Output caps - or no output caps?

[qusp]

have a look for some posts by Steve Eddy for solid state headphone avps with transforver coupling, he'll tghrow a transformer in anywhere if you let him =) but he does know a lot about using them for both sand and glass amps

 

[Earfanatic]

Thanks qusp!

 

[Wolfsin]

I had fought the blocking cap issue for too long with LME49600 output pairs on a pair of stereo boards bridged to rewired HD600 cans. I finally rewired the bridging so that the DC was practically unmeasurable and removed the caps. Wow, what an improvement--perhaps of the elna SILMICII 100mfd--but I am now a believer in allowing the 49600's to have their way with my cans.

Maybe I am running a risk but will wire 'the wire' bal-bal pcb the sameway when it arrives.

'gardz, Dick

 

[Andrew Eckhardt]

I don't mean to detract from the desire to engineer a more "responsible" headphone amp circuit, but the minute you mention "cost no object" maximum performance as a design goal, to me that suggests using the finest available amplifier with your phones connected directly to it, and if you burn them up, well, cost no object, right?

 

[regal]

I don't mean to detract from the desire to engineer a more "responsible" headphone amp circuit, but the minute you mention "cost no object" maximum performance as a design goal, to me that suggests using the finest available amplifier with your phones connected directly to it, and if you burn them up, well, cost no object, right?

Been there done that, with a crappy dc servoed hybrid design by someone I won't mention here. Sometimes custom phones and drivers are not replaceable at any cost (like HP1000's hand tuned by Mr Grado.)

Here is the test I do, turn on the headphone amp during peak AC summer hot day. Then connect a 32 ohm resistor across the amp output.

With the DMM probes across the output have someone plug in a 1500W heater on the same breaker as the amp.

Most of the time your mains will swing with this test, a well regulated power supply will not swing with the mains and pass the test.

Even cap coupled amps can fail this test. If your coupling cap is sized for say 10 hz, and your mains are oscillating at .001 hz a bad design will pass this straight thru the cap and fry the voice coils, seen it happen.

 

[Conrad Hoffman]

So nobody thinks they can build a direct coupled amplifier that's immune to line problems, doesn't thump and has 99% reliability over say, I dunno, a decade?

 

[fubar3]

1) Those who are using DC coupled amplifiers, how do You make sure Your headphones are safe all the time?

I use 49610 buffers with no blocking caps anywhere. There are LM317,337 regulators supplied by a full-wave rail splitter. If a large offsetting DC signal is applied, one of the regulators becomes unstable causing a noise in the headphones. The phones are saved because the regulator takes the heat. I had to keep it simple because I used SMD surfboards to mount on an old-school protoboard.