As probably quite a few people arround here, I also own a BasX A-100. And it is a nice “small” speaker amp with a powerful headphone out.
I have the jumper-position “modded” to put the output resistance down to 110Ω (stock is 220Ω, jumpers in is close to 0Ω). That helps with the noisefloor (the A-100 is a speaker amp first!) a bit, on some more sensetive headphones, with my mod, you still get a lot of hiss.
Instead of taking the screws out everytime to unplug my modded resistors, I decided to make an external resistor box. It will do the exact same as the internal resistors, just in a more convenient form factor.
In my project, I used a 3-pole (2 is enough) 4-position (can vary this to whatever you want/can buy) switch.
In case you want to build something like this yourself, here is the schematic:
- 3-pole, 4-position switch
- Wirewound Resistors (In my case: Vishay G220-series, 47Ω, 100Ω and 220Ω. Make sure yours are at least rated for 3W)
- 2x Neutrik NR-J6HF (6.3mm TRS jack)
- 2x Neutrik NR-series nuts
- 2x Cliff FT-6320 (3.5mm TRS jack)
- plastic box
To make this easier, get a bigger box than I did.
You see the inconvenience clearly with just the jacks installed:
The resistors have to “stand” next to the switch. Laying them down would result in having to “hot-rod” the case with them sticking out either side.
Resistors for both channels installed. The “return” from the left channel runs between the switch and the case. If I was to do this again, I would buy a bigger case.