What i build when i'm not doing power supplies...

[Th3_uN1Qu3]

I pulled out a LM1877N amplifier IC from an ISA-based ESS soundcard that i got in a box of freebies. After taking a look at the datasheet and noting the high maximum voltage (24 volts), and the fact that it can also be used with a split supply, i immediately thought "this will make a really nice headphone amp". The datasheet shows 16 vpp output with a 24v power supply - that's 1W @ 32 ohms, just about perfect.

I really needed an amp because my laptop runs out of signal headroom when applying proper EQ for my headphones, so there i went. I was too lazy to cut a PCB up again, so i thought i'd do a full sized 120x80mm board. So the board didn't end up empty, i designed it with quite a bit of space for the large components like bridge rectifier and caps, so i could use larger ones if i felt like it. Since that wasn't enough by itself, i dropped a 7812 and a 7912 on there as well. This proved a good idea as i want to use a 12-0-12 AC transformer to power the thing, which rectified would be too high for the IC if left unregulated.

I did a few changes to the schematic in the datasheet, which i'll let you know of in a bit. What i did is make the -3dB point of the highpass filters in the input and feedback sections very low, so the amp does not modify sound in any way, and lower the gain to 10 (which btw is the minimum gain guaranteed stable by the datasheet).

I found a project box i'd bought a while back, complete with screw standoffs. It fit the 120x80mm board like a glove! So i adjusted the PCB layout to suit the standoffs, printed it, transferred it, and started building it.

For testing i did not fit the regulators (i don't actually have them on hand right now) and used a 9v-0-9v transformer instead. When unloaded, this provided a little over +/-13v, so i thought the IC might blow up. Initial testing was thus with no headphones connected and no signal. Nothing weird appeared on the scope and the IC didn't smoke, so i plugged my headphones in. Just a little background hiss. Now, i still had no idea whether the thing actually worked, since it took quite a bit of work with the heat gun to get it out of the soundcard. I plugged in my SE w595 and fired up the walkman player. Hey... i got sound!

FYI: It's always a good idea to use a battery powered signal source when you're first testing some audio gear, laptops in particular can give weird glitches.

Initial impression? I'll have to be careful not to blow my headphones.. It's loud. I quickly started to notice distortion - but checking with my oscilloscope proved that the cellphone wasn't even able to drive it at full level and there was no clipping - the distortion was coming from the headphones because the bass was cranked up too high. The IC runs moderately hot, i'd say around 60C. This is perfectly safe.

I'll come up with some measurements tomorrow, but so far i'm very happy with it. Once i get it fitted in the box i'm sure it'll serve me well for years to come. Here's some preliminary pics.

[c_hegge]

Re: What i build when i'm not doing power supplies...

You used Jamicon capacitors?

Looks good otherwise

[lti]

Re: What i build when i'm not doing power supplies...

Those caps will work fine.

I was afraid to blow my headphones with a TDA2822M powered by 12V. There aren't many headphones that I can afford that are rated for more than 100mW. That might be why my Cyber Acoustics MMS-20 amp blows headphones.

I tried building a CMoy headphone amp using an LM833 op-amp, and it had weak bass and +0.4V DC on the output no matter how balanced or unbalanced the split power supply was.

[Th3_uN1Qu3]

Re: What i build when i'm not doing power supplies...

You used Jamicon capacitors?

I actually pulled 'em from another transistor-based headphone amp i built a while back, which i later scavenged for parts... This isn't a SMPS you know. Jamicon general purpose capacitors are decent for, well, general purpose applications. The caps in the audio signal (input coupling and feedback) are Rubycons.

Anyway, it looks like i will need those regs after all. Sustained low bass, even at reasonable levels, will cause audible mains hum. Sounds like that small transformer i used isn't up to the task.

I was afraid to blow my headphones with a TDA2822M powered by 12V. There aren't many headphones that I can afford that are rated for more than 100mW.

Working off the top of my head, the TDA2822M will deliver around 400mW in 32 ohms when fed with 12v. This is still enough to blow headphones with small drivers. I never really liked how the 2822 sounded tho, i built both stereo and bridge circuits myself, not skimping on caps like the Chinese do, and the highs always sounded bad.

Next time you see an ISA soundcard check it out. A lot of them have the TEA2025 and clones (which is another pretty low-end chip), but you will occasionally find better ones. There's another TDA (can't remember the exact model) encountered on soundcards that is capable of 4W/ch. That will power a pair of small speakers quite nicely.

Maybe you should get better headphones. I have a pair of those i usually use when i'm making beats. I picked them up for like $5 a couple years ago because they had a broken cable and broken support arm on one of the cans. Superglue ftw... They are a bit midrange shouty (they emphasize freqs around 2kHz) and somewhat light on bass, but they're not peaky, they can be EQ'd flat, and they sit really well on my head. I used a good quality microphone capsule, TrueRTA and a 31-band EQ VST plugin to calibrate them flat. Everything i've mixed on them since translated good everywhere else.

I want to upgrade to a cleaner sounding pair that does not need so much EQ, but i want something in the $100-$150 range so i can get something sturdy that'll be good for a few years. Anyway that's just on my wishlist coz the Altecs still work, and i got other things i'd rather spend my money on right now.

I tried building a CMoy headphone amp using an LM833 op-amp, and it had weak bass and +0.4V DC on the output no matter how balanced or unbalanced the split power supply was.

The DC offset sounds like a wiring mistake, but regardless of the 500mW power rating, the LM833 is still an opamp. It would need an output buffer to properly drive 32 ohm headphones. It'll probably do fine on 300 ohm ones which is what i believe it's been designed for - but how many of you have any of those, really? Speaking of which, i just checked the DC offset on my amp - it's between -6.3 and -10.3mV, depending on the headphones i use. Good enough for me.

[lti]

Re: What i build when i'm not doing power supplies...

Working off the top of my head, the TDA2822M will deliver around 400mW in 32 ohms when fed with 12v. This is still enough to blow headphones with small drivers. I never really liked how the 2822 sounded tho, i built both stereo and bridge circuits myself, not skimping on caps like the Chinese do, and the highs always sounded bad.

You should hear an APA3541. Samsung used that IC to power the headphone jack on their optical drives. I modified the circuit so it matches the application circuit and it didn't sound any better.

There's another TDA (can't remember the exact model) encountered on soundcards that is capable of 4W/ch. That will power a pair of small speakers quite nicely.

Is it the TDA1517? I have a pair of Harman Kardon HK-206 computer speakers (the ones that use the weird curved enclosure) that uses the TDA1517P, and every electrolytic cap except for four 0.47uF caps was bad. The output coupling caps were bulging and leaking out of both ends. If I remember correctly, the only caps I could find with good enough specs to replace the originals were Panasonic FMs or motherboard grade caps.

There is also the TDA1515BQ, which my Compaq has on its motherboard. That is the only amp I have that doesn't throw a fit when powering a pair of Peerless W3-LK76-PBK drivers. Their impedance seems to be slightly lower than four ohms, and they make any amp that is designed to drive 4Ω speakers clip or overheat. The TDA1515BQ is a car audio amp and can drive 2Ω speakers.

Maybe you should get better headphones.

I should look for better headphones, but I don't have much money to spend. The $10 Philips headphones I currently use are okay, but there isn't much bass. I didn't realize how little bass there was until I tried to use them without the Cyber Acoustics amp. That amp has a slight bass boost.

The DC offset sounds like a wiring mistake, but regardless of the 500mW power rating, the LM833 is still an opamp. It would need an output buffer to properly drive 32 ohm headphones. It'll probably do fine on 300 ohm ones which is what i believe it's been designed for - but how many of you have any of those, really?

Those were the cheapest dual op-amps I could find. How would I add an output buffer?

[Agent24]

Re: What i build when i'm not doing power supplies...

Looks nice, how did you make the board?

[Th3_uN1Qu3]

Re: What i build when i'm not doing power supplies...

You should hear an APA3541. Samsung used that IC to power the headphone jack on their optical drives.

I did something like that too on several cdrom drive boards with several different chips... All sounded bad.

Is it the TDA1517?

Yup, that's the one.

Those were the cheapest dual op-amps I could find. How would I add an output buffer?

A few transistors and a biasing network. Like the last circuit here: http://ludens.cl/Electron/audioamps/AudioAmps.html

Looks nice, how did you make the board?

Toner transfer. And some help from the OHP marker because i didn't iron it very well (i'd grown used to doing very small boards), so the toner didn't stick in a few places. I'll show the solder side too once i'm done with it. PCB layout with parts values is attached, it's done in ExpressPCB like pretty much everything else i make. It's not the best PCB software but it's really trivial to use and i can do stuff quickly. Btw, the regulators are intended to be mounted on the solder side. And check out the cutoff frequency of the highpass filters in the input and feedback...

[Agent24]

Re: What i build when i'm not doing power supplies...

My personal preference is KiCad, I also use toner-transfer (with a laminator).

I thought from the colour of the etched-away parts you'd done it on a CNC mill but I guess that's just the brand\type of board you used.

[Th3_uN1Qu3]

Re: What i build when i'm not doing power supplies...

Heh, i wish i had a CNC... The board i used for this is some sort of glass-based material, compared to the cardboard-based ones it's a royal pain to cut.

Anyway, in with the regs. Can you guess what happens now? Well... they drop out of regulation because the 12-0-12 transformer is too small (200mA). I also broke my last good drill bit (lasted a good few months tho), and i need some resistors for the LM339 PSU protection board i am building, so it's time to put my shoes on and head for the store.

[Agent24]

Re: What i build when i'm not doing power supplies...

CNC is alright I guess but I never liked it much for some reason. Probably something to do with the fact that when I tried it I needed to spend about an hour clearing trace pieces of copper from between the tracks to prevent shorts.

So far my laminator has produced pretty much perfect results for single-sided boards so I'm happy with that, although it does depend a lot on the laser printer to produce a good image. Ground planes are the biggest problem for most printers of course.

The UV exposure method looks like a much better way for double-sided boards though, so I might look into that sometime.

Don't know what you've got but for drilling I've got a Proxxon tool and drill press stand. Works infinitely better than the old pin vice I used to use by hand. If you can afford one, get one, I reckon it's worth it for the amount of headaches you won't get, and you'll save money on drill bits!

Also good for other things, like opening Apple laptop chargers...

[momaka]

Re: What i build when i'm not doing power supplies...

Initial impression? I'll have to be careful not to blow my headphones.. It's loud. I quickly started to notice distortion - but checking with my oscilloscope proved that the cellphone wasn't even able to drive it at full level and there was no clipping - the distortion was coming from the headphones because the bass was cranked up too high.

I guess I'm not the only one that abuses my headphones (and my ears) in this way.
I have a cheap pair of Sony MDR-023. They came with a Sony Walkman (the cassette player, that is) many ages ago. Still work well and sound pretty decent. I can push quite a bit of bass through them before they start distorting.

There's another TDA (can't remember the exact model) encountered on soundcards that is capable of 4W/ch. That will power a pair of small speakers quite nicely.

TDA1517, like lti said. According to the data sheet, it's actually capable of 6W per channel.
I have an old Pentium-based AT motherboard from a Compaq that has this amp mounted on the board on a heatsink. The audio chip is a ESS AudioDrive. Not sure how it sounds, since I never tried it.
I also have a Yamaha DS-XG -based PCI sound card (YMF-724??) that may have this amp, but I'm not sure since I checked so long ago. Anyways, the output on that sound card is so loud that I can push my MDR-023's in distortion at less than 1/4 of the full volume (half Master, half Wave). The sound quality on that sound card is great as well with very clear high tones and bass. I don't even need to use any EQ's to get good bass out of my headphones.
Wish I had another one like that.

I like your project, by the way. Very nice and clean. Maybe if you build another one, you can add analog bass and treble controls? The cheap Saturn speakers I use with my computer have that, and I can get them to crank quite a bit of bass through my headphones.

[lti]

Re: What i build when i'm not doing power supplies...

I haven't made a circuit board for any of my projects. I just use Radio Shack prototyping boards.

I have an old Pentium-based AT motherboard from a Compaq that has this amp mounted on the board on a heatsink. The audio chip is a ESS AudioDrive. Not sure how it sounds, since I never tried it.

My Compaq has an ES1869 audio chip, and it sounds terrible using the default audio settings. To get good sound out of it, you have to open the volume control, click on the Advanced button, and disable the "spatializer." The spatializer just makes certain midrange frequencies extremely loud and makes the bass distort. On larger speakers, you will hear the same noises that a blown woofer makes.

The Presario 2200 and 2400 series computers use the TDA1515BQ amplifier, but Compaq messed up the circuit design so you have to turn all of the volume sliders in Windows all the way up and put your ear against the speakers to hear anything. I fixed that on my motherboard by cutting the trace between pins 2 and 3 of the IC and placing 100KΩ resistors between pins 12 and 3 and pins 2 and 3.

Strangely, pins 2 and 12 (the two inputs) have to be connected together for sound to come out of both speakers, but I still get stereo sound. If the inputs are not tied together, both channels will be mixed together and played from the left channel output. The right channel will be completely silent. Also, the amp distorts easily and has a bass boost because of other flaws in the circuit.

I might make some passive speakers for that computer using the Peerless drivers I mentioned above. They are useless for any other application due to their low impedance. They don't sound very good either and have very strong magnets.

[Th3_uN1Qu3]

Re: What i build when i'm not doing power supplies...

I have an old Pentium-based AT motherboard from a Compaq that has this amp mounted on the board on a heatsink. The audio chip is a ESS AudioDrive. Not sure how it sounds, since I never tried it.

lti answered that first, i'll second him - ESS sound chips are pretty awful. The ESS1869 in my DOS gaming laptop sounds pretty good tho... I guess circuit design plays a big role.

I like your project, by the way. Very nice and clean.

It'll be very nice and clean when i'll have it in the box... i need to buy some more drill bits of various sizes to accomplish that. I'll post more pics then. Btw, i bought a 12-0-12 400mA transformer which works mighty fine with it.

Maybe if you build another one, you can add analog bass and treble controls?

It did cross my mind tbh, but since i only use it for monitoring i'll have a 31-band EQ plugin set up to make the response flat on my headphones. Tone controls would just be an approximation.

[shovenose]

Re: What i build when i'm not doing power supplies...

That's a really cool project. Now I want to create something cool too. Lol.

[Agent24]

Re: What i build when i'm not doing power supplies...

There's many designs around of interesting things to build... just pick something and start! Good idea is something that's of practical value to you, like the amplifier here. Then you have a reason to build it and you'll use it for more than 5 minutes afterwards.

[kc8adu]

Re: What i build when i'm not doing power supplies...

reminds me i need to post my 4-1000 2 holer i am building.

[shovenose]

Re: What i build when i'm not doing power supplies...

There's many designs around of interesting things to build... just pick something and start! Good idea is something that's of practical value to you, like the amplifier here. Then you have a reason to build it and you'll use it for more than 5 minutes afterwards.

OK. I will try (once I moved cuz all my stuff is in boxes, etc), I have plenty of old sound cards, etc. around.
Maybe be useful to make my phone louder Now that I've rooted it and install CyanogenMod7 on it I've got a cool equalizer

Also thinking of a solar charger for my phone. Even more useful since all I ever do is whine about that I need some power...and it's easier than making a sound card

@The_unique: got any more cool stuff you made?

[Th3_uN1Qu3]

Re: What i build when i'm not doing power supplies...

In case you were wondering, here's the end result. Just stumbled upon it again today and thought what the heck, let's finish the job. And this is how it turned out. Considering everything was done only by eye, i think it looks alright.

[Agent24]

Re: What i build when i'm not doing power supplies...

Looks good. I like the transformer out the back, kinda makes it look like a valve design. I hope you've got some kind of strain relief on the mains lead though.

[Th3_uN1Qu3]

Re: What i build when i'm not doing power supplies...

I hope you've got some kind of strain relief on the mains lead though.

First i need a proper mains lead... The current one is recovered from an old hair drier, it's white and ugly.

There's also a bit of hum in the background, a tad more than i recall from last time i used it. I'll check that out sometime... it's not annoying unless whatever i'm listening to is REALLY quiet.