Update on CMoy using OPA637

[JTT 0]

But the amplifier is not required. So little gain is required for this application that a buffer amp with reasonable current drive capability will be more than capable of doing the job. And, incidentally, the 637 spec warns of instabilty for gains less than 5.

 

I could stoop so low as to suggest that the venerable LM380 would adequately do this job - and don't rubbish it if you haven't tried it.

 

JohnT

[jasonhanjk 0]

The schemactic configuration is at gain of 11.

 

There are plenty of reason the people here should not use LM380 (power audio amplifier), not forgoting that we use headphone rather than loudspeakers.

 

1. Lowest THD is 0.2%. This is only acceptable for tube amp. Solid state worst condition should be 0.1%.

2. No spec indication of noise. Since the headphone is very near the ear, noise will be audible. Or maybe noise is included in the THD+N.

3. Need to get additional heatsink to cool this baby. (more money needed)

4. Cannot be made portable.

5. Voltage gain at 50 requires a multi-turn (4 maybe) good quality volume control knob thus increasing the price.

6. This amp is only suitable for AKG-1000. (The best headphone followed by HD600)

 

Just my 2 cents...

[JTT 0]

Ah .......... well ..

 

1&2 ... If you think you will detect 0.1 - 0.2% distortion, then fair enough.

 

3&4 ... This IC has quiescant current of only 10 - 12 mA, and is the most useable un-bridged low power amp I know of, which is probably why it's been in production for 15 - 20 yrs. I use it as a battery powered amp, in conjunction with a laptop, for loudspeaker freq resonse testing. I use it with both 12v (lead acid) and18v (12 x AAA) rechargeables with no component changes required, and there is no requirement for external heatsinking with output powers below 1W rms.

 

5 ........ The (relatively) high fixed gain does offend my sense of proportion, and there seems to be no way to add additional external feedback without causing instability (I've tried). So you have to attenuate at the input if you don't need that much gain. However, for audio listening you would be using a LOG law pot, and a bog standard single turn job, with a series resistor to provide the adjustment range you want, would be fine.

 

6 ........ I don't use headphones, so I'm not really qualified to comment, but I'm a bit doubtful about your contention.

 

JohnT

[jasonhanjk 0]

You have your point for speaker and mine for headphone. We are both correct.

 

AKG-1000 is a speaker like headphone.

[JTT 0]

You're right, and I s'ppose we could go on forever discussing the merits of one view vs another.

 

None the less, the LM380 is so cheap and easy to implement that it would be interesting if some headphone-owning enthusiast would try it, and comment on the result.

 

JohnT