Eros 2 Phono Preamplifier Kit

When we were working up the Seduction phono preamp design in 2000 we tried several different circuits that Paul Joppa had cooked up. One of those was a direct coupled EF86-to-6DJ8 circuit, a very simple design with a unique passive RIAA eq and a very basic power supply. Up against the equally simple Seduction circuit that used a 6DJ8-to-6DJ8 design, the circuit was deemed too tubey and dull sounding, and so the simple all 6DJ8 circuit was the design we developed into the Seduction kit.

Somehow that breadboard EF86/6DJ8 phono preamp prototype managed to avoid being scavenged for parts for other projects, and over the years it was given a shunt regulated power supply and eventually C4S active loads were made to work in it. The result was a dramatic improvement in performance with just the right balance of open highs, smooth midrange and bass punch. Once upgraded like this the redesigned circuit seemed to stay in our reference system in place of our best Seduction. From there the circuit was further refined and used in our $4000 Tube Repro amp for tape playback, and also put into a custom built phono version of the Tube Repro. The Eros is a direct descendant of that top of the line phono/tape preamp, streamlined to be cost effective and easy to assemble without sacrificing sonics.

There are a number of changes from the Seduction design. The input stage is now an EF86 pentode rather than a 6DJ8. The EF86 is perhaps the finest sounding low noise pentode made, being used in some exceptional microphones. At low signal levels like those of phono cartridges and tape heads the high gain of the tube can be taken advantage of without the sonic penalties often associated with the use of pentodes in higher power amplifier circuits.

Our unique use of the C4S constant source on this pentode offers a high level of isolation from power supply noise that might otherwise be amplified by the high gain tube, resulting in an all tube phono preamp with great resolution that can work with medium output cartridges without adding excessive noise. A servo circuit on the cathode of the EF86 accommodates production tolerance variations of various brands of EF86s and 6DJ8s, keeping the operating point at its optimum.

The power transformer is our own Bottlehead PT-11, a new low noise design made specifically for the Eros. It is the same design as the PT-5 from the original Eros, but has a universal primary to be configured for overseas use. The hybrid shunt regulator provides separate high voltage regulation for each channel and gives the Eros an added sense of speed and a sense of frequency extension that exceeds that of Seduction. The heaters are also regulated.

Gain is up from the Seduction’s 40dB to 50dB. This extra gain allows easy use of high output moving coil cartridges into the 1mV range. In fact, while we don’t recommend it, we have used the Eros with LOMCs in the 0.3mV range. For LOMC cartridges we suggest the use of a step up transformer in the 1:5 to 1:20 range to keep noise levels and impedance matching optimal. Mounting holes are provided next to the input jacks to mount step up transformers internally, if desired.

The chassis is 8″ x 12″ laser cut .080″ random brushed aluminum – big enough to accommodate the two extra tubes, a bigger, more quiet power transformer and easy to stuff PC boards for the circuitry that doesn’t carry audio signals. The wood base supplied is the same beautiful Pacific Northwest alder as our other kits, which you assemble and apply your favorite finish to. The kit is supplied with two EF86 tubes, a 6922 tube and a 12AU7 tube for the regulator.

I am sharing this experience for those who are considering building the EROS.

I’ll start by saying that in the system I’ll be using it, the EROS is the single cheapest component. The turntable (Rega RP6), the Amp combo (Naim 72/hi-cap/140), the streamer/DAC (Auralic Aries / Vega) and the speakers (Larsen 6.2) all cost at least 2X-5x at minimum it’s price.
 
I have been using the on-board Naim 72 phono board in the pre-amp, and I’ve been annoyed by the fact my streamer/DAC streaming Tidal sounds better than my records – as that demotivates me from playing records – despite the fact I prefer the ritual of record playing.

Enter EROS. After, well, 15 minutes of warm up and no prior burn-in, using cables half the price my streamer combo (for now) I can confidently say, records sound better than the digital chain.

EROS brought a new level of transparency, delicacy, depth and expansiveness to the sound with all my records. From Nils Frahm and Talk Talk, to ’50s blues records or HipHop. It also brought a focus to all the voices on records with both female and male voices that previously was missing.

Records + Eros + Rega RP6 with $50 interconnects beat Auralic Vega + Auralic Aries + $300 cables.
Glowing Tube magic: 1 vs Cold Bits: 0

Thank you Bottlehead team and the community who commented and helped me build it.
Can’t wait to build more glowing tube things from Bottlehead.

-arisrock 

Well the Eros was singing beautifully all day yesterday – I tried a lot of Genres: Jazz, Vocals, Pop, Classic Rock, Classical (chamber music and orchestral), Blues…

I had the Seduction in the system for a long time and some of the initial things I’m hearing are the shock of the new.

But, Wow. Very happy. The Eros seems to have more bounce and dynamics, better, cleaner bass, and more inner detail than the Seduction. I expect a lot of that is the MUCH better power supply in the Eros, since it looks like Paul Joppa has mad skills at RIAA.
 
Especially good moments: Nina Simone ‘Little Girl Blue’, Eagles ‘What Kind of Love Have You Got’, Holst ‘Mars’, …
 
-pRC

Impressions so far…WOW. This thing sounds amazing. I’ve been mostly listening to new music that I’ve been accumulating while building the Eros, so it’s hard to do much A:B comparisons, but I did go back to a couple of old favorites and have been stunned at the sound.

Only question that remains is how long can I hold off before ordering the BeePre… 🙂

–dave-tx on the Bottlehead Forum

 I trashed the Shunt regulator board and Eileen was great on getting me replacement parts. I received them last week and was finally able to complete my Eros build today. Everything checked out and I fired it up like Doc recommends in the instructions. Impression…… Wow!!! The soundstage is huge, both breadth and depth. The bass is much tighter and deeper. Overall everything is just so much more focused. I have listened for 2 hours and am really impressed.

I can’t wait to couple it with the BeePre I have ordered. I think it is going to be really outstanding compared to using my FPII with every mod. Any feel on when the BeePre is going to be shipped??? Not that I am anxious or anything.
 
Thanks Doc, Paul, and Eileen. You have allowed me to take my LP listening to a new level.

Richard

–rockpassion on the Bottlehead Forum

 
Dear Bottlehead folks,

Just wanted to let you know how impressed I am with my new Eros phono stage. I built the Eros to replace my budget tube phono pre (Bellari VP 130) and, in short, the sonic difference in my system is night and day. Even without a burn-in period, the Eros has highlighted all the strengths of my current setup (Pro-Ject Debut TT with external PSU and Ortofon 2M Blue, Ayon Orion integrated valve amp, and PSB T6s). The gain is awesome, the sound is better in every way (I’ll spare you the hi-fi jargon), and, most noticeably, my system is dead quiet now. I hadn’t realized just how much extra hum and interference I was putting up with before the Eros. I would definitely recommend this kit to anyone. The build is tedious but fun, and the result is beyond rewarding. Thanks for a great product. And thanks for shipping the parts that were missing from the kit in such a timely manner.

Happy new year,
Mike
—
Michael McGriff

 
Founding Editor
Tavern Books