Ultra Compact Club

The Ultra Compact Club



Welcome to the Ultra Compact Club where our perception of Push Pull amps were ruined by this article. However, instead of building this little amp ala Melvin Leibowitz, we proceeded further by tweaking the circuitry to loftier heights via the usage of constant current source, hence it’s no longer the Compact amp but — Ultra Compact.


I admit, I’m guilty of "corrupting" the fine folks here with my Simple EL84 articles but I assure you I’m not the only Evil one here.

Ferry Prasetyo, Jakarta, Indonesia uses this little amp to drive his Infinity behemoths.





Waily, Singapore, is an EVIL diyer. Read about his other works here.


CY Liew, Malaysia, needs a tube cage to protect his sons from those smoking hot EL84s. Or is it protecting his tubes from his son?



The guys above use basically the same circuit — Simple EL84.


Here we have "puff"s Double Compact. puff is based in Denmark. "I like the version with diffential amp in the input stage best, (The Double Compact) which I tried because of the idea: `If it sounds good at the output, why not try it at the input also?’ The sound is better and I have the possibility to use balanced wiring when I build a preamp instead of using CD direct in."


Then we have keto (US) who proved not only the Compact circuitry is usable with DHT tubes, but how about Direct Coupling? At time of writing, this devil of a guy is still tweaking his circuit. Hey ya keto, remember to send me your latest and greatest!


From Germany, we have Helmut Tripphahn who wrote:

Hi Yeo,

I built one stereo channel in conformity with your Simple EL84 amplifier circuit and tested it today. It works unobjectionably, although I’m not using the output transformer and the power supply you recommended. B+ is at only 280V, Ik is at 43 mA per tube (using a matched pair of STANDARD BRAND tubes I even didn’t need to install the trimpot and 15 ohm resistor). Hence the total constant current is at 86 mA.

The bass sounded very clean, but there seemed to be a lack of heights at first. After I’ve replaced the driver tube (one of my "test" tubes for experiments) with an new-old-stock Siemens EL84, the mid-range and trebles sound excellent, too.

Unfortunately the Easter holidays are coming to an end. But I’ve decided to complete the amp as soon as my daily work will allow me to. After several rather disappointing experiences I made with conventional ECC83/ECC82 phase splitter circuits (paraphase, long-tailed pair, cross-coupled cathode followers) I am convinced that the "like-drive-like" approach is the perfect solution for me.

Long before, I’ve read an article in an old German magazine where a self-regulating EL84/EL84 output stage/phase splitter circuit was described, however, I thought that such a strange "inexpensive" circuit wouldn’t be worth of trialing. So it was your publication that lead me to the step in the right direction (in addition, I like your unconventional writing style).
Thank you very much!

Kind regards,


This pretty one’s called Norah! By Sylvain FAUVEAUX.


Description of the amp :
– Modified power supply
– All caps are MKP SCR (a.k.a. Solen, France) and mica’s except two Silmic II for the two preamp stages
– 6x6PI14PI-EB tubes
– Lazy man current source
– "ESO Magnetic" (France) power tranny and choke
– Audax TU-101 (France) output trannies
– Remote volume control (Selectronic kit)
Making the chassis was a real pain in the ass (you know what i mean …)!!! But it worth the effort! (I’m planning to built a SimpleEL34 this time! ) I want to give her the name of Norah if you agree. Because the first CD (beautifully recorded) I played through this amp was Norah Jones "Come away with me" : completly delighting!! Her voice is so attractive through this little amp! That’s why!


Thanks guys for all the excellent work!

If you have built any variation of the Compact amp, send me a BIG note!
If you haven’t… tsk, tsk, tsk…


  1. Shoog August 4, 2010
  2. Shoog August 4, 2010
  3. yeo August 5, 2010
  4. malcolm October 8, 2010
  5. Eric July 19, 2011

Leave a Reply