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Old 17th April 2010, 12:09 AM   #1
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Lightbulb Small and portable headphone amp Crisis



Hi All!

Been a While since I got into portable audio... but at this point I'm Starting to panic since I don't have the right "sound"...

I bought a new pair of earphones and found out that my Zen mp3 player doesn't drive them "good" (reference: Skull Candy Ink'D earphones 16ohm in ear).

my first idea was to make an headphone amp... but at about the 3rd time I took the BUS and Subway to work.. I noticed I needed something more...

so: (the actual interest on this post)

I want:
-"real" headphone amp (capable of driving 16ohm)
- cross-feed (ESP like) to have a 'better' stereo image
- parametric EQ (since I cant seem to find the sweet spot and can eventually change headphones)
- active noise cancellation (feeling so lucky :P )

Note: This is not massive-hi-audio-quality "system" and it uses SMD components for 'size-sake' issues. the objective of the unit is to minimize the noises in the bus/train/subway and share some point's ans ideas. maybe there is little to approve or reject, but I'm here to discuss and learn and share

(Continuing
obviously... it all needs to be neat and small and comfy for every day use... so I tough... My ZEN Clear Case would be great! (since I don't like it for my player)

and for powering an ready available BL-5C Lithium Battery From Nokia! (keep reading, now it gets interesting):
Since a single supply of 3.6V is just about useless... I have to "boost" the voltage... so, at this point my friend MAX682 will come to place!
now you ask: "why 5V? still useless!" You are Right! but this is the first step... the next one will be a newest friend called MAX743 that will provide me the so needed +-12V for the headroom!

and on this story I'm stuck about here since the MAX743 samples are not with me yet... and I need to test the "thing" before moving on.

(one of my problems is the actual current consumption of all the circuits, since the step-up IC's pull about to much amps... EG: 5V in to 12Vout, 11,6mA out equals 39.4mA on the 5V input... imagine that with lots of mAmps on the +\-12V )

so, I'm starting this post to overcome some "details" on the further testing...

-the parametric EQ will be the last block to develop in the system.
-the noise cancellation will be the most difficult block to overcome
-the output block, feed on steroids and testosterone :P is a must have!
-and the cross-feed (ESP Style or others, I'm open for new ideas! please share).

for the output block I found some information on the BUF634 and practically feel in love... so, unless the current consumption is to high or someone shows me another "steroid based" way to drive my earphones... I'm gonna stick to it.

(on this matter... I tried an NE5532 parallel output (ESP Style) and didn't have a good result... I'm gonna test 'the thing' again and evaluate, since a BUF634 + OPA2134 stage... may be hungry for power and drain out my small 850mAh 3.6V Li-on cell)

the active noise cancellation is based on the headwize project (reference: HeadWize - Project: Build These Noise-Canceling Headphones by Jules Ryckebusch) updated to fit into this idea... based on an MAX4466 mic preamp IC and an DS1669s Digital pot (actually two. for stereo)

the parametric EQ is based on another forum (reference: 5-Band Fully Parametric EQ) crossed with the parametric EQ from ESP (reference: Parametric and Sub-Woofer Equaliser)

finally... I real the post on headWize of the Cmoy headphone amp and the "Designing A Pocket Equalizer For Headphone Listening" (reference: HeadWize - Project: Designing A Pocket Equalizer For Headphone Listening (A HeadWize Design Series Paper)) and I think that this article explains a few interesting things...

for completeness... the battery can be recharged with and MAX1555

by tomorrow I'll test some blocks and Ideas and post the results.

At this time... I Do have a plan B for the power unit. but I wont talk about it now since it is getting late (GMT Time zone ), its a big post by now... and before testing, it's not reasonable to left out the symmetrical power supply with MAX743.

I hope to have some kind of reply to this idea and hope to share some good things with others!

final note: all layouts, tests, ideas, programs used, and on and on, will be noted here! I'll even give away all the board layouts (Altium based - I hope to manage the footprints [but that is another issue :P] and share my knowledge on soldering SMD components.

Cya all in about 10H :P
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Old 18th April 2010, 04:31 PM   #2
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Hi again!
since there were no replies... i just continued the project silently...

I'm needing more than one block on this project... I'm testing the lithium batteries chargers and by now I found out that:

MAX1811 sucks!
MAX1555 Rocks!

they are (both) not hard to use but the "suker" heats-up to d*mn much and fails!

MAX1555 controls the output current correctly, so: if is is heating up... it lowers the output current accordingly. (just like the datasheet says)

at this point I can say that all my "single lithium cell units" are gonna have a pretty controlled battery charger
(instead of the massive overkill from "fly electric" 2A lithium charger (it works great btw... but it is huge for some of my units...)

I have a few lithium batteries lying around (taken from old cell-phones, laptops and PMP's)

note:
doing the burn-in on the MAX1555 as I type this post... did not fail yet... on both "USB" or "DC" inputs. it is hot as hell! (more than 100șC but within ratings from the datasheet)
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Old 18th April 2010, 09:07 PM   #3
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previously when I said that this was not a "massive-hi-audio-quality 'system'" I meant that:
I can't use premium op-amps because some of them are a bit power hungry (quiescent current and all...) I know that a low power op-amp will have a lower quality on sound... but I'll have to deal with that to have a small, usable, portable unit.

About to talk to myself again but... I Don't Care, here it goes:

I gave another try to the output section from ESP (Reference: Project 109) and actually liked it!

took some time to test is all the way and come up with some results:

the current consumption of the IC (NE5532) was about 7mA @+/-5V (one channel, 16ohm earphone) at a normal listening level.

tried the thing out with more voltage and got 8mA and about the same sound on the output (more volts could get louder but I was pretty much on my "normal" SPL limit) so at this time, I might be looking at a +5/-5V supply voltage for my unit without the MAX743.

this will make the part count lower and probably be enough for my 16ohm headphones.

I've also tested the "real ground" and "virtual ground" and noticed that, real ground sounds better... so, I'll use the MAX682 for the +5V and an inverter (TPS60403) for the negative 5V.

I'm looking forward to make more tests and get back to the forum to post the results for myself to look at.

btw: cross-feed network to correct the "super stereo effect"... does anyone want to share "the right circuit" for me to look at? is no one shows a better one... I'll Stick to ESP Cross-feed from project 109.
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Old 23rd April 2010, 10:13 PM   #4
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this tread has gone cold!

no one seems to want to share anything!

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Old 24th April 2010, 10:26 AM   #5
Gordy is offline Gordy  United Kingdom
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Hello firefart_1st,

I think you have put much research into this project and I hope it goes well for you.

However my feeling is that most people here want to build home based equipment not portable, so they have no need for 'small and compact', and they can use a mains power supply. SMD is very difficult for many. Also, many do not want paramentic EQ, etc., and when you say "This is not massive-hi-audio-quality" some people will think "Good luck, but it is not for me".

Perhaps your target audience is asleep here and this bump might help? If not then maybe the DIY section at head-fi.org may produce better results for you?

Either way, I wish you success.

G.
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Old 24th April 2010, 11:26 AM   #6
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G, thanks for listening.

the SMT is the minimal detail on the hole unit... most of the parts have either PDIP and SOIC packages.

the parametric EQ may be "the worst thing in audio from all times!" but its just what I need since:

a while back I've had an ear disease and now I have a HUGE difference from the left ear to my right ear. I will never be able to enjoy a "of the shelf" equipment since I need "special" equalization for my left ear...

after the disease got cured I noticed two things:

I have a white/pink noise generator built-in my left ear (white or pink depends on many factors...)

and I have a low sensibility to high frequencies and a high sensitivity to the low ones.

I've been testing with an waveform generator and a piezoelectric thingy (clipped to my ear) and started from 1kHz to 20kHz (low volume) and the left ear "cuts" at 6kHz while the right one only fades out at 16kHz or more...

on another hand... if you don't want one of the parts of the unit... you can leave it out and do the ones you need. I often leave out the "pcb made from others" and make it myself from the (modified) schematic of the thing. its the only way to get the perfect match of pcb to available parts and all.

SMT are not that difficult to solder... there are packages that are practically impossible at ("normal") home. some need an hot-air gun to solder (or an oven like in my work)
the thing is to try... SOT23 ( 3 5 or 6 pins) are plain easy... SOIC is either easy... SSOP are impossible... just need some patience and even the SSOP are possible.

just try an FT232RL and you will see. (I tried and succeeded with home-made PCB etching.) (but then... at my work I can afford to blow one unit from time to time... :P)

part from that... I need some information about cross-feed networks and all... and didn't see anyone pointing out one. I've searched for a few...

headwize forum might be the most helpful. (as soon as they start working again) (will look for the head-fi.org and see thanks)

I've always tough that a forum has born to "pass time", share toughs and help out others... I try to do it when ever I can.
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Old 24th April 2010, 12:25 PM   #7
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I think you will have better luck over at headfi.org
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Old 9th May 2010, 08:47 PM   #8
qusp is offline qusp  Australia
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indeed, head-fi for this area is your forum. I cruize this place for home gear or general ideas on more high end circuits (thats not to say they dont like hi-end over there) and headfi 's DIY section for anything specifically portable headphone related.

agreed on SMT, I actually love it and its ethic really appeals, but its not for everyone and many who could most likley do it without a problem, think that they cant. in fact in many cases its easier, because you dont have to be quite as diligent about the order things go in at, because mostly things are fairly low profile and dont get in the way of others as easily. BUT, once on, some things are pretty much impossible to get off unless you have the right gear.

but over there as here, you may not find so many people using buck boost and that sort of kit, this is the place that is famous for using speaker amps to power headphones and 1.4W to power custom IEMs of 28 ohms (guilty as charged) and you know what they are going to tell you?? and I concur?...buy yourself some decent headphones that get you most of the way there. because skullcandy are pretty atrocious mate and you are trying to get blood out of a stone IMO. you could do most things you want, including the special tuning, by getting some custom IEMs that are tuned differently on each ear. these are made for musicians who often have hearing damage.

buf634 is your problem here, there are good quality opamps around that will drive 16R headphones with the right design, what you need is good damping factor, not more current necessarily. dont get me wrong, i'm running 2 stacked plus discrete diamond buffer per channel in my portable amp, but I have more room and much more current at my disposal than you do and I also like to use my HD600 portable sometimes, but in my ibasso D10 I can run with bypassed buffers using OPA211 without any problem.

so you could try something like OPA211, OP1612/11, OPA1641/2 these last 2 in particular are low current, but high quality opamps from the 'soundplus' range, and all I mentioned are unity gain stable, so you could even team them up together and use one as buffer. then you could use an old ipod video and install rockbox on there, (alternative firmware) which gives a pretty decent quality and very adjustable parametric EQ. but get rid of those NE5532 and OPA2134, boring as hell IMO

but most importantly, get yourself some nicer headphones with a good seal, install rockbox on an ipod video and maybe you wont need an amp at all

good luck!!

anyway, theres a little bit of head-fi right there hehe, check me out over there if you like, i'm the one with a bulge in my pocket from my rig
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Old 10th May 2010, 07:41 PM   #9
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Hi qusp,

I agree on almost everything you say... but for clearance:

I have a ZEN mp3 player (32Gb) [sheep enough for my current budget] and I don't intend to switch to any kind of ipod since they are kind of 'costy' for me...

The Zen player is not (by far) capable of driving the headphones decently... even with the detail that the SK are not good... but again, the budget kick in. With another headphones I notice the same lack in "power" from the small player... (in comparison with my laptop [which is the cleanest sound output at the moment...]) so, if I get some really good headphones... I will still lack in "power".

hearing damage: Of course... that's the main issue on building this unit. I can't afford to buy "musician equipment" and I really rather buy expensive headphones, if I get the conditions to run them properly and compensate the hearing issues...

another extra to this "thing" is the active noise cancellation. of course, bypass is included for avoiding "artifacts" in my music.

(and again. SK headphones are perfect for this. they are ready available everywhere, they are in-ear and comfortable, and by tacking of the "brand" diamond on the side, I have a perfect hole to glue the mic on it. (custom headphone cables and sleeving has to come to life...))

on noisy environments I wont be able to enjoy the "perfectness" of expensive headphones, so SK are mostly the "1st choice on combat headphone" of course... later on I might find better ones at a good price, but on that time I would love to have a portable unit to run the headphones with "hear damage enhancement"

(with a bypass switch on the EQ and noise cancellation, I'll have (or might have) a decent headphone amp to get the sound right of the headphones) even if one day I buy a better portable music player I may need the independent EQ.

all in all: thanks for the reply and I'll take a look on your output section advices!

I still haven't decide on the voltage of the hole unit. for the EQ I might be looking for micro-power op-amps, and that limits me to +-5V. if I keep the input gain at control... I might be able to have a clean sound after the EQ and add gain before or on the output stage.

anyhow, the unit will be powered from an BL-5C nokia Batt - 3,6V Li-on 850mAh. (boosted to as least +-5V)

[I can boost the voltage to something like +40V but... I can't pull much more than 5mA from that voltage... and I would kill the Li-on cell in minutes]
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Old 18th May 2010, 12:46 AM   #10
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I think you will have better luck over at headfi.org
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