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Can someone school me in signal flow of headphone tube amps?

Jul 24, 2020
I am looking for some wisdom from someone that understands the signal flow in a headphone tube amp.

I am experimenting with running my mixes out of Protools (music production software) and into headphone tube amps. I'm using the headphone amps to distort the signal on purpose before sending the signal back into Protools. Using a Schiit Vali 2, I was able to get some really awesome distortion going. Mixing the distorted signal with the original mix sounds pretty magical and I'm happy to share the results with anyone that's interested.

I tested this out with 5 different tubes and they all sounded more or less exactly the same. I'm wondering if the difference in tubes would be more pronounced using an OTL tube amp instead of a hybrid. My hunch is that the "pre output" of an OTL tube amp will not be any different than the "pre output" of a hybrid tube amp (like the Vali 2) because the pre outs only use the buffer tubes in both situations.
^...If this is the case ...^ I'm also wondering if it's dangerous to go out the headphone output in a OTL tube amp into the line inputs on another device (my Audient line amps)

I go from laptop headphone outputs right into my mixer all the time in live music situations when the "musicians" are playing along with tracks coming out of their laptops. In that situation, it's usually their Macbook (10 ohm output impedance) going into my Zoom LiveTrak mixer line in (10k ohm input impedance) and I experience negligible signal degradation (for live music purposes).

Looking at the Schiit Valhalla 2 (14 ohm output impedance) going into my Audient line in (8k ohm impedance) - It doesn't look like it'll be so different or cause problems. I use the pad on the Audient to knock the signal level down coming in and keep it from clipping those converters. I'm not worried about raising the noise-floor - the whole point is harnessing the tube distortion.

  1. Are the "pre outs" on a tube hybrid amp and a OTL amp going to use tubes differently? Or is the OTL only different when you're listening out of the headphone output?
  2. Is it safe (using caution) to run the headphone output of an OTL into a line level input on another device (assuming I don't care about signal degradation)?
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-Old Cob
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