How to safely drive headphones with a speaker amp?
Jun 26, 2015 at 11:00 PM Thread Starter Post #1 of 27

Music Alchemist

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'Kay, so...my current system includes a Lepai LP-2020A+ speaker amp, STAX SRD-4 electret adapter, and STAX SR-30 electret (a type of electrostatic) earspeakers. I frequently have non-electrostatic headphones in my stable (such ironic use of language, if you know me, I know) and figured I might as well drive them with the speaker amp if possible, since I don't have a conventional headphone amp at the moment. What are the easiest and most affordable ways to go about this? I don't want to do any DIY projects. I would much rather buy a cheap adapter that can do the job, as long as it's safe. Will I definitely need separate speaker cables, at the least? Or are there adapters out there that have speaker connectors on one end and headphone outputs on the other? (The STAX adapter is like this.) Thanks so much for whatever assistance you can provide. I'm sure many others are wondering about this too.
 
Jun 28, 2015 at 10:42 AM Post #3 of 27

goodvibes

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There's no great way other than keeping the volume down. Inline resistors were common in the day of receivers but raised the output impedance. Basically there to drop noise and gain. Same you could do if for single driver dynamic headphones. Best bet is to find a speaker switch that includes headphone jack to accomplish this.
 
Jun 28, 2015 at 10:48 AM Post #4 of 27

StanD

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Besides having a 6.8 mm TRS adapter for your speaker taps, you can make your wn LPAD (resistors) that match the impedance and sensitivty needs of your headphones (Gogle is your friend). You might be able to find a stereo LPAD that uses a dual rotary attenuator, usually used for speakers. If you are using Planars that are between 38 and 59 Ohms (Hifman) you might not need an LPAd since the wattage at those impedances will most likely be much lower than the 4 or 8 Ohms that the amp is rated for.
 
Jun 28, 2015 at 11:05 AM Post #5 of 27

Music Alchemist

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  There's no great way other than keeping the volume down. Inline resistors were common in the day of receivers but raised the output impedance. Basically there to drop noise and gain. Same you could do if for single driver dynamic headphones. Best bet is to find a speaker switch that includes headphone jack to accomplish this.

  Besides having a 6.8 mm TRS adapter for your speaker taps, you can make your wn LPAD (resistors) that match the impedance and sensitivty needs of your headphones (Gogle is your friend). You might be able to find a stereo LPAD that uses a dual rotary attenuator, usually used for speakers. If you are using Planars that are between 38 and 59 Ohms (Hifman) you might not need an LPAd since the wattage at those impedances will most likely be much lower than the 4 or 8 Ohms that the amp is rated for.

 
Any links to adapters that could work? (Preferably the most affordable ones.)
 
I know about the HIFIMAN HE-Adapter, but that's only for certain headphones.
 
Note that I'm a total novice to speaker amps, so any help is appreciated.
 
Jun 28, 2015 at 11:10 AM Post #6 of 27

StanD

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Any links to adapters that could work? (Preferably the most affordable ones.)
 
I know about the HIFIMAN HE-Adapter, but that's only for certain headphones.
 
Note that I'm a total novice to speaker amps, so any help is appreciated.

Spades or banana plugs as needed at the amp, 6.8 mm female TRS jack at the free end for headphones to plug into. Search Google or Amazon, etc. I made my own.
 
Jun 28, 2015 at 11:17 AM Post #7 of 27

Music Alchemist

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  Spades or banana plugs as needed at the amp, 6.8 mm female TRS jack at the free end for headphones to plug into. Search Google or Amazon, etc. I made my own.

 
Thanks, but that isn't specific enough to even tell me what to search for exactly. What do you mean by at the free end? How do I do this without it being DIY? I just want to buy the cheapest things I need to get the job done.
 
Jun 28, 2015 at 11:58 AM Post #8 of 27

ProtegeManiac

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You'll need to wire the headphones as balanced as a safety measure. This is because some amplifiers might have some kind of problem if the ground is shared (if the L+ and R+ ever meet, say bye-bye to any amp), without feeding the 4-channel* signal into an L-Pad or other such circuit first, unless you're sure that that particular model doesn't have such issues (ie if anyone's used that same amp in that manner). Conventional headphones, particularly a single-entry (ie cable goes into left cup) design, uses a common ground with independent L+ and R+ conductors; even a dual entry headphone like Grados and some Sennheisers have independent conductors all the way to the plug, but once in there the GND are soldered into the same terminal on the TRS plug (obviously, a balanced HD800 with a 4-pin XLR plug has them separated). 
 
So basically you rewire in one of two ways:

1. Rewire the headphones and terminate the amp end of the cables with banana/spade plugs (depending on what your amp can use, but I'm biased for banana plugs if it can use them)
2. Rewire the headphones to end in a male XLR plug; then make an adapter for the speaker amp made of cables with banana/spade plugs on the amp end then a female XLR on the other end. You then plug in the headphone's male XLR into that female XLR. Make sure both are 4-pin and you solder them appropriately.
 
One thing to note though, AFAIK Class D amplifiers have some kind of issue driving high impedance loads (can't remember if THD at some point starts piling on faster, or if it has to do with damping factor). I remember there was someone who was able to wire a T-amp and the results were good considering the price of the amp, but all the same if you're going to use anything above 100ohms don't expect much; also, you're probably going to have less than 100mW into 300ohms.


*By "channel" here I mean the conductors as when people describe what configuration their Beta22 is in, not channel as in stereo or surround
 
 
 
 
Thanks, but that isn't specific enough to even tell me what to search for exactly. What do you mean by at the free end? How do I do this without it being DIY? I just want to buy the cheapest things I need to get the job done.

 
Googled and found these links:
 
"Spade plug"
http://www.amazon.com/Sewell-Premium-Degree-Connector-Pieces/dp/B0050CEA40
http://www.speakerrepair.com/ebaypics/new-spade-plate-500.jpg
 
"Banana plug"
http://www.nakamichiplug.com/product-2503.html
https://www.youtube.com/watch?v=ybRqeCkgXWs
 
 
And from my post above:
 
"Male 4-pin XLR plug"
http://www.amazon.com/Neutrik-NC4MX-Connector-Nickel-4-Pin/dp/B002EDO2K0
 
"Female 4-pin XLR plug"
http://www.bhphotovideo.com/c/product/748113-REG/Neutrik_NC4FX_B_NC4FX_B_4_Pin_XLR_Female.html
 
Jun 28, 2015 at 12:36 PM Post #9 of 27

Music Alchemist

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Originally Posted by ProtegeManiac /img/forum/go_quote.gif
 
You'll need to wire the headphones as balanced as a safety measure. This is because some amplifiers might have some kind of problem if the ground is shared (if the L+ and R+ ever meet, say bye-bye to any amp), without feeding the 4-channel* signal into an L-Pad or other such circuit first, unless you're sure that that particular model doesn't have such issues (ie if anyone's used that same amp in that manner). Conventional headphones, particularly a single-entry (ie cable goes into left cup) design, uses a common ground with independent L+ and R+ conductors; even a dual entry headphone like Grados and some Sennheisers have independent conductors all the way to the plug, but once in there the GND are soldered into the same terminal on the TRS plug (obviously, a balanced HD800 with a 4-pin XLR plug has them separated). 
 
So basically you rewire in one of two ways:

1. Rewire the headphones and terminate the amp end of the cables with banana/spade plugs (depending on what your amp can use, but I'm biased for banana plugs if it can use them)
2. Rewire the headphones to end in a male XLR plug; then make an adapter for the speaker amp made of cables with banana/spade plugs on the amp end then a female XLR on the other end. You then plug in the headphone's male XLR into that female XLR. Make sure both are 4-pin and you solder them appropriately.
 
One thing to note though, AFAIK Class D amplifiers have some kind of issue driving high impedance loads (can't remember if THD at some point starts piling on faster, or if it has to do with damping factor). I remember there was someone who was able to wire a T-amp and the results were good considering the price of the amp, but all the same if you're going to use anything above 100ohms don't expect much; also, you're probably going to have less than 100mW into 300ohms.

*By "channel" here I mean the conductors as when people describe what configuration their Beta22 is in, not channel as in stereo or surround
 
Googled and found these links:
 
"Spade plug"
http://www.amazon.com/Sewell-Premium-Degree-Connector-Pieces/dp/B0050CEA40
http://www.speakerrepair.com/ebaypics/new-spade-plate-500.jpg
 
"Banana plug"
http://www.nakamichiplug.com/product-2503.html
https://www.youtube.com/watch?v=ybRqeCkgXWs
 
And from my post above:
 
"Male 4-pin XLR plug"
http://www.amazon.com/Neutrik-NC4MX-Connector-Nickel-4-Pin/dp/B002EDO2K0
 
"Female 4-pin XLR plug"
http://www.bhphotovideo.com/c/product/748113-REG/Neutrik_NC4FX_B_NC4FX_B_4_Pin_XLR_Female.html

 
Oh wow, looks like there are some safety issues I wasn't even aware of!
 
As mentioned, I don't want to do any DIY stuff. Too lazy for that.
 
Besides STAX, my current headphones don't even need an amp anyway. I was just curious how to go about it if I were to want an amp for future headphones without spending more on a normal headphone amp...but by the time I can afford more headphones that do need or benefit from an amp, I guess I'll just get the JDS Labs The Element.
 
Jun 28, 2015 at 12:37 PM Post #10 of 27

StanD

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Most SE amps have a common ground for both channels. If that's the case an XLR is not required, one must do their homework.Perhaps consult the Service Dept. of the manufacturer or check the owner's manual.
 
Jun 28, 2015 at 12:57 PM Post #11 of 27

StanD

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This Lenai amp appears to to have inserts for bare wires, not banana or spade terminations.
If a common ground is not an issue then a short headphone extension cable can be used, cut off the male plug and use the wires directly. You might use a meter to find which wires connect to the TRS connections and thus ground, left and right. If the cable has independent ground wires for each channel, then you can use any amp.
 
Jun 29, 2015 at 1:53 PM Post #12 of 27

ProtegeManiac

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As mentioned, I don't want to do any DIY stuff. Too lazy for that.

 
If your headphone cables are dual-entry detachables then buy a new cable, strip the wires, and hook them up to the speaker terminals, making sure to wire them up correctly to R+, R-, L-, L+.
 
Or if the amp is safe for common ground use then look for a Spade to TRS adapter, but Im not sure if you can hook up the GND spade to just one of the Neg(-) terminals or if you have to wire that up to both.
 
Jun 29, 2015 at 2:31 PM Post #13 of 27

Music Alchemist

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  If your headphone cables are dual-entry detachables then buy a new cable, strip the wires, and hook them up to the speaker terminals, making sure to wire them up correctly to R+, R-, L-, L+.
 
Or if the amp is safe for common ground use then look for a Spade to TRS adapter, but Im not sure if you can hook up the GND spade to just one of the Neg(-) terminals or if you have to wire that up to both.

 
Even this is way too DIY for me. I want to buy something, plug it in, and press play. hehe
 

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