –
Quote from: Rotareneg on
pretty much the only modern uses of tubes are in are in high power high frequency situations like microwave ovens, radar, and radio transmitters.

I feel personally offended that you've omitted guitar and bass amplifiers!

First adventure into DIY: making my own headphone amp based on the A47

Reply #14 –
They're included in the "pretty much" part.

And since being able to intentionally add massive amounts of distortion is a selling point of many guitar amps, I'd guess that they're not exactly a design you'd want to use in a headphone amp that you're going to use when listening to anything other than guitar solos.

First adventure into DIY: making my own headphone amp based on the A47

Reply #15 –
If I wanted a lot of added complexity, I could create a frankenstein that has both the ability to use tubes and solid state... But that would probably also give me a rather large headache just trying to get both circuits able to function and switch between them...

Yeah, I think I'm sticking to solid state, probably going with that design I mentioned using the National Semi parts.

Also, after reading a review of that FiiO E3, that's really not what I'm looking for. I have low impedance headphones, and according to this review that is not likely a good thing with that amp... Plus, I'm not gonna be using my amp with an MP3 player any time in the near future, so I don't need anything that tiny anyway.

First adventure into DIY: making my own headphone amp based on the A47

Reply #16 –
Quote from: Bobbias on
Also, after reading a review of that FiiO E3, that's really not what I'm looking for. I have low impedance headphones, and according to this review that is not likely a good thing with that amp...


I use my E3 with low impedance headphones and have no problems.

The guy's use of technical teminology is suspect - he's complaining about hiss, and that would afflict high sensitivity headphones which can be either low or medium impedance.

First adventure into DIY: making my own headphone amp based on the A47

Reply #17 –
I've also checked http://musicalmusings.themindofgame.com/20...e3-mini-review/ and http://www.head-fi.org/forum/thread/356177...amp-e3-upgraded, and both mention hiss, and like I mentioned before, I'm not trying to be a cheap bastard, nor am I simply looking for a relatively cheap way to get a headphone amp. A LARGE portion of why I want to do this is because I want to make my own. I just want it to sound good in the process.

I don't appreciate basically being told "don't do it" with essentially 0 logical reasoning behind it. Price isn't an issue as long as it stays within a reasonable limit, and I came here looking for technical help, not input on whether I should do it or not. So if you're finished, I'd appreciate not seeing another post that essentially says "go buy a cheap amp" because that is not the purpose of this thread.

First adventure into DIY: making my own headphone amp based on the A47

Reply #18 –
Wow

I would like someone to offer their free time and give me assistance, BUT, I would like to control the responses.
Good luck

First adventure into DIY: making my own headphone amp based on the A47

Reply #19 –
I appreciate the fact that anyone responded to this thread at all, it's just that I'm pretty sure that the title implies I want to make a headphone amp, not buy one.

I may be new to these forums, but I don't think that gives anyone an excuse to treat me with the thinly veiled condescension that Arnold has been.

First adventure into DIY: making my own headphone amp based on the A47

Reply #20 –
Quote from: Bobbias on
I may be new to these forums, but I don't think that gives anyone an excuse to treat me with the thinly veiled condescension that Arnold has been.
"Thinly veiled condescension"? Give your head a shake. He's giving you solid technical advice and not making any remarks about you as a person.

First adventure into DIY: making my own headphone amp based on the A47

Reply #21 –
Quote from: Bobbias on
I think the reason I'd most not want to use breadboard like that is simply that I'd be lugging this thing around with me all over the place (I take my laptop and headphones everywhere) and would like my connections soldered... I might even take the opportunity to try my hand at home etching anyway.


There's a reason they call them prototyping boards.  If your first shot at this is all soldered connections on an etched board then it better work right the first time.

You can get the amp working to your satisfaction on a prototype board then transfer all the components and jumper wires to a "real" circuit board that has the same copper layout as the proto-board.  The circuit boards should be available from the same places that sell the proto-boards.


First adventure into DIY: making my own headphone amp based on the A47

Reply #22 –
Quote from: Bobbias on
I've also checked http://musicalmusings.themindofgame.com/20...e3-mini-review/ and http://www.head-fi.org/forum/thread/356177...amp-e3-upgraded, and both mention hiss, and like I mentioned before, I'm not trying to be a cheap bastard, nor am I simply looking for a relatively cheap way to get a headphone amp. A LARGE portion of why I want to do this is because I want to make my own. I just want it to sound good in the process.


I've read enough internet reviews to look at the whole genre with a jaundiced eye. This is a case in point. Two people say that an item that serves me well has hiss. What am I to believe - their unsubstantiated claims or my own experience.

First off, how do I tell that the hiss wasn't due to the signal source they used?

How do I know that the hiss they were hearing was even really a hiss and not the low roar that one can hear in a really quiet room with earphones stuck in our ear, and everything turned off?

There is a natural bias in many people against everything that is inexpensive. E3s are clearly inexpensive.

Actually measuring the noise that comes out of headphone amps is far from rocket science. Yet, none of these do any measurements.

Here's some of the gobbldegook from one of them:

"The E3 doesn’t sound like it actually amplifies your headphones; instead, it merely makes them louder, which sort of misses the point of amplification. A headphone amp isn’t supposed to merely make your headphones louder, but to drive them to reach their full potential. When I listen to my RE0s through the E3, I don’t get the feeling that their sound quality is actually being improved."

The above is of course complete nonsense.  The standard he is using to judge this product is completely subjective. I can easily read it as saying that for some unknown reason he really doesn't like the E3, which of course is his privilege, but he's basically libelling a good product.

The other guy says "But I notice much hiss with my Meizu M6 and electromagnetic interference when I getting too close to my TV ".  I tried to duplicate this with my E3 and a Sansa Fuze and no go. It is possible that his problems are actually with the Meizu M6. 

These headphone amps are just about the simplist things in the world, and yet there is this monumental obsession with them. Many of them are imputed with mystical powers.

As a new EE I agree that it would be good for you to actually build something and listen through music through it.  It would also be good for you to migrate it from an awkward breadboard device to something that you is so robust that you can carry around with you and use on a day-to-day basis.  I think that if you do that sucessfully it will make you really appreciate the E3 at under $10. 





First adventure into DIY: making my own headphone amp based on the A47

Reply #23 –
    
Quote
"The E3 doesn’t sound like it actually amplifies your headphones; instead, it merely makes them louder, which sort of misses the point of amplification."
     

Bobbias,
I think this is a GREAT starter-project!!!  One of the main reasons I got interested (or stayed interested) in electronics was because I was also interested in audio.    And on a limited budget, I could build stuff that was better than I could afford to buy.

I don't do as much anymore.  The economics have changed a lot over the years, and it's now cheaper to buy than build.  About the only time I build something now is if I want something unique that I can't buy.  And the only home-built components  in my current audio system are speakers and an amplifer that I re-built from one that had "blown" a 2 or 3 times.      I'm using it as a subwoofer amp.  I don't remember why I rebuilt it...  Maybe the parts were no longer available, or I just got tired of repairing it, but I used the case, power transformer, and some other existing parts and built a new power supply and new amplifier circuits.

Oh...  The 1st time my amp blew, it was my fault.  I was trying to build a preamp, but I ended-up building an RF oscillator!      I guess that amp didn't like getting blasted with a MHz signal!  I didn't have an oscilloscope, and since it was supersonic I didn't hear anything.  I hadn't hooked-up a signal yet, and I was thinking "Wow, this preamp is dead-quiet!."  Then I heard a small "poof" and the power amp was dead...    It wasn't so funny at the time, but I learned something about op-amps called "zero gain compensation".

I didn't learn much about audio electronics in school either, but that's where my passion is and most of the projects I've built are audio related.

First adventure into DIY: making my own headphone amp based on the A47

Reply #24 –
The constructive advice I'd give you is don't bother building something with tubes. As Arnold suggested, build something solid state because your performance will always be better.