I’m in the process of repurposing a B4 for headphone use. My question is about the output cap value. My headphones are AKG K701 with impedance of 62r so I think with the 100r resistor a 60uF film cap will give me just under 10ms time constant. I’m looking at 60uf because the Panasonic EZPV polypropylene is a good price at RS. I’m fairly confident on those calcs but the only fly in the ointment is that this cap is four pin. Question is can i just link each of the two pins at each end?
B4 Headphone Question
- Thread starter timH
- Start date
a.palfreyman
pfm Member
You have 160R total. 60uf gives a time constant of 60miliseconds or a corner frequency of 16Hz [from F= 1/(2pi.R.C)]
You want at least 100uF (-3dB at 10Hz)
Why not use a nichicon ES bipolar of say 220uF?
You want at least 100uF (-3dB at 10Hz)
Why not use a nichicon ES bipolar of say 220uF?
statman308
Apprentice bodger
The original build notes also include a DC coupled option:
"Some uses (many) may need an output capacitor. Value depends on load impedance. If you go DC coupled, the output offset will typically be 20mV or so. If you replace one of R3 or R4 by a trimmer, you can adjust it to null."
Might be worth trying?Would that be safe for headphones?
martin clark
pinko bodger
yes, 20mV will cause no harm. You will get a pop on plug-in/unplug (loudness wil depend on sensitivity of the headphones)
I'd fit the trimmer as suggested to null it out.
I'd fit the trimmer as suggested to null it out.
