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Using Behringer DI4800a as a line-level converter

Aijan

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Jul 13, 2021
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My Denon X2500h doesn't have pre-outs, and I thought using a DI box (in my case a Behringer DI4800A) might be a good idea to convert the speaker level output to line level. I know the conversion can be done by other means, but the convenience of using an active DI box for connections and the added benefit of unbalanced to balanced conversion is nice.

The Behringer DI4800A's input level can be up to 20 dBu (~7.75V RMS), so I reduced the channel level to -10 DB on the AVR to limit the speaker output to around that range in my high volume listening levels. I then engaged the -20 db pad on the DI box to reduce the max output level to around 0.75V, so it can be used as an input for my MiniDSP 2x4 (noisy, I know, but it's not in the signal chain for the following measurements). The output pad is optional if the DSP or external amps can handle high input levels.

I've made some measurements using my Focusrite Scarlett 4i4 Gen 3, and I would like to get your opinions about the measurements.

First the loopback measurement for the Scarlett 4i4 Gen 3 audio interface (the bandwidth limited ~93 dB SINAD appears to match Amir's measurements of Scarlett 2i2 in line mode):

scarlett_1khz_sinad.png


The DI4800A measured (SINAD is about 84 db):

di4800a-1khz-sinad.png


Direct measurement of Denon's center channel out into Scarlett's 60 kOhm input impedance. SINAD is about 83 db. Notice the high 2nd harmonic but otherwise clean.

denon_x2500h-10db.png


Finally, the DI4800A is in line between the Denon and Scarlett. Center channel speaker out (-10 db volume on the AVR, effectively -20 db because channel level is set another -10 db). The output should be around 0.4 volts RMS as measured by my multimeter after the -20 db pad on the DI box (4 volts out of the AVR into 20 kOhms). SINAD is slightly better at 84 db. The second harmonic is reduced greatly only to be offset by the increased third harmonic. I think this is because the unbalanced to balanced conversion. What do you think?

denon-di4800a-1khz-sinad-10db.png


If I haven't made any major errors during the above measurements, I think getting 84 db SINAD out of the AVR's speaker outs isn't half bad. Please let me know what you think.
 
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