18 dB self-made attenuator pad for line-level signals
Ok, the Zoom's line input is too hot. What we need is an attenuator pad to get it right. Fortunately this can be fabricated easily with just a few resistors. All the technical details are here.
I have played with a couple of variants (9 dB, 12 dB, 18 dB and 24 dB) and found the 18 dB worked best. This pad will give you a record setting between 30 and 40 with strong line signals.
24 dB is a little over the top. You may not be able to get to 0 dBFS even with hot signals and a record level of 100. The other too pads may be too weak for strong signals.
I recommend using a U-bridge as in the circuit diagram on the left. You will need three resistors per channel. One is 680 ohms and the other two are 2.6 kohms. It is not important to use exactly these values - just see which resistors you can get. But make sure you use 1% metal film resistors for improved common mode rejection.
The input impedance of this pad is a little low (only 5.9 kohms) but a fair compromise. The output impedance is 680 ohms and that's pretty ok.
The attenuation is exactly 18.7 dB and perfect for our needs.
I have played with a couple of variants (9 dB, 12 dB, 18 dB and 24 dB) and found the 18 dB worked best. This pad will give you a record setting between 30 and 40 with strong line signals.
24 dB is a little over the top. You may not be able to get to 0 dBFS even with hot signals and a record level of 100. The other too pads may be too weak for strong signals.
18 dB U-bridge pad
I recommend using a U-bridge as in the circuit diagram on the left. You will need three resistors per channel. One is 680 ohms and the other two are 2.6 kohms. It is not important to use exactly these values - just see which resistors you can get. But make sure you use 1% metal film resistors for improved common mode rejection.
The input impedance of this pad is a little low (only 5.9 kohms) but a fair compromise. The output impedance is 680 ohms and that's pretty ok.
The attenuation is exactly 18.7 dB and perfect for our needs.
If you examine the image closely you'll discover three identical 680 ohms resistors per channel. This was my first version with 9.5dB attenuation. It turned out that was ok but not quite good enough. For standard line signals the Zoom's record level had to bet set to 10 which still meant quite a lot of distortions.