There are a few tweaks that you can experiment with on the BantamDAC. Of course the greatest "tweak" you can accomplish is by constructing the BantamCableDAC. Several connections are elminated in the CableDAC. The result is a slightly quieter and much more convenient-to-use DAC.
Of the other tweaks, they all consist of capacitor changes. These changes are divided into two categories:
I. Power Capacitors
This is the de-coupling capacitor for the DC voltage Common Mode pin for the DAC chip. A super-low ESR capacitor will provide the most benefit here, something like an Os-con or other super-low ESR organic polymer electrolytic is a good upgrade. Anything up to about 330uf will work well, but the pads are limited to 6.3mm diameter and 2.5mm lead spacing.
Mouser has a very good "off-brand" alternate for an Os-Con, a United Chemcon sized at 220uf and 6.3V: 661-PSA6.3VB220M This capacitor is also available at Beezar.com
This the primary power cap in the BantamDAC. The highest-quality, most powerful electrolytic you can find up to the limits of 10mm dia pads on the board, 5mm lead spacing, and 12.5mm height.
- Panasonic FM, 1000uf 6.3V - This is the preferred capacitor listed on the BOM. There is a Mouser version of Nichicon's comparable UPW, but its performance in ESR and ripple is not as good as the Panasonic FM (Panasonic FC's and Nichicon UPW's are typically equivalent, but Panasonic FM's are better than both). FM - 0.038Ω, 1290ma. (UPW or FC - 0.09Ω, 755ma) This capacitor is available at DigiKey and at Beezar.com
- Nichicon UHN 1500uf 6.3V - Since the BOM was originally forumlated, a couple of outstanding Nichicon capacitors have become available at Mouser. These capacitors exceed the performance of the Panasonic FM at the same dimensional size, but at a higher cost. The UHN is one of those caps. UHN - 0.018Ω, 1760ma. This capacitor is available at Mouser and at Beezar.com
- Nichicon UHZ 1500uf 6.3V - Another outstanding power cap at a significantly higher cost than either the Panasonic FM or the Nichicon UHN is the Nichicon UHZ. UHZ - 0.012Ω, 2280ma. This capacitor is also available at Mouser and at Beezar.com
II. Signal-Coupling Output Capacitors
Of all the tweaks you can perform on the BantamDAC, the signal-output coupling capacitors - CL and CR - are the most signficant. Since a USB/PC power supply is +5VDC, the analog output of the DAC is offset at +2.5VDC (this allows a signal swing of +2.5VDC and -2.5VDC in theory). Because of that, coupling caps are needed to block this DC offset. The result is that the coupling caps pass every bit of the signal. That means the audio quality of the coupling caps is very important. It also means that the coupling caps form an RC filter with the resistance of the connected load (usually an amp). So, unless the caps are sized for a minimum capacitance, bass frequencies will be filtered out. Generally speaking, 1.0uf is sufficient to guarantee all audio bass frequencies for most amps. 0.66uf is probably OK in many circumstances, but with a 10K pot (input impedance) on some amps, 0.66uf might be a little low.
Still, 1.0uf and the pads on the BantamDAC (5mm or 10mm - also length) allow a lot of good choices for CL and CR:
- Vishay-Roederstein MKT1817510064 - 1.0uf, 63V. This cap is recommended as the default film capacitor for the BantamDAC. A light green box 11.5mm tall with 5mm lead spacing, this cap is also the default film cap in the power supplies for the Millett MAX/MiniMAX headphone amplifiers. The construction is metalized polyester. These caps are very neutral, with good bass and sparkling highs. They are very fast. However, some consider them a tad lean and the mids are perhaps recessed slightly. Those qualities serve them in good stead when combined with a tube amp such as the MAX/MiniMAX, which has ample mids, bass and presence. These capacitors are available at Mouser and at Beezar.com.
- Wima MKS2 - 3.3uf 50V. This cap is an alternative film capacitor for the BantamDAC. Again, a metalized polyester film cap, these look very similar to the MKP10's used on many amps. Initially they will sound a bit thick and bassy, but eventually break in to some of the best and strongest mids available on the BantamDAC. These capacitors are also available at Mouser and at Beezar.com.
- Black Gates NX HiQ - 47uf 6.3V. The default selection for the AlienDAC, these caps perform superbly in the BantamDAC. Give them a chance to break-in: it won't take as long as the larger caps used on MAXes and such, but allow them a couple of nights and days of running before deciding whether you like them or not. Unbelievably transparent for an electrolytic cap, they differ from the film caps above by some of the punchiest, dynamic bass available with a BantamDAC. Highs are not quite as transparent or sparkly as with the Vishay-Roedersteins, but only by a tad. Highly recommended for a full-bodied, dynamic sound signature. These capacitors are available at Soniccraft and at Parts Connexion.
- Elna ROA Cerafine - 47uf 10V. At 10V rating, these caps are still only 6.3mm dia and 11mm high. The traditional description for Elna Cerafines has been "same as Black Gates, but without the break-in requirements." These capacitors are available at Beezar.com.
- Elna RFS Silmic II - 47uf 6.3V. These caps are 5mm dia and 11mm high. They are Elna's replacement caps (new and improved?) for the Cerafines. Some people have expressed a preference for these caps over any other on the AlienDAC. As the BantamDAC is very similar, they should perform equally as well. These capacitors are available at Beezar.com.