Dumb Headphone Amp Schematic...

[gez]

I fried the TDA2822 I was using for the headphone part of a circuit I'm working on.  A few calculations and ten minutes preliminary testing with the scope, and I came up with the above circuit.

Fired it up and it works perfectly.  Not only that, but it sounds amazing!  And it's incredibly quiet too.  A great little headphone amp for guitar...

The drawback? Er, current consumption is (a mere) 43mA.  :shock:  :oops:  :lol: PSU only folks!

I haven't subbed in different 4049s, but should imagine that some will be better than others (ones with higher current consumption).

Use your guitar vol knob to control level (or use 1M pots for the feedback resistors).

Anyway, I was going to use this until I get round to ordering some more chips, but I might just stick with it, I really like it!

[JimRayden]

I'm considering on making a little practice amp:
Professor Tweed -> Condor -> some headphone amp

I'm sure this one qualifies. But how's the loudness with earphones? Could carry a tiny speaker also?

------------
Jimbo

[gez]

But how's the loudness with earphones? Could carry a tiny speaker also?

For me, the level is just right.  If you want more volume then just drive it with a low gain amp.

The output is severely loaded as it is so I doubt it would be good at driving a speaker (it sounds great, but is pretty inefficient).

[JimRayden]

If you want more volume then just drive it with a low gain amp.

I mean, is it loud alone driving headphones?
Can anyone point me to a good clean loud simple headphone amp schematic? I know, I'm too lazy to search.

------------
Jimbo

[gez]

I mean, is it loud alone driving headphones?
Can anyone point me to a good clean loud simple headphone amp schematic? I know, I'm too lazy to search.

------------
Jimbo

Yes, but best to breadboard it first, your version of loud may differ from mine...

[JimRayden]

I mean loudness as pushing the headphones to the limit (but not making them crackle)

Like if I want to jam with a loud drummer. Yes, a real drummer and a guitarist with his headphones.

That's about the loudness I need.

--------------
Jimbo

[gez]

I mean loudness as pushing the headphones to the limit (but not making them crackle)

Like if I want to jam with a loud drummer. Yes, a real drummer and a guitarist with his headphones.

That's about the loudness I need.

--------------
Jimbo

As drawn, no.  Stick a pre-amp in front of it and it should do what you want...though you'll f*ck up your hearing for certain! (no joke)

[B Tremblay]

I quickly breadboarded this circuit and it was loud enough for me.  The sound was quite good as well.

Nice job, Gez!

[gez]

I quickly breadboarded this circuit and it was loud enough for me.  The sound was quite good as well.

Nice job, Gez!

Thanks!  A little booster ahead of it should be enough to achieve life long tinnitus for those that want it...

[Ge_Whiz]

43mA consumption for a 4049? I thought the whole point of CMOS was low current!

Are you sure you haven't got some stray HF oscillation raising the current? If you can get 43mA through a CMOS chip, no wonder you fried the 2822...  :wink:

[B Tremblay]

Thanks!  A little booster ahead of it should be enough to achieve life long tinnitus for those that want it...

Well, I've learned that there are many different opinions of "practice" volume levels.  As drawn, the circuit's output volume is perfect for me.

Would adding a J201 as a current regulator help?  I'm referring to the setup used by Tim Escobedo in his Ghost Dance.

Also, I know that you've often run the 4049 at 5v.  Is there anything to be gained with that approach, in terms of tone or power supply concerns?

[gez]

43mA consumption for a 4049? I thought the whole point of CMOS was low current!

Are you sure you haven't got some stray HF oscillation raising the current? If you can get 43mA through a CMOS chip, no wonder you fried the 2822...  :wink:

Firstly, CMOS logic chips are designed for logic and not audio use.  They're also designed for use a logic levels.  When used for audio applications (and from a 9V supply) current consumption is much higher due to the class A nature of the circuit.  There's a full explanation in the Art of Electronics.  

If you check data sheets you'll see that current consumption for a single inverter stage biased as a linear amplifier is dependant upon supply voltage.  At low voltages these chips can be really efficient, but the trade-off is high output impedance.

In the Earwig, it's run at 9V, so you'd expect a few milliamps per inverter at that voltage, and that's what you get.  The devices are paralleled to lower output impedance so that the inevitable loading by the cans isn't too great.

Secondly, I came up with the above circuit simply because I accidentally fried the 2822.   :oops: ( )

[gez]

Would adding a J201 as a current regulator help?  I'm referring to the setup used by Tim Escobedo in his Ghost Dance.?

I’ll see if I can improve the efficiency a little this afternoon.  I doubt that regulation will improve matters as it will lower current consumption/increase output impedance of each chip, which means the cans won’t get enough current.

Class A, pain in the backside…

Also, I know that you've often run the 4049 at 5v.  Is there anything to be gained with that approach, in terms of tone or power supply concerns

As I mentioned above, current consumption reduces dramatically.  I've lost my bleedin' data sheets so I can't check the figures (grrrr), but current draw with a 5V supply is about a third of what it is when powered from 9V.  At 5V, Gain increases two to threefold also, and, if you're using these chips for a TSF, the lower headroom means more distortion.

As far as clean goes though, no real difference in tone unless you go down to even lower supply voltages and use large feeback resistors - the higher output impedance, combined with the gate capacitance of the following stage (if one is used), forms a low pass filter, so things can get muddy.

Edit: If you download the Phillips 4069 data sheet, figs 9,10 & 11 contain useful info (not far off 4049 figures):

http://www.semiconductors.philips.com/pip/HEF4069UBP.html

[Peter Snowberg]

Very cool Gez!

[gez]

OK, I did some testing this afternoon and tried running the circuit off a 5V supply (thanks for suggesting this B).  As predicted, there’s a drop in output, but it’s still useable and all is not lost (more to follow).

I did some A/B testing using the same circuit but with a 5532 chip.  The 5532 does the job no problem, output is much stronger.  The quiescent current consumption was only 7mA, but with an input signal of 1V peak-to-peak this rose to 37mA.  Any attempt at increasing the input signal resulted in a clipped output - nice quiet amp but I’ve never liked using it due to the low headroom - so only 3V peak-to-peak available.  Not really a problem though as gain would be reduced in a working circuit (the output was too loud for my liking), and this would reduce current consumption too.

The Earwig, as drawn, isn’t very efficient.  Gain is less than unity due to the heavy loading, but at least this is a known quantity and can be factored into the equation.  The biasing method I used isn’t ideal as there isn’t enough gain to provide the necessary negative feedback, but I did things like this to save on components - although decoupling AC feedback provides slightly more output I felt it wasn’t worth the extra components as the level was just right with the circuit as shown.  At 5V though, it is worth decoupling AC and the following gives an ouput that is just about feasible:



At 5V, quiescent current consumption dropped to only 8.6mA but rose to just under 9mA with a 1volt sine.  There’s 50% attenuation of the input signal though, but this could be boosted with a FET input buffer/amp.  With a 5V input signal the output was comparable to that of the 5532 circuit (set up for voltage gain of around 3), but current consumption is less, only 16mA.  So, run at 5V, and with a little booster at the input, despite its inefficiency current drain on a battery would be less for the Earwig (assuming some careful design is done for the regulation and input stage).

I used a LP2950CZ-5.0 regulator to get 5V, which is micro power (only 75uA extra on the bill), though you could just wire up a 3V3 zener between the cathode of the protective diode connected to V+ (9V) and pin 1 of the chip (plus wire up a 100u cap between pins one and eight).  The zener is a cheap and cheerful way of doing things (and sometimes it can introduce noise), but it works…

[gez]

The regulator I used is sold here in the US

http://www.lynxmotion.com/Search.aspx?txtSearch=LP2950CZ-5.0

Data sheet here:

http://www.lynxmotion.com/images/data/lp2950.pdf

& for the Brits...

www.esr.co.uk

though I think rapid sell it too

www.rapidelectronics.co.uk

[B Tremblay]

OK, I revised the breadboard to reflect the changes and supplied 5v with a 7805 regulator.  Sounds quite close to the first version and the current draw was only 8.78mA!

I think that with the Condor Cab Sim, which can provide a boost in addition to its nice filtering, this is a damn fine little headphone amp.

By the way, excellent name!

[gez]

Excellent!  

I'm wondering if it's worth slinging another 4049 in front of it, set up as a TSF type circuit and run off 5V too?

Anything will do really, just so long as it has a tiny bit of gain...

[gez]

PS It might be worth including some input protection if you're going to run something in front of it.  A 10k between the input cap and inputs of the 4049, the 1M connecting to the junction of the 10k and input cap (hope that was clear).  Plus some reverse biased Schottky diodes on the inputs?  

All depends on the output of the previous stage...