For audophiles

On Tue, 22 Oct 2019 15:02:50 -0400, bitrex <user@example.net> wrote:

On 10/22/19 3:00 PM, bitrex wrote:
On 10/22/19 2:02 PM, Jan Panteltje wrote:
On a sunny day (Tue, 22 Oct 2019 11:56:11 -0400) it happened bitrex
user@example.net> wrote in <wEFrF.70497$hB2.52985@fx42.iad>:

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.

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 ..

Sounds like a recipe for oscillation to me in that circuit as-is, with a
GBW that high.

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.


Another interesting amp topology is this:

https://www.tubecad.com/2004/12-2-2004_Sandman2.gif

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.

With grounded load: <https://www.tubecad.com/2004/12-2-2004_Sandman11.gif

In this configuration, the low power amplifier(s) need to be full
voltage swing versions, but only low current capable.

The question is, is the low power amplifier input taken from the
correct point. IMHO, it should be taken between the actual output
voltage of the big dumb booster and the preferred output voltage.

 

On Wed, 23 Oct 2019 15:00:38 GMT, Jan Panteltje
<pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 23 Oct 2019 09:04:26 +0300) it happened
upsidedown@downunder.com wrote in
inqvqeps4op523hb6b7mip7g09jq3eh8ku@4ax.com>:

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.

Is the LM386 up to this ?

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.

 

[Jan Panteltje]

On a sunny day (Wed, 23 Oct 2019 19:48:33 +0300) it happened
upsidedown@downunder.com wrote in
<jf01re5umh6k2ej2gnmjqtn9ubgrmf4djg@4ax.com>:

On Wed, 23 Oct 2019 15:00:38 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Wed, 23 Oct 2019 09:04:26 +0300) it happened
upsidedown@downunder.com wrote in
inqvqeps4op523hb6b7mip7g09jq3eh8ku@4ax.com>:

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.

Is the LM386 up to this ?

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.

Sometimes I sleep with wax earplugs in, no problem listening to my own blood flow / breath / snoring ;-)
Although I live in a small village, activity never stops here at night it seems.
In the toilet you hear the air sucking fan, big fan in the attic that I always leave at the lowest speed,
'cept after taking a shower as just now.

Silence?
I my younger days I lived above a bar, and 20 years ago across from one.....
Working in shifts... No problem, even fun.
One street away from here is a football field and often at Saturday night some band plays there at the new community center..
to deep in the night,

 

[bitrex]

On 10/23/19 12:54 PM, upsidedown@downunder.com wrote:

On Tue, 22 Oct 2019 15:02:50 -0400, bitrex <user@example.net> wrote:

On 10/22/19 3:00 PM, bitrex wrote:
On 10/22/19 2:02 PM, Jan Panteltje wrote:
On a sunny day (Tue, 22 Oct 2019 11:56:11 -0400) it happened bitrex
user@example.net> wrote in <wEFrF.70497$hB2.52985@fx42.iad>:

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.

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 ..

Sounds like a recipe for oscillation to me in that circuit as-is, with a
GBW that high.

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.


Another interesting amp topology is this:

https://www.tubecad.com/2004/12-2-2004_Sandman2.gif

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.

With grounded load: <https://www.tubecad.com/2004/12-2-2004_Sandman11.gif

In this configuration, the low power amplifier(s) need to be full
voltage swing versions, but only low current capable.

The question is, is the low power amplifier input taken from the
correct point. IMHO, it should be taken between the actual output
voltage of the big dumb booster and the preferred output voltage.

Nah, I think it's taken from the right place. Lower amps job is to
amplify and invert distortion. If the upper amp were "perfect" the
voltage at the inverting input would be exactly 0 always, same as the
other input which is at ground. Any signal that does appear there
implies that the upper amp is not behaving like a perfect amplifier,
that is to say it's distortion.

 

[Jan Panteltje]

PS
forgot the mil airport Leeuwarden just a few miles from here,
sometimes you can hear them all day long,
once a heli flew over so low it sucked the tiles of the roof.
F35 was here too, and more are ordered.
2 fighters fell out of the sky already since I live here -)

Raining? No planes...
Oh and even normal rain will bring the noise level up to way above audiophile panic threshold.