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Can Impedance and SS vs Tubes

post #1 of 3
1/1/10 at 6:00pm
Thread Starter 
I've been doing some reading on and off head-fi about Headphone impedance. I read some of the history and understand now that low impedance cans need a good current swings/response to be driven accurately, while high impedance cans need good voltage swings. SS amps are typically good at providing current while Tube amps are good at providing voltage.

My question though is:

Within the realm of full size, well powered SS and Tube amps, does the concern about headphone impedance still apply? Or do we expect that well powered SS amps (non-portable with decent power supplies, built-in or dedicated) shouldn't have problems driving a high impedance can? In the same way, a well powered, very good Tube amp shouldn't have trouble driving a low impedance can. It would seem that good SS or Tube amps shouldn't have a problem with most of the production cans out there and that the idea of amp/can matching is more down to sonic characteristics more than whether or not the amp is capable of properly driving a particular pair of cans.

Comments?
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post #2 of 3
1/1/10 at 8:49pm
tubes are inherently limited in current handling capacity - boiling electrons off of a hot metal cathode and forcing them to fly mm thru a vacuum is just darn hard

few tubes can handle the several hundred mA required for driving K701 to 120 dB SPL - even worse, popular SE Class A stages can require > 2x more bias current in the output device than can be supplied to the load

so OTL tube amps either require massive exotic tubes or paralleled output tubes to be true "universal" amps

Transformer output tube amps can be sized to handle any impedance headphone with fairly common tubes - but a good audio output transformer will cost the manufacturer > US$50/channel and is unlikely to be seen in < US$500 amps


SS headphone amps can be designed to handle both higher V for high impedance cans and have more current capacity than needed for low Z cans

however common monolithic op amps are short on both V and I and require a litlle help such as discrete buffer output stages for higher output current and possibly bridged operation to fully drive 600 Ohm cans

but many desktop SS amps are designed for either low or high Z cans but not both
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post #3 of 3
1/3/10 at 5:08am
If you are careful about buying a transformer coupled tube headphone amp with decent quality output transformers, tubes are generally the way to go.

Having said that, for a budget amp, solid state will offer more flexibility.

If you see a 6AS7/6080 OTL tube headphone amp specified as needing <250 watts to operate, you can rest assured that only higher impedance headphones will work well.
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