EAR 861 Power Amplifier
Copyright 2017 © Troels Gravesen

I've been looking for a small high-quality tube amp for my workshop, meant to operate with my Hypex Ucd amp for bi-amping. As my Hypex amp is working fully balanced and has input attenuators, something similar would be nice for amp supposed to run the midrange-tweeter drivers. Now, having these demands really points to a very few amps on the market except for PA amps, where these features are common - and always solid state or digital. Not what I was after, rather something like my GlowMaster.

Some EAR power amps have these features and being happy with my EAR-912 preamplifier I might give one of the power amps a try. Doing the usual google study reveals quite a few positive reviews and I was lucky finding a nice looking and "non-smoking" amp on eBay. I've bought used gear before and given a current retail price of 7000+ EUR for a new amp, which is a crazy price for 32 wpc, I took my chances - and was lucky. The amp is like NOS despite being 11 years old. Based on the looks of tubes and circuit board, this amp has had very little use and no need to tube replacements.

Here the description found at Needledoctor website:

Push-pull power amplifier operating in pure Class A, enhanced triode mode. Zero overall negative feedback. 32 wpc stereo (bridgeable to 64 watts mono) into 4, 8, or 16 ohms. Uses EL519 output tubes. Self-biasing. Balanced and unbalanced operation.

After years of research, development and day-to-day manufacture with the EL519 series of pentode tubes, Tim de Paravicini has come up with a new and exciting Triode configuration. Conventional triode connected pentodes have the second grid tied to the anode, which results in a halfway compromise between a pentode and a triode. This neither has the efficiency of the pentode, nor the linearity of the triode. Tim de Paravicini's Enhanced Triode Mode (ETM) goes one step further, and creates a true, highly linear triode from a robust pentode tube.

Instead of driving the normal Grid One with signal, this is tied down to the cathode, and thus becomes an invisible, transparent element, and part of the cathode. Signal is fed into the tube's Grid Two, and in this configuration, Grid Three has no effect - it can either be connected to earth, or left floating. The ETM behaves like a true triode and is in fact more linear than the majority of directly heated triodes. Compared with the latter, it has the additional advantage of being a tough, more robust tube, capable of much longer operational life.

The first amplifier to use the ETM configuration was the '859, and with some justification the '861 could be regarded as a push-pull version of the '859. However, this is more than a slight understatement: each output transformer has a massive 5 kilogram weight, with no feedback applied around it. The circuit is balanced push-pull from input to output, allowing balanced (professional-style) inputs as well as conventional unbalanced (RCA phono jack socket). Similar to the '859, the circuit is direct-coupled. Tube choice is not critical; perfect operation does not rely on matched tubes, nor on user adjustable bias.

Output power is 32 watts per channel, 20 Hz - 20,000 Hz. The half power bandwidth is in excess of 16 Hz - 60,000 Hz, both with low total distortion, and no overall feedback. Tube complement: 2 x ECC83, 6 x PCC88 and 4 x EL519. Amplifier weight: 27 kilograms.

Subjectively the amplifier has the same 'family' sound as the EAR 859. Listeners will find it builds heavily upon this, with an increase in authority and attack. The lower bass has real grip and feel with this amplifier, way in excess of the 32 watt power rating while the treble is smoother, cleaner and sweeter, mainly due to the lack of overall feedback. A single word can sum up the 861: ''effortless.'' It has real power and control, the power to convey the emotion of the most demanding of recordings, whether the source be our preferred analogue or digital.

First thing I did was measuring the gain of the power amp to be able to align the gain of my Hypex modules of the ATS4-HE speakers. I cannot understand why manufacturers are so reluctant to state the gain of their products. So much needed.

The measurements here were done on the 8 Ohm taps and with an 8.2 Ohm resistor across terminals. 24.6 dB average gain is excellent. Only need to tune down the Hypex modules by 1.5 dB. So done, overall low-end balance is perfect.

I didn't expect the EAR 861 to be a sonically fully compatible with the GlowMaster, but it's close. The GlowMaster has an edge in far field ambience and overall resolution of dynamic complex material and maybe we're down to the difference in power, where the GM excels in dynamic head-room. I does have twice the power of the 861.
This 861 amp is kind of "annoying" as my standard tweaking tool-box seems to run short. I mean, orange-drop polyester coupling caps against VCap CuFT... Which points to the fact that there are more to tube amps than just a couple of coupling caps. The 861 does have an enticing ability to bring us close to the music and let us forget about subtle details.
What stands is a magnificent sounding power amp with more than enough power to run the mid-tweeter of the ATS4-HE and similar constructions, thus an ideal partner for bi-amping. *

After a few weeks of use with a variety of speakers I've come to like this amp even more. What strikes me the most is its ability to drive low-efficient, 4 Ohm speakers from its 8 Ohms taps. For some reason it doesn't sound as good from the 4 Ohms taps.
It's simply amazing the drive and punch this amp can deliver.

Only flaw I can point to is the inscription on the top plate: "TECHNOLOGY AT IT'S BEST!". First of all you don't put an exclamation point on an amplifier! And the error of using an apostrophe in "IT'S" is hard to believe from an English product. Had it been Chinese... Even with my limited English skills it should be "ITS". I guess EAR have had hundreds of these made as it is found on several amplifiers. Bottom line is you don't have to brag about an amplifier like this. I know, "it ain't bragging if it ain't lying", as Americans would say, but still...Given the current 861 retail price it's like Rolex adding "TIME AT ITS BEST" on their 10 kUSD watches. Bad taste!

*: Replacing the coupling caps with Rike cupper foils caps did the trick. Not an easy tweak due to size! Look below. I don't think this amp gets much better.

 

In Danish we have the word "rør-slæde", which means tube-sleigh. This is what it is.
Beauty is in the eye of the beholder, but I love the design of the EAR 861.


On later versions the 16 Ohms tabs have been omitted. I don't think anyone will mind.
I use the amp on its 8 Ohm tabs, even for 4 Ohm speakers like the SBA-MTM. By the way, a very good combination.

 


Rock-solid chassis from 2 mm steel plate.

 

 

 


Click image above to view large

 

 

These orange capacitors are likely to be changed to some better ones, but as-is, this amp sounds darn good. Actually tried inserting four super-caps (double-lane metallised PP) - and surprisingly this wasn't for the better, so the orange drops were back again. The super-caps made a slightly aggressive top and no apparent improvement in transparency. Hmm....
Having transformer coupled line stages I did short the input caps (red circles above). See schematics below. No need for potentially degrading caps here. I fully understand EAR's concern for people having DC coupled pre-amps. If something can go wrong, it will.
Another thing would be bypassing the input potentiometers and switches, but this is unlikely to make any significant difference.

Analysing the schematics for possible bottlenecks can be hard. The obvious coupling capacitors between amplification stages are the usual suspects and possibly the 100k anode resistors, although I'm highly sceptical about the latter. So, I made a cautious investment in four 0.68 uF Mundorf tin-foil capacitors - and then things finally started moving in the right direction. Bass and mid as good as it gets, only the treble range - despite being very smooth on the ear - leaves some far-field embience to be desired. Not much, but significant compared to my GlowMaster. Next I by-passed the tin-foil with 10 nF Silver/Mica caps from my former riaa-stage, and although I don't believe this makes any difference, it sounds darn good! So, either the micas or my brain i doing the job.
Next stage in testing is four Rika copper foils caps.

 

Now, these Rike caps are huge! Fortunately we have lots of space in the 861 and the solution was to add two bars next to the tube row and mount the caps as seen on photo. The caps I got from Rike were not the same "packing", which was kind of a disappointment, one pair was in tubes, the other with standard wrapping. Nevertheless, having the bar some 60 mm above the circuit board, there is just enough space for the caps, having a diameter of 50 mm! Length is 35 mm. This doesn't allow placement between the valves.

These Rike caps are a serious alternative to VCap CuFT caps and are close to 25% of the CuFT. 238 EUR/four compared to 297 $/ea. What the Rike caps produce compared to tin-foil/silver-mica is the far-field ambience I have from the GlowMaster. This doesn't mean the two amps sound exactly the same. The 861 has some triode character, slight midrange emphasis. There's nothing soft or tuby about the 861 sound. Clear transparent midrange and shimmering highs. The ability to run low-impedance speakers from the 8 Ohms taps is amazing! Mission accomplished. 


Power transformer.

 


OPT.

 

 

Should you like the 861 so much you buy two, the amps can be bridged to make 64 watts. 

 

The manual includes this handwritten schematics.
This is not fully identical to the product I have, but it may give an idea of how Tim Paravicini designed the 861.
Click image to view full-size.



Schematics as found in manual. As mentioned above, the input capacitors (0.47uF/100V) were by-passed . Actually they are 1 uF.
Also the driver stage appears significantly changed compared to this simplified draft.