Chu Moy Headphone Amp?

So I've been digging around for designs for headphone amps for my monitor controller and ran across the most dead simple one yet:

Chu Moy Headphone Amplifier

The gist of it: hook an OPA134 up to your headphones. Done.

Anybody tried this one yet?

chris

Depends on the headphone impedance... they range from 600 ohm to 3.2 ohm.

I did an interesting one where I drove the sleeve with a (-L + -R) signal then drove left output with L-R, right output with R-L. This was useful to pick up 2x voltage swing using typical +/- 15v rails. Drivers were just opamps with transistor buffers. I crudely power limited the lump supply (R in series with winding) so it wouldn't thermal out if someone hooked them up to speakers.

JR

To ask a stupid question...what is the point of a headphone amp between a portable cd/mp3/minidisc player and the headphones?

Obviously they are all capable of an adequate volume...so what's the deal?

Brian,

it all depends on the headphones they are driving.

Low impedance headphones require more current output for the voltage the headphone amp is supplying. Some MP3 players and walkmans run out of juice and start distorting.

Adding an additional amplifier like is more about adding a decent power stage that can handle the demand of high quality low impedance headphones.

Personally, If I was designing a headphone amp, I'd look at the TPA6120A2... that little sucker can drive 150mW ino 32Ohms... that's plenty of juice to deaphen drummers

There's an Eagle library for it around here somewhere... hehehe

So people use them with headphones that aren't designed for portable audio devices...

> The gist of it: hook an OPA134 up to your headphones. Done.

No news. Sennheiser published plans for a 741/558 opamp booster for their 2,000 ohm phones. RCA used the uA709 op-amp as broadcast console can driver.

And everybody and his Chinese competition uses one of the NJR hi-current dual opamp chips for headphones. It works.

> Anybody tried this one yet?

Who hasn't? www.headwize.com has a forum, check out the DIY section.

> what is the point of a headphone amp between a portable cd/mp3/minidisc player and the headphones? Obviously they are all capable of an adequate volume...so what's the deal?

Many of them are not so good.

A particular problem was: in the Old Days (1999), many "good" headphones were 100-300 ohms, and would not suck large power from a 2-AA power circuit. 2-AA = 3VDC = 1Vrms or less than 10mW in hi-Z phones. At 88dB SPL/mW, that's under 98dB SPL peak and probably under 85dB SPL un-clipped speech/music. And 1Vrms from a 3V supply will tend to be un-clean, because of the low voltage and low available gain.

The need is less now. Many "good" phones exist in 32 ohm flavor. 1Vrms in 32 ohms is 30mW which is generally ample. But a few low-sensitivity phones (and some low-sensitivity users or high ambient background noise situations) need more.

My own interest is wall-power faultless phone amps which can beat the level of a live stage act (>115dB SPL) if only for a few seconds a night (WHAT???!). In hi-Z phones this can be >5Vrms; I use 24V rails. (This hot-box is a far cry from a cMoy mint-tin amp.)

> look at the TPA6120A2

Yes, telephone-line drivers and headphone drivers have the same historic roots, and this DSL crapola has forced insanely excellent line drivers on cheap chips.

And yet some geeks must roll-their-own. Headwize forum currently has a hyper-complicated brainstorm posted.

[quote author="PRR"]My own interest is wall-power faultless phone amps which can beat the level of a live stage act (>115dB SPL) if only for a few seconds a night (WHAT???!)[/quote]
I tried to resist the urge to ask what on earth that for an application could be, but as you see I failed...

Burglar alarm meeting DIN45500 ?

>>>one of the NJR hi-current dual opamp chips for headphones.

NJM4556, I think...

oops...

A popular technique when using a bare opamp or dedicated headphone IC (I recall some old National parts) is to use a few hundred ohm build out resistance. This will not cost much power into 600 ohms cans, and provide much more graceful interfacing with very low Z loads or shorts.

JR

back to the chu moy however, I built quite a few of the headphone amps out there when I was doing a monitor controller and headphone distro/talkback box for my studio.
Without resorting to tubes or anything too overkilled. Of the Amps I tried I really thought that PRR's Tori amp sounded the best. used that for my main's listening.

The 5532 circuits I tried all had varying degrees of success... they looked much easier than they were. The problems seemed fairly layout dependant and I always had to add extra parts -usually capacitance- to tame oscillations etc, and a few layouts were total scrap. .

The chu-moy just worked easily every time and it sounds pretty good.
I usually have them turned up to about 3. If you open these all the way up
you could probably drive even the most ineffecient phones to pretty good levels.

Gonna try buttas LM386 phones one of these days.
It's basically just a little stereo power amp.

(WHAT???!)

Click to expand...

sometimes you want to hear something specific while the band is blasting
your phones need to be LOUD. you don't want to do this for very long periods of time.

Kelly

I have a couple of the Rane units I use in the studio to provide headphone 6 controled feeds and they will drive the daylights out of any phones connected to them. The schematics are on their site. Same with headphone boxes from Symetric, Rolls, and Apex. Why re-invent the wheel?

Hi Jim,
I've personally reinvented the wheel a number of times in order to understand it better, use up parts from my cabinet, learn a lick or two, pass the time on a rainy day, solve a problem when I was rich with free time and poor with cash, to get something rolling on tuesday that I needed on wednesday, and sometimes to keep me from doing what I should really have been doing instead and more than a few times because I knew if I made the wise choice in terms of budget vs. performance I'd have to live with racks full of Behringer gear... If pride were a sin I'd be on my way to hell a long time ago. oh sh*t it is a sin. see you in hell. :wink:

Kelly

Rochey said:

Brian,

it all depends on the headphones they are driving.

Low impedance headphones require more current output for the voltage the headphone amp is supplying. Some MP3 players and walkmans run out of juice and start distorting.

Adding an additional amplifier like is more about adding a decent power stage that can handle the demand of high quality low impedance headphones.

Personally, If I was designing a headphone amp, I'd look at the TPA6120A2... that little sucker can drive 150mW ino 32Ohms... that's plenty of juice to deaphen drummers

There's an Eagle library for it around here somewhere... hehehe

Click to expand...

I'd agree with Rochey, the TPA6120 a damn fine chip, I've used it many times. You'll need a dollop of solder paste for the heat sink pad.


Frank B.

I would be inclined to just parallel a few opamps with build out resistors and call it a day.
Or any one of the National semi "overture" series chip amps would be more than sufficient: http://www.national.com/mpf/LM/LM4780.html

There's much more distortion in the headphone drivers than any modern chip amp could ever approach.

It depends on the cans... there were some up as high as 2k ohm load so you could drive those with a TL074, some modern uber opamps have pretty robust output drive current so some of those could cover many of the cans out there with no help.

paralleling opamps for more current is pretty much using the wrong tool for the job, while I have done that before too, in a design using a pile of tl07x with only one socket that needed slightly more current. It made economic sense to parallel a pair of TL07x for just that one place instead of adding a different PN to the BOM.

The last commercial headphone amp I sold (decades ago) used transistors hanging off the back of opamps...

Be aware even if you source an uber opamp that can pull the load, the PCB layout needs to consider the current draw and ground flows. One of the common newby mistakes made by wet behind the ears console designers is not accounting for ground current in master section headphone amps.

Gee where's that crosstalk coming from... ?

JR

Yeah I was thinking that paralleling a couple of the modern opamps that boast about being able to drive a 600ohm load would be an easy solution. Perhaps it would be better to use a few power transistors as a current booster at the output of the opamp? Just throwing out ideas. To the OP, don't listen to me, listen to John. 

spacelabstudio said:

......digging around for designs for headphone amps for my monitor controller an......

Click to expand...

I used a couple of JLM headphone units for exactly this purpose. Though I can't comment on the design, it worked for me.
http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=120

- Mike

In the mid 1990s I was looking at a power limit (rather than current or voltage alone being limited) in a headphone amp design... Using one of the National Semi overture power amps as the headphone driver because of its high voltage rails for things like 300/600 ohm cans... Less expensive than the Apex Technology high voltage opamps at the time (R.I.P. Granger Scofield)...

The idea was to use a multiplier or bastardize an LT1166 application (automatic A/B bias with multipliers etc.)...  Essentially an analog computer to get volts X amps = power and limit when power threshold was exceeded.. perhaps marginal given that some cans may have a better or more efficient electrical to mechanical to dB conversion factor based on input power regardless of impedance...

Having been involved in the design of headphones recently, even their frequency response is all over the map (even between L vs R ear cups) when working towards limiting noise induced hearing loss (even for kids with their hippin' and a hoppin' and ear buddin' buds)... 85dB at the pinnae was the limit, 95 if by OSHA standards (for 8 hours; can't forget the dosimitry)....

I like aircraft headphones as they block out ambient sound... although they also create new safety hazards if walking about out in public/traffic....  caveat...

some interesting headphone threads:

Headphones: Driving the Transducers at Both Ends Using M/S
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=499

Headphone/PA with defined Ro
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=500

Headphone Outputs: Build-Out vs. No Build-Out
http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=497