True Headphone AMP?

Not sure that using an ordinary amp would be a good idea in most cases. Keep in mind that dynamic headphones typically produce in the rough area of 100db spl for an input of 1 MILLIWATT (0.001 watts).

Also, a low powered tube amp (or any other tube amp that is designed to drive speakers) would not be a good choice because the higher impedance of the headphones (compared to speaker impedances) would not properly load the amp.

Regards,
-- Al

Al & Elizabeth or other members who have experience with this.

How would one hook up their amp so that it could power a pair of headphones? I have a Hafler DH-220 and from looking at the manual it says it can be used to power a set of headphones. From looking at the Hafler and seeing a lack of a headphone jack and just conventional speaker terminals I haven't the faintest idea as to how to hook up headphones to it. I was thinking about using the Hafler DH-220 as a headphone amplifier since it is just lying around unused right now. The preamp I plan to use in this set-up doesn't have a headphone jack. The headphones I plan to use are either the AKG 701 or Sennheiser HD580s.

Thanks so much for starting this topic Nikturner920. I've been curious about this topic for some time now.

The only headphone I know of that can be driven directly off an amplifier is the AKG K1000 which has been discontinued for many years. Very unconventional in appearance and design but still only requires 5-10 wpc to operate properly. They are spec'd at 104 dB SPL with 1000 milliwatt (1 watt) input. Remember, those drivers are still VERY close to your ears, and each halving of distance from a point source increases SPLs by 6 dB. So if your normal listening distance is 8', by the time you get to 3" you are at a 30 dB increase in volume for the same output from the amp, assuming of course equal efficiency. Bottom line is with your Hafler you would be operating in the very non-linear portion of any attenuator's range, where channel tracking is typically poorest, distortion is highest and volume increases are logarithmic, and you would have an extremely difficult time adjusting the volume. So the K1000s work w low wattage tube amps, and due to their high impedance and unusual design, they require the most power of any headphone I know of. They do sound fantastic but given their replacement cost and difficulty in finding spare parts, I'd think very carefully before hooking them up to a high powered amp.

The headphone amp of your choice would be a better approach than your Hafler. ..better sound, easy connection, etc. Look at Headphone.com

Antique sound lab UHC signature amp to headphone converter may work.

Go browse around Head-Fi. Lots there.

I run a Sonic Frontiers Line 3 that Bill Thalmman did his magic (and it is magic) and retubed it with NOS Siemens CCAs and E88CCs. I love this preamp - this mod/retube took a very good preamp and made it great.

The Line 3 has a SE headphone jack which I used for a while. After reading tons and exchanging e-mails with Head-Fi members, I auditioned a Rudistor RPX-33 (now the RPX-35 due to a few minor updates), a dedicated, SS, SE head phone amp. I run it from the tape outs on my preamp.

The unit never went back. The improvement over the Line 3 head phone jack is immense.

There are several very prominent, quality head phone amp manufacturers (SS and tube) out there. It tends to be kinda boutique - even more so than big rig hi-fi.

Good luck.

I learned that headphone amp or headphone jack off your preamp or any component needs to be synergised with headphones.
I had used Consonance M20 tube headphone amp and it wasn't better than headphone jack off my Alesis ML9600 CD-player for AKG K701. It certainly was louder but presentation, imaging and bass responce was better in CD-player.

05-05-11: Jedinite24
How would one hook up their amp so that it could power a pair of headphones? I have a Hafler DH-220 and from looking at the manual it says it can be used to power a set of headphones. From looking at the Hafler and seeing a lack of a headphone jack and just conventional speaker terminals I haven't the faintest idea as to how to hook up headphones to it. I was thinking about using the Hafler DH-220 as a headphone amplifier since it is just lying around unused right now. The preamp I plan to use in this set-up doesn't have a headphone jack. The headphones I plan to use are either the AKG 701 or Sennheiser HD580s.

Back in the old days (the 1960's and earlier, and perhaps a little more recently than that), headphones generally had much higher impedances than they do today (thousands of ohms, instead of ten's or hundreds of ohms). The higher impedance directly reduces the amount of power delivered into the phones, for a given amplifier output voltage. That was probably one of the reasons that the DH220 manual referred to using it with headphones, that amp being from the 1980's.

Also, from that manual:

Headphones are normally operated from the loudspeaker outputs, but are usually connected through a junction box which provides switching from phones to speakers. Such a box usually provides some added resistance to reduce the sensitivity of the phones, and thus minimize the likelihood of hearing component noise, because of the low setting required at the volume control. Some headphone boxes utilize a “common ground” system which makes it particularly important that you carefully observe the proper connections. While the black ground terminals can be connected together, the red ones must not be.

Some headphones, such as electrostatic types, are less sensitive and may need little or no resistance in series for normal operation. These could be easily interchanged with the speakers through the use of double banana plugs.

The AKG K701, with 105db sensitivity (presumably for 1 mW) and 62 ohm impedance, would be totally out of the question for use with that amplifier. The Sennheiser HD5801, with 97db sensitivity, 300 ohm impedance, and a "load rating" (which I would guess means maximum rated power handling) of 200 mW, might be marginally within reason if an in-line attenuator is placed between preamp and power amp, but I still would not recommend it. BTW, the 300 ohm impedance would reduce the amp's maximum rated power capability from 115 watts to around 3 watts, plus some additional amount due to dynamic headroom and margins that are provided in the specs.

FWIW, though, a way of connecting a phone plug to the output terminals of a hypothetically suitable power amp (although with less than ideal mechanical integrity), would be to use an in-line female phone jack, such as this one. Its housing would be temporarily removed, and three wires soldered onto the terminals within the housing, for the tip (left channel), ring (right channel), and shield/ground connections, respectively.

If the amp is not bridged or balanced or in monoblock form, the negative (black) speaker terminals on the amp will normally be connected to ground and hence to each other. So you would connect the L wire to the red terminal of the L channel, the R wire to the red terminal of the R channel, and the ground wire to either black terminal.

If the amp is on a single chassis but is bridged or balanced, so that the black terminals are driven with a signal rather than grounded, you would do the same except that the ground wire would go to amp chassis.

For monoblock amps, you would do the same except that the ground wire would go to preamp chassis.

Best regards,
-- Al

Are headphone junction boxes still available?

05-06-11: Almarg
If the amp is on a single chassis but is bridged or balanced, so that the black terminals are driven with a signal rather than grounded, you would do the same except that the ground wire would go to amp chassis.

Correction: The reference to the black terminals being driven with a signal applies to balanced amps, but may or may not apply to a bridged amp, depending on its design. In either case, with a bridged amp the signal wire would be connected to the output terminal that provides the non-inverting output signal, and the ground wire could go either to amp chassis as stated, or to a grounded output terminal.

Regards,
-- Al

Thanks for the replies. I'm not sure I'm interested in a DIY connection to my main amps. It would be a pain to connect and risk of shorting when pluging in and out seems to much of a risk with 300W monos.

My prime interest would be connection to my Pre amp line out to an amp specifically designed to drive headphones.

I guess to narrow things down does anyone know of a head phone amp where you can bypass the volume and drive directly off my preamp?

I'll poke around more at head-fi, but first look found nothing.

If I were you I would still connect the headphone amp onto the tape(record) outs if you have such. I would not want my headphone amp depend on the preamp volume settings. If you don't want the signal go to the main speakers just use MUTE (once again if you have it). It will not mute the record out.
In DIY area to build a descent headphone amp is a matter of within $100 that would match your headphones AND your preamp perfectly.
In consumer market area not all of them may please you for the budget. The ultimate champ in budget-no-option is Grace M903 which is also an excellent preamp and 24/192kHz USB DAC. I've also heard lots of goodies about Violectric.

I've done this in the past to check for sound characteristics at low volumes. This was to see if what I was hearing was caused by the amp, or speakers. I would not want all of these amplification stages altering the sound in my headphones though, when a headphone amp doesn't need or use them. But for safety reasons, I would use a 1/4 to 1/2 amp fuse in each channel.

Others with more electronic knowledge might give a more appropriate value. This would be in case something happens to go wrong for example, an output transistor shorting and passing 50 volts or more to the headphones. Besides the loud volume, the phones can catch on fire (if not protected), with all of that power there.

If people reading this are considering doing this on a tube power amp, make sure you keep a reasonable load on the speaker outputs on amp at all times. I would guess a 8 ohm non- inductive capable of handling the output power from the amp.

I think most preamps have enough gain to drive headphones but have to high of an output impedance to work. Is there a non active way to drop the impedance down enough to work with headphones?

I think atmasphere preamps can drive headphones from their main outputs. I believe that is because of their low output impedance.

Please correct me if i'm wrong.

Sarcher30 raises some interesting points. A preamp having very low output impedance, and the ability to drive low impedance loads without significant frequency response issues or increases in distortion, should work well into many headphones (especially those that combine high impedance with good voltage sensitivity). But those are a lot of constraints, and if the preamp and phones were not chosen very carefully it would be easy to end up with poor sonic results.

Is there a non active way to drop the impedance down enough to work with headphones?

A suitably chosen step-down transformer would lower output impedance, while also reducing gain. I'm not aware of any transformers that are specifically designed to interface between preamps and headphones, though, and again I would imagine it would require careful selection of all of the components to achieve a good match. It might also cost more than many dedicated headphone amps.

Regards,
-- Al

Thanks Al.

I figured there was some good reasons that such a device does not exist. I thought there might be some issues but do not have the technical knowledge to know what they would be.

Might make an interesting project. But sounds like it would not work for but one combonation of pre and phones.

Sean

I bought a little tubed Bravo V2 headphone amp (cute) recently and drive it from a set of unused single ended outputs on my preamp. It allows the use of the preamp remote volume control, works perfectly, sounds great, looks cool (the amp, not me necessarily). I can see absolutely no reason why you wouldn't want to drive a phone amp from main outs...you can mess with the gain all you want...heaphone up/preamp down, vise versa...I run the V2 at about 50% or so of its gain to allow appropriate preamp adjustment headroom. It has no audible deletirious effects on the preamp's other outputs (balanced outs to the main amp, another single ended pair to an aux amp rarely used for extension/outdoor speakers).

How about a MiniWatt amp with the headphone out adaptor? And then bypass the MiniWatt's volume control, which I have read improves the sound of the MiniWatt

I haven't read all of these, so it might have been mentioned. Go over to HeadFi.org. This is a forum just for headphone enthusiest. You will find solid recommendations in any price range. This is a very knowledgable bunch.
Tim

If you are still interested, here is the link to the ASL headphone junction box
http://www.divertech.com/asluhcsignature.html

My girlfriend walked in and caught me on my computer hanging out in a room full of HEADPHONE ENTHUSIASTS! Or, "hey Bob...are you forgetting to iron your tunic or are you a headphone enthusiast?"
Or "a priest a cowboy and a headphone enthusiast go into a bar"....

There are a number of headphones still in production that can be run directly off a speaker amp. HiFiMan's line of orthodynamics, for example. Do a search on Head-Fi and you'll find some very experienced members who prefer this approach to a dedicated headphone amp. No need for an attenuator beyond the volume pot and some common sense.

05-10-11: Bjb_nva
There are a number of headphones still in production that can be run directly off a speaker amp.

I've been in this hobby for decades and can say I never seen, or heard of a pair of headphones made to hookup directly to a power amps speaker outputs. Would you provide us a link to a pair. Would they compete against regular good mid-price headphones like the Sennheiser HD-600? Thanks.

At head-fi.org there is a 246 page thread with 3,677 posts about the Hifiman HE-6 which most there agree sounds best with a speaker amp from the speaker outs. A number of vendors are making pigtail adaptors for this. I myself recently purchased a vintage sansui au-717 just to drive an HE-6, a fantastic sounding headphone.

Greetings everyone.

This thread has been very helpful to me and I'm very happy that lots of members have chimed in. I’m going to be very careful as I proceed with this attempt of using my Hafler DH-220 as a headphone amp. I’ve made lots of notes to myself on things to watch out for from the posts here. I don't like heading to head-fi that much because while there are some good threads and posts there are way too many bad ones to sift through. I like the membership here a lot better.

I contacted Divergent Technologies about the Antique SoundLab UHC Signature Headphone Listening Device and here is what they said:

"ASL UHC Signature is a passive impedance transformer that converts amplifiers loudspeaker outputs for headphones.
It is equipped with a set of inputs, a set of output loudspeaker binding posts and a bypass switch to shut off the loudspeakers when listening to headphones with your amplifier."

I was lucky enough to find an older Realistic headphone junction box that was made in Japan. It even says Tandy on it but it still looks like a quality piece that I think this unit may be from the 70's. If it doesn't work out then I may buck up for the ASL UHC Sig or try that Bravo V2 Headphone amp Wolf_Garcia posted about. I have some other budget headphone amp makers in mind.

Swampwalker. I looked into the AKG K1000 headphones. They are quite cool looking and must sound amazing but I saw a new pair being listed for $1150 or best offer on another popular auction site. Very nice set of headphones but way out of my price range. I also took note about what you said about volume. I will be proceeding with extreme caution. I wasn’t able to win the auctions for the Sennheiser HD 580 headphones as well as the AKG K701 headphones. I may now look into BeyerDynamic DT-880 250 ohm or 600 ohm headphones.

Almarg. Thanks again for your very detailed posts. They were very helpful. I should have read the Hafler DH-220 manual in more carefully regarding the need of a junction box. I found from looking at the instructions provided with the Realistic junction box that the wiring you wrote about is very similar to how I have to hook up the Hafler to it. The Hafler DH-220 I’m working with is the regular 2 channel version.

Now I was going to try make the wire you wrote about and when I went to Radioshack to get the appropriate wires and tools I found a Y-Adapter that had 2 male RCA jacks on one end and a female headphone jack in the other. I decided to give this a try before I start making the wire. This was all before I found the headphone junction box. I used this Y adapter on one of my preamp’s outputs with a pair of Sony MDR V6 headphones and the sound was horrible. I believe I had issues due to what you are Sarcher30 were discussing.

Again many thanks everyone for your help. Whether or not I get this to work properly I'll post my results.