Carbon Composite Mojo?

[Silent Fly]

I noticed that in the Xotic RC Booster schematics there is a 470R Carbon Composite on series with the output. I am intrigued by why a small resistor in that place is carbon composite and I would like to ask your opinion about it.

I understand the psychological (aka mojo) factor but just for the sake of it I calculated the contribution of this resistor to the signal.

Considering the output impedance of the emitter follower close to zero, a relatively heavy load of 100k, the resistor create of a voltage divider that attenuates the signal by 0.099 (-0.08dB).

If the resistor is non-linear by 50% (235R-705R) the attenuation would vary between -0.12dB and -0.16dB.

I may have made some mistake in my calculation but if I am right, the difference between carbon composite and metal film should be inaudible – or not?

[Silent Fly]

...the attenuation would vary between -0.12dB and -0.16dB.

Sorry

with R = 235ohm => -0.04dB
with R = 470ohm => -0.08dB
with R = 705ohm => -0.12dB

[soulsonic]

I would say it's there for good luck mojo, but since it's hidden under goop the psychological theory doesn't hold up. Really, the only reason I can see to use a single carbon comp in a circuit full of metal film would totally be for psychological effect, which means it would need to be shown off.
I personally love mojo parts, but there's no point in using them if you're going to hide them!

Sure, sure... there can be very specific circumstances where a carbon comp would be preferred to a metal film... like a pulse-handling circuit where the minute inductance of a metal film would affect the wave in a negative way. But that is certainly not the case here!

[JHS]

There's a simple formula for caps ans resistors in audio stuff: different material = different sound

No mojo, just a matter of personal taste.

Often you find CCs in military and industrial stuff. Due to vibrations the boards are stressed a lot and CCs are not as fragile as other Rs and won't fail under such conditions.

JHS

[Silent Fly]

There's a simple formula for caps ans resistors in audio stuff: different material = different sound

No mojo, just a matter of personal taste.
[...]

True... but can you hear a difference between 0.12dB and -0.16dB

[JHS]

True... but can you hear a difference between 0.12dB and -0.16dB [/quote]

You can hear a difference in sound if a LP guitar is wired old or new style. In theory there should be no difference, you can't measure different values, but you can hear that tone nuances and timbre are different.

A piano will be always tuned by ear and not with a strobe tuner or similar things and if you ask those guys they will tell you that their ears are the best eqipment and that no high tech stuff will do the job as good.

In terms of tone nuances the last judge should be your ears (of cause only if you not a deaf metalhead).

JHS

[lolbou]

A piano will be always tuned by ear and not with a strobe tuner or similar things and if you ask those guys they will tell you that their ears are the best eqipment and that no high tech stuff will do the job as good.

That's because a piano is never in perfect tune. Remember the well-tempered stuff and so on?

A piano can't be exact on its whole range because of its inharmonicness (?), due to the different nature of its strings (plain or wound)...

Therefore, a strobo tuner will give you the good pitch for each note, but your piano will sound awful... There comes the ear

[Scruffie]

Hence why, (well in my experience and knowledge) alot of piano tuners are actually blind as it heightens there hearing, where as i would say maybe i should find a piano tuner to do my intonation after my last comment i can't help but feel a bit bad then.

Scruff.

[B_of_H]

the only difference i've noticed in using them is that I have to check their true values because all of the ones I get are 5% tolerance or so they say. I'm terrible at math but when a 100k resistor can be 91k or 104k isn't that more than 5%.