[Marshall969]

I see many people say a chip such as a 2020 cannot drive headphones, why is this?

 

[kiteki]

Headphones have transducers in them just like speakers, however they're usually happy with 40mW+40mW, they don't require 80W+80W.
 
The difference there is 2000.

 

[obobskivich]

IIRC the T-Amp chips also can't be bridged/run into SE loads and remain stable - they'll run differential into headphones just fine (and there's people have have driven stuff like K1000s with them).

 

[wje]

Just head to Parts-Express and look at all of the Topping amps they sell.  They'll based on the T-Amp chip, yet these portable amps also feature headphone jacks for use with headphones.  Many of them have built-in DACs, too.

 

[KimLaroux]

Quote:

Just head to Parts-Express and look at all of the Topping amps they sell.  They'll based on the T-Amp chip, yet these portable amps also feature headphone jacks for use with headphones.  Many of them have built-in DACs, too.

 
They use an op-amp for the headphone output. It's not driven trough the T amp chip.
 
Edit:
 
I had to go refresh my memory by reading a few web pages. Class T amplifiers are switching mode amplifiers. They work just like a switching power supply. These thing use, to simplify things, a fully ON, fully OFF cycle, and then smooths the output. For this to work, the filtering has to have a load. The T amps were designed to work with 8 ohms loads, which pulls a lot of current. Headphones are very small loads that demand very small amount of current. They are way bellow the "minimal load" requirement for the filtering circuit to work properly. With only headphones on the output of a T amp, the amplifier will be "shooting trough the roof" as the load won't be enough to prevent the voltages to spike.
 
TLDR; The T amps were designed to drive speakers, and headphones are bellow the minimal load requirement for the amplifier to work.

 

[OJNeg]

Quote:

 
They use an op-amp for the headphone output. It's not driven trough the T amp chip.
 
Edit:
 
I had to go refresh my memory by reading a few web pages. Class T amplifiers are switching mode amplifiers. They work just like a switching power supply. These thing use, to simplify things, a fully ON, fully OFF cycle, and then smooths the output. For this to work, the filtering has to have a load. The T amps were designed to work with 8 ohms loads, which pulls a lot of current. Headphones are very small loads that demand very small amount of current. They are way bellow the "minimal load" requirement for the filtering circuit to work properly. With only headphones on the output of a T amp, the amplifier will be "shooting trough the roof" as the load won't be enough to prevent the voltages to spike.
 
TLDR; The T amps were designed to drive speakers, and headphones are bellow the minimal load requirement for the amplifier to work.

 
This is the best answer here.
 
Simply put, switching amps are designed for specific loads. If you change the load, the amp is not stable and does not function correctly.

 

[JadeEast]

I've driven headphones from T-amps. You needs dual mono wired headphones and proper loading of the output of the amp.

 

[wje]

Quote:

 
They use an op-amp for the headphone output. It's not driven trough the T amp chip.
 
Edit:
 
I had to go refresh my memory by reading a few web pages. Class T amplifiers are switching mode amplifiers. They work just like a switching power supply. These thing use, to simplify things, a fully ON, fully OFF cycle, and then smooths the output. For this to work, the filtering has to have a load. The T amps were designed to work with 8 ohms loads, which pulls a lot of current. Headphones are very small loads that demand very small amount of current. They are way bellow the "minimal load" requirement for the filtering circuit to work properly. With only headphones on the output of a T amp, the amplifier will be "shooting trough the roof" as the load won't be enough to prevent the voltages to spike.
 
TLDR; The T amps were designed to drive speakers, and headphones are bellow the minimal load requirement for the amplifier to work.

 
While yes, this is correct, one who has a hard headphone to drive (e.g. Ortho headphones), they could easily build a speaker tap and use the actual power from the amp itself to drive the headphones.  No need to go through the included op-amp at the headphone stage on the amp.
 
Edit: Here's all you need to build the taps for the speaker output: http://home.comcast.net/~wayne.ernst/taps.pdf

 

[MDR30]

Quote:

I've driven headphones from T-amps. You needs dual mono wired headphones and proper loading of the output of the amp.

JadeEast is right  - T-amps don't like left and right ground being connected, as normal TRS 3,5 and 6,3 mm plugs are, a problem shared with tube/valve transformer outputs. They may run into havoc.

 

[Comfortable]

I know this might sound eccentric, but I have a pair of Sennheiser HD650; 300 ohms.  I'm thinking of rewiring it-dual mono for each driver; 4 banana plugs in total.   Would this be safe or is the voltage spike still a dangerous issue?