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awangotango 28th July 2012 11:10 PM

headphone amps vs headphone inputs?
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I have a 70's pioneer integrated amp I prefer to use with my headphones (schem below) and after comparing it to several $2-500 dedicated hifi headphone amplifiers, I prefer the basic headphone input on the pioneer. While I can hear and appreciate the 'enhancements' of the modern dedicated opamp based headphone amplifiers, I feel they are a bit artificial and unatural at basic music reproduction and prefer the pioneer with my grados, which don't seem to require any 'amping' my question, can anyone confirm what's going on in this circuit and if it is indeed just a headphone input and no 'amping'......and are there any headphone 'amp's on the market that would sound similar for basic headphone input usage....thanks

fwiw, I use a nos (non oversampling) dac before the headphone input and that is what really shapes the music to my liking and feel no need for a 'headphone amp'.

after some research,,, I've partly answered my own question in that what I am using and prefering is a BUFFER and not an amplifier.....

dry joint 29th July 2012 04:18 AM

I think your amp is amping the voltage with the first bit and then adding current with the last transistor, just as you get with a modern amp, thats how amps generally work. I think the middle transistor is part of the voltage gain but not sure what its doing. Overall it must be close to as simple a design as possible. I have no doubt that a better design made without jfets* is possible, its just not what amp designers are doing, NVA sell one, but its just a speaker amp with an extra power resistor on the output, and various diy/kit sellers do JLH variants.

*Jfets are used in the opamps that are the first stage in most modern affordable headphone amps, also used as discrete transistors in kits/projects, 'cept when its valves. I've found amps with jfet input stages to be more detailed yet somehow lacking a quality like realness/naturalness/musicality. It has to be remembered that the output circuits of most DACs/CD players etc willl be using the same opamps, and these can power heaphones dirctly and sound terrible.

Most commercial amps are opamp based, and some people that take engineering measurements claim to show how their accuracy is so good that improvements aren't worth bothering with, human ear holes just not being up to the task; people that trust their ears do not believe them, I'm in the latter camp but its not an argument worth getting into on an internet forum( objectivist vs subjectivist.)

jcx 29th July 2012 01:52 PM

headphones vary in impedance and sensitivity by orders of magnitude - you need to size amp I,V, gain, any output coupling C for some range of headphone parameters - a "universal" amp for headphones is impractical

so the very 1st question about headphone amps is - for what headphone?
you need the specs: Z ohms, dB SPL sensitivity re 1mW (or increasingly common today re 1 Vrms)

awangotango 29th July 2012 08:00 PM

right, it seems alot of the headphones sold these days are hard to drive, but my grado500 and koss ksc75's don't seem to benefit, and even suffer from the extra device in the chain.

barefootwhistler 29th July 2012 11:19 PM

The schematic you posted doesn't appear to be a headphone amp at all, but rather the first stage of the amplifier. I found the schematic for the Pioneer SA-800 when I searched for "W21-007" which that schematic has at the top. is the one I found first. In both the SA-800 and SA-1000 amps, the headphone jack is connected to the output of the main amplifier and padded with 150 ohm resistors (it is marked "PHONES" on the SA-800 schematic).

I wonder if it is the output resistance that makes you prefer that amp. Across the board, Grado phones have an impedance bump in the 100Hz region and a slight bowl shape to the rest of the audible range. When combined with a high output resistor value, this will boost the mid-bass and slightly emphasize the highs when compared to a low output-impedance amplifier like many headphone have. Unfortunately, I don't know of any headphone amps with an output resistor that large.

awangotango 30th July 2012 12:31 AM

yes, the amp is the sa800. It works well with the koss headphone too, not just grado, althotugh both are similar ohmage and sound signature, so maybe as barefoot suggests, there may be some synergy going on with this particular head 'amp'/input (still don't know what it should be called) and my phones.........So let's say I wanted to duplicate the headphone 'amp' of this integrated amp so I can have it in a smaller chassis/ what parts would I need to salvage (could someone possibly circle them on the schematic below)............Why would they label the entire circut board as 'headphone amp' on the schematic if it's not used for the headphone input ? ........It's not that the head input on this is spectacular in any way, it's that it doesn't seem to affect/ruin/take away/add anything annoying or odd, which every other dedicated headphone amp i've tried does. (matrix m stage, purity audio caliente, pico, 02 (no I don't find it 'transparent' in real world listening - ime, it seemst to take away 'body'), nuforce, rega, cambridge, NAD are some i've tried)........ The sa800 input's unremarkable qualities are what I like about it although it does add a touch of 'atmosphere' and soundstage vs coming straight out of a cd player's headhone input, which I enjoy. Otherwise it is pretty transparent and unremarkable........I really just need a jack to plug into, I don't want or need the extra help of these modern headphone amps that make things more 'euphoric' or more of a 'headphone experience'. Just a basic headphone input device is hard to find paradoxically. It should be the easiest/cheapest. And my guess as to the reason why is because most people who don't have hard to drive phones would be entirely satisfied with such a humble and inexpensive device, and therefore would take away $ from the market of the multi hundred dollar headphone amp industry. Once I found my monica nos DAC, I really don't need any more 'help' from ancilliary devices. I love that DAC ! perfect balance of hifi/midfi qualities and natural music reproduction. Sadly, it's not in production any longer it seems......

awangotango 30th July 2012 12:40 AM

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gabdx 13th October 2012 01:36 AM

Your right, you don't need any amplification at all, the dac produces already enough voltage after the i/v stage active or passive, all it needs is to lower the output impedance and deliver enough current.

I use : akm dac , passive i/v, 1 parallel tube buffer , headphones. there is only 2 capacitors and one tube. Sounds good...

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