EMRFD Message Archive 9484
Message Date From Subject 9484 2013-12-02 17:00:11 Ashhar Farhan Recommendations for a headphone amplifier Does anyone have a recommendation for a low component count headphone amplifier that doesn't distort too much? I looked at Cmoy configuration. Here are the links:However, the Cmoy needs dual voltage supplies to work well as it uses no caps in the entire signal path!In a low distortion receiver, a swap of the LM386 with a professional audio mixer revealed the world under the cross-over distortion. It was like taking a scuba dive into the noise!- f 9487 2013-12-03 02:18:29 Roelof Bakker Re: Recommendations for a headphone amplifier Hello Ashar,
G4OEP's design is excellent:
I have build a couple and it is hard to beat for audio quality, though not
especially designed for low power consumption.
Roelof Bakker, pa0rdt
9488 2013-12-03 04:29:15 Ashhar Farhan Re: Recommendations for a headphone amplifier Roelof,
That's a nice one. I probably have a TDA2003 in the junkbox. It scared
me once. I was using it in a direct conversion radio and I asked my
good old friend paddy VU2PEP to give me a shout from across the town.
Given the headroom of the TDA2003, the signal literally blew me out of
the chair. I had never before experienced anything that loud. (I am
used to loudness thr drummer in our band broke a few sticks every
I think some sort of limiting called for with such amps.
On 12/3/13, Roelof Bakker <firstname.lastname@example.org> wrote:
> Hello Ashar,
> G4OEP's design is excellent:
> I have build a couple and it is hard to beat for audio quality, though not
> especially designed for low power consumption.
> Roelof Bakker, pa0rdt
Sent from my mobile device
9490 2013-12-03 06:36:12 John Levreault Re: Recommendations for a headphone amplifier FWIW, I use a CMoy headphone amp and like it very much.
There are ways of driving headphones without large coupling caps going to the headphones. Basically, you create a voltage reference of half the supply using a resistive divider (or zener, if you wish) with a bypass cap. This is used to bias an opamp (or half a dual, see below) so that its output sits quiescently at half the supply. This opamp then amplifies or buffers the audio and is direct-coupled to the + of the headphones.
This reference voltage is then buffered by a 2nd opamp and connected to the - of the headphones. A good choice for a dual opamp here is the NJM3414, as it has good output current capability and can run off a 12V supply. It will drive plenty of power into low-Z headphones. There's no need to resort to bridge mode.
Let me know if you need a schematic and I'll post it in the files section.
9491 2013-12-03 06:51:30 John Levreault Re: Recommendations for a headphone amplifier 9492 2013-12-03 07:02:00 email@example.com... Re: Recommendations for a headphone amplifier Ashar illustrates the greatest shortcoming of most simple receivers. The lack of a suitable AGC makes the use of headphones a questionable choice. And being quick to slam the signals with the RF gain makes using them a laborious instrument.
Has anybody found a discrete AGC that works? Audio derived AGC leaves me wanting as I've tried many topologies and simply don't like the touch and feel. Huge capacitors for the time decay can rival the rest of the radio in size. AGC beyond 455KHz have been miserable experiments in futility.
9493 2013-12-03 07:33:42 Jim Miller Re: Recommendations for a headphone amplifier I've never quite understood the need for a special headphone amp. The earbuds I often use produce >100db SPL with only 1mW input. Nearly any competent opamp can produce the necessary voltage at the 32ohms of impedance to drive these.73jim ab3cv 9494 2013-12-03 07:42:41 Tayloe, Dan (NSN ... Re: Recommendations for a headphone amplifier
I like to at least make sure there is diode limiting in the output stage. This is either back-to-back diode limiting before a unity gain op-amp driving the headphone, a last op-amp stage with diode limiters across the gain resistor to limit the output, or a series resistor/back-to-back clipping diodes combination right at the headphone output.
With an arrangement like this, static crashes sound a lot different. With audio AGC, a static crash is very loud and sudden (not enough limiting), then the AGC hangs and takes a while for the receiver to recover. Meanwhile the signal is gone. With diode limiting, a static crash is much less distracting as just the energy peaks get clipped. When the crash is gone, the signal is back like nothing happened. I can often even hear the signal during the crash.
I started adding diode limiting to the output of my QRP receivers since almost having my ears blown out by a very large signal by a LM386 output stage. It seems a good thing to protect your ears!
- Dan, N7VE
>Ashar illustrates the greatest shortcoming of most simple receivers. The lack of a suitable AGC makes the
>use of headphones a questionable choice. And being quick to slam the signals with the RF gain makes using them a laborious instrument.
>Has anybody found a discrete AGC that works? Audio derived AGC leaves me wanting as I've
>tried many topologies and simply don't like the touch and feel. Huge capacitors for the time decay
>can rival the rest of the radio in size. AGC beyond 455KHz have been miserable experiments in futility.
9495 2013-12-03 07:43:43 rlramirez77 Re: Recommendations for a headphone amplifier Ditto Jim, or swap the LM386 for an LM380.
9496 2013-12-03 08:17:45 John Levreault Re: Recommendations for a headphone amplifier Understood and agreed. But then again, I'm fortunate to still have my hearing, unlike my brother who spends his life with his head under the hoods of vintage automobiles. And I suspect most of us are getting older, many with some age-related hearing loss, so louder might not be a bad thing.
The primary objective of my scheme (and it's certainly not "mine") is getting rid of a potentially bulky output cap. You can use any old opamp you'd like. However, if you choose to parallel the 32-ohm headphone channels, you get a 16-ohm load. Take a typical opamp, something like a TL07x, which has an output current limit of around 20ma. That means it can drive 14ma-rms (sinewave) into a 16-ohm load, which is only about 3mw. This does not offer much headroom for loud adjacent signals in a simple receiver, and the resulting [clipping] distortion can be quite fatiguing. Hence the need for clipping/limiting becomes more critical.
But for normal listening, I'll take an opamp any day over an LM386.
9499 2013-12-03 10:44:14 William Carver Re: Recommendations for a headphone amplifier > But for normal listening, I'll take an opamp any day over an LM386.Hear hear! For anything beyond a code practice oscillator the SNR of the
> John NB1I
LM386 is abysmal.
9501 2013-12-03 19:15:04 kerrypwr Re: Recommendations for a headphone amplifier G'day Roelof.
I can't open the G4OEP link; has anyone else had this problem.
It looks as if Farhan was able to view it.
9503 2013-12-04 02:38:36 Russell Shaw Re: Recommendations for a headphone amplifier