In my design I need to drive headphones with nominally 10 ohm impedance with an audio signal. The supply for the audio is +12V single supply (this is created from the main 2.5V-3.3V battery supply using a DC/DC converter). The output swing does not need to be all the way to the rail, something like 7..8V peak-peak is acceptable. The input signal is
0..2.5V.
The signals are synthesized sine waves and tone bursts coming from a DAC, with frequencies from 250Hz to 1kHz. Not music or speech.
Important is that the quiescent power consumption is low (
Check out the National Semiconductor "Boomer" range of amp chips, many are designed specifically for headphones and include class-D designs and ones with built in supply rail boosters.
I think you may have jumped to an invalid conclusion. I would say that the noise you hear is passing through the LM386, but not necessarily being generated by it. Have you done a listen using a battery as a power supply?
have a look at the LT1010 from linear, specificaly P.14 in the data sheet You could possibly use the discrete equivalent, with a "normal" opamp in front. Of course you would have to mash it up for single rail working, maybe
I use a similar setup with LM386, and never heard any 'white' noise. Are you certain it comes from the LM386 ? They are good at picking up power supply noise.
--
Regards,
Adrian Jansen adrianjansen at internode dot on dot net
Design Engineer J & K Micro Systems
Microcomputer solutions for industrial control
Note reply address is invalid, convert address above to machine form.
These are special in-ear phones for use in a medical setting to use diagnosing the balance organs in your ear. The low impedance allows high short-time power levels with a relatively low supply voltage (12V).
I never said I would apply a constant sine wave with this power. Just a short toneburst of, for example, 5 cycles long, once every 200 milliseconds or so.
Yes I have. I NEED to generate something in the order of 150 dB SPL briefly during these tonebursts (at the maximum power setting, obviously in most cases (healthy people etc.) the required power will be much lower).
I am designing an application to specifications from the medical doctors here. Please don't jump to conclusions about my criminal intentions are stupidity without knowing anything about my application.
Dont think a rational explanation will prevent the abuse. Just ignore him, he's one of a couple of lunatics at SED that fly off the handle at the slightest provocation such as, in your case, asking a sensible question.
You will probably get abused further, for failing to disclose every nuance of your aplication, regardless that its not actually relevant to the original question.
BTW this is probably the single best debunking of one of PA's rants I have ever seen! Well Done sir!
Thank you, that looks like an interesting part. Its ~8 ohm output resistance is on the high side for a 10 ohm load, but if it stays sufficiently constant I can compensate for that. It swings to within 3V from the rails, which is also OK (this is less relevant for the 10 ohm headphones but important for 50-ohm impedance bone-stimulating actuators which could also be used instead). The +-150mA current limit should also be just enough to meet my specs. I'll try to get my hands on some of these parts to try them out...
Someone FAR FAR more technically competent and wise than *YOU* needs to be given the task.
The audio driving circuits to those earpieces MUST have safety interlocks desigjed in and 100% fool proof automatic trips if input power levels EVER exceed what is known to cause hearing damage .
thats why I suggested the "discrete version", cheaper, and you can choose your own o/p transistors, emitter Rs , magic smoke level (tm), etc. I think TI and Analog do equivalents
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.