generic op-amp, TL082, feasibility for "Cmoy" style

[elmer_dudd]

Hallo all,
i recently got a decent deal on an ipod nano since apple has redesigned them, and although i was very surprised with the quality and clarity of output, I wasn't very impressed with the volume that was readily available-- mostly because i have to ride public transportation, so i have to max out the volume if it's too crowded or noisy. so I looked up a diy pocket amp and found a bunch of pages on cmoy's pocket amp and was rather impressed with the simple design.
i was so impressed that i ran out to radioshack and spent a slew on project parts to crank up my investment on the ipod!
i even found some opamps there-- i picked up a couple of each : 741 single channel, TL082 dual bifet, LM324 quad channel, and LM386 single channel. their prices weren't great, but i'm more or less of an experimental type of person so i got a bunch. i'm actually rather clumbsy too -- I blew out one of the lm324's anyway, so it was a good idea for education's sake.

(i reversed the input voltages by accident and the chip went up in smoke

wah wah)
so anyway, I got the other LM324 to "work", and even though it makes the output a bit clearer, it actually runs the volume down by almost half, only to my frustration.
the TL082 on the other hand, actually *does* add a bit of volume and punch but it sounds way too "treble-ey" to me, and it distorts easily also. (the total volume output doesn't sound that much louder than without the amp)
(i forgot to mention that i wired it up electrically verbatim using tangent's modifications to cmoy's schematic, same resistor/cap values) found under the tutorial here:
http://tangentsoft.net/audio/
so anyway, i'm just wondering if anyone else hass had as disapointing results as I have on their first amp... I'm kinda upset because i went and spent so much money at radiocrap and wound up with sub-par results)
I'm using their .1uf polyster caps on the input lines, and i'm wondering if they are possibly crappy caps to use--I was using crappier ceramic caps before, and it sounded even worse (even more distortion at low levels), so i'm assuming that the input caps make a big difference.

the other thing that might cause this effect, is that i'm running it all off a breadboard with full length leads on all the components.

so i dunno.. through pure conjecture... maybe... by some freaky scientific occurance, the vibrations from the line signals are being resonated on the breadboard and through all of the leads, and are thusly being amplified by the tl082. sounds pretty screwey, i know... but these are the best explanations i can come up with right now

maybe the tl082 is just worse than an ipod's built-in amplifications...
btw, here is tangent's quick review on op amps:
http://tangentsoft.net/audio/opamps.html
is there any way to tweak the tone by adding an rc circuit on the output somewhere?
i figured that my audio source sounds good and full anyway, a little oomph from a generic chip couldn't *hurt* the sound as much as this tl082 seems to be doing.
and i'm just not sure at all why the lm324 is "halving" the source's total output..
i've yet to try these setups on other input sources...

 

[ex0du5]

Myself I don't know yet as I'm getting the parts for my first cmoy tomorrow

I will also be building it on a breadboard so I will give you feedback...I bought the best headphone jacks available to me and the appropriate resistors/caps (the bloody input caps cost 3$ a piece -_-, .470uF though). I'll post my feedback probably tomorrow night.

I am somewhat concerned about your listening volume levels though....are you listening to maxed out ibuds? even 80% ibuds could damage your ears...at 100% your ears would be ringing quite a bit after you take them off. I'd suggest invensting in a pair of closed cans or IEMs if possible.

Anyhoo, good luck with your project...I myself cant wait to get started tomorrow ;D

 

[elmer_dudd]

ooh! i knew i left out something,
i havn't even unpacked those earbuds!! can't stand them, never could stand them even on my original gameboy

(edited: ) i was originally using some crappy foam type headphones, but picked up a new set from the audio/video store: i'm using sony mdr-150's... they feel pretty nice on my ears, and they are closed design (perfect to keep my corny music tastes my own secret when i've gotta share a seat next to another cranky guy next to me in the morning

)... only paid $20 retail so maybe they are kinda cheezy and can't handle the amped trebles..

(another edit

after listening to it again, it almost sounds like it's clipping on midrange.. maybe i'm just being too economical here to have as much ambition as i'd like with this project!

thanks for the feedback, looking forward to hearing your experiences

 

[Filburt]

It seems probable to me that the TL082 drives low impedance, reactive loads worse than the internal amp of your nano (which is designed to handle those). I suspect you're going to need to make some sort of internet order to get a suitable op-amp.

Secondly, you don't mean you have 470uF caps on your actual input, right? Rather, they're rail caps (on the power supply section)? If you followed tangent's schematic and setup, then the caps you'd have at the input would probably be 0.1uF.

 

[ATAT]

Dear lord, get some good opamps, STAT! those opamps you picked cant supply teh current those headphones want / need (well.. its a MDR-150, but you get the idea)

not all opamps are created equal, esp important are the voltage and current ratings. For low impedance 'phones, the important value is current, larger the better. For high imp 'phones, the important one is voltage (and rail-to-rail). basically, voltage determines volume and current determins clipping.

So go to mouser electronics, grab an OPA2107, you'll thank me later.

^^^ (filburt, he said .470, not 470 =) )

 

[elmer_dudd]

i was afraid i might have to wait for an order to come in!! which sucks, because... well i hate twiddling my thumbs

i'm sure it's not the headphones now (as bas as i thought it was) because i can crank my pc fairly loud and they seem to handle it o.k.
thanks for the tips you guys!

 

[ATAT]

If you want it to work with what you have, try an A47 type setup with what you have.. that should up the current output and give you something listenable. (maybe, if the ICs arnt pure garbage)

http://headwize.com/projects/showfil...=opamp_prj.htm

Figure 12a.

Should double your current output

 

[tangent]

Quote:

Originally Posted by elmer_dudd maybe the tl082 is just worse than an ipod's built-in amplifications...

Bingo. Not only is the 082 one of the worst "audio" op-amps you can choose for driving headphones directly, you're competing with a very respectable audio output stage in the iPod. You can do a better, but you can also do a whole lot worse.

 

[dsavitsk]

Quote:

Originally Posted by elmer_dudd I wasn't very impressed with the volume that was readily available-- mostly because i have to ride public transportation, so i have to max out the volume if it's too crowded or noisy.

Before worrying about opamps, I'd pick up same noise blocking headphones (Ety4p or something) so you can listen at reasonable levels and don't end up damaging your hearing. Listening that loud is a bad idea.

 

[Filburt]

Quote:

Originally Posted by ATAT ^^^ (filburt, he said .470, not 470 =) )

Ah, okay. Just misread

Anyhow, the TL082 drives low impedance reactive loads like headphones very very poorly, especially if you don't have gobs of supply voltage and if the headphones require even a semblance of significant drive current . Additionally, it can oscillate without bypassing/decoupling at the rails when driving this sort of load. I wouldn't use this op-amp for audio, personally.

 

[elmer_dudd]

so is there anything the tl082 is good for? would using it as a first stage amp wreck the total output down the line?
a big part of what i wanted was to save the battery life, so ideally, i'd like to listen comfortably with the source volume at less than halfway-- whereas, right now it's at about 2/3 or 3/4 of the max volume to listen comfortably.. which is not bad, really... i just don't like the idea of having to remember to charge the ipod every night. (i can see the battery level dropping a pixel or two more when i crank up the volume so the battery life kinda concerns me)

so i've been cruising mouser and cant seem to find the opa134, but found a whole bunch of others manunfactured by texas instruments. are there even better options than the opa134's? should i go 2-channel or 4? how much is too much (money and power) on these higher quality amps? am i going to blow my eardrums out if i use a quad channel and power it on at max by accident?
on the design side, i can see how it makes sense to use 2 bi-channels as opposed to one quad channel, unless they both manage to blow out due to a power problem... but it all seems to be 6, 1/2 dozen, and the other to me at this point.
are there any standard/hi-quality selections at mouser? when i searched their site for opamps, they all seem to look the same to me, although they do have a filter devoted solely to headphone amps
let's see if this works:
http://www.mouser.com/search/Refine.aspx?Ne=1447464+254016+688267+1524181&N=132 3038+4294783769+1524181+0&Msb=0&Mkw=op+amp&Ns=P_Br and|0||P_SField&Ntx=mode%20matchall&Ntk=Mouser_Wil dcards&Ntt=*op*+*amp*

(oops there are only three at the top that you can buy in single quantities)
are general purpose opamps ok to use?

 

[Filburt]

OPA134 is a single channel op-amp. You want the OPA2134 or 2132. You could also try the OPA2107 which IMHO sounds better.

The TL082 is not very useful for audio, pretty much entirely, except maybe for something like a DC servo which wouldn't be in the signal path. Sorry :/

This is perhaps a good lesson in how impatience can lead to expensive and unsatisfying result

 

[tangent]

Quote:

Originally Posted by elmer_dudd so is there anything the tl082 is good for?

Sure, it's good for all kinds of general line stage applications. Filtration, impedance conversion, undemanding output stages....lots of things.

It takes a special sort of chip to be a good headphone driver.

Quote:

a big part of what i wanted was to save the battery life, so ideally, i'd like to listen comfortably with the source volume at less than halfway-- whereas, right now it's at about 2/3 or 3/4 of the max volume to listen comfortably..

First off, probably around 90% of the battery power in an iPod goes to running the screen, memory and disk drive, not to driving the headphones. Second, even if you did get a significant gain in battery life in the iPod, you'd give it up and more in the headphone amp, because it's going to be less efficient.

Increased battery life is always the wrong reason to add a headphone amp.

Quote:

i've been cruising mouser and cant seem to find the opa134

Generally speaking, you don't buy analog ICs from Mouser. They have some, but Digi-Key and Newark do much better at this. Mouser does better at other things. No one distributor is excellent at everything.

Quote:

are there even better options than the opa134's?

Sigh...I have a large article on the topic, and it ignores at least half of the chips that are popular for this. Do some searches...this topic comes up again and again and again...

 

[elmer_dudd]

tangent-- it's more of an all around upgrade i was looking to make on the ipod.. the nano uses flash mem for storage, so luckily there's no disk access (pure serendipidy, since i hadn't even realized that the larger ipods used disks at the time of purchase)
i did browse through your article, but there's just so much info on so many op-amps that it was difficult for me to absorb.. and i suppose my problem with impatience is fairly evident at this point

so let's say that i use the tl082 as a low level amp, and use a opa2134/2 or opa2107 as the headphone driver-- is there any advantage to this setup rather than simply using an opa2134/2107 alone?
is there any reason why the 2107 is $12.something as opposed to the 2132's $5.something? surely, it must be at least 2x as better as the opa2132!! right? (edited for accuracy)

i better get back to work
add: i guess what i'm getting from this is that i've gotta tweak the amps and setup to "taste" for the most part

 

[elmer_dudd]

another dumb question:
does anybody know if there is a set of op amps that will interchange at will?
ie. does the family of OPA2xxx dual channel amps interchange without circuitry rewiring?