strangeandbouncy

Headphone amp
« on: September 16, 2010, 06:36:52 PM »
Hi,


  I've been looking at headphone amps. Someone recommended the Grado ra 1. It is Cmoy, or summink like that . . . .


   what i don't get is this. It is ok for 32 Ohm headphones(apparently). How the [email protected]@k can a JR4556(just an ordinary op-amp. no?) possibly drive 32 Ohms??????



    much puzzled,


       ANdyP
. . . . RUH ROH . . . . .


sahib

Re: Headphone amp
« Reply #1 on: September 16, 2010, 07:18:42 PM »

I could not locate the data sheet as it comes up as obsolete but it will drive. I have tons of headphone amp modules removed from pro broadcast equipment with cheap JR opamps. If you want to fiddle about pm me your address and I'll send you a couple.

PRR

Re: Headphone amp
« Reply #2 on: September 16, 2010, 08:32:05 PM »
> JR4556(just an ordinary op-amp. no?)

No. Look it up.

It is the good-old 4558 but with a fat 70mA output stage (and cleaner processing than early 4558s...).

> it comes up as obsolete

The chip is still available... but the company is trying to change its name away from "radio" and (stupidly) changed their part-numbers.

Look for NJM4556

http://www.datasheetarchive.com/NJM4556-datasheet.html
http://www.datasheetarchive.com/pdf/getfile.php?dir=Datasheets-22&file=DSA-438447.pdf
http://www.datasheetarchive.com/pdf/getfile.php?dir=Datasheets-110&file=DSAP00646.pdf
« Last Edit: September 16, 2010, 08:34:55 PM by PRR »

strangeandbouncy

Re: Headphone amp
« Reply #3 on: September 17, 2010, 04:17:39 AM »
Hi PRR,



  thanks for your reply and links. Datsheet quotes that it will drive 150 Ohms. That is a lot greater than 32 Ohms! I guess that that figure is at full power(?) Surely running into a lower load will compromise the distortion performance, even at lower power(?)


    I think that I should break out some of my spare 2520's or OA10's for headphone application . . . . plenty of grunt there


    Kindest regards,


     ANdyP
. . . . RUH ROH . . . . .

12volts

Re: Headphone amp
« Reply #4 on: September 17, 2010, 08:35:43 AM »
Behringer use millions of them - have a look inside any of their kit.


Frank

12volts

Re: Headphone amp
« Reply #5 on: September 17, 2010, 08:51:48 AM »
Forgot to add, the best headphone amp (by miles) is made by Texas Instruments, the TPA6120.
This implementation is damn good, just ignore the PSU bits of the circuit.


http://sjostromaudio.com/joomla/index.php?option=com_frontpage&Itemid=1

http://sjostromaudio.com/joomla/index.php?option=com_content&task=view&id=43&Itemid=27


Frank

Jarno

Re: Headphone amp
« Reply #6 on: September 17, 2010, 09:06:37 AM »
Grado RA1 uses a LM386s, those are power amps in a dip8 package. Not sure how well they sound, but that Grado amp is pretty well regarded I think.
CMOY uses a dual opamp in parallel per channel, will not cut it for your 32ohms Grado headphones.
I use a super simple headphone amp for my Grados, based on the Szekeres (google). It's a IRF610 fet with a LM317 as it's current source, class A, sounds fine.

0dbfs

Re: Headphone amp
« Reply #7 on: September 17, 2010, 11:30:46 AM »
Thoughts about using the LM4765T to drive headphones?

http://www.national.com/ds/LM/LM4765.pdf

Best,
jonathan
Music is everything!
Audio is everything else!

EmRR

Re: Headphone amp
« Reply #8 on: September 17, 2010, 01:16:07 PM »
There's a Gyraf design on their site somewhere, and there's also this THAT based solution.
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

12volts

Re: Headphone amp
« Reply #9 on: September 17, 2010, 02:02:31 PM »
Thoughts about using the LM4765T to drive headphones?

http://www.national.com/ds/LM/LM4765.pdf

Best,
jonathan


You really want to use 30+ watts on headphones????
Here in the UK, we would call you a screaming nutter.

Frank


0dbfs

Re: Headphone amp
« Reply #10 on: September 17, 2010, 03:02:10 PM »
You really want to use 30+ watts on headphones????
Here in the UK, we would call you a screaming nutter.

Frank
Ha!

Well, we used to use 75 or 150 watt crown amps with a passive cue box like this:
www.skeng.com/Simon_Systems_files/CB_4.pdf
 :-X

It sounded pretty good.
 :-\

So, a 30W driver doesn't sound unreasonable based on that.

This part is about $7.5 from digikey and with an input-buffer->10k-pot->buffer->amp you could use a wall-wart to power it all.

Best,
j
Music is everything!
Audio is everything else!

Gus

Re: Headphone amp
« Reply #11 on: September 17, 2010, 03:47:51 PM »
In the first schematic in this thread I don't see a series output resistor to keep the amp stable into different loads.   Opamps that are connected to unknown loads can oscillate.  Length of cable adds capacitance and the drivers inductance.

I also see something else I question.  Anyone want to guess?

strangeandbouncy

Re: Headphone amp
« Reply #12 on: September 17, 2010, 06:14:39 PM »
HI Guys,



  I guess the schemo might not be accurate then, LM386 'n all . . . .


  Sahib, thousand pardons, I somehow missed your kind offer. I would love to try 'em out, yes please! PM on it's way.


   Thanks for all your replies. I will look into the szekeres idea. Looks interesting!


   Kindest regards,


      AN dyP
. . . . RUH ROH . . . . .

Gus

Re: Headphone amp
« Reply #13 on: September 17, 2010, 07:05:23 PM »
found this

http://www.ecp.cc/ra1.html

http://www.parttimeprojects.com/audio/diy/CMoy%20Headphone%20Amplifier.php

What I would do is use a 100Lin with a 20/22K input to ground for the 100K and I would scale down the feedback resistors so the || value was about 20/22K. 

I would guess most things that would drive this circuit could drive 100K|| 20/22K.  The 20/22K will adjust the volume control curve and the lower value resistors will case a little lower noise.  I would also add a 10 Ohm series output resistor. 

A 386, really?

What about current drive with the headphone driver as part of the feedback?

trapiche2

Re: Headphone amp
« Reply #14 on: September 17, 2010, 07:07:32 PM »

dinesh

Re: Headphone amp
« Reply #15 on: September 18, 2010, 12:51:53 AM »
Hi,

I have PCBs for Headphone AMP. I have copied the circuit from my Alesis X2 Desk. Circuit is good & sound nice.

Regards
Dinesh


 

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