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Headphone amp
Old 31st December 2010
  #1
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Headphone amp

Hi guys,

I've just built a headphone amp based on this http://benfeist.com/a47/images/a47_a..._schematic.pdf

I'm powering it with +/- 15v rails

i'm using ne5532's for now, but may swap, put them to start with.


my volume pot is a little strange,

full on is off.

9 (nearly full on) is really loud.

0 (off) is stupidly loud.



I am feeding it with a line level signal.

I presume i have the pot wired wrong. but i would have thought it would be backwards, surely i should just get loud to quiet rather than louder to loud to off?
Attached Thumbnails
Headphone amp-pot2.jpg  
Old 31st December 2010
  #2
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Minion's Avatar
 

Yes , you have the pot wired backwards ..... it goes from off to loud quickly because it is a Log pot which has most of it"s Volume at the last part of travel and wired backwards would give the opposite effect .....

Just switch the 2 outer wires on the pot , that should fix it .....

Cheers

You should be useing a Dual Pot if it is a stereo headphone amp and each channel should be wired to each pot section ....
Old 31st December 2010
  #3
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Quote:
Originally Posted by Minion View Post
Yes , you have the pot wired backwards ..... it goes from off to loud quickly because it is a Log pot which has most of it"s Volume at the last part of travel and wired backwards would give the opposite effect .....

Just switch the 2 outer wires on the pot , that should fix it .....

Cheers
thanks mate,

it is a dual pot
Old 31st December 2010
  #4
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okay, so I swapped the pot round. it works now.

but ....

with the pot off I get some signal (some bleed) , if the source is playing both channels some buzzing (in both channels of headphones) if one or other channel is playing no buzzing? (grounding ??)

also the headphone amp seems to distort easily? I have several other devices ( samplers / mixers etc) that i have tried in place of this headphone amp I have built and they sound okay, so I am sure it is the headphone amp.

is this indicative of this design? (its basically a cmoy)

its got ne5532's at the moment. I can swap, but would rather not if I've done something wrong? I'd rather fry the ne5532's than the bur browns.

I am listening while typing, and occasionally the left channel is distorting, (quite a few times actually)
Old 31st December 2010
  #5
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okay there's def a problem with that channel. that may be causing the problems.

i plugged a 1/8" to Dual XLR in and tried running my monitors via it. and only one channel works. so I will check that channel tommorow. probably one something silly.!

I think I may revise my grounding scheme,


btw I am running this inside the same box as the source. as the monitor / headphone board doesn't work.
Old 2nd January 2011
  #6
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seems to work fine with headphones now?

I need to work out a good scheme for auditioning op-amps?
Old 3rd January 2011
  #7
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Minion's Avatar
 

If you want to try a bunch of different opamps then use sockets on your PCB Board , the opamps just slip into the sockets and are easy to remove and best of all they only cost pennies .....

Cheers
Old 4th January 2011
  #8
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Quote:
Originally Posted by Minion View Post
If you want to try a bunch of different opamps then use sockets on your PCB Board , the opamps just slip into the sockets and are easy to remove and best of all they only cost pennies .....

Cheers
they are socketed all ready,

i mean, a fair way of comparison?

maybe setup a pro-tools session with various different sounds, in sequence?

couple of full mixes,
snare track,
vocal track,
kick drum,
bass,
Old 5th January 2011
  #9
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Minion's Avatar
 

Well Personally , I don"t have a great ear for subtle differences in opamp sounds , I know what sounds good to me and what sounds bad , and I can generally tell the differance between Fet and BJT opamp .....

For me a well designed and layed out circuit makes way more differance than the opamp used , maybe that is why i find it hard to tell the differance ......

I would suggest as one option is trying one opamp in one ear and another opamp on the other ear and see what one you like best and go through the opamps like that .......

what opamps are you going to try ?
Old 6th January 2011
  #10
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Quote:
Originally Posted by Minion View Post
Well Personally , I don"t have a great ear for subtle differences in opamp sounds , I know what sounds good to me and what sounds bad , and I can generally tell the differance between Fet and BJT opamp .....

For me a well designed and layed out circuit makes way more differance than the opamp used , maybe that is why i find it hard to tell the differance ......

I would suggest as one option is trying one opamp in one ear and another opamp on the other ear and see what one you like best and go through the opamps like that .......

what opamps are you going to try ?
at the moment, I'm not sure the console its working correctly. I think one channel is eqing slighlty different that the other, so i best fix that before changing op-amps. Its been recapped so hmmmm. Maybe one of the pots is bit weird.

I have quite a few op-amps to try I'll post a list when I'm back in the same building as them!
Old 6th January 2011
  #11
Gear Addict
 

Quote:
Originally Posted by oxide54 View Post
at the moment, I'm not sure the console its working correctly. I think one channel is eqing slighlty different that the other, so i best fix that before changing op-amps. Its been recapped so hmmmm. Maybe one of the pots is bit weird.
Could be bad resistors (shifted values). Best is to replace all with 1% tolerance parts, but this can prove time consuming. So, measure the ones in the "good" channel and compare with the "bad" then replace as needed. Use TrueRTA software or similar to make sure the spectrum is flat with the pots at center position. It'll also show you how the EQ shapes the sound.
Old 6th January 2011
  #12
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oh okay,

thanks mate, I was thinking of replacing with metal films anyway. I'll give that a go.!
Old 8th January 2011
  #13
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Op Amp Headphone amp.

What make & impedance phones are you trying to drive? A 2 chip 5532 is not going to have enough output to drive 32 ohm, 300 & 600 ohm phones.

I design & make H.P. amps.
Old 8th January 2011
  #14
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audio technica - MTH-50

Audio-Technica - Products - Headphones - Monitor - ATH-M50

any suggestions welcomed bill!

i thought I read 32ohm, but i just checked and their 38ohm apparently
Old 8th January 2011
  #15
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Minion's Avatar
 

Quote:
Originally Posted by Bill Wilson View Post
What make & impedance phones are you trying to drive? A 2 chip 5532 is not going to have enough output to drive 32 ohm, 300 & 600 ohm phones.

I design & make H.P. amps.
NE5532 has no problems driving 600ohm loads ......
Old 8th January 2011
  #16
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Quote:
Originally Posted by Minion View Post
NE5532 has no problems driving 600ohm loads ......
personally i didn't think it would have a problem. the original headphone amp this is replacing was ne5532.
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