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TOPIC: Can pedalSHIELD accept a line level signal?

Can pedalSHIELD accept a line level signal? 8 years 4 months ago #99

  • Promit
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Just as the title says. It sounds like the input and output stages are designed for guitar level inputs rather than line level. Would it be difficult to change to line level? I'm not much of a hardware guy.
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Can pedalSHIELD accept a line level signal? 8 years 4 months ago #101

  • JR
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Short answer: The pedalSHIELD was designed to handle electric guitar signals, it could also handle line level signals, but depends on the particular voltage level of this signals (if they are too big the shield will be overloaded).

"The exact definition of line level signals for consumer audio is hard to pin down--different manufacturers adhere to slightly different standards, sometimes even within their own product line. But the Line Level voltage for consumer audio is pretty much defined as a maximum signal voltage of around 5-6 volts. Measure the output of your typical CD player or Tape Player component and you will see maximum voltages in that range." (extracted from beavisaudio)

In theory:
- Equipment is generally referred to as +4dBu (3.4Vpp) equipment (professional) or –10dBV (0.9Vpp) equipment (consumer)

In practice:
- Microphones and passive electric guitars = very tiny signal size
- Keyboards and consumer recording gear = small line level
- Pro recording gear = large line level

In pedalSHIELD:
I would try to explain it as easy as possible: Arduino DUE analog to digital converters work with signals fom 0 to 3.3V (3.3Vpp). pedalSHIELD has an input stage which can amplify the guitar signal from 1 to 20 times. So with the RV1 on-board trimmer you can adjust this input stage gain.
  • Guitar signals go from lets say 0,2Vpp up to 2Vpp (depending on the pickups) so with the RV1 you can amplify the signal close to 3.3Vpp optimizing the ADC range.
  • Consumer line level signals go from 0,3 to 2 Vpp, this range is not far from the guitar signal levels, so it should work (I cannot guarantee it cause I dont have any line level device around).


note:
Signal level in dBu = 20 x log (signal voltage / 0.775)
Signal level in dBV = 20 x log (signal voltage)
keep it simple
Last Edit: 8 years 4 months ago by JR.
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Can pedalSHIELD accept a line level signal? 8 years 4 months ago #104

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So if I understand correctly, signals above 3.3 V will clip, which means systems designed for pro audio (+4 dBu) may overdrive the input stage when turned up to their maximum levels? But none of these signals will damage the shield, merely cause clipping?
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Can pedalSHIELD accept a line level signal? 8 years 4 months ago #105

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Signals over 3.3V will clip, right.
Signals over 5V could damage the input buffer (TL072 supply is ±5V).
keep it simple
Last Edit: 8 years 4 months ago by JR.
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