Okay, so the second-generation Fulla would be designed for a desktop. But how big would it be? The original Fulla was a tiny product. It had to be bigger than that. At the same time, it should be smaller than the Magni and Modi stack. In the end, I chose a footprint exactly half the size of a Magni/Modi stack—and shaved off a quarter inch of height. So, 2.5” wide, 3.5 deep, and 1” high.
A mockup looked pretty cool. It even could use the same potentiometer and the same volume knob as a Magni, which was a big plus. The potentiometer on the Magni was a lot better than the one in the original Fulla in terms of tracking and durability. And the knob would save us having to do another custom part.
With the size decided, I needed to make some decisions on features. First up was how to get more power out of the product. Fulla’s 200mW output into 32 ohms wasn’t really worth getting excited about. It was plenty for most headphones, yes, but I wanted to do better.
Doing better, though, meant both a better power supply and a more beefy amplifier stage. This wasn’t as simple as it might sound, though, because unlike all of our other amps, Fulla uses a switchmode power supply, and op-amp output stage.
Horrors! Some of you are clutching your pearls and looking for a safe space. How can Schiit, bastion of linear power supplies and discrete design, sully ourselves with such inferior technology?
Well, here’s the super-complex rationalization for such a drastic decision: price.
Yes. It is that simple. Horses for courses. When you’re asked to create a power supply that can deliver a reliable +/-5V from USB’s single 5V rail, and to make the most of the 500mA-1A that USB ports can supply, you’re looking at a switchmode supply. Period. End of story. No magic fairy dust or wishful thinking will get you around that fact.
Now, of course, we could do much better than the previous Fulla’s power supply, which used a charge pump to create the -5V rail, but passed the +5V along from USB (after filtering). This asymmetrical arrangement meant that the -5V rail couldn’t deliver the same amount of current as the +5V rail, and it was the main reason why the original Fulla’s output power was limited. With more space in Fulla 2, we were able to use a symmetrical rail generator with a better, inductor-based switchmode supply for each rail, delivering more than 3X the current of the original Fulla’s supplies. With some filtering, it’s a good, solid, quiet power supply.
Similarly, when you’re asked to create an output stage half the size of a postage stamp that can swing the output from rail to rail, you’re not going to do it with discrete parts. Enter op-amps. Specifically, the same exotic, high-current op-amps we used with the first Fulla, the LMH6643. This fast, high-current, rail-to-rail device has only one downfall—its current output is still less than we’d like. So, in Fulla 2, we simply used two of them per channel to double its output current capability.
Now, we have an amp stage that can deliver 550mW into 16 ohms—much better. Still not a Jotunheim, or even a Magni, but there you go. Sometimes you have to know when to say “When.”
Beyond power output, though, what kind of I/O should Fulla 2 have? I waffled a bit, wondering about having just a preamp out, or not having an analog input, but in the end, I threw them all in: fixed and preamp outs, as well as an analog in. Fixed so you could use it as just a DAC, variable so you could use it as a preamp (it amplifies the analog input, too), and an analog input in case you have a phone or something (that still has a 1/8” output) that you’d like to connect to Fulla.
The catch to all of this I/O? It all has to go in and out on 1/8” jacks. Yeah, I know. But 1/8” to dual RCA cables are easily available.
Bluetooth? Nope. Yes, it’s convenient, and yes, it sounds like ass. Yes, I know, it doesn’t sound completely like ass, but it doesn’t sound as good as a cabled connection. Buy a cable. Don’t be lazy.