Minimal Headphones Amp

[ruffrecords]

This has been a really interesting thread ,
I was aware of the limitations of low powered H/P amps a long time , my answer was 2x EL84's , SE triode connected , transformer coupled , with a 3 ohm secondary winding .

Definitely an alternative. Unfortunately this is a small tube mixer so there is no room for such a beauty. It is lack of space that is the ONLY reason I am using a semiconductor solution.

Cheers

Ian

 

[NOON]

I've been using the TPA6120A2DWPR chip and they sound great, good reviews from a couple of mastering and mixing engineers. Powerpad is tricky to hand solder but there's ways. I design the footprint to have 2 holes big enough to fit a fine soldering iron tip. Heat the pad until you can melt solder into the other hole. You can always glue a little heatsink on top if necessary.

 

[Tubetec]

I used an old Philips bakelite radio to house my HP amp ,
Between the mains transformer , a pair of 20 H chokes ,O/P transformers and a built in speaker ,it must weight 15 pounds . I also needed to drop back the raw HT to around 220V at the anodes , so theres extra RC filtering there too trying to loose heat . No prizes for efficiency , but it has simplicity in its favour .

Its definately not something Id try shoehorning into a mixer .
With the Sony cans your past the threshold of pain before distortion becomes objectionable .

 

[Newmarket]

I really do not care what pair of cans you're listening with. Continuing down this path and this will turn into nothing more than a mess of a thread with no clear end. At the end of the day what is going to matter is which set of compromises best suit the requirement (power, space, cost, etc...).

Ruffrecords mentioned he was looking for some NJM4556s. I happen to have some on hand and am willing to part with them, and subjectively I do not mind their sound. They are at least worth a try as they may or may not be adequate. All I did was offer some viable and simple methods of constructing a headphone amp. That is all. No need to interject your opinion on everyone's post with your two cents.

to check - this in response to Thor's input here ? Or ?

 

[Tubetec]

Is it not in all of our interests to take account of others experience ?
Were all entitled to express an opinion .
What might be adequate in a control room listening situation may not cut the mustard at all out in the studio with loud sound sources going on ,
Gross distortion in the talents cans can be a show stopper and as a sound engineer it something you never ever want to happen .
Were not sure the exact usage Ians mixer will face when it finds it new owner ,so a range of opinion on the subject allows better choices to be made .

 

[apzx]

.

 

[Newmarket]

Yeah Thor, I should have made that a bit more explicit. Apologies.

No problem. Just wanted to check before responding. Have to say your comments seem a bit on the harsh side for me. Thor has his "style" but I don't see anything objectionable in what he has posted on this topic. Obvs you can make of the subjective remarks what you like. But there's always a question around dedicated parts (that might go obsolete) or "ground up" designs using common part types.

 

[thor.zmt]

At the end of the day what is going to matter is which set of compromises best suit the requirement (power, space, cost, etc...).

Ruffrecords mentioned he was looking for some NJM4556s. I happen to have some on hand and am willing to part with them, and subjectively I do not mind their sound. They are at least worth a try as they may or may not be adequate. All I did was offer some viable and simple methods of constructing a headphone amp. That is all. No need to interject your opinion on everyone's post with your two cents.

All I did was to offer my relative views and make my own suggestions.

As long as someone is building one item for personal use, use whatever you have, takes your fancy etc. and assemble any way you like (dead bug in clear acrylic resin with extra LED's, vero board.

But Ian is basically making custom gear for customers.

So he will likely make a nice PCB and put a fair bit of work in and once a new feature (like headphone Amp) is out of the lab, it will often become standard, so the long term supportability of the design is likely important, as is the sound quality experienced by the customer.

So my comments are slanted towards that angle. Take them as always with a grain of salt and in context.

Thor

 

[thor.zmt]

I decided to bite the bullet and buy some from Mouser. Good thing is they are pin compatible with NE5532 and many other dual op amps I could try in this configuation.

Most will lack the required current.

NJM4556 are rated at 70mA output current into 150 Ohm, which is 10.5V peak. Few other Op-Amp's come even close. By comparison a 5532 only provides 38mA short circuit current (typical) less with load.

Downside, 3V/uS slew rate, 8MHz GBWP and 10nV|/Hz Noise.

Hence my suggestion for a multi-loop / current dumper design.


If using duals, that's 5 dual packages, 10 Resistors, a bunch of 100nF local decoupling cap's, 18V maximum supplies and 310mA peak current into 33 Ohm loads (1.7W into 32 Ohm).

Input Op-Amp can be anything with low noise and with 30mA+ output current capability and able to drive 600 Ohm.

OP-27 is low noise, as is 5532/34 but more modern designs exist.

With Bipolar Op-Amp's instead of low offset Fet types, DC blocking and matching DC & AC impedances on +in & -in will be required. Good reason not to use them.

Thor

 

[apzx]

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[Tubetec]

Apzx ,
So your a member here more than 6 years and you have a grand total of 34 posts on around 7 topics over that time .
You might be as well trying to establish yourself better before going on the attack is my advice .

 

[apzx]

.

 

[Tubetec]

I didnt make any assumptions in my previous post .
I stated facts and offered some advice ,
Disregard what I said if you wish ,

 

[k brown]

Uggh !

This place is starting sound more like Gearspace all the time . . . pity.

 

[JohnRoberts]

I won't lock this thread because I am curious to see what Ian comes up with, the rest of you can argue with yourselves.

JR

PS: Trying to herd cats on the internet is so hard as to be classified a waste of time.

 

[apzx]

It is honestly disappointing that so few people actually take the time to read and comprehend.

 

[JohnRoberts]

It is honestly disappointing that so few people actually take the time to read and comprehend.

no that's just life on internet forums... while it is hard to complain too loudly about free advice.

me me me.... you, me me me....

JR

 

[Tubetec]

Apzx,
So you accuse me of making an assumption ,which I didnt ,
yet you turn around and yourself make an assumption about the people reading what you said ,

Your digging yourself a hole here ,

 

[JohnRoberts]

we all think we are correct, we all think other's are not.... we are all wrong most of the time.

JR

 

[gswan]

Most will lack the required current.

NJM4556 are rated at 70mA output current into 150 Ohm, which is 10.5V peak. Few other Op-Amp's come even close. By comparison a 5532 only provides 38mA short circuit current (typical) less with load.

Downside, 3V/uS slew rate, 8MHz GBWP and 10nV|/Hz Noise.

It's a headphone amp, not a PA power amp. 3V/us is more than enough. For headphone volumes that aren't destructive you won't normally be using more than about 250mW. That's about 6V (150 ohm). So about 2us slew. No problem for audio. They are used as unity-gain outputs drivers so 8MHz GBWP is also sufficient for audio.