EL84 DIY Amplifier Update: An Amplifier Like This One (Only Better) Could Be Yours!
By Steve Graham
As promised in the preview, a prototype of the EL84 amplifier based on the Tubelab.com circuit board is now built and playing music. It went together with only one hitch. An intermittent resistor was giving me fits…but once diagnosed and replaced, it was all smooth sailing. I gave it at least 100 hours of break in before some serious listening commenced.
The Finalé Audio F-7189 II had been returned, so my Dynaco ST35 clone was used as a reference to quantify the Tubelab’s performance. No, the Tubelab isn’t a Black Friday deal that would smoke the Finalé. At about one fifth the price of the Finalé, that can’t be expected. But the Tubelab is still darn good.
Listening to the Tubelab (TL):
Compared to the ST35 clone, the TL sounds a little fuller in the bass. It doesn’t seem to slow it down though, it still has good pace and drive. The system was the same used in the Finalé F-7189 II review, see link immediately above. In the highs, neither the ST35 nor the TL has the pellucid clarity of the Finalé. But through the midrange, the TL beats the ST35 clone. The TL has a deeper, wider and better-defined sound stage. It unravels Mark Knopfler’s guitar and his vocals with Emmylou Harris in greater detail – yet in a smoother, more engaging manner. Space, depth and the recording venue of naturally-recorded classical music is more clearly presented by the TL.
All in all, both amps are pretty good, considering that their output transformers are at least 50 years old. I suspect that the TL could sound even better with some new “iron” (transformers).
Step up, be our patron, get a great amp:
Update: A patron has been found! Build cost will be about $900 Canadian, roughly $700 US, for that our patron will, once I have detailed the build process for everyone, get themselves an amplifier like the one pictured above: assembled, tested and ready to plug and play. HOWEVER, it will have all new parts, including tubes, a chassis like the one pictured above, and especially, Hammond transformers. Shindo, the Japanese builder of exotic amplifiers, considers the Hammonds sufficiently decent to use in their Montille line.
All the money a patron pays goes into parts to build the amp. My labour to machine the chassis, assemble and test the finished amplifier is free. The final parts selection isn’t cast in stone. A volume control like the prototype is possible (if desired), as well as multiple (line level) inputs. Transformer selection is open for discussion too.
Oh, yeah. I goofed a bit on my parts order. The finished amp will have dress-up rings in the top plate like my N-F-P phono project from earlier this year.
Late breaking news:
The prototype amp was exhibiting a very low-level hum. As may DIY’ers know, getting rid of the last bit of hum can be a chore. The amount of hum was so slight, I had to put my ear practically right on the woofer of a medium-efficiency speaker to hear it. I had a $15 Hammond power supply choke kicking around, and once installed, the residual hum was gone! It was just an educated guess but it worked. Sometimes it’s better to be lucky than good-looking.
Editor’s Note: I just want to thank Steve for continuing to offer these great projects to interested readers. As the song goes, get it while you can…
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Hi! I think saying the TL isn’t as good as the Finale is a bit misleading as that could be understood as the circuit of the Finale is superior to that of the TL. Which may indeed be the case but as we know one of the most significant factors in the end result is the output transformers and in this case the TL is using a 50 y/o one compared to whatever is in the Finale. The Hammonds are not too pricey and it would be interesting to try a pair with the TL.
I have never heard the Finale or the TL EL84, so everything said with a grain of salt.
I personally have built and use Tubelab SE, one with 45’s as a headphone amp and a recently built 300B.
Thanks for your comments and please feel free to share your experiences with the Tubelab SE builds.
*Two people have already contacted me today interested in becoming patrons!
My intent was not to slag the TL SPP. I think it performs very well with the fifty year old trannies. No doubt it will be better with modern ones.
As with the Tetra phono stage and the Aikido line stage builds, I like to build a prototype or proof of concept model first. I want to have a foolproof amp so I don’t have to do any debugging on a patron’s.
Thank you for your interest in Wall of Sound.
Regards, Steve Graham
I’ve been looking at EL34 and KT88 amps to power my Klipshorns. I’m curious to how much power this amp puts out. I dont need alot, (10 WPC minimum) so maybe 15-20W per side. My question is, can this circuit be modified to switch between UL/Triode/or pentode modes?
Thank you for your interest in Wall of Sound. 10 watts should be lots for your K horns, unless you have a listening room the size of a basketball court and like to listen at heavy metal-like concert levels. I’d say this amp is good for 10 watts easy, most probably fifteen.
The necessary thing for high efficiency speakers is low-noise amplification. Any hiss or hum will show up right away. A test I like to determine amplifier noise is as follows:
-Set the amp or preamp to ZERO volume.
-Connect a pair of inexpensive earphones or ear buds directly to the speaker outputs. The speakers (or loading resisters) should remain connected. The inexpensive buds/phones are typically low impedance/high sensitivity devices meant to be powered by mobile devices.
-Listen to the level of hum, hiss or other system noise.
If you do this with your current amp and preamp and are satisfied with the noise level, or lack thereof, this will form a basis for considering other amps when auditioning them.
As for the prototype above, once I had installed the power choke in the B+ supply the hum level dropped appreciably. I checked it with a set of ‘phones just now and it has one of the lowest levels I’ve heard from a tube amp and noticeably lower than my ARC REF110!
The amplifier PCB uses screw terminals for connection to the rest of the circuit. Though not “switchable” it can be configured/reconfigured for UL, Pentode or Triode. Though in triode mode the power will likely drop to 5 WPC.
If you are DIY competent, at least a bit anyway, THIS MIGHT BE THE AMP FOR YOU! If you decide to go ahead don’t scrimp on output transformers. Get Hammonds of if you aren’t broke after the holidays spring for a set of Lundahls. Your Kilpsches are high res devices and deserve good trannies.
Cheers, Steve Graham