Why have HF cut in a DI box? - diyAudio
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Old 31st August 2011, 03:04 PM   #1
diyAudio Member
Join Date: Jul 2007
Default Why have HF cut in a DI box?

As suggested I'm re-asking this question in this part of the forum.

Have just got an Inote Millenium DI box. I'm puzzled by the instr/spkr switch. In spkr position it gives an extra 40dB attenuation plus some hf roll-off (100k in series/47nF to ground). I understand the attenuation, although it seems a bit excessive (I'd have thought -20dB would be more usefull), but when would you need to use a first order hf cut?
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Old 1st September 2011, 06:59 AM   #2
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I guess the silence answers my question. No one else can think of a good reason for having hf cut in a di box either.

Anyway, I've cut out the capacitor and reduced the series resistor to 10k. Now I have a flat DI box with switchable -15dB (from the transformer only) or -35dB attenuation.
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Old 1st September 2011, 07:06 AM   #3
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It's for electric guitars, most players don't like all the HF that's produced when plugging directly into the desk, so roll-off simulating the response of a guitar amp is welcomed.
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Old 1st September 2011, 08:29 AM   #4
Enzo is offline Enzo  United States
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Agreed. PLug your guitar into a PA channel set flat and listen to it. Now plug the guitar into an actual guitar amp - much different sound. Guitar speakers tend to be rolled off by 5kHz. Direct boxes made for guitar amps often include "speaker emulator" features, so the sound it feeds to the mixer or recorder soounds more like what comes out of a guitar amp. Basically rolls off the highs. Guitar amps don;t have tweeters.

Well, "acoustic guitar amps" often do, but those are different from "guitar amps."
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Old 1st September 2011, 10:52 AM   #5
DF96 is offline DF96  England
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Guitar amps can be rolled off by 5kHz too, because of the huge grid stoppers they often use.
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Old 1st September 2011, 08:00 PM   #6
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Originally Posted by Enzo View Post
Guitar speakers tend to be rolled off by 5kHz.
That is so, but all the 12" guitar speakers I've measured have had huge 10-20dB peaks in the on-axis response before they finally roll off. So, combined with an open back cabinet, they sound very toppy indeed (off axis is a different story).
This DI box started to cut off around 100-200Hz. I don't think that's anything like a guitar/guitar amp combo would sound (even with the heaviest flatwound strings and highest inductance humbucking pickups).
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