Super HeadBanger (??) Review request

[evandude]

that sounds really good... I might check into the maxim devices. it's rather ironic that I work a couple hundred feet from national semiconductor's main plant, on the same grounds, (at fairchild semiconductor) and yet it would be easier and faster for me to get a sample chip from maxim.

running off a single cell sounds like a very good thing to me, although I'd rather not have to modify my headphones if possible, so it could be used with other headphones easily. is there any way around that?

personally I have no knowledge specifically in audio electronics, although i do have a good general knowledge of electronics (Junior in EE in college, so I know circuit analysis, S-domain, filters, etc. so most audio stuff makes sense to me, but it's not intuitive enough yet for me that I could just sit down and design an entire audio circuit)

if you happen to know of any schematics anywhere that make use of the IC's you mentioned, I'd appreciate seeing them. I will look into the data sheets, etc. when I get some free time.

thanks!

 

[audioguru]

Hi Evandude,
None of these new headphones amp ICs use bridged amps like the MC34119 does, so the headphones don't need re-wiring.
The datasheets have detailed circuits and some even have PCB layouts for you. But if you want bass-boost like Wellington has, then you will have to make your own calculations for it (and see if you have enough headroom, etc.).
Sorry that I didn't link to the datasheets, because I didn't know where you are (many countries can't get new stuff).

 

[wellingtonuemura]

Hi Wellington,
Your final circuit is almost identical to National Semi's, isn't it?
But their datasheet for the LM386 doesn't mention the "snapback" distortion at low supply voltages that was discovered by the author of The Headbanger.
The MC34119 is bridged, therefore stereo headphones will need to be re-wired to be 4-wire.

Hi audioguru,
What do you mean when you said almost identical?
What is this snapback any way?
What is re-wired to be 4-wire?

Thanks!

 

[audioguru]

Hi Wellington,
Your circuit is very similar to the one in National Semi's datasheet for their LM386, attached here.

"Snapback" distortion is shown in a 'scope pic by the Japanese gentleman. A piece of the negative-going part of his sine-wave is missing. It makes even-harmonics distortion throughout many octaves.

All headphones are wired with only 3 wires: left, right and a common wire for both channels. A bridged amp must have the channels to be completely separate, without a common connection, so both channels in a headphone will need 4 wires.

 

[wellingtonuemura]

Got it! :wink:

Yes, because the bass frequency response was near the range the bass i like with thouse values so the 10k and 0.033uF capacitor came from that and latter 20k resistor came out that japanese site, it was a trial and error because i don't know how to calculate the same response for a 40R load, in the schematic was for a 8R load (i will also try the 0.015uF latter).

Now I understand about the 4 wires
Did you use it?
Have you build a circuit based on it?

If is not that much different from mine i think is good the way it is, but any feedback about it will be appreciated because of his small size, i could use it inside some device that i have.

Thanks!

 

[audioguru]

Hi Wellington,
For the frequency response to drop 3dB in an RC circuit, the formula is:

----1-----
2 pie RC

but I use almost the same:

.16
RC

So, National Semi's circuit drops 3dB from its maximum at 91Hz. Since their 10K/33nF network is still boosting a bit at 91Hz, their response at this frequency is down less than 3dB, then rolls off below it.
Your output capacitor is huge for use with its 64 ohm load, so drops 3dB at only 5.4Hz. Therefore your response doesn't have the peaking of the National Semi circuit. This is what I think your response will look like:

 

[wellingtonuemura]

Hi audioguru,

Thank you for the formula
I have one question:

- Do you think that if I change the capacitor 33nF to 15nF, this could increase the noise or harmonic distortion some how?

Thanks

 

[audioguru]

Hi Wellington,
Changing the 33nF capacitors to 15nF will not affect noise but will increase the distortion at very low frequencies just a little bit. The low frequency boost will sound louder since it will be shifted up about 1 octave to frequencies that you can hear better as I show here:

 

[wellingtonuemura]

Thank you audioguru, i reallly don't know how to pay you for thouse informations, thank you very much!

 

[audioguru]

Wellington,
OK, OK. I'm glad to help you.
Sharing ideas and experience is what this forum is all about.

 

[wellingtonuemura]

Hello All!

I've done the final **broken link removed**, click at the last photo to download the zipped PDF. I'll work on the portable version soon as i could get some SMD components.

 

[audioguru]

Hi Wellington,
You have a very good PCB layout.
Your distortion analyser plot does not show how good that your circuit really is. It shows a 2KHz harmonic at about -57dB, which would be 0.15 percent, but the level of the 1KHz fundamental is 0dB on your plot instead of the +6dB that is on your list. So the curve on your plot should be shifted downward by 6dB, making the 2KHz harmonic disappear!
When stating a distortion figure, you should also state the output voltage or power that it was measured at. Worst case distortion usually occurs at the highest output voltage level, but just before clipping, which is probably about 1.4V RMS with your circuit. Was the distortion measured at that level?
Does your Super Headbanger produce enough output level? 1.4V RMS isn't much into those parallelled limiting resistors. Your 40 ohm headphone will have a maximum of only 19mW RMS per channel. Using a 7809 regulator without a diode would allow the circuit to give 64mW per channel to your headphones.
Your schematic has a typo for C12 and C17: "100uF" should read 100nF.
Your schematic also has a typo for the transformer: ...12V "DC" Out should read ...12V AC Out.
Which brings up other problems with the transformer:
1) Your pic shows that it is quite large and is rated at 500mA. But your circuit draws no more than only 25mA. A much smaller 50mA or 100mA transformer would be fine.
2) Another transformer problem is with its output voltage. With its rated current load, its output will be 12VAC. But with a load of only 25mA its output will probably be 14VAC or more. When rectified and filtered, the voltage at the input to the 7805 regulator will be about 18VDC or more. The 7805 with its boost diode needs a minimum voltage of only 8V, so 18V is excessive. A 9VAC, 100mA transformer that is rectified and loaded with only 25mA will produce about 14VDC, which is still plenty. A 9VAC, 100mA transformer will work fine in your circuit and will be much smaller than yours. Also, the regulator won't heat-up as much.

 

[wellingtonuemura]

Hi audioguru!

Thanks man, this was my first attempt to build a board using the computer.

Thank you for pointing that out, i will work the plot out latter and make the ajustments, the distortion was measured at the max level (1.2V RMS).

When i've came out with the final design of this circuit i was always considering the final level output to keep it at a secure level of decibels to prevent **broken link removed** on my self and other people that want to try this circuit out. That is why the circuit is not at his full potential of delivering lots of decibels out, so i've decided to play safe and be safe about this issue and cuted out most of what the circuit is capable of.

To listen music with a headphone in an **broken link removed** is more like having a gun at your head, i know that over the years we have a natural hearing loss, but why accelerate this process?

I have some friends with hearing problems, they were thouse "let's rock babe" type of guys, you know, wear a set of headphones and punch their heads with lots and lots of decibels (Guns, Metallica and so on) all day long and i didn't want to know some one that have give my circuit a shot and punch their heads with lots of decibels, i really don't want to be responsible for that.

Believe me, with my 40 ohm headphone set, this circuit can deliver enought power to it, but i still think that is too much loud for me at max level. I know that people that uses a headphone with 100 ohm or more impedance the circuit have to be changed (remove R7/8/12/13 and maybe R4/9 also).

The schematic was fixed, thank you!
I will upload a new version soon.

About the transformer, here in Brazil it's very hard to find components, to me also a 50mA or 100mA would be fine, but i didn't find any good around, but any way, thank you for this!

Some friends of mine that have builded this circuit, they told me that the correct name should not be "Super Headbanger" but subwoofer headphone amplifier.

I also have a question....
Some friends asked me to make this circuit portable (small board, batery based) and i will try to find some components to build the circuit with a **broken link removed** and make some tests with it to see how much batery i can save with and with out the step down converter.

The question is about the coil, can i use thouse micro (dont know the name) ones?
They are small like a capacitor, blue and with the same value.

Thanks!

 

[audioguru]

Hi Wellington,
I agree that it is not good to have the volume too high. But having headroom so that occasional peaks don't distort is important. I think that distorted peaks are harder on your hearing (and nerves) than clean peaks. If you add a good clipping-indicator, you will be amazed at its activity, especially with your bass-boost.
It is too bad that you can't get stuff down there. Here (Canada), I can get just about anything. The latest Digikey catalog came in the mail today, with 1458 pages and 17,805 new parts! Next-day delivery! I don't go to stores anymore, except for food and beer, which can also be ordered over the 'net.
To make it portable, why bother with a step-down converter? A small rectangular 9V alkaline battery (with 1000uF across it) will power your Super Headbanger for hours, and then you don't need the regulator and its boost-diode. But a rechargeable 9V Ni-Cad or Ni-Mh won't last long, use 6 AA cells instead. An Australian magazine has a small step-up converter circuit that can power 9V things from 2 AA cells longer than a 9V battery. Using batteries, a "low-batt" indicator is important.

 

[evandude]

that 9v converter sounds really cool. I googled it and found the page (I think)

https://www.siliconchip.com.au/cms/A_100886/article.html

not as compact as I might have hoped... but still very cool none the less!

 

[audioguru]

Hi Wellington,
That's the one! But of course they want you to buy their subscription to see the details. TI's datasheet for their TL499A has those details for free and Digikey has stock (but not surface-mount) and a pretty cheap price.
Other companies (Maxim) also make surface-mount voltage-converter ICs to drive strings of series white LEDs in cell phones. You could easily make one fit on a coin.
If you power a red LED power-on indicator from 3V, then it will save power and dim for a low-batt indication. I know, it's kinda dim right now, but is it any dimmer than it was a couple hours ago? It won't have a reference for your eyes. Instead, make a low-batt indicator turn-on when it should, so it can drain the remaining life from those batteries.

 

[wellingtonuemura]

Hi audioguru, evandude!

audioguru have you build my Super Headbanger circuit?
You know too much
We can find stuff here in Brazil, but not that easy like Canada, US , we have to walk (burn fat) a lot.

About the step-down converter i was thinking if I could for example, use a SONY battery (7.2v Li-ion) and feed the circuit with 5v (step-down converter), than when the battery drops to 4.5v lower the circuit will switch to a step-up converter and use the rest of the batery.

SONY uses (of course, much more complex) circuit like this with portable devices to increase usage life, that is the idea, longer life run. I will try to find out ways to make that possible or if you have something better in mind :wink:

evandude Google for step-up converter there are some similar free circuits and schematics around.

 

[audioguru]

Hi Evandude,
So it was you who found the Australian article, not Wellington. Thanks.

Hi Wellington,
No, I've not built a headphones amp circuit. I have Sony and Kenwood headphones somewhere, but I never use them. I like to feel the bass beat with my whole body, by using speakers.
You are thinking of using what is called a boost-buck voltage converter.
7.2V or less is too low for your 7805 regulator with its boost diode, that needs at least 7.5V to regulate properly.
You must be careful with Li-ion batteries because discharging to a voltage that is low will ruin them. I don't know about your Sony battery, but lightweight Li-Po batteries catch fire when over-charged. As you have probably measured, rechargeable Lithium batteries continue to drop in voltage when discharging, unlike nicads or Ni-Mh which have a fairly flat voltage. They can be discharged down to nothing and still work again but the weakest one may be charged in reverse by the stronger ones and be ruined.

 

[wellingtonuemura]

Hi audioguru!

I also like to feel the bass with my body too, i've a Yamaha HT here, alot of power, horse kicking!!

The portable version of this circuit will have a different design to make it compatible with many differen portable devices that has different output levels, when power up the circuit with battery the regulator part will be off and when used from AC the battery part will be off, i don't know if i could do a automatic selector with some diodes and transistors, i've to try some stuff out to see what i can came out with.

The idea is to make the circuit work with 4.5V when used with battery and try to keep up untill it reaches 4.0V and shutdown the circuit. The SONY battery that i was talking about was thouse Info-Lithium ones (i have a lot of that around) but I'll try to make it generic and not battery specific.

Maybe i will try this CI first.

Do you have any more good ideas, considerations that i must know?

Thank you!

 

[audioguru]

Hi Wellington,
When you select a boost-buck voltage converter, choose one that gives a positive voltage output with a positive input, then switching between battery power and AC will be much easier. Get one that supplies at least 25mA output current.