Crack speedball input sources

[wayward]

I've started to think about leveraging some of my other gear for the preamp + DAC stage. I have an apogee symphony mki which I'd like to use in the chain. I'm guessing folks generally use line level to feed into the inputs, but I've often wondered about whether there's any issues with using speaker outs vs line outs vs headphone outs into the Crack and what the implications are for each. I don't have the technical background here so hoping someone can help shed some light.

many thanks

[Paul Birkeland]

You should find that a line output will put out around 2V of signal with an output impedance that's maybe a couple hundred ohms at most.  A headphone output may only be able to swing that much voltage, but there will be a volume control and a higher current buffer at the output to drive the output impedance down (likely to somewhere around 5-20 ohms).  A speaker output will further decrease the output impedance and increase available current swing, and really you'd end up finding that the voltage swing available will likely be quite a bit higher.  The potential problem with the speaker output is that there's no assurance that speaker negative is actually audio ground, so you may find that grounding a speaker negative connection can damage a speaker amplifier. 

Still, I'd use the line output into the Crack since it should have everything you need without anything extra that you don't need.

[wayward]

Thanks for the response, Paul. I'm still a bit unsure of the practical implications. One of the reasons why I was compelled to post was because I found it odd: I have a Centrance Dacport lx feeding into the crack currently and it's marketed as a line level with a very hot usb bus class a amp. However, I have to keep the digital (iTunes) volume at close to 10% and the Crack at around 10 o'clock to realize ~85db on a set of Sen 6602s2 which I wouldn't have expected. So this lead me to wonder a) is the attenuator on the Crack in need of some adjustment (the max output the centrance is 2.07V - at 80-90% iTunes volume the Crack would have to be at 7, maybe 8 o'clock for that same 85db) b) generally would it be better to crank the Crack up so it's doing most the work and manage volume though the source / preamp or vice versa. What do people normally do here to manage gain and what's the best way to think about this?

As it relates to the symphony, the xlr main outs are meant to drive active monitors which I assume are basically line level - in that case would your point around audio grounding be an issue if fed into the crack?

Again, thanks if there's anything else I can elaborate on please let me know!

[Paul Birkeland]

FAQ 3/4 applies here for sure:
https://forum.bottlehead.com/index.php?topic=4295.0

XLR outputs for active monitors will just be variable line level outputs.

[wayward]

Thanks