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

[KeriJane]

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.

Built by "eye" in the finest Scandinavian tradition....

Just like all of my projects!

It looks just fine to me.... even better, it works!


Ahhh.... plans are for the unimaginative

[Agent24]

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

I wonder if the hum comes from having the transformer in close proximity to the rest of the amplifier?

I know this is a problem on valve amplifiers, which is why on some designs they move the transformers on a 45 degree angle.

[Th3_uN1Qu3]

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

I wonder if the hum comes from having the transformer in close proximity to the rest of the amplifier?

Can't be, the transformer is on the rear and is only close to the bridge rectifier and caps, also, touching the transformer brings no change so it's something else. Although the board is using a ground plane i might've created a little ground loop somehow.

I'll check it out in the next few days, i'm really busy right now. Today my girl will be coming over, and tomorrow me and my friend David will be going to a studio to mix a track with one of the major house/dance groups here (yes, we FINALLY get a real collaboration, all the work will start to pay off i guess). So, it's going to be crazy... ie just the way i like it.

[Th3_uN1Qu3]

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

Finally bothered to track down the hum - it was due to a little PCB routing mistake which created a small ground loop on the negative regulator GND pin. A couple jumpers fixed it. Now the amp is nothing short of a straight wire when it's not playing - there is ZERO background noise. With my walkman earbuds there is a tiny bit of hiss from the IC itself, but with headphones it's dead quiet. It sounds incredible.

Screw all that audiophile BS - this IC-based headphone amp will serve me well for years to come.

Anyone want the updated layout, let me know.

[shovenose]

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

Finally bothered to track down the hum - it was due to a little PCB routing mistake which created a small ground loop on the negative regulator GND pin. A couple jumpers fixed it. Now the amp is nothing short of a straight wire when it's not playing - there is ZERO background noise. With my walkman earbuds there is a tiny bit of hiss from the IC itself, but with headphones it's dead quiet. It sounds incredible.

Screw all that audiophile BS - this IC-based headphone amp will serve me well for years to come.

Anyone want the updated layout, let me know.

Yes please
Hey is there any way this could be made battery powered?

[Th3_uN1Qu3]

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

Yes of course - the classic method of using 2 9v batteries in series, with the center point as ground, instead of the 7812 and 7912 regs. But they'll wear out pretty quickly. Besides, the way i did this board, it's pretty big to be pocketable, don'tcha think?

Updated PCB layout attached, in the same ExpressPCB format. The jumper shown near the negative rail capacitors should ideally be placed on the underside, straight from one cap lead to another, use insulated wire.

I also did a little cosmetic upgrade: it now sports a big and shiny volume knob. I'll show that off tomorrow.

[budm]

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

If you DIY audio, look here also:
http://sound.westhost.com/

To help reducing hum:
I would also ground the pot casing and also line the inside bottom of the box with aluminum foil and put plastic sheet on top of the foil so you will not short out the board and ground it to the power supply GND point. Also twisted the transformer wires so the AC magnetic fields will cancel each other out. Did you also use star grounding on the PCB layout?

[Phaihn]

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

i need to build a new control board for my logitech speakers i am picking up radio signals on them the pcb is kinda burned out.

[Agent24]

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

i need to build a new control board for my logitech speakers i am picking up radio signals on them the pcb is kinda burned out.

Did they always do that? If it's a recent thing it's likely some component designed to filter that out has failed.

[Phaihn]

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

Did they always do that? If it's a recent thing it's likely some component designed to filter that out has failed.

not as far as i could remember when i opend the volume control part i found burnt pcb i dont know yet if any parts have failed.

[Th3_uN1Qu3]

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

If you DIY audio, look here also:
http://sound.westhost.com/

I know it.

I would also ground the pot casing and also line the inside bottom of the box with aluminum foil and put plastic sheet on top of the foil so you will not short out the board and ground it to the power supply GND point.

That's not needed in my case. The input doesn't pick up hum at all, it was the negative power supply which had a ground loop.

Did you also use star grounding on the PCB layout?

Not exactly star grounding, i make my boards with a ground plane which covers all unused areas... Makes it easier to etch too. But since this is a single sided board, it's more of a ground mesh than a ground plane... and i managed to create a little loop while i was at it. The 7912 has its tab connected to Vin rather than GND on the 7812, and i left it some extra area for heatsinking (not that it was needed at the consumption of this circuit, but just for good measure), and this area ate into the ground plane and made the path from the GND pin of the reg to the GND of the filter caps a little too long.

i need to build a new control board for my logitech speakers i am picking up radio signals on them the pcb is kinda burned out.

Measure the resistance between input and ground. Then use this calculator to pick a capacitor for a cutoff frequency of 60-100kHz. That will get rid of the radio pickup. This is best done at the pins of the chip amp itself.

[Phaihn]

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

I know it.



That's not needed in my case. The input doesn't pick up hum at all, it was the negative power supply which had a ground loop.



Not exactly star grounding, i make my boards with a ground plane which covers all unused areas... Makes it easier to etch too. But since this is a single sided board, it's more of a ground mesh than a ground plane... and i managed to create a little loop while i was at it. The 7912 has its tab connected to Vin rather than GND on the 7812, and i left it some extra area for heatsinking (not that it was needed at the consumption of this circuit, but just for good measure), and this area ate into the ground plane and made the path from the GND pin of the reg to the GND of the filter caps a little too long.



Measure the resistance between input and ground. Then use this calculator to pick a capacitor for a cutoff frequency of 60-100kHz. That will get rid of the radio pickup. This is best done at the pins of the chip amp itself.

i dont have that tool yet.

[Th3_uN1Qu3]

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

Um, you only need a basic multimeter for those measurements.

Anyway, back to my headphone amp. Threw it on TrueRTA for a test and it seems it lives up to my claims of "being nothing short of a straight wire". It measures ruler flat from 10Hz to 50kHz! Actually, i can't see lower than 10Hz on the graph, it could be flat even lower than that. If you recall from the first pages, the parts are chosen so that the -3dB frequency is 1.6Hz - this thing will happily pump loads of subbass into your 'phones. Admittedly this test was done with 600 ohm load while headphones are usually 32 ohms, but as soon as i find my jack splitter i'll test again with the headphones themselves as load. I see little reason for the frequency response to change with load though, as this is a split supply amp so there's no output coupling capacitors that could limit bass response.

Distortion is also lower than distortion of the laptop soundcard input itself, which does 0.017% at best. I'll try using the DV5 for measurements as i recall its audio input was better. This was at low levels (about 1/3 volume) as to not overload the laptop's input, but with the amount of headroom this thing has, unless you have some really badass DJ headphones, the drivers in the 'phones will distort long before the amp does.

Please note that extended listening at high levels will damage your hearing. Do yourself a favor and turn down the treble when listening loud.

[momaka]

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

Looks great! The new volume knob is very cool .

Gotta look at your schematics one of them days. I have a junk board from a Panasonic TV. It has a Panasonic AN5272 4W amplifier on it. I thinking of building something similar to your amp. Any ideas if AN5272 will be any good for this? The built-in audio in the 939Dual-SATA2 motherboard I found recently sounds pretty good but is very weak. Besides, a good headphone amp is always nice to have since I use headphones pretty much all of the time.

[Th3_uN1Qu3]

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

I just used the appnote of the LM1877 for split supply configuration, all i did was lower the gain a bit and use appropriate values for the coupling caps for a very low corner frequency of the input and feedback HPFs.

As for the AN5272 i wouldn't be too sure. First of all, it's a single supply amp which means it will require big output coupling capacitors. You could try running it split supply by connecting the GND pin of the IC to the negative rail, all other ground connections remain referenced to ground (0v). However by doing that it's likely that you'll also need to wire the DC volume control between the negative rail and circuit ground instead of between ground and 5v, as it's likely tied to the GND pin internally. There's no schematic drawing of the internals so i can't tell. And even if you do get it to work with split supplies, you may find out that DC offset is too high and you'll need those coupling caps anyway.

Second, its distortion spec is just lousy at 0.3% typical. I don't think you'll like too much how it sounds. The LM1877 has a spec of 0.055% at 1Wpc output - almost an order of magnitude better. AN5272 would be good for powering cheap PC speakers, not much else.

[momaka]

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

Aw man... and I was reading your thread and getting all these crazy, elaborate ideas how to build mine .

Thanks for the insight, though. I really appreciate it .

I guess I'll still try building the amp. These parts just don't do any good sitting like that so I might as well use them. Of course I'll likely ditch all of my elaborate ideas and perhaps just cobble something together. I'm thinking thereifixedit.com -style, most likely (see attached pic) .
Yes, my amp may not have the sound quality, but who cares - quantity is the new quality


...
Then again, I also have a TDA1517 on an old Pentium board... but that board is still working so I feel bad tearing it apart.

[Agent24]

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



Wouldn't those bottles rattle like crazy?

[momaka]

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

Wouldn't those bottles rattle like crazy?

More than likely, but I don't know. Would have been nice if the person who built this put a video as well.

By the way, I tried the AN5272 amp as it was on the TV board. I just unhooked the audio inputs from the tuner card going to the amp and soldered a home-made 3.5mm jack (very , I know). Then I soldered another home-made jack on the output and hooked the volume control to a potentiometer so I could control the volume (the TV uses PWM to control the volume so I couldn't use that). Finally wired everything to a 19.5V laptop adapter.

The result: a mess of wires and jumper cables on the floor - but it works!
It's hard to comment on the sound quality, though. The amp is just too noisy (as in loud hissing), and the hiss noise increases quite a lot as I increase the volume knob. Moreover, it's also doing a fine job of picking up AM radio signals and mixing them with the input audio . I guess this is the first amp that let's you listen to both music and radio at the same time .

Then again, the audio output is quite loud as well. 1/4 to 1/3 of the volume was already painfully loud on my headphones. If you can't decrease noise, drown it out with louder music . And at least it has no problem pumping out loud bass. I was using my old portable Panasonic CD player with it, and with the S-XBS (super, extra bass? ) setting enabled, I got some pleasantly loud bass on my headphones without distortion.

So overall, I think Th3_uN1Qu3 was right - the audio quality didn't seem too great. But of course this could be due to the way the circuit was built on that TV board - it is almost an exact copy of the sample circuit in the data sheet. If I build a headphone amp with this amp IC, I will likely change a few things in the circuit. I don't know that much about amplifiers, but from what I remember reading, it's the high gain that's responsible for the noise at the output. I thinking about lowering the gain from 30 to 10 dB. Any ideas if this will be okay?

[Th3_uN1Qu3]

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

Amp's still doing fine if anyone was wondering. However, i feel i shouldn't be offered the option to push close to 2W/ch into my own ears, especially if i'm pissed off and (ever so slightly ) drunk.

Ahh well. 'phones are still fine, as for my ears... I'll let you know the following days.

[kaboom]

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

However, i feel i shouldn't be offered the option to push close to 2W/ch into my own ears, especially if i'm pissed off and (ever so slightly ) drunk.

Smart move.

I also built a "headphone amp" years ago with some LM386s. These were some that were much quieter than others typically are. Four NiMH AA cells powered it. A few years ago, I deconstructed it, for the same thing you mentioned above. It was nice having the tone controls for the 'phones, but I didn't want something so accident prone.

Ahh well. 'phones are still fine, as for my ears... I'll let you know the following days.

Old sound guys never die- they just become amplitude and bandwidth limited.