NXP TDA8932 as a headphone amp

[alphaman]

I am looking to drive 600-ohm headphones -- notably beyer dt880-600 and sennheiser hd420 -- with guts and control. None of my headphone-dedicated commercial and modded amps or DIY projects (eg, Tangent) can do the job w/o extensive modification.

One way around the issue is use vintage receivers or int amps with their featured/OEM headphone out. Most of those tap speaker lines with 200-300 ohm, 3-4W R's, and that can work well, especially if one uses "audio-grade" R's. And one can also use a stand-alone headphone jack, with similar Rs wired in, for power-amp speaker terminals. But a heavy, cumbersome speaker amp is not practical for the desktop.

Maybe a TDA8932 mono amp kit is a better solution, especially if it has a vol control option.
The basic mono PCB kit boards are very cheap, and readily avail. even on Amazon. And the DIY "audiophile" community can upgrade performance (see links below)

Any one experiment with the TDA8932? Or maybe one of the other chip-amps popular with diy? Again, the goal is to safely power high-Z cans.

https://www.diyaudio.com/community/threads/tda8932-dual-stereo-amp.380726/

https://www.diyaudio.com/community/threads/fasten-seat-belts-tda8932-pessimistic-review.277130/

https://www.diyaudio.com/community/threads/transformer-input-tda8932-mono-amp.357678/

https://www.diyaudio.com/community/threads/transformer-fed-tda8932-25w-8r-mono-amp-kits.359193/

 

[dunring]

I've had those several times and the most practical way is an SMSL HO150X with a 5 volt DAC like the DO100Pro. They have the same output on both sides so you don't need to convert to balanced. Audiosciencereview did measurements so its worth checking out for the bass distortion limit they have.
The only thing tuned similar but sounded even better is the Fiio FT3 350 ohm, but the ear cups are smaller and don't fit everyone.

 

[alphaman]

I've had those several times and the most practical way is an SMSL HO150X with a 5 volt DAC like the DO100Pro. They have the same output on both sides so you don't need to convert to balanced. Audiosciencereview did measurements so its worth checking out for the bass distortion limit they have.
The only thing tuned similar but sounded even better is the Fiio FT3 350 ohm, but the ear cups are smaller and don't fit everyone.

I have the SMSL SP200. Which I forgot about until your mention.
And yes, it is better than any other amp I own for hi-z can.
But the sp200 sounds a bit overclean and boring.
BTW:
This is a DIY sub-forum. Not sure why dunring suggested commercial devices?
We need to build or mod amps. Right?

 

[ericj]

Terrible idea. Class-D is optimized for low-Z loads, not high-Z.

Build an O2 or some other headphone amp kit that runs on more than 12v.

 

[alphaman]

Terrible idea. Class-D is optimized for low-Z loads, not high-Z.

Build an O2 or some other headphone amp kit that runs on more than 12v.

Good to know. The D kits are very compact hence, and will fit existing chassis, so my interest.
O2? The Objective 2 from NWAVG? Didn't know it meant for watts-level power? I.e. greater than mW.

 

[ericj]

Good to know. The D kits are very compact hence, and will fit existing chassis, so my interest.
O2? The Objective 2 from NWAVG? Didn't know it meant for watts-level power? I.e. greater than mW.

The Beyerdynamic 600-ohm drivers have a power handling capacity of 100mW max. Per Beyer. So, how many whole watts do you imagine that you need?

The O2 will put 88mW into 600 ohms, fwiw.

Edit: Further data point, just based on amps i have here, with a 40v power supply, AMB's M3 will put 6 watts into 8 ohms or 1.6 watts into 33 ohms. By my math, that means it will put about 100mW into 600 ohms.

 

[alphaman]

My senn hd420 (600 ohm) also is spec'd at 100mw max.
This might be a CYA for the manufacturer. This max will not lead to high volume, or powerful sonics at any listening level.
Not sure how much power my dedicated hp amps put out. The meier corda 2 has the most volume of my inventory, and that includes a souped up Tangent ppa v2.
But no dedicated headphone amp I own can power the 600 ohmers v. loud.
But even with lower-z cans, a direct connection to a loudspeaker power amp, even a high wattage amp, can transform sonics to another level.
This is w/o those 'phones jack current-limiting R's noted previously, for receivers that tap the loudspeaker outs for "'Phones" jack.
This is for experiment only. The amp volume must initially be absolutely minimal. And the amp should be turned on first, before plugging in cans. (To avoid turn on thump). Take dc offset measurements and make sure amp is biased properly. The amp must be in absolute prime condition.
Not sure why this sounds so good. Maybe because power transistors have it so easy with cans, they operate super cleanly.

 

[ericj]

My senn hd420 (600 ohm) also is spec'd at 100mw max.
This might be a CYA for the manufacturer. This max will not lead to high volume, or powerful sonics at any listening level.
Not sure how much power my dedicated hp amps put out. The meier corda 2 has the most volume of my inventory, and that includes a souped up Tangent ppa v2.
But no dedicated headphone amp I own can power the 600 ohmers v. loud.
But even with lower-z cans, a direct connection to a loudspeaker power amp, even a high wattage amp, can transform sonics to another level.
This is w/o those 'phones jack current-limiting R's noted previously, for receivers that tap the loudspeaker outs for "'Phones" jack.
This is for experiment only. The amp volume must initially be absolutely minimal. And the amp should be turned on first, before plugging in cans. (To avoid turn on thump). Take dc offset measurements and make sure amp is biased properly. The amp must be in absolute prime condition.
Not sure why this sounds so good. Maybe because power transistors have it so easy with cans, they operate super cleanly.

Ohm's law is still a thing. 8vpp across a 600-ohm driver should be some ear-splitting volume.

Class-D should be avoided for this because their THD is *better the lower-Z they are driving. Look at the datasheet for any class-D chip. Look at THD vs. Power. The graph will have a couple hockeystick lines on it, one for 4-ohm and one for 8-ohm. The distortion for the 8-ohm starts at less power output than the 4-ohm. The dirty secret of class-D is that the distortion goes nuts at like 15% of the rated power output. The good news is, between all the lies told about amp power and speaker power handling, it'll probably still be alright within a reasonable range.

You could of course strap a 4.7-ohm resistor across the output in parallel with your headphones but it'll get hot and if you are on batteries that's a bad thing.

Not all speaker amplifier designs are stable with a 600-ohm load.

A whole lot of people have been very happy with an opa2134 cmoy amp powered by a pair of 9v alkaline batteries driving their 600-ohm DT-990s. The O2 is kind of the same concept taken to an extreme, but with commodity parts - njm2068 gain stage, as found in countless pro audio and recording studio designs, with a pair of njm4556 paralled to offer 140mA per channel. In the low-Z game, the Grado RA-1 uses a single 4556.

You could use more expensive chips, but you don't need to, and in the buffer stage i don't think you'll do better than the 4556. I say that as someone with amps that use the buf634 for their output buffer.

Something with a 24-36v supply that has a discrete transistor output stage inside the feedback loop of an ultra-low-noise opamp like an opa1612 could be fantastic. Look at old sijosae designs maybe. I'm talking about to92 transistors, too.

The 600-ohm headphone standard exists because 50 years ago 600-ohm loads were sort of a standard in professional studio settings. When the input impedances of amplifiers were that low.

 

[alphaman]

My Tangent Pimeta v2 uses high current output buffers. LMH6321 x3 [one for virtual ground]. And dedicated "high-current" buffers should be able to power most cans. But I only use the Pimeta for portable/iem.
My Tangent ppa v2 uses a discrete output , bd139/140 constructing the final amplification [these are not quite to220 power transistors; but they aren't weaker to92, much less a puny opamp]. Still, the ppa v2 can't be driven loud--volume pot at max-- with a lot of cans, not just the 600 cans.
I haven't tweaked the bias pots; still all original Tangent default suggestions.

Not sure about 600 ohm use in transducers other than a potential benefit of using thinner voice coil wire, which allows more wraps on a given bobbin.

 

[ericj]

Ohm's law is still a thing. 8vpp across a 600-ohm driver should be some ear-splitting volume.

Class-D should be avoided for this because their THD is *better the lower-Z they are driving. Look at the datasheet for any class-D chip. Look at THD vs. Power. The graph will have a couple hockeystick lines on it, one for 4-ohm and one for 8-ohm. The distortion for the 8-ohm starts at less power output than the 4-ohm. The dirty secret of class-D is that the distortion goes nuts at like 15% of the rated power output. The good news is, between all the lies told about amp power and speaker power handling, it'll probably still be alright within a reasonable range.

You could of course strap a 4.7-ohm resistor across the output in parallel with your headphones but it'll get hot and if you are on batteries that's a bad thing.

Not all speaker amplifier designs are stable with a 600-ohm load.

A whole lot of people have been very happy with an opa2134 cmoy amp powered by a pair of 9v alkaline batteries driving their 600-ohm DT-990s. The O2 is kind of the same concept taken to an extreme, but with commodity parts - njm2068 gain stage, as found in countless pro audio and recording studio designs, with a pair of njm4556 paralled to offer 140mA per channel. In the low-Z game, the Grado RA-1 uses a single 4556.

You could use more expensive chips, but you don't need to, and in the buffer stage i don't think you'll do better than the 4556. I say that as someone with amps that use the buf634 for their output buffer.

Something with a 24-36v supply that has a discrete transistor output stage inside the feedback loop of an ultra-low-noise opamp like an opa1612 could be fantastic. Look at old sijosae designs maybe. I'm talking about to92 transistors, too.

The 600-ohm headphone standard exists because 50 years ago 600-ohm loads were sort of a standard in professional studio settings. When the input impedances of amplifiers were that low.

Oh man, i have a Meta42 or whatever it was called here somewhere. The one with Elantec buffers. It was never great. Which is probably why i don't know where it is. I think i may have attempted to cobble diamond buffers that could sub for the elantec buffers. Multi-looping the opamp was probably a bullflop concept. At the time, most of my favorite headphones were 600-ohm, including oldschool DT990, etc.

I *do know where my Mini3 is, though i don't use that either. I was never able to embrace walking around with source + amp + big headphones. I did use my y2 dac in conjunction with my O2 for years at work. Same enclosure so they stack nicely.

I did consider sewing up a sash, bandolier, or maybe utility belt with fitted sleeves for a USB power pack, iRiver H120, y2 dac fed by optical from the iRiver, and then either the O2 or my SRM-001. For giggles. Four boxes so i can have high quality audio while i, idunno, mow the lawn or grocery shop. whee.

I wish i knew where my perfboarded SOHA v1 is. Also, it blows my mind that it was 20 years ago when i helped prototype that project. And i regret that i never built a SOHA II and those boards don't seem to exist anymore. My life was a vortex of poo right at that moment and i didn't have the bandwidth.

I know the community isn't exactly rallying for another mid-tier hybrid wall powered amp but part of me wants to lay out a board for some kind of SOHA SE variant with to92 diamond buffers inside the loop of the opamp but the rest of it just like the old SOHA.

 

[brunosanii]

I have the SMSL SP200