Bypass Resistor for output coupling capacitor

[brightcity]

Hello all, I recently experimented with the addition of a 1MegaOhm resistor between the pos and neg leads of the output coupling capacitors used in the Bottlehead Crack. I used a 2W Carbon Film as it was the only high ohm and wattage resistor I had around.

The amp has certainly become more lively with this addition. It should also help to prolong the life of the coupling caps as it helps it drain after shutdown.

 

[Doc B]

I can't think of any good reason to do this. There is already a resistor to ground on both sides of the coupling caps that will drain off any potential when the amp is turned off.

 

[brightcity]

I agree completly, but it made a very significant impact. There is a slight loss of low level detail but the amp is significantly more fun to listen to.

 

[Doc B]

I want to be very clear here that, if you damage your headphones by putting DC through them, we said not to install that resistor. If you are willing to accept responsibility for that potential outcome, best of luck with your experiments.

 

[brightcity]

Thanks, if I damage them I can live with it.

 

[Paul Birkeland]

Hello all, I recently experimented with the addition of a 1MegaOhm resistor between the pos and neg leads of the output coupling capacitors used in the Bottlehead Crack. I used a 2W Carbon Film as it was the only high ohm and wattage resistor I had around.

The amp has certainly become more lively with this addition. It should also help to prolong the life of the coupling caps as it helps it drain after shutdown.

Argh, I sure wouldn't do this.  The caps drain themselves when the amp turns off (you can measure this if you want to double check), and you're creating a path for DC to damage your headphones.  Also, the impedance of those output capacitors is well under 100 Ohms across audio frequencies, so you aren't gaining anything in terms of performance by putting a resistor across the cap.

Your resistors will put 0.25V of DC offset on the headphone jack with no headphones, and that offset will vary depending on your headphones.  The application of some DC offset to headphone drivers is audible, but not in a good way.

 

[brightcity]

I agree, that is a lot of DC. I haven't soldered them in yet, so if the phones blow then I can remove em.

 

[Paul Birkeland]

Yeah, several solid state amps will actually turn themselves off if the DC offset climbs that high (seems like the highest accepted level for a speaker amp is 100mV).

Applying a DC bias to your headphone drivers will warm them a bit, and the voice coils/suspension will not be centered at rest.

 

[brightcity]

That must be what I am hearing. The mod gave it that kinda nightclub feel where they crank the volume so high.

I didn't pay much for the Beyerdynamic DT990 pro so I'll keep it.