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High-powered headphone amps

Ariamella

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I want a project to keep me busy for a week or so but I'm getting slightly overwhelmed by all the options available so I thought I'd start a new thread to collate all my options.
  • I have IEMs, planars and dynamics so ideally it can drive all of those, but being able to drive planars and dynamic cans is a must whereas IEMs are optional.
  • Something more powerful than my current Atom amp would be very nice, especially as I want to power hard to run planars.
  • I want something fully discrete as the Atom is opamp-based.
  • Class A would be nice but not necessary.
  • Since I live in Hong Kong, getting a cheap chassis from taobao isn't a problem, so there's no need to set aside too much money for that.
  • I have a hot air gun and know how to do SMT soldering.
  • Nothing too expensive please, I'm a student!
 
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solderdude

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I want a project to keep me busy for a week or so but I'm getting slightly overwhelmed by all the options available so I thought I'd start a new thread to collate all my options.
  • I have IEMs, planars and dynamics so ideally it can drive all of those, but being able to drive planars and dynamic cans is a must whereas IEMs are optional.
  • Something more powerful than my current Atom amp would be very nice, especially as I want to power hard to run planars.
  • I want something fully discrete as the Atom is opamp-based.
  • Class A would be nice but not necessary.
  • Since I live in Hong Kong, getting a cheap chassis from taobao isn't a problem, so there's no need to set aside too much money for that.
  • I have a hot air gun and know how to do SMT soldering.
  • Nothing too expensive please, I'm a student!


https://sjostromaudio.com/pages/index.php/hifi-projects/122-qrv01-headphone-amp

For the IEM's build a passive attenuator into it.
 

levimax

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You might want to take a look at this one as well. Not quite as fancy as the Sjostromaudio.com one but simple and easy and since it uses discrete output transistors instead of an op-amp it can put out a lot of power. I built one and it is quiet and sounds goods and measures better that my equipment allows ... and has way more power than I need. https://sound-au.com/project113.htm
 
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Ariamella

Ariamella

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You might want to take a look at this one as well. Not quite as fancy as the Sjostromaudio.com one but simple and easy and since it uses discrete output transistors instead of an op-amp it can put out a lot of power. I built one and it is quiet and sounds goods and measures better that my equipment allows ... and has way more power than I need. https://sound-au.com/project113.htm
Had a look at that (and the DoZ headphone amp) but the DoZ is capacitor-coupled which made me not the biggest fan. This one does have an op-amp but it's cheap enough that I might ignore that and go for it anyways :)
 

muslhead

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I have planars that are power hogs. The Schitt magnius ($199) is one that has lots of power. Mine has died 2x in a year so i cant recommend it unless you don't mind that risk. I liked it because of its preamp out. The Topping A90 ($499) has just as much and have their own reliability skeletons (not on this unit ... yet). Both measure well.
Do you care if its balanced or unbalanced output as balanced will run you a bit more (usually)
 
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Ariamella

Ariamella

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I have planars that are power hogs. The Schitt magnius ($199) is one that has lots of power. Mine has died 2x in a year so i cant recommend it unless you don't mind that risk. I liked it because of its preamp out. The Topping A90 ($499) has just as much and have their own reliability skeletons (not on this unit ... yet). Both measure well.
Do you care if its balanced or unbalanced output as balanced will run you a bit more (usually)
Want a DiY project sorry
 

levimax

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Had a look at that (and the DoZ headphone amp) but the DoZ is capacitor-coupled which made me not the biggest fan. This one does have an op-amp but it's cheap enough that I might ignore that and go for it anyways :)
While capacitor coupled has a bad rap with some people it really is an easy, cheap, proven and effective solution. Any alleged audio degradation is not shown by measurements so I would not worry too much about it. I have built amps with DC servos and it is a cool but way more complicated and expensive for I'm not sure what the real benefit is.
 
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Ariamella

Ariamella

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Thought so but decided to post ... just in case
I did look at the Magnius but decided I wanted something with my own hands instead :)
While capacitor coupled has a bad rap with some people it really is an easy, cheap, proven and effective solution. Any alleged audio degradation is not shown by measurements so I would not worry too much about it. I have built amps with DC servos and it is a cool but way more complicated and expensive for I'm not sure what the real benefit is.
Fair enough, DoZ does look interesting but it is class A and a lot of work...think I might go with either that or P113, thank you for the suggestions :)
 

JeffS7444

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There's a great headphone amp bargain which is all DC-coupled save for a single DC-blocking capacitor at the input, it has balanced inputs and has massive power reserves for even the most difficult-to-drive headphones:
https://www.crownaudio.com/en/products/d-75a
Input is opamp (DIP) but all else is discrete. Headphone outputs are wired directly to main outputs (for better or worse). Noise levels are very low, though not quite inaudible. Mechanical hum from the power transformer is typical, but how often do you find a 55 watt headphone amplifier? Planar designs are no challenge at all for it. Pretty sure there were 220 volt versions (maybe branded as Amcron).
 
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Ariamella

Ariamella

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There's a great headphone amp bargain which is all DC-coupled save for a single DC-blocking capacitor at the input, it has balanced inputs and has massive power reserves for even the most difficult-to-drive headphones:
https://www.crownaudio.com/en/products/d-75a
Input is opamp (DIP) but all else is discrete. Headphone outputs are wired directly to main outputs (for better or worse). Noise levels are very low, though not quite inaudible. Mechanical hum from the power transformer is typical, but how often do you find a 55 watt headphone amplifier? Planar designs are no challenge at all for it. Pretty sure there were 220 volt versions (maybe branded as Amcron).
Not interested in ready-made options.
 

MRC01

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At first I was thinking opamps: something like AD797 with BUF634 in output stage should be clean and drive just about anything. But for discrete design, the above looks like a neat project.

A passive attenuator / voltage divider of metal film resistors should be quieter than using a volume knob, especially when turn it down -30 dB or more like you would with sensitive IEMs. But it means high output impedance, right? That could give non-flat frequency response. How do you avoid that?
 

solderdude

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At first I was thinking opamps: something like AD797 with BUF634 in output stage should be clean and drive just about anything. But for discrete design, the above looks like a neat project.

A passive attenuator / voltage divider of metal film resistors should be quieter than using a volume knob, especially when turn it down -30 dB or more like you would with sensitive IEMs. But it means high output impedance, right? That could give non-flat frequency response. How do you avoid that?

A passive attenuator can have an output R of just a few ohm. This is not a problem for almost all IEM's and may even be a blessing for a select few IEM's.
 

Bob-23

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I want a project to keep me busy for a week or so but I'm getting slightly overwhelmed by all the options available so I thought I'd start a new thread to collate all my options.
  • I have IEMs, planars and dynamics so ideally it can drive all of those, but being able to drive planars and dynamic cans is a must whereas IEMs are optional.
  • Something more powerful than my current Atom amp would be very nice, especially as I want to power hard to run planars.
  • I want something fully discrete as the Atom is opamp-based.
  • Class A would be nice but not necessary.
  • Since I live in Hong Kong, getting a cheap chassis from taobao isn't a problem, so there's no need to set aside too much money for that.
  • I have a hot air gun and know how to do SMT soldering.
  • Nothing too expensive please, I'm a student!
If a minimal gain of 10 x (& opamp-based) is acceptable for you, the Gaincard LM 1875 could also be an option for a headphone power amp, at minimal cost, including a muting/dc-protection with Omron relays G2R-2, 12V DC. You gonna need attenuators. I built a such one recently.

1621934590500.png


I got mine from TooGoo via amazon.
https://www.amazon.de/TOOGOO-Verst?Rker-Platine-Gaincard-Verzerrung-schwarz/dp/B07XYBJ8TP/ref=sr_1_1?__mk_de_DE=ÅMÅŽÕÑ&dchild=1&keywords=lm1875+gaincard&qid=1621934108&sr=8-1
 
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Ariamella

Ariamella

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I've decided on the ESP P113 or the X-Altra HPA-1, I'm currently waiting for my TPA3255 project to arrive so I won't order parts until that's done but I laid out a compact form of the P113 for funzies, waiting on feedback to see whether my layout is any good and then we'll see where to go from there :D
 

levimax

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I've decided on the ESP P113 or the X-Altra HPA-1, I'm currently waiting for my TPA3255 project to arrive so I won't order parts until that's done but I laid out a compact form of the P113 for funzies, waiting on feedback to see whether my layout is any good and then we'll see where to go from there :D

You probably know but just in case ESP sells a PCB for the 113 which makes things easy and reliable. You said a "weeks project" and while soldering up the PCP takes little time you also need to build a PS (ESP P05 is really nice and quiet and has power on and shut down delays to prevent pops) and of course then comes the hard part of the heat sinks, cases, pots, indicator lights, etc. For me personally laying out and testing and troubleshooting a one off PCB could take me a week or more :)
 
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Ariamella

Ariamella

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You probably know but just in case ESP sells a PCB for the 113 which makes things easy and reliable. You said a "weeks project" and while soldering up the PCP takes little time you also need to build a PS (ESP P05 is really nice and quiet and has power on and shut down delays to prevent pops) and of course then comes the hard part of the heat sinks, cases, pots, indicator lights, etc. For me personally laying out and testing and troubleshooting a one off PCB could take me a week or more :)
I don't mind it taking more than a week, I need something to do over summer break anyways~

https://github.com/Ariamelon/ESP-P113-Compact here's the initial design files if you're interested :p
 

AnalogSteph

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I don't think P113 as-is is going to cut it if you want substantially more output power than the Atom... at 8.66 Vrms into 150 ohms and 5.66 Vrms into 32 ohms, that's not exactly a slouch to begin with. Basically, what you'd want is an output stage with gain running on higher supplies, regulated down to +/-15 V for the opamp (we're only talking a few mA, so 78L15/79L15 series parts would be easily sufficient). The SMPS modules you are using are also available in 24 V, that would be a starting point.

1. Q1/3 are using the wrong symbol, and Q2/4 are connected wrong entirely.
2. I am not sure whether the simple diode bias circuit is going to get you enough bias... generally you want to be running output transistors like these at 20-30 mA minimum, or else their fT will be competing with a sloth on valium. (Not good for stability. Generally, you want buffer fT >3 * opamp GBW / (noise) gain.) 8 A parts seem a tad oversized in general. I might try some 2SC5200/2SA1943... even the shady second-sourced ones ought to be robust enough for this application. Make sure you get some silpads for mounting, I think those should be adequate in a headphone amp and they're practical and reusable (I doubt there'll be enough heat dissipation to make mica washers worth it).
3. The two 100 µF capacitors in series can be replaced by a single part across both with no substantial detriment, according to simulation.
4. At lower gains, it is generally advisable to add a small capacitor from opamp output to inverting input, say 22-47 pF, to aid stability. I would consider adding a Zobel network on the output for the same reason. And speaking of gains, having a way of selecting at least two different ones would be good.
5. Your secondary-side ground planes have no business being anywhere near mains input nodes - mask out at least 1-2 cm around these areas if you can. You have some reading up on electrical safety and creepage distances to do. What you want is more or less an IEC Class II device. Use heatshrink to cover solder joints, and when mains wiring has to be routed alongside case panels (e.g. for the power switch), use double-insulated mains cable. You always want two layers of insulation between mains and the entire secondary side (a decent distance in air also counts though).
6. If a PE connection is commonly available from outlets (I guess Hong Kong uses British plugs?), you can make use of that... use a Y2 rated safety capacitor, ca. 10 nF, to connect incoming PE to chassis ground. Route out a slot in the board underneath the cap, maybe 2-3 mm across and about 1 cm wide. PE can be treated like L and N otherwise. Depending on chassis available, consider an onboard IEC power connector.
No amplifier with unbalanced inputs should have audio ground and PE firmly connected, this is just asking for trouble with ground loops. The Atom is using a transformer plug pack for good reason.
 
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