~misfit~ wrote:
On 16/07/2019 3:14 PM, Paul wrote:
~misfit~ wrote:
On 16/07/2019 10:38 AM, Paul wrote:
wrote:
I want to learn some Chinese, but find these old ears cannot hear the
audio very well at

https://chinesecharacteraday.com/one-word-a-day/

at least.

All I have is an old set of earphones plugged to audio on a W10 PC.
Even at max audio. The phones have no volume control of course.

I want to buy something cheap to make the volume higher. Thinking of
buying a new set of earphones with an amplifier, or just the latter to
add to what I've got. Or maybe USB instead?

What do you think?

Wei


There is a *lot* of crap on the market.

Take those NE5532 products for $15.
Without additional transistors and a crafted output
stage, and good VCC supply, you can't get ear-blistering
sound levels.

Another product I saw for $36, one commenter said "it's
not loud enough". Which means the circuit is probably only
driving about 1VRMS into 32 ohms.

Stereophile amps of that sort, start at nice round numbers
like $199.00 for the "beginner amp", and going up in
increments of hundreds. This is obviously not the way to
get an amplifier. I'm sure there is plenty of level on those.

The audio industry is just as crooked as it was
fifty years ago.

You can find kits to assemble, for conventional amplifiers,
but they expect a speaker load of 4 ohms or 8 ohms, and
that's not a good match for 32 ohm headphones. I use
a 40W bridged Canakit for my Test Machine audio output,
which works OK. But it just isn't the right beast
for headphones. The signal would probably still be
a bit on the weak side. While the amp is 40W (2x20W),
in actual usage into 8 ohm speakers, the output is
just 2W per channel. And fortunately, with a tuned port
speaker, this is good enough.

I got a kit for a headphone amp that runs off a micro USB power
supply (so can be pocketed and powered from a 'powerbank') from
Aliexpress for about US$5 complete with a case but haven't assembled
it yet.


Is it just a 1V output ?

Or is it one of the ones with much higher output ?

A simple OpAmp can manage a pretty good swing, but will
likely go into current limit with a 32 ohm load.

I'm not sure where I put the kit and when I go to my purchase history I
can find the purchase but the page doesn't exist anymore (which could be
a problem if I need reference pics when I make the kit - lesson learned,
any other kits I buy I'll download the pics).

It was very similar to this one, same 'brand' but USB powered
https://www.aliexpress.com/item/32723001937.html This one requires 12
- 18V DC input.

So OpAmp, and I remember the blurb saying they're socketed so that the
end user can change to different / better OpAmps if they want to.

I thought the OP might be interested as a cheap solution to their problem.

There might be an OpAmp with better power output.
The ones I've used in the past, run out of steam at
around 25mA or so. It's probably related to how much
heat the tiny 8 pin DIP can handle.

When you place a push-pull stage after the OpAmp,
that's when it gets interesting. You can do Class A
(power wasting, but no crossover distortion), or
Class AB (where as the signal goes through zero,
one transistor is switching off while the other
transistor comes on, and it's a bit non-linear).

To get ear-splitting volume, you need a good
voltage swing. One powered with +5V, could use
a boost converter to achieve higher voltages,
but not at the $5 price point. Designs running
off 12 to 18 volts would have more options
in terms of driving 32 ohm headphones.

Paul