music, guitars & other obsessions

What’s Old Is New Again – Introducing the 3Watter

[Update – July 15, 2014] Well that did not last very long, after hearing clips of the JCM-145 (a special version of the JCM-1 made for Anderson Music’s 45th Anniversary), I just had to try it out. Using the schematic made by Matec here (thanks!) It was a short order to convert the 3Watter into a JCM-145 clone, it sounds pretty good considering I am using a surplus line-distribution transformer, with reflected impedance of 26k Ohms, which is quite a bit higher than the spec 20k Ohms.

RIP, 3Watter…

[Update – October 30, 2014] The line-distribution transformer just did not cut it… When the amp is turned up, its core would saturate and cause severe distortion – not the right kind! So I finally replaced it with a rather large 10k:8 OPT (loaded with 16R speakers), which really is an overkill for this little amp. But the result is well worth it, now the amp sounds much fuller, and the LF is surprisingly loud coming off the little 12AU7.


After taking the Princeton clone apart, I decided to re-use the chassis for another build – and I settled on a mash-up of the Princeton and the AX84 4-4-0 Studio, it’s a very simple circuit – even though I re-use the TMB tonestack from the Princeton, the amp actually sounds much better with it bypassed, so there’s really not much between the input jack and the speaker – less is more!

Here is the schematic:

3Watter Schematic*Note: 6N8P is the Chinese equivalent of 6SN7.

Most of the parts were mounted on a surplus terminal strip board.

Terminal Strip

Terminal Strip

The completed amp, note that another 6N8P/6SN7 was added after the shot was taken, that boosted the output power to a whoppin’ 3 Watts.



With the volume ~ 2 O’Clock (single 6N8P/6SN7), here is the scope shot of the output into a dummy load:

Output Waveform

Output Waveform

The soundclip was recorded with my mobilephone, the volume was around 1 O’Clock, I used DI tracks straight into the amp, each clip starts with the DI track played on my hi-fi speaker followed by the amp played through an Emience Ragin’ Cajun in the AX84 cabinet. Sorry about the poor recording quality – the amp sounds much fuller… anyhooo, here’s clip:

3Watter With DI Tracks 

To me, this little amp sounds better than both the Princeton clone and the much larger AX84 SEL… It was a very quick and enjoyable build, since I had all the parts and the chassis ready to go, it’s definitely recommended for those looking for a small bedroom practice amp.


2 responses

  1. djgibson51

    Very nice jazbo8. 3 watts can be more than loud enough if your neighbours are close. Love the LED bias – as you know 🙂
    I’m about to show my new 3 watter on tone per buck club sometime in the coming week – yep, LED bias on the 1st tube, and gave up on the TMB tonestack.

    May 1, 2014 at 5:47 pm

    • jazzbo8

      Thanks! I got the LED bias idea from one of your designs;-) They work wonderfully… If I had more room, I would add another stage, since with the TS the output is pretty low, alas, no room left, so it is what it is…

      May 2, 2014 at 1:59 am

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