I was asking a similar question on placing a pad between the DAC and the amp. I proposed what you could call a balanced L pad it's a simpler design than the H pad. https://www.audiosciencereview.com/...d10-balanced-review-usb-dac.25094/post-853758I am again writing about the issue because the Rothwell attenuators I took turned out to be unsuitable. The volume was not turned down by 20db and there was also a noticeable channels imbalance, in addition to the impression of a "bad" sound compared to the digital attenuation alone.
Generic commercial products are probably not suitable for all combinations of devices, as I understand the relative output and input impedances matter.
Having said that, I saw that inside the Rothwells there were three 8.2k resistors in U scheme.
If I did it right, the calculations had to correspond to 10db of attenuation, so I also have the doubt that there was an error in the product I purchased.
Anyway, I decided to build the attenuator myself because it's really simple. What is less simple is to understand how to calculate the resistance values.
I target always to -20db, considering 100 ohm output impedance of Gustard A18 and 47k ohm of input impedance of HYPEX NC502MP.
What is not clear to me is whether the declared impedance is relative to the single pole or to the sum of them... but I think I understand that it is for single pole.
Leaving this aside, from the table of k factors it results that 20db correspond to k = 10, therefore a ratio of 9 between the series and shunt resistors.
So, since I read that the shunt resistor determines the impedance seen by the amplifier, I consider that they must be about 200 ohms (100 X 2), and consequently the series resistors must be 900 ohms each (200 X 9 / 2 because it's balanced). As a result, the DAC should see 2000 ohms of load.
Now, I understand little of these things, I simply applied to the letter a tutorial found online (uneeda-audio.con/pads/).
Could anyone kindly tell me if all this is correct?