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If a K1000 runs off of speaker outputs, why not any headphones? - Page 2

post #16 of 28
Thread Starter 
Quote:
Originally Posted by ericj View Post
2: If there's going to be a TRS plug involved, find out whether the amp's output is single-ended or not. If the output is differential (aka push-pull, etc), then the 'ground' side of the signal isn't so much ground as it is negative signal, and connecting the two negatives together could damage the amp. Notably, the T-Amps have differential output, and it is not safe to tie the negative outputs of a T-amp together.
I'd probably just convert the headphones to balanced, making this moot.

Quote:
Originally Posted by ericj View Post
3: You should probably still pad the output from the amp with a resistor. Whether you decide to do it in parallel (so that the resistor is getting some fraction of the power output) or in series. If i were trying it, i would put a pair of 5-watt 33-ohm resistors in parallel with the 38-ohm headphones. The amp will see an impedance of, what, like 18 ohms, and the resistors will absorb a little more than half the amp's power output. the ancient pioneer jb-21 actually puts 8-ohm resistors across the speaker terminals and then puts a 110-ohm ressitor in series with the headphones, which turns out to be wasting too much audio power as heat for really hard to drive headphones to benefit from it.
I'll try to figure out how to make this practical.

The Nuforce amp I've got is designed to use Cat5 cables as speaker cables, so I was just going to recable the headphones with that. This opens up a cable-entry can of worms that I may or may not bother with. I'm also not sure where I would put the resistors -- inside the headphones seems like it would be a bad idea.
post #17 of 28
In this thread http://www.head-fi.org/forums/f6/spe...dphone-316075/ I have been trying to do this DIY thingie to convert the speaker amplifier output to a headphone.

Headphone Adaptor for Power Amplifiers

And I need some help over there.
post #18 of 28
I've got no idea about the neuforce technology, it is digital I know and I haven't had the best results driving headphones from a tripath amp. I do run a pair of akg-340s off of a speaker amp as well as some orthodynamics. The amps have been modified to lower the gain and are tube mono blocks.

I would go for dual mono cabling with 10ohms across the outputs and 100 to 200ohms in series with the can as a test. The 10ohms across the outputs should keep the amp seeing near it's expected load, other
digital amps need a specific load for their output filter to work.

Of course you could screw up things up and how the combo works can't be guaranteed watch for heat and be sensible about your hearing.
post #19 of 28
JadeEast,

About putting 10 ohms (or something like that) resistor across made sense to me. In the link that you post me on the other thread, they specified 120 ohms instead. What do you think?

Edit: Do you think putting a volume knob instead of a fixed resistor in series with the can would work better? Would signal quality take a hit with variable resistor instead of a fixed one?

Edit again: How much power would a headphone need per channel? Can I assume 1W maximum? If my speaker output is 50W at 8 ohms per channel. Would 10 ohms across the channel and 500 ohms in series with the can work well? Of course the signal will be pre regulated through a preamp.
post #20 of 28
the main problem is the high gain of a speaker amp and the current limiting (if there is any) been adjusted for speakers. I use an one currently with resistors on its output and it works quite well but that's only because the headphones that were used with it when constructed were HD-430's which have a simlar impedance and effeciancy to the HD-650's,it completly fails to drive grados. Many early headphones were designed to be driven not off a 0ohm output impedance but a 120ohm output impedance because it was expected that they would be plugged into the headphone out of power amps with headphone jacks mad using resistors.
post #21 of 28
How would a headphone impedance rating differ (or not?) from those using inline resistor ala ER-4P -> ER-4S?
post #22 of 28
I use speaker amplifiers as amps for my headphones without any problems. I never understood why people would pay premium for headphone amps anyways, especially if they use opamps (except for portable use).

You can have an excellent, all discrete 20W/ch audiophile speaker amp for less than
$1500. In this regard, the Headroom amps are GROSSLY overpriced. On a tighter budget, you can get nice Arcam and Rotel integrated amps for less than $1000 and they sound excellent.

I made my own resistive conversion box and have some fixed resistors to bias the amp a little more into class A (as ericj said). I have no problems with the noise when I use a pad divider, but the headphones all sound best when driven directly from the speaker outs, but there is a bit more noise. However, noise doesn't matter anyways because I listen to music quite loud.

Using a speaker amp is the best/cheapest way to be sure the amplification is up to the task IMHO. However, I suggest lower wattage amps (20W, 40W, 60W) because they usually sound better.

Also be careful to know the topology and analyse the schematic of the amp before buying so you can be sure it's not a class D/T/H/G amp. Class A is better but rare and expensive. Class AB+B is very good, since the amp will run in simili class A for the low voltage requirements of the headphones and only switches to class B to drive more voltage to the speakers.
post #23 of 28
Thread Starter 
Quote:
Originally Posted by Philco View Post
Also be careful to know the topology and analyse the schematic of the amp before buying so you can be sure it's not a class D/T/H/G amp. Class A is better but rare and expensive. Class AB+B is very good, since the amp will run in simili class A for the low voltage requirements of the headphones and only switches to class B to drive more voltage to the speakers.
Why not use a class D/T/H/G amp? Would it work if used with balanced headphones?
post #24 of 28
The sound quality of those amp topologies is normally inferior to what the audiophile community expects, especially class D and T amps, as they are switching amplifiers. Also, most of those expect the load to be speaker-like (2,4,8 ohms) to function properly. I prefer to use Class A, Class AB and Class AB+B for serious audio.

Quote:
Originally Posted by pdennis View Post
Why not use a class D/T/H/G amp? Would it work if used with balanced headphones?
post #25 of 28
Thread Starter 
Quote:
Originally Posted by Philco View Post
The sound quality of those amp topologies is normally inferior to what the audiophile community expects, especially class D and T amps, as they are switching amplifiers. Also, most of those expect the load to be speaker-like (2,4,8 ohms) to function properly. I prefer to use Class A, Class AB and Class AB+B for serious audio.
Sure, I can understand a personal preference.

I do believe that my amp would prefer to see an 8 ohm load. Seems like the best possibility at this point would be converting to balanced (yielding two 19 ohm loads), then running 10 ohm, 10 watt resistors in parallel. I'd still have lots more voltage than I'd need though.
post #26 of 28
What makes you believe your amp would like to see an 8 ohm load ? Just curious. Most "linear" amps are designed for the lowest output impedance possible using negative feedback, hence the effect of the load is greatly reduced. Most companies specify to use 8 ohms load minimum in order not to damage the ouput transistors or the power supply. Using higher ohmage loads shouldn't do any damage except if the amp is class D/T in which case the load is most often part of the filtering process. If this is your case, then your solution should work good.

Quote:
Originally Posted by pdennis View Post
Sure, I can understand a personal preference.

I do believe that my amp would prefer to see an 8 ohm load. Seems like the best possibility at this point would be converting to balanced (yielding two 19 ohm loads), then running 10 ohm, 10 watt resistors in parallel. I'd still have lots more voltage than I'd need though.
post #27 of 28
Thread Starter 
Quote:
Originally Posted by Philco View Post
What makes you believe your amp would like to see an 8 ohm load ? Just curious. Most "linear" amps are designed for the lowest output impedance possible using negative feedback, hence the effect of the load is greatly reduced. Most companies specify to use 8 ohms load minimum in order not to damage the ouput transistors or the power supply. Using higher ohmage loads shouldn't do any damage except if the amp is class D/T in which case the load is most often part of the filtering process. If this is your case, then your solution should work good.
Yes, this is the new Nuforce Icon -- best amp I can afford at the moment! It's a class D/T. It also has a discrete headphone amplifier included, but I'm curious about trying this, because I believe that the power amp is more sophisticated (and also just out of sheer perversity).

Anyone know a good website that can explain how different transducers have different voltage and current requirements? I'm used to dealing just with matching power requirements.
post #28 of 28
No, don't do it. The Nuforce amp is designed to driver only low-impedance load, and could dump a lot of current. There is a reason to put extra effort in adding a dedicated headphone circuit, not because the headphone circuit is cheaper than 2 padding resistors.

Nuforce circuit is a closed-loop fast feedback design, and if the impedance is way out of range (330 ohm vs. 4-8 ohm speaker load), you'll throw the feedback circuit out of whack and destroy either the amp or the headphones, depending on your luck.
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