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October 05, 2022, 06:11:47 AM

Author Topic: Left-Handed Eros II Base Finally Finished and In System with Lundahl Step-Up  (Read 202 times)

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Offline jminassi

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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

Online Paul Birkeland

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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?
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Karl5150

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Kudos on working out the build. You could also refer to it as a 'Stranger Things' build.
Karl
Karl
Downstairs: Planar3>Eros>Stereomour II>diy OB Betsy+
Upstairs: DIY RP1>Reduction / CD5004>Seductor/SEX 3.1.1>FH3/DT770 pro/HE-4xx
Office: Schiit Modi Uber 2 / Sirius Tuner>SEX 2.1.1>µFonken FF85WK with diy subs
Garage: CA x12 streamer>Quicksand>Minimus 77

Offline jminassi

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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


Offline jminassi

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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

Offline jminassi

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Re: Eros II and Step-up Transformer Gain Congigurations
« Reply #5 on: September 07, 2022, 08:42:19 PM »
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