Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: jminassi on July 10, 2022, 07:03:58 PM
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Hi Folks,
I finished my Bottlehead Eros II months ago. I call it left-handed because I inadvertently finished the backside of the chassis plate. I finally got around to putting a finish on the base.........oil-based stain and three coats of oil-base polyurethane: picture below.
I wanted to mention another step-up transformer option. I built a K&K Audio Basic Step-Up Transformer from a kit that includes two Lundahl LL9226 transformers. So this is an outboard step-up transformer. Since the Eros II has a healthy gain of 50 dB I set the gain of the step-up to 5 or 14 dB for my Phasemation PP-500 MC cartridge which outputs 0.3mV. Phasemation suggested a resistive load of 50 ohms so I put two 2200 ohm resistors in the box in order to get the required load. I want to tell you that it sounds awesome. Plenty of gain and dead silent. See it on the third shelf of my rack in the second photo.
I also want to say that in addition to the Bottlehead Eros II I have built the VTA SP16 Phone Stage, the ANK Signature L3 and the Akitika solid state phono preamp as part of the PR-102 preamplifier. The Eros II is the best sounding phono pre I have built. Price is competitive with the others except, of course, the ANK, which costs twice as much.
Best wishes to all,
John
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That Lundahl is a nice option, though I have to admit that I'm surprised that in a 1:5 configuration with a 300uV cartridge that the noise level is OK. When you are feeling bored I would definitely try the 1:20 step-up with just the 47K resistors at the input and with an extra pair of 47K resistors in parallel to tweak the loading for comparison. The 1:5 and the gain of the Eros will produce about 500mV of line level signal which is somewhat low, but certainly not unusable. The 1:20 configuration and the Eros will put you a lot closer to the typical output level of a DAC and there will be more music signal relative to the tube rush of the Eros itself.
How sensitive to positioning have you found the Lundahls to be?
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Kudos on working out the build. You could also refer to it as a 'Stranger Things' build.
Karl
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Hi PB: With MC cartridges in the 0.3-0.5uV range I have found that 60 dB combined gain works fine. When I use the Acoustic Signature Table with that 0.3 cartridge with the Manley Chinook I have it set to 60 dB of gain even though I could set it to 65 dB. Another turntable I have is generally using the phono section of a McIntosh C2300. The output of an Ortofon Cadenza Bronze is 0.5uV and gain using the MC input is 60 dB. Again no issue.
When I first set it up I had both the tonearm ground and the turntable ground cables connected to the step-up transformer. It made a loud buzzing noise until I disconnected the turntable ground and connected it to the Eros II. I still had a hum that was completely eliminated by tightening the RCA input jacks on the step-up transformer. The transformer is well shielded in it's little box. Unfortunately I had to decide what the step-up should be by soldering jumpers. As you know you can set it 1:5, 1:10, 1:20. My theory has always been use the lowest amount of gain possible to eliminate noise. But based on what you are saying this is wrong. I am not against experimenting. Instead of tearing this step-up transformer apart my plan is to buy another one that is switchable (literally) between 1:10 and 1:20. That would add 20 dB or 26 dB of gain respectively. I'll report back after I get it. I'm using Tannoy Turnbury Speakers and I hear no tube rush........no noise at all. I admit I was surprised.
To answer your last question: I have not found the Lundahl transformers sensitive to position although I haven't played with it. I'm using short MIT interconnects....nothing fancy. You can see that the step-up box is about a foot from the Eros.
You designed a really great phono pre Paul. Thanks!
John
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Thank you Karl! I love the Stranger Things series. I just finished watching the last two episodes of Season 4. Apparently Season 5 will be the last. But Netflix and the Duffer Brothers have a spin-off show waiting in the wings. It's a shame those cute kids in the show couldn't stay little a bit longer, but if they could now that really would be science fiction!
Best,
John
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I bought a second Lundahl step-up transformer with the same transformers (LL9226, I think) as the ones in the kit I bought from K & K Audio. K & K Audio is no longer trading as Kevin Carter has retired. You can still buy the Lundahl step-up transformer as a kit from Erhard Audio as the principal at Erhard has taken over Lundahl distribution in the U.S. But I found a less expensive alternative.
Pat LaMastro at PJL Electronics makes step-up transformers using Lundahl transformers for a very reasonable price. The one I bought has switchable gain of 10x and 20x.
When I use 5x step-up with the Phasemation PP-500 cartridge (0.3 mV) I have the volume on my Elekit TU-8600S integrated 300B amp set at about eleven o'clock for normal listening. Speakers are Tannoy Turnberrys with sensitivity in the low 90s. I hear no tube rush. Switching gain to 10x I find I can't move the volume much beyond 9:00 as things become very loud. I haven't tried 20x as there is no need. Noise simply isn't an issue.
I would recommend the Lundahl step-up transformers that PJL Electronics sells. Pat offers them in different configurations, and having the switch to change gain is very convenient. The only issue I have is that the ground post is mounted of the output side of the chassis. If your turntable has a cable with a flying ground lead, it may not be long enough to reach the ground post. I am thinking of drilling a small hole on the input side and moving the ground post to the location where the RCA connectors for the turntable signal input is.
Has anyone else used a 5x step-up with the Eros II with similar results?
Many thanks,
John