It's just distortion I think. It's a very simple 3 stage amp inside the diff pair doesn't even have a current source in the tail and its open loop gain is relatively limited. THD is already at 10% with a 9V supply pushing 500mW.
It doesn't have to be an 8 dollar chip but for a headphone amp with two op amps in parallel if you're going to use op amps as drivers the parallel combo I think should be able to at least push 100mA peak, symmetrically, across the full audio band, into your headphone impedance of choice. NE5532 not really up to the task for 64 or 32 ohm headphones.
On a sunny day (Tue, 22 Oct 2019 11:56:11 -0400) it happened bitrex wrote in :
Yes OK. I found 5 LM380 for 3$50 free shipping on ebay, ordered. That chip has some real power, maybe not HiFi, but reasonable low distortion. I have used those before in a (not HiFi) monitoring system in a radio transmitter 19 inch rack many years ago. That LT1364 and LT1365 seems interesting, 70 MHz gain-bandwidth is a lot... not sure if I can .. Output is a complementary emitter follower x 2, feed-forward via Rc Cc (LT datasheet page 10), interesting, crossover compensation? Output current is a bit low though.
Sounds like a recipe for oscillation to me in that circuit as-is, with a GBW that high.
Another interesting amp topology is this:
The upper amp is a slow, beefy class B or lean AB amp with meh THD specs. The lower is a fast lower-power amp with much better THD. The second is used to clean up the first and keep it in line.
I once built a pair of electrostatic headphones to a design published in Wireless World. It involved rubbing Aqua Dag (graphite colloid) onto cling film to make the high resistivity diaphragm. They were driven with a hybrid transistor-valve amplifier. The sound was superb, but they were a bit impractical.
What is the noise characteristics of the LM386, it doesn't appear in those data sheets I have seen.
With headphone sensitivities in the order of 100 dB/mW so to reach 120 dBspl at least 100 mW of power is needed. Thus 0.9 Vrms is needed for
8 ohm, 3.1 Vrms for 100 ohm or 7.7 V for 600 ohm load impedance. Multiply by 3 (actually 2sqrt(2)) and add two or four Vbe drops and you get the minimum supply voltage needed. Of course, this is the clipping limit, so even a higher supply voltage is needed to cleanly produce 100 mW. In practice, the LM386 could produce 100 mW into 8 ohm without too much THD at 1 kHz using a 6 Vdc supply, but not much higher impedances.
The question about noise is interesting. In power amplifiers signal to noise ratio is specified at full nominal rated power. Even in good amplifiers this is often only 100 dB SNR. If the usable low distortion output power is well below rated power, this directly reduces the available SNR by many dB.
At least with closed headphones more than 100.to 110 dB SNR should be available. Thus the output noise density for 8 ohm load should be less than 63 nV/sqrt(Hz). Divide this by voltage gain to get input related noise density.
Of cause these days, the dumb high signal patch could be implemented with a class-D amplifier, while the low power path could be a class-A linear stage.
On a sunny day (Tue, 22 Oct 2019 15:25:04 -0700 (PDT)) it happened snipped-for-privacy@gmail.com wrote in :
Somebody once showed me one, I listened to it for a short while, it sounded nice, transparent.. no idea who made it, but i as not excessively big, had some small box that drove it.
Like 'electrets' could you not use a self biasing membrane?
On a sunny day (Wed, 23 Oct 2019 09:04:26 +0300) it happened snipped-for-privacy@downunder.com wrote in :
All good and well, indeed my Sennheiser HD201 does attenuate much of the outside noise. But... 2 PCc with fans, airco fan in room, OK turn it all off for the ultimate experience clock ticking in kitchen OK pull battery out, far away farmer working at night with tracker in field, OK wait till he is gone (>2 at night), now early traffic on main road, mm I have double glazing it helps, dogs, maybe for me a more realistic achievable value is 50 dB or do, conversations,..
I know a real audiophile has his/her own dead room, but I have no progressed that far yet, The LM380 is a bit better but very much like the LM386, but can be run from a 3 cell lipo if must be. And then there is the sort of music you listen to, I m sure there is classical music that need that high dynamic range but lot of stuff I have comes from old vinyl .... live audience noise, etc etc.. It is gonna be allright!!!
In my country house in the toilet, (which is in the middle of the house with no windows) in the middle of the night, the only sound I can hear is the noisy blood rushing through my veins. No problem counting my heart beat.
The situation is similar in an unechoic chamber.
With a fully enclosed headphones, you can get similar situations in somewhat noisier environment. Unfortunately, wearing such headphones for more than half an hour can be challenging.
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