Eros Phono
The phono version of the Eros - a tape head version is coming very soon!
Eros Phono preamplifier - skill level 2
Our Seduction phono preamp kit has been making sweet music in audio systems for eight years. It was designed to work with the original Bottlehead Foreplay stereo tube line stage and the combination of the two has become part of many a fine vinyl playback system. A few years ago we gave the Foreplay line stage a major revision in the form of Foreplay III (and the ultimate version, Extended Foreplay) and we feel it is time to bring out a phono preamp kit that is designed to the same sonic standard. And so after two years of development we proudly introduce Eros, a new phono preamp (also configurable as a tape head preamp) with higher gain, better signal to noise ratio and hybrid shunt regulation.
What's different?
Oh boy, we were hoping you would ask! Here's the rather interesting development story -
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 soon to be released 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-5, a new low noise design made specifically for the Eros. 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. There is enough room "under the hood" to accommodate some of the smaller step up transformers offered by today's winders, and a resourceful individual should be able to figure out how to mount them very near the input RCA jacks if he so desires.
The enlarged 8 x 10" chassis - laser cut .080" grained aluminum - now matches our other kit chassis footprint and is 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. We even managed to retain the option of adding a Hammond aluminum box from the Seduction design, to shield the circuitry for those who live in high RFI/EMI environments. 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 6DJ8 and a 12BH7 for the regulator.
Components
Signal wiring is all point to point with Teflon insulated wire and solid core shielded twisted pair cable. The power supply is easily assembled on PC boards. It is an efficient Schottky rectifier supply feeding dual active loaded hybrid (12BH7/LM431) shunt regulators in parallel with each channel of the preamplifier circuit. The DC heater supply is a full wave bridge of super quiet Schottky rectifiers feeding a Linear Technology regulator. Each channel of the preamplifier circuit is a C4S isolated EF86 voltage amplifier direct coupled to 1/2 of a C4S isolated 6DJ8 voltage amplifier, with the passive RIAA equalization network positioned between the two gain stages. Only one output coupling capacitor is in the signal path of each channel - a metallized polypropylene type. Resistors are a combination of high quality metal film, carbon film and carbon composition resistors, each chosen for optimal performance in the intended application. Filter capacitors are overrated for long life. Tube sockets are high quality ceramic with aluminum shields. A ground post is provided for phono cable and turntable grounding.
Performance
Gain is 50dB
Input impedance is 47K ohms
Output impedance is 4K ohms (a preamp of at least 15K input impedance and interconnect cables of 1 meter or less are recommended, naturally we recommend the Extended Foreplay III as a great match for the abilities of the Eros)
Phase is not inverted.
We worked hard to make this one even easier to assemble than Seduction. Assembly can be accomplished in a few evenings, and is tailored for the builder with little or no kit assembly experience. A very thorough assembly manual is included in printable Adobe PDF format on CD ROM. It contains step by step instructions you check off as you go, detailed photographs of the assembly that can be blown up for great detail, and a detailed checkout procedure, along with tips on soldering and tool selection. All the builder needs to supply is solder. You will need a copy of the free Adobe Reader software to use the manual.
Delivery is estimated to begin around the end of April.
Eros Phono Stage Kit $749 plus shipping.
Your pre-order will be charged the day the kit is ordered. We do this to allow cash in advance payment to our vendors to keep the price you pay as low as possible.
Before ordering, please read: About Ordering
Eros Phono Stage Kit plus UPS shipping ($25) to US address
Eros Phono Stage Kit plus Priority Air shipping ($35) to Canadian address
Eros Phono Stage Kit plus Priority Air shipping ($55) Worldwide
Notes for Our Customers Outside the U.S.
Eros kit will soon be available in a 240V mains version. Stay tuned!
or call us at 360-697-1936 M-F 9-5 PT
Impressions
I just tried comparing my Seduction with my new Eros. I only needed to listen to one cut (Radiohead OK Computer) on both the Seduction and Eros to conclude that the Eros is a significant improvement; the sound quality was so much better that I don't plan to do any further comparisons.
I have listened to a few albums with the Eros now, they all seemed to sound more transparent/detailed, with better low and high end extension. I agree with an impression posted earlier, "In comparison to the Seduction highs and lows are extended, midrange is cleaner and more dynamic, and I found it much easier to follow individual instruments."
I expect that the sound will improve as the Solen caps get some time on them and when I replace them with some Vcaps that I have.
Posted by jb0194 on May 13, 2009 at 21:26:19
Spun about 3 hours of music through the Eros tonight.
Well worth the upgrade from the Seduction, even fresh from the box.
Bass definition and tonality first caught my ear, but very balanced overall.
Soundscape is clearly wider and deeper than the Seduction presents.
Voices are rendered with great realism.
Dynamic recordings explode from the speakers (Adrian Belew's "Twang Bar King" - my daughter's chihuahua jumped a few times on that one).
Congrats guys, you really whipped up a good one!
jb