Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: ohshitgorillas on August 10, 2020, 04:10:49 PM
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Just showing off my Eros 2! I finished Friday night, and spent the weekend spinning records late enough to screw my sleep schedule up worse than COVID already had. I am upgrading from a Hagertech Bugle2 that I built myself with Vishay resistors and Nichicon FG caps.
This is my second Bottlehead kit, unless you count rebuilding my Crack a few times as multiple kits :) It's paired with the Schiit Sol turntable. I rushed through the Crack and never bothered to make things look really good, a lesson I learned well for the Eros. I took my time to get things just right. I gave the top plate a glossy black coat, and the trafo cap, silver. A spritz of silver accidentally got onto the top plate, and I decided that actually, that looked really good. Both got a layer of glossy clear coat after that. The wood base is unfinished, but will be stained with dark brown 'kona' and Danish oil, and also finished with glossy clear coat.
Since this is my end-game, I wanted it to be beyond perfect, so I agonized over a lot of the parts selection.
- For the power supply and shunt regulator wiring, I chose Neotech UP-OCC copper in PVC (20 awg). I made a twisted shielded pair to run from the AC inlet to the trafo and grounded the shield on the earth tab.
- For the signal wiring and ground, I used a combination of Jupiter cryogenic OCC copper in cotton, and Duelund silver in cotton/oil (both solid core). For the ground 'strip' along the bottom terminals, I used Connex OCC 5N silver (sold bare). I also used Cardas quad-eutectic solder, which turned out to be fantastic stuff and so easy to work with.
- I used upgraded tube sockets. For the shunt reg and output tube, I used Belton, and for the input tubes, I used some silver plated sockets. This was a dumb idea, because apparently not all socket manufacturers orient their pin layout the same relative to the mounting hardware... not a major issue, but some of the wiring is a little cockeyed.
- For the RCA sockets, I used KLEI's top of the line low-mass silver RCA sockets. For the outputs, I chose DH Labs CM1 gold-plated copper.
- I used matched boutique resistors for the 47kohm 2W and the 75kohm on the C4S board.
- Awaiting a matched pair of Tung Sol EF806-S.
I put * on the word 'completed' because for near future upgrades, I am thinking:
- Replacing output capacitors with vintage soviet caps, a combination of paper in oil (1 uF) and Teflon (0.22uF). I think 1.22 uF should be sufficient for a 20kohm destination?
- Replacing 100 uF/160V caps in C4S with Dayton or Solen PPE film caps. Maybe I could get away with 90 uF?
- Bypassing 10,000 uF caps on input with ???. I have a matched pair of Audyn True Copper Max caps at 0.1uF, but I'm not sure if I'd rather put these in my speaker amp, or if this is the best place for them.
I'm happy to say I only made one mistake early on, and caught it during the first power supply voltage test. I had swapped some resistors, something like red red black brown vs brown red black brown, on brown resistors of course. All other voltage and resistance checks passed the first time! There was a small amount of hum at first, but since removing the ground wire between the Eros and my table, and playing records all weekend, the hum is now barely audible above the background noise at full volume! Not to mention, I have to dig way past listening volume to find said noise floor. This thing is damn quiet!
The sound was harsh, brittle, bass-light, and splashy during the first two hours of playback... to be expected with a set of new tubes. It was actually, in spite of that, still pretty nice sounding and the tubey benefits were clearly audible. After about ten hours, the Eros had fully matured into something that exceeded my expectations. It is amazingly resolving, such that I described to my friend that during quiet passages it could feel like I was the needle gliding through the grooves... because I could clearly distinguish the low, quiet rumble of the needle passing through silent grooves (listening through a heavily modded Crack > HD800)... but as soon as the music started back up, I was lost in the recording again. Staging, placement, and separation are all superb. To me, this is a very tubey sounding amp. This is not one of those "solid stateish" tube amps... the tube flavor is right up front: spacious, fluid, lush, smooth, but also exceptionally clear, detailed, textured, and dynamic. Just how I like it. On the one hand, it's hard to believe that this isn't digital... on the other hand, digital only wishes it could have this kind of fullness, body, and sense of realism.
Kudos to the Bottlehead crew for the last phono preamp I'll ever buy or build! ;D
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I saw this on Instagram and nearly commented that I have the same preamp and turntable combination but decided not to. I really like that raw piece of granite you’re using as a base.
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That's a handsome setup.
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Very nice!
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Nicely done, congrats!
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I have been slowly adding upgrades to my Eros 2, which I've attached pics of...
- Bypassed output caps with 0.22uF Teflon caps (vintage Soviet FT-3)
- Replaced shunt regulator 0.1uF capacitors with Clarity Caps
- Bypassed cathode coupling(?) 100uF caps with 0.1uF Obligatto PPE film caps
I've been impressed with the upgrades so far. Teflon output cap bypasses are gloriously resolving and clear, and I was pleasantly surprised at how much difference the Clarity Cap upgrade in the shunt regulator made.
My system's preamp, Schiit Saga, has a 10kohm input impedance, which is too low to be ideal for the Eros 2. P.B. suggested that I could put 10k resistors across one of the Saga's inputs in another thread, for a 20k load. I went beyond that, I found a matched pair of 47kohm resistors last night and put them into a pair of dedicated Eros2>Saga cables, on the end of the cable which plugs into the Saga. The difference is... holy shit!! It's a huge improvement across the board, much tighter and cleaner sounding. I didn't get a ton of listening time in last night, but I was very pleased with what I heard.
Using those cables, I've got a minimum input impedance of 47kohm... so based on my calculations, I could get away with 0.3uF on the output with a cutoff frequency of ~10Hz. Given that my system is probably not even capable of going down to 20Hz, 10Hz is a perfectly acceptable cutoff to me (when I listen thru headphones capable of bass, I use my Crack with a 100kohm input impedance).... so this weekend, I will remove the stock output caps and replace them with 0.1uF Audyn True Copper Max capacitors. hat will give me a total of about 0.32uF, in conjunction with the FT-3 Teflon capacitors. I think this combo should sound very nice and I will definitely report back with photos and impressions once the caps have had a week or so to break in.
Future upgrades:
- Replace cathode coupling capacitors with 100uF Panasonic film caps
- Bypass 10,000uF caps with 1uF paper-in-oil caps
- Replace 0.01uF and 0.03uF EQ caps with vintage Soviet silver mica caps. I can find these in the correct values at 1-2% tolerances, but it's difficult to find someone willing to match them...
With respect to the impedance issue, I may still decide to open up the Saga and add resistors on one of the inputs to increase the loading, so I'm not restricted to one pair of cables. With respect to the value of the resistors going into there, does it actually matter as long as it's large enough? e.g. I could use a pair of 10kohm resistors... but why not instead use 90-100kohm? Are there drawbacks to raising the input impedance like that?
edit: another 'mod' was building a power cable, similar to the Bottlehead kit (in terms of braiding), but I used 20awg solid Neotech OCC copper in PVC, same as I used in the power supply wiring. I terminated it with some surprisingly affordable Furutech plugs with copper contacts, so that the power cable is high purity copper from tip to tip. This was originally intended for the Eros 2, but it ended up being so good that I ended up using it for my Crack instead. I haven't been able to sleeve it yet, so it looks like shit, but I'm going to have to eventually build another for the Eros.
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I would still recommend 10K resistors and the stock value of coupling caps.
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I suspected that might be the case.... but why? What's the problem with raising the input impedance to an even higher value?
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The resistors you add are like adding output impedance to the Eros, which we don't want. At least adding them at the passive pre avoids some cable capacitance issues, but not all of them! (don't ignore that most amps have some input capacitance as well as the cable capacitance between the passive and the amp) Add too much resistance and you risk treble response issues and you throw away potentially useful signal in the process. You can also create noise issues by doing this, but you're still a decade away from doing that in my opinion.
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To be clear, Saga has active and passive modes. I use active (tube) mode with Eros 2 exclusively. I didn't notice any treble or noise issues, if anything the signal quality was dramatically improved from before (at least, it is doing more good than harm). I will listen in more detail tonight for such issues.
I'm a bit confused with respect to the resistors adding to the output vs input impedance... impedance is something I still struggle to understand conceptually. Do the resistors increase both?
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Ah, that's right, that's less concerning then if you're using the active configuration of the preamp. There shouldn't be a ton of input capacitance in the active circuit of the preamp.