I posted some time ago a note about my Velleman K4040 amplifier. The sound of the amp as built from the kit was unremarkable and definitely not in line with the price. Lacking experience with tubes, I was looking for some time for well documented mods to the kit.

I found two 2006 posts here and here and implemented them rather directly. The only difference is that I used IXCP10M45S instead of a pair of J508 current sources in each channel and replaced the 1N5408 rectifiers with UF5408 instead of adding noise suppressing capacitors in parallel to them.

The mods did not leave much of the original Velleman design in place; the result, however, is a remarkable improvement in sound!

However, two problems remain: (1) I got hum that wasn't present before the mods; and (2) a two-year old running around doesn't get along with eight hot, attractively glowing tubes. The project is shelved until a better time.

For future reference: The toroidal...

I just built a Distortion Cancelling Push Pull (DCPP) amplifier designed by Peter Millett. It sounds very nice, was fairly easy to build, and is rather inexpensive. Thank you Peter for the great design!

Elekit TU-879S is the best sounding kit I have ever built. Thank you TubeDepot.com for selling these kits. With my DIY full range speakers I mentioned a couple of posts earlier, the sound is fantastic.

Update: one of the original 6L6 tubes got blue sparks inside. As this amp can use KT88, KT66, or EL34 without any adjustment or modification, I replaced both 6L6s with EL34s left from the K4040 project, but the sound deteriorated. A replacement 6L6 from TubeDepot.com restored everything.

Then was the K4040 from Velleman. Contrary to some reviews, I found this amp sounding rather nice, particularly after I replaced the EL34 tubes in the output stage with separately purchased matched quads. However, the sound does not quite match the price, and I keep this amp mostly for its looks.

Update: I modified this amplifier, leaving little of the original design. See a later post with the details.

I started with a Model 8LS stereo amp from S5 electronics. Later I put it into a Hammond enclosure and replaced the tranformers with Edcors.

Separately, I built a Model 16LS, which is the same thing with a doubled output stage, giving a very similar sound. Both use a 5670 double triode in the voltage amplifier and phase splitter, and 2x6005 (4x for the 16LS) in the PP output stage.

Both versions are very easy to build, nice with vocals, but not quite HiFi - see the FFT charts. Matching tubes and the resistors in the split-load phase splitter circuit helps to reduce distortion.