Bridged CMoy

natumbri

Member
2007-12-01 7:31 am
Is there any interest out there in bridged headphone amps?

Here's a suggestion for a simple "bridged CMoy". Maybe a good choice for a portable amp for high impedence headphones?

Cheers,
Nik
 

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jcx

Member
2003-02-17 7:38 pm
..
for what headphones?

only as a special purpose amp for hi Z cans with moderately high sensitivity

"CMOY" usually means simple circuit, PS, and amost always DIP op amps to allow easy construction and rolling

few DIP op amps have the output current to allow bridging to advantage with most headphones
 
only as a special purpose amp for hi Z cans with moderately high sensitivity

"CMOY" usually means simple circuit, PS, and amost always DIP op amps to allow easy construction and rolling

few DIP op amps have the output current to allow bridging to advantage with most headphones

Do you convert the phones to a 4 wire connection ? How do you use a bridge amp on a load with a common (3 wire) connection?

What is the purpose of the 4K7 resistor to ground on pin 2 of the opamp?

 
I built something similar several years ago but with output buffers nested in the feedback loops. It was a fun project.

The 4.7Kohm resistor on the inverting input of "IC1a" is not necessary, and may lead to problems. IC1a will get its input ground reference from the output of the other op amp. Problems may come from the 10Kohm resistor (between the output of the non-inverting op amp and the inverting input) and the 4.7Kohm resistor working as a voltage divider and screwing up the balance.
 

natumbri

Member
2007-12-01 7:31 am
only as a special purpose amp for hi Z cans with moderately high sensitivity

Yes, I agree that this is one for high impedance headphones.

"CMOY" usually means simple circuit, PS, and amost always DIP op amps to allow easy construction and rolling

The circuit is pretty simple and uses DIP op amps for, as you say, easy construction and rolling. I didn't include a PS, but any of the virtual ground type circuits typically used in a CMoy would be fine. We've all seen them a million times, so seemed like little point including one. I tend to use a TLE2426 with a BUF634. See here for more: Virtual Ground Circuits

few DIP op amps have the output current to allow bridging to advantage with most headphones

Really? Please elaborate.

Do you convert the phones to a 4 wire connection ? How do you use a bridge amp on a load with a common (3 wire) connection?

Yes, you would have to convert the phones to a 4 wire connection. I guess that is why people don't bother with bridged headphone amps. Then again, there are some commercial headphone amps that offer bridged (or "balanced") outputs: eg. HeadRoom Balanced Ultra Desktop Amp | HeadRoom Audio

I built something similar several years ago but with output buffers nested in the feedback loops. It was a fun project.

That sounds like it would be great for those low(ish) impedance headphones that require plenty of voltage and current, like AKG K501s or Sennheiser HD-570s.

The 4.7Kohm resistor on the inverting input of "IC1a" is not necessary, and may lead to problems. IC1a will get its input ground reference from the output of the other op amp. Problems may come from the 10Kohm resistor (between the output of the non-inverting op amp and the inverting input) and the 4.7Kohm resistor working as a voltage divider and screwing up the balance.

The (4K7) resistor on Pin 2 is important for opamps that are not unity gain stable. If the opamp used is unity gain stable, the resistor can go.

Cheers,
Nik