Dual headphones?

[Duzzy]

Hi all,

Please excuse my ignorance. Old person but new to electronics. Breadboarded guitar fuzz pedals is how I am teaching myself but I have gotten sidetracked.

I am trying to drive 2 identical sets of headphones from my phone.

I have a Y cable but the sound is just not the same. I do not want any gain or volume control. Just that when both are plugged in the sound is the same as when one is plugged in.

After trawling the web and getting thoroughly confused I think what I am going to build is a circuit with the phone stereo output going to the input of a dual op amp (probably a 5532)  and the output of that feeding a quad opamp (TL084CN) with that driving both headphones. These amps have been specifically hand selected based on that's what I have.

I think I want all the amps set to unity gain and that this is kind of a buffered distribution amp thing.

Am I on the right track or am I way off?

D

[Marco]

No need to put two buffers behind each other. Just use the TL084. You'll need to add some resistance on the output of each opamp to limit the current caused by offset voltages. What do you have as the power supply? Those opamps don't get very close to their rails.

[Duzzy]

OK. That saves some work.

I don't think I have much choice but to use 2 9V batteries in series. Having checked the datasheet the TL084CN wants  a minimum +/- of 5V.  Unless I source a different chip.

In my fiddling about I have been using a TL081CP and managed to get that working with 9v and a voltage divider to 4.5v where I think something to do with DC offset shifted what the amp saw as 0. I also used the square wave output of my FG085 and a couple of capacitors and diodes to get a - voltage. That blew my mind. 

I thought about a 555 in place of the function generator but it was starting to get a bit complex.

I will look into output resistance.

Is this connected with impedance? In my mind I just want the phone to think it's driving a set of 32ohm headphones and the amp to think the same but for each pair.  The Y cable halves the impedance which may have something to do with the loss of quality? I have been trying to understand input and output impedance matching but I am finding it tough going.

Many thanks,

D

[Audioguru]

You did not see the datasheet of the TL08x opamp.
Like most opamps, its minimum spec'd load is 2000 ohms and a graph of its typical output current shows zero mA into 100 ohms. Some of them might produce a little peep into 32 ohms headphones.
An NE5532 opamp can drive very expensive 600 ohms Sennheiser headphones.

The Ruby headphones amplifier is used to drive a few pairs of headphones with a guitar input and is powered form one 9V battery:
http://www.runoffgroove.com/ruby.html

[picandmix]

Hi,

You can buy one of these 4 channel units which work well.
https://www.ebay.co.uk/itm/Behringer-HA400-Micro-Amp-Headphone-Amplifier/292419453087?epid=1305621109&hash=item44158ec09f:g:QE8AAOSwr~lYsG0f

If you want something with really high quality output then can recommend this design, though you will need two.
It looks a complicated and lengthy thread but all the key info is on page 1, have built it myself, really good sound.
http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb.html

ps  - have got the little used Behringer for sale if interested..

[Duzzy]

Hey cheeky! 

My eyesight may be failing but I definitely saw the datasheet.

I think maybe you meant to say that I didn't understand the datasheet which is a fair and accurate assessment.

Anyway thank you for educating me on what graph to look at. 

D

[Duzzy]

Hi picandmix,

I have seen those but I am after a portable solution. M-Audio do a small amp as well but as I am trying to learn some electronics I thought this would make a nice simple little project  .

I have seen this page

http://e2e.ti.com/support/amplifiers/ti_precision_labs_op_amps/f/1000/t/518233

a few times during searches and I should probably check out the amps mentioned there. I was just trying to get something going with bits and pieces I picked up from Maplin as they closed down.

One more question and then I'll bugger off and leave.

I have a scope and would like to fake the load of 1 or 2 sets of 32ohm headphones well enough that I am not risking the actual headphones when looking at output waveforms.

Cheers,

D

[Duzzy]

No worries. I found this.

https://tangentsoft.net/audio/hp-dummy.html

[Buriedcode]

Unless I've missed something.. all you wish to do is drive two headphones from one output.  I am assuming these are 16/32 ohm headphones (most are) and as such will require a headphone amp/driver.  If you wish for the volum eot be the same as the original signal, a gain of 1 is required.

The easiest option for you would be to order headphone amp modules:
https://www.ebay.co.uk/itm/Differential-balanced-Stereo-Headphone-Amplifier-Board-TPA6132-Hifi-Amp-for-BT/262968162345?hash=item3d3a1fb829:g:YYUAAOSwR29ZDEFz

something like that.

Of course that isn't very "fun" in that it isn't true DIY.  But if you were to build your own you would need either an amp that has enough current drive (I have used a ts922 before with success) or transistor output drivers.  Also, if you don't want large capacitors on the output to block DC (which will kill your headphones) you will need a bipolar power supply - positive and negative. 

You can use a single supply but then your output will be centered around VCC/2 - something you will probably be familiar with in fuzz pedals that use opamps (think Tube screamer, proco rat etc..) and will require the caps on the output.  As these caps form a high-pass filter with the headphones, they should be >220uF to not cut the bass. Preferably larger, like 470uF.  With these caps comes annoying things like  a "pop" when power is applied or removed.

There are also a lot of "headphone amp" schematics on the web, ranging from crap (LM386), to simple, but requiring dual power supply and generally quite large (cmoy amps) to ridiculous "audiophile" style ones that use expensive parts for the sake of using expensive parts.  This means its a minefield if you're not sure what you're doing.  This is why I suggested a pre-built module with a chip-amp like the TPA6132, the max9722 or the PAM8908.  These are hard to solder, but if you can get them as *modules* they're small, work with anything from 3-6V (think AA batteries), don't have the "pop" problem, can be wired in parallel, and sound pretty transparent.

If you're making something that'll sit on a desk, and size or power isn't and issue, then by all means, start tinkering   It just requires a high current opamp/driver, preferably specified for audio.  I recommend downloading LTspice for simulating designs so you can simulate for things like frequency response, distortion etc.. even for relatively simple things like headphone amps.

[Duzzy]

Fantastic! Many thanks for your lovely response and nope you missed nothing and didn't even have to resort to implying I'm blind to help out.

Yep, the wife and I occasionally walk and like to listen to the same thing. I just want 2 sets of 32ohm headphones to sound the same as 1 set when plugged in. No gain required.

Possibly leaping from breadboarded fuzz's to actual 'hi-fi' signal duplication was trying to run before I can crawl. After all, if my guitar circuits distort and clip and generally mangle the source then there is a good chance all is working correctly. 

I have learned a bit about virtual grounds.... dc-offset and de-coupling capacitors came sometime later  but I am making progress. I started learning in December and have only killed one chip so far so I reckon I am doing ok.

Those little modules look just the ticket. 

I had kind of decided on this chip http://www.ti.com/product/tpa152 however as you said I was a bit concerned about soldering etc.

I have got LT Spice installed but I really need to sit down and get familiar with it.. (and Eagle and ARTA and Fritzing and Autocad and and and....I'm running out of years!)

You know I spent a good hour the other day going through the manual and trying to find out how to trigger my scope and get the result to stay on the screen.....hmm, too much time spent with digital devices....analogue scopes don't have memory. 

I am off now to check out these modules. Thank you so much for your suggestion.

D

[senso]

The simplest and proven working solution would be to just make a pair of CMoy headphone amps:

https://tangentsoft.net/audio/cmoy/

[Audioguru]

Like the TPA152 amplifier, the cmoy headphones amplifier cannot drive multiple headphones loudly, only one set.
How much power do your headphones need and how loud do you want?? The maximum loudness of music that is not over compressed allows loud peaks but normal loudness for average. Movies might be over compressed and are very loud all the time. You do not want sounds that are loud enough to destroy your hearing.

[Buriedcode]

Yep, the wife and I occasionally walk and like to listen to the same thing. I just want 2 sets of 32ohm headphones to sound the same as 1 set when plugged in. No gain required.

Ahh so it should be portable.  That means, small(ish.. I'm not suggesting you require something the size of a pound coin) and battery powered.  A lot of cmoy type headphone amps run off a 9v battery.  Whilst this is fine, provides enough headroom for opamps that aren't rail-to-rail, is small, light, and generally does the job.  But I hate them - they are expensive, and have crap capacity.  Then again......... they are convenient, you can buy them anywhere, and they don't have the added complexity (and possible slight danger) or lithium polymer).  Like everything in engineering, its all a compromise depending on the requirements!

So really the decisions on what kinds of amps you use could be down to the sort of enclosure you want to use, rather than features.  Those modules were just a suggestion, I haven't found somewhere in the UK that sells them, so the shipping can take weeks which is annoying.  But they're cheap and do the job.

I'll stop flooding the topic with ideas/suggestions - quite often it is a hindrance to have more options, I end up paralysed by indecision.  Good luck, and making guitar pedals was how I got started in electronics - it actually provides quite a good grounding (punn intended?) in analogue because even though fuzz boxes are meant to distort, its all the same principles.

[Duzzy]

Hi all,

Thanks for taking the time to discuss this with me.

The C-Moy is where I started but on the front page of the tangent site there is a link for the question "Can I make it drive multiple sets of headphones?" and the answer is 'Not with the circuit as-is. You have to create a distribution amp instead.' which is where I started to disappear down the rabbit hole....

I am obviously ignorant here and audio signals, well to me, are just plain weird. I come from a level where AC means a minimum of mains 240v and a capacitor is like a battery not a filter. Ok I may have known for years what the visual representation of a sound wave looks like, but I never made the connection between that and electricity. Well, not properly.

I used to do digital logic and protocol analysers and that kind of stuff in a previous life but always worked several layers above the hardware.  I also didn't want my first ever post on EEV to start rambling. That said... 

My phone, Galaxy S5, drives my headphones (SONY - MDR-EX650APT) just fine. When I plug in an additional identical pair of headphones via a Y cable, into my S5, the sound quality diminishes (presumably on both sets of headphones, but my wife is not keen on me stuffing her buds into my ears to check. Fair play.)

I think I might be running into the issue this webpage http://nwavguy.blogspot.co.uk/2011/02/gain-and-headphone-ampsdacs.html describes as "Non-Zero Output Impedance" as it seems to be the bass that I think starts to.. well actually, get muddy.

All I wanted was a zero gain doo-dad that I could plug my phone into so that it thought it was driving a single pair of 32 (yeah. I found the obvious button  ) headphones and then the same doo-dad took that signal and drove 2 pairs of 32 headphones as if each output (dual) was the phone, same volume, same quality, nothing added, nothing taken away.

Also I am listening to mp3's so 'quality' is already hmmm.

Honestly it sounded so simple to me.

Duplicate a signal.

How hard can it be? 

Blimey this has taken so long that I've got a warning about a new reply whilst I have been typing!

D

[picandmix]

Cannot help with the detail, but that Berhinger 4 way headphone amp I mentioned uses an individual op amps chips for each output  similar to the cmoy, but also has an input op amp of the same type to drive them.

btw , the cmoy gives a fair sound, but if you want a noticeable sound improvement then that diyaudio link  amp can be build as a portable version, see his thread and home page.
The guy whos thread it is, is very helpful and may be able to suggest a good way to drive 2 sets of cans.

( have built and used both the cmoy and the diyaudio  amps myself)

[Duzzy]

For twenty quid I have purchased a selection of the headphone amp modules. Something to play around with at least. 

picandmix. How much did you want for the Berhinger if it is still for sale?

D

[picandmix]

picandmix. How much did you want for the Berhinger if it is still for sale?

Sorry, someone else PMed me

[Duzzy]

No problem. I didn't really need it.

Better someone use it than it get gutted by an idiot 

[pardo-bsso]

Hi,

perhaps I'm not seeing something but have you considered using a passive splitter?

That's only three jacks and six resistors (around 8-12 ohms would do) wired as a star, three for each channel, to make a passive and symmetric widget.

[Audioguru]

A passive splitter wastes half the power in the resistors so each headphone gets half the power and might have audible resonance booming.

[krappleby]

relatively new. but

would the solution be to create a small self contained box, containing 1 input and two outputs, and place two op amps just before the outputs. (1 amp per output) then modify the resistors based on the sound boost you want?

would this not work>

sorry for my ignorance.
keith

[Duzzy]

That's kind of where I started with this. However my choice of op amps was way off. I was just going to use what I has because I didn't understand the spec sheets.

This is why I have ended up buying some small modules, with suitable amps already on them. This way I don't have to solder SMD stuff because most, if not all, of the newer chips that looked suitable only came in teeny weeny sizes.

I also thought about the resistor approach but putting something inline which would potentially suck more current just didn't seem right. Of course that decision was based on nothing more than a hunch.

I will update this with my verdict on the modules. Bought 4 types based on MAX4410, TPA6112, TDA1308 and TPA6132 and yes. I intend to put 2 of them in a box with a battery and set them (probably) to 0 gain. I don't need more volume, I just need audio clarity. The Y cable messes with the bass response.

D