Aiyima A07 MAX - Initial Comparison and Review

[]eep]

Hi. I'd like to hear more about this. What does a resistor in series do to the mids and highs? I assume it modifies the sound somehow.

I had thought that most amplifier inputs have such high input impedance that splitting the pre-output to two amplifiers using a Y-cable doesn't actually halve the input to the amplifier, and so causes no appreciable change to the sound. Is that incorrect?

Tossing out some numbers as an example: the SMSL SU-1 is a popular inexpensive DAC, with 47 ohm output impedance. The Aiyima A07 is measured at 23 kOhm input impedance. So if you divide that input impedance in half by wiring two amps in parallel, it's still 11,000 ohms (input) vs. 47 ohms (output). I'd think the signal would still be full strength. But I could easily be missing something, so please let me know!

I don't have all ins and outs of this. But one simple thing I do know: a resistor resists. Meaning it reduces you signal. But sometimes it's needed to reduce oscillation. And f.i. in a tube amplifier you need a load to operate. If you connect the + and - with a transformer: a wound wire with no resistance to speak of, you simply short the amp. That's not good as you can imagine. Same for a dac etc. So there's an R placed to short the output. Not in the signal path but from + to ground (or -).

You need a little bit on the dac out, and a lot on the amp in. Or you won't get a good signal: 47kΩ is a pretty standard input impedance. Now the dac I worked on, an R2R with 4 Philips TDA1543 chips needed 520 or 470R to sound good (full, wide soundstage with enough damping). The same effect as you get with a tube amp with high impedance speakers changing from 16 to 8 to 4Ω taps. It sounds either to wide and woolley or tight and timid.

My Denafrips Ares II has 600Ω output impedance. So does my Laiv Harmony. That's why they advise to not use both RCA and XLR outputs connected. If you connect that to an amp with a lower than usual input impedance you will run into sonic trouble. The ratio starts getting too low.

Now if you put a resistor in the signal path you will lower the output, that's what your volume does. You don't want a 500W amplifier that is invariably throttled to 5%. Not if you need to run insensitive speakers.
But you want that power to go to your Aiyima AO7's poweramp sections input. So you guide the flow to that part and just a tiny bit to the sub-out. The sub wil have its own input opamp to boost the signal back up, with some extra noise and hiss but subs don't care about that. Also if you use a wire wound resistor that fall off in the treble because of inductance, subs really don't care about that. But for a preamp a tiny metal resistor works fine to create an extra output.
So you always need to think what type of capacitor, resistor or inductor fits my need in this particular spot.

I hope I explained it a bit with my autodidact insight. I only learned the basics+ in physics, I'm not an EE, I did some other study. I always hate it when I ask an EE and they just brush me of as if I'm stupid. Not everybody understands medicine, French, chemistry, acoustics, construction, architecture, history etc. I'm not a one trick pony and I love learning new things. And helping others do the same.