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I was looking for some simple headphone amplifiers for translation booths, to give the translators the ability to adjust the volume of their headphones. No need for super Hi-Fi quality in a relatively noisy place, but they should be of sturdy quality.

My expectation was to find some gadgets below $20,- but it turns out that there's hardly anything on the market below $60,- (besides unassembled do-it-yourself kits).

This seems crazy since a headphone amp is already built into almost every gadget that can produce audio. Looking at USB audio interfaces, these do drop under $40,- and could also do what I want, but it still feels like an overkill.

Would it hurt the original amplifier if I adjust the volume to an excessive level and simply solder a stereo resistor between some jack-plugs?

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Integrated circuit power amplifiers reach a point of negligible incremental return quite low on the cost curve. From a reputable source you are not going to see a measurable improvement beyond $20. It's an extremely mature technology, about the oldest and most active of any electronic technology. Correlating the quality of a headphone amp with price is simply silly.

There's always an argument whether audio performance is objectively measurable and that too is simply silly.

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    This. I don't think most people realise that the BOM for a no-frills headphone amp barely adds up to $10.. The prices are all market-driven. Such amps are bought by audiophiles for "the sound" or pros for better impedance matching. Sometimes the circuit designs are patented. In terms of quality, I wonder if it's possible to get these things wrong at all.
    – georgi
    Jan 27, 2014 at 21:09
  • I agree, and I'm marking this as the answer, the price is indeed "market driven".
    – Louis Somers
    Jan 28, 2014 at 0:08
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Well, to be perfectly fair, you get what you pay for with these things. I think $20 is not a reasonable expectation for a headphone amp at all. Headphone amps are definitely in the professional sound market, and as such, they command both a certain build quality and price range. For any decent headphone amp I would expect to pay at least $100-200 minimum, if not more if it had other features. There is a market for good quality product and people will buy it. Many of us don't blink an eye when we buy a Sound Devices 7-series recorder (which clocks around $800-900 per preamp). So considering that price gamut, and that many are willing to even pay that type of price, I wouldn't keep your hopes up for something around $20 with any sort of amp or preamp

Most gadgets with basic headphone outs can't drive anything more than the 60-80 Ohm consumer headphones. For studio headphones in the 250-600 Ohm range, it needs a more powerful amp to drive it. And, the cost of that piece in said gadget is subsidized/wholesale to the manufacturer (that iPhone or MP3 player aren't $20 even though the part may be). You also pay for higher quality components, better linearity of signal, and ruggedness usually with increased cost.

Personally, and this is just my opinion, I would rather have piece of mind paying $200 than be worried and only paying $20.

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    Thanks for your perspective. It would hold for a hi-res studio environment but in our case the only thing we need is an extra volume knob at the correct location (similar to a DI-box). We are using "cheap" consumer closed headphones (I guess they were under $100,-) that can easily be driven by any iPod or portable device. Comfort is a greater concern than sound quality (they're translating speech and not much else). While the price of a cheap mp3 player can be under $5,- it seems crazy for a device that does less than 1% to be so expensive. Probably there's just no market (or a big hole).
    – Louis Somers
    Jan 25, 2014 at 21:37
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    Any gadget that can drive a an 80 Ω pair of headphones can also drive 600 Ω, the only concern is that it won't be as loud. Compared to mic preamps (where noise, impedance etc. matters greatly), headphone amps are pretty trivial from an electronics engineering point of view. Nonlinearities – allright, there'll be some, but unless the headphones are at least four times as valuable than the amp you should expect their mechanical characteristics to dominate these.
    – leftaroundabout
    Jan 27, 2014 at 6:44
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    Your first sentence proves my exact point. You get what you pay for. Furthermore, it doesn't matter if you run a set of 7506s or DT880s, gain level will always succumb to the downfalls of the Equal Loudness curve. Without a proper amplification level, frequency linearity will not be as accurate as allowable for the headphones in question. The same goes for studio monitors.
    – Stavrosound
    Jan 27, 2014 at 10:14
  • The limiting factor for driving high impedance headphones is generally the supply voltage. Many devices today run on 5 V and the end result often is that the sound level in high impedans headphones is low.
    – ghellquist
    Apr 10, 2020 at 7:32
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If you want to save money look for used gear. If quality is not that important you should find something cheap on ebay,etc.

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  • Even on E-bay these things are over the top, I did a bid of $15 (maximum $25,-) on a Matrix m-stage wich I thought was quite allot, but I lost it. It finlly was sold for $151,-. I now have a 2nd hand firewire audio interface that I'm going to test, it does some extra AD/DA in the process which would cause some delay, but I'm hoping that won't be noticeable. It cost 20EUR which is still allot, but at least I feel I'm getting something for it, even if I'm currently not utilizing most of it.
    – Louis Somers
    Jan 30, 2014 at 23:03
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    I agree with Michael. If you have no issues, you can easily go with the cheaper one. Cheaper one doesn't always have to be the bad one.
    – user16377
    Sep 18, 2015 at 7:42
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Here's a simple headphone amplifier for $20.

http://www.bhphotovideo.com/c/product/422075-REG/Behringer_MA400_MA400_MICROMON_Miniature.html

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  • Yeah, I did see it, according to the reviews it doesn't amplify, but it does what we want (and a little more) so maybe it's the best solution after all. I want to fasten it under a shelf so we'd have to remove the mic-level knob in order not to confuse the user. I've just bought a 2nd hand FCA202 F-control since it has just one volume knob and the output jack on the front (just like we need), and I'm hoping it will route the unbalanced input to the headphone by default when powering it on. If not, we might go for the MA400 after all.
    – Louis Somers
    Jan 26, 2014 at 18:22
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    this one is made to under a desk it's a bit more pricey though. bhphotovideo.com/c/product/603058-REG/…
    – lukester
    Jan 26, 2014 at 19:30
  • Yes, I found allot more on ebay like the SMSL sApII Pro and so, but I don't understand the price. A flat 15-25000 frequency response is not needed here (and is probably more dependent on the headphone than the amp, as long as the amp can deliver enough power). That model is exactly what I'm looking for, rather without the double stereo knob though, but it's the price that's bugging me. I see a plethora of applications for these devices (a volume knob and phones jack in a convenient place), so why isn't anyone producing these for the masses?
    – Louis Somers
    Jan 26, 2014 at 19:53
  • I've used this or the HA400, can't remember which. It does what it says on the tin. And tin box it is. The thing likely to break is the power supply, which is a small dirt-cheap transformer.
    – georgi
    Jan 27, 2014 at 21:13
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I'm currently running a SMSL sAPII (which was mentioned in the comments) on my music/general purpose rig and this supposedly should drive anything up to 600 ohms, based on the chip it runs. 2 inputs (RCA and 3.5mm and switchable) one big knob, and least to me, sounds great.

Mine feels surprisingly solid, and sounds great, even when my source is something less than stellar.

Its 50-60 dollars at various places (I got mine at DX at the lower end of that but they're out of stock), and I wouldn't be surprised if there weren't similar low cost units made by other similar, less known companies.

Cost I suspect is heavily a matter of what people are willing to pay, design (the designs these amps use are dead simple) and what parts are used.

However in your case, what you probably need is an inline volume control system - it goes into your source, and your headphones plug into it. Google is likely to give a few decent suggestions, and they should let your users finetune volumes to their need. Considering you don't actually need powered amplification, this is a much more sensible option

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I read that you want to distribute the same signal to several headphones. This could be done using a normal power amplifier normally used to drive loudspeakers. The signal would be distributed to all users booths. Each user would connect the headphones using a potentiometer to regulate the volume. I would believe that one amplifier (you could by a used one for little money) could drive a lot of headphones.

Set the power amplifier to give something like +/- 10 V signal. Connect each potentiometer between signal and ground, connect the headphone between the viper of the pot and ground. I would probably experiment a bit with potentiometer value (use a log pot), maybe 5K might be good. And perhaps put a limiting resistors between the signal and the input on the not. Use a dual (stereo) pot if the signal is stereo. Put the pot and connectors in a nice little plastic box.

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