I've been using my "Brute Force" mu follower amp for headphones for many years but I needed something that could drive lower impedance headphones. I found the Glassware schematic for the Aikido/WCF amp online so I decided to build it point-to-point. I've got it working now, it sounds great with my Grados. It uses the same (6SN7/6BX7) tubes as the old amp and I've configured it for 32 ohm operation.
But since it's optimized for 32 ohms, what happens if I plug in higher impedances? I have 4 headphones ranging from 32 to 320 ohms and I'd like to use them all.
But since it's optimized for 32 ohms, what happens if I plug in higher impedances? I have 4 headphones ranging from 32 to 320 ohms and I'd like to use them all.
It will put out higher voltage before distortion hits, also distortion will be lower, for the same input (32R vs 300R) in a WCF we are talking of almost an output current swing of 2X the output quiesent current, certainly the lighter the load the better.
Should work as well or better with light loads. If for some reason you do prefer it with heavier loads,
just add a parallel output resistor.
just add a parallel output resistor.
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I found a schematic that looks like it's scanned from the building instructions for the octal Aikido, so I'm not sure if I can post it... But there's also a schematic in one of the eBay listings for an Aikido headphone amp, it's pretty much the same and probably won't get anyone (me) into legal trouble 🙂 It also has jumpers to switch between 6BL7 and 6BX7 operating points, I'm thinking of using a 4PDT switch for the same since I have a pair of 6BL7s too.
I kept the tube-regulated 310V power supply from the old Brute Force circuit since it was already wired up and works fine, and used some 330uF/200V caps from my junk box for the outputs, bypassed with 2.2uF SCR caps.
I kept the tube-regulated 310V power supply from the old Brute Force circuit since it was already wired up and works fine, and used some 330uF/200V caps from my junk box for the outputs, bypassed with 2.2uF SCR caps.
