Upgrade parts questions

[ohshitgorillas]

I recently posted about my finished build, which already contains a fair number of 'boutique' parts, but I thought I'd start a new thread for upgrade questions.

My kit already contains:

• Neotech UP-OCC copper in PVC wiring in power supply and shunt regulator
• Jupiter cryogenic OCC 6N copper for signal wiring w/ silver input signal grounds (my experiments with interconnects suggest this is a killer combo)
• 'Upgraded' tube sockets (note to future builders: don't do this, the wiring will end up cockeyed)
• Vintage Soviet FT-3 Teflon caps (0.22uF) added to output*
• Top of the line KLEI low-mass SPC RCA jacks on input, DH Labs gold plated copper on output
• Boutique matched 47kohm 2W and 75kohm resistors on C4S board

*I am running Eros 2 into a 10kohm preamp (Schiit Saga), so the extra capacitance has most notably brought out a lot more kick/slam, along with impressive textural microdetail. I'm aware the low input impedance isn't ideal and will be constructing a cable with matched 10k resistors on the Saga end. I'm seriously eyeing Moreplay, which I assume will have a higher input impedance (any word on what this is expected to be?). Side note, since my speakers are highly sensitive and I'm running a 10WPC amp, I think the extra gain Moreplay would bring will be welcome.

With regards to future upgrades...

• I saw it mentioned somewhere in this forum that the 100uF/160V capacitor on the C4S board 'could be lower'. How much lower? Would an ~80uF PPE cap be too low?
• If one were to replace the 100uF/160V capacitor with a big ol' PPE cap, would there be any sense in removing/jumpering or upgrading the Z5U bypass?
• I've also seen it mentioned that it would be worthwhile upgrading the 0.1uF caps on the shunt regulator board. Does this just mean with fancier capacitors, e.g. paper-in-oil, or would a larger value be beneficial as well?
• I am curious if the kit could handle a 6SN7 in the output tube slot? I also have a Schiit Vali 2, and in tube rolling that, I picked up a socket saver and a 6DJ8 to 6SN7 adapter. I know the Vali 2 and the Crack kit can handle the 6SN7, but can the Eros?
• What about a 6SN7 in the shunt regulator? Probably pointless and asinine, but thought I'd ask anyway... 
• Besides the caps in the shunt regulator, are there any other power supply upgrades that might be worthwhile? CREE diodes? Power cap bypasses? I was really pleased with the results of power supply upgrades with Crack (bypass caps, choke, CREE diodes), but I also understand that the shunt regulator may make similar upgrades pointless (hence Crackatwoa).
  
• Still trying to decide on a needle/cart, so the jury's still out with respect to the need for SUTs... how much space should I reserve just in case?

I am also planning on bypassing the 10,000uF/5V cap in the input stage with 1uF paper in oils (any point in seeking out matched pair here?), and the 0.01uF cap in the RIAA circuit with matched Audyn True Coppers (copper foil w/ 2% tolerance, which I saw mentioned elsewhere that >3% was important here). Once finished, I think this thing is gonna be one hell of a phono preamp I'd love the opportunity to compare it with commercial TOTL stuff to see how it would fare... my guess is very, very well.

[Paul Birkeland]

Do not remove the Z5U caps.   Based on the function they serve, there are no "audiophile" parts that will function better than they do, and you will risk stability problems by going down that road.

If you want to change the 0.1uF caps on the shunt regulator board, they should remain 0.1uF and not be any larger.

The 6SN7 is not an acceptable substitute for the 6922 for a variety of reasons.  It's unlikely to bias up properly, it has less gain, it has more noise, and it will increase the output impedance of the preamp (which is already really borderline for your setup).

The Eros comes with Cree rectifier diodes.

If you get the SUTs we recommend, they mount in the holes up by the RCA jacks and don't take up much space below the chassis.

[ohshitgorillas]

Excellent info, thanks PB. Much appreciated. I understand the Eros 2 is already a pretty high-end kit as is, and as such there are fewer upgrade paths compared to a budget kit like the Crack... but without a solid grasp of the circuit theory, it's difficult to know where and what. Reading back through about seven pages of this forum has been very helpful to that end.

I'm still curious about a couple things, for example, replacing that 100uF/160V Al cap. I've seen it mentioned that the capacitance could be lower... I want to replace these with PPE caps, so the smaller the capacitance, the smaller and easier the cap will be to fit and mount. I am eyeing Solens at ~80-100uF/250V.

Lastly, with respect to the 10,000uF/6.3V caps... I'm having a hard time finding them in the circuit schematic. Perhaps the position which is labeled 2200uF/4V? With respect to bypassing these, would it be worth seeking out matched pairs?

Thanks!! I'll be keeping my eye out for the Moreplay 

[Paul Birkeland]

You could try a 47uF there and see how it sounds.  I wouldn't change any parts when you do that change, just so you can be 100% sure you like what you're hearing.  Since that cathode bypass cap also stabilizes the EF86 screen grid supply, staying at 100uF isn't such a bad plan.  There are 100uF film caps at Mouser that could be glued to the chassis in front of the coupling caps then wired to the PC board in place of the electrolytic caps. 

We changed the 2200uF 4V cap that was in the original Eros to a 10,000uF cap mostly from noise measurements.  The 0.1uF ceramic bypass aides in stability (and it's super important that it stays a ceramic cap). 

If you run the numbers for the audible impact of a 6800uF cap vs a 20000uF cap in that position, you are likely talking about hundredths of a dB or possibly thousandths of a dB of gain difference, so matched pairs there won't buy you any additional performance.

-PB

[ohshitgorillas]

Okay, excellent, thank you again! If a lower value in the 100uF position would potentially sacrifice any kind of performance in the input stage, then I think 100uF will do just fine. I think I'm familiar with those (Panasonic?) squareish 100uF caps you're mentioning... that's an attractive idea relative to attempting to mount some big soup can Solens or Daytons, although I'm still leaning towards the latter for tolerance/matching reasons (iirc the Panasonics are ±10%).

I also realized, as you said, the 0.1uF Z5U bypasses the 10,000uF cap, not the 100uF like I had originally thought. I might throw a pair of 0.1uF Obligatto PPEs across the 100uF in the meantime.

Cheers!

[Paul Birkeland]

although I'm still leaning towards the latter for tolerance/matching reasons (iirc the Panasonics are ±10%).

The tolerance between parts is often really tight, but may vary a bit from the value.  You might get two 100uF Panasonic caps that are both 96uF, for example. 

[ohshitgorillas]

I suppose if Mouser will match parts, that would be a good option. My understanding was that it does carry the signal, so an 'audiophile' quality cap might have been worthwhile, but if any ol' film will suffice as an upgrade then I agree that those would be the way to go and by far the easiest to mount... and much cheaper to boot.

[oguinn]

I don't think they do match parts. They've always seemed to be a volume shop. I read Paul's comment as "you might through chance" instead of "you could request it".

Maybe I'm wrong.

[Paul Birkeland]

I suppose if Mouser will match parts, that would be a good option.

They will not.

My understanding was that it does carry the signal, so an 'audiophile' quality cap might have been worthwhile,

What is the difference between an audiophile metalized polypropylene capacitor and a DC link metalized polypropylene capacitor on Mouser?

[ohshitgorillas]

What is the difference between an audiophile metalized polypropylene capacitor and a DC link metalized polypropylene capacitor on Mouser?

Well, I guess the difference would be the lower tolerance and the option of matching. While I certainly could luck into two ~96uF caps, I assume it's also possible that I'd end up with a 92uF and a 107uF.

I made the assumption that that matched values would be worth pursuing in this case, but your responses suggest to me that it isn't terribly important in this case. I'm more than happy to save my money if there's no point to having matching values here.

[Paul Birkeland]

Well, I guess the difference would be the lower tolerance and the option of matching.

LCR meters aren't all that expensive these days.  You could buy 10-20 caps and hand match them.  As far as tolerance goes, a lot of the "audiophile" parts don't even list one

While I certainly could luck into two ~96uF caps, I assume it's also possible that I'd end up with a 92uF and a 107uF.

And even with that spread, that's not going to be audible.

I made the assumption that that matched values would be worth pursuing in this case, but your responses suggest to me that it isn't terribly important in this case. I'm more than happy to save my money if there's no point to having matching values here.

It's worth matching the caps in the EQ.  When I build our Tape Repro amps and occasionally the phono version, I will sit with a bin of caps and measure EQ caps until I get a pair that are dead nuts on to the correct value.  A cathode bypass cap and the coupling caps don't really benefit from this treatment.  If your corner frequency at the output is 3Hz on one channel and 2.5Hz on the other, that's not particularly critical. 

[Doc B.]

IME the way most film caps are manufactured today the tolerance in a given batch is pretty tight, so chances are you would get a pair of caps that are within a percent or two even without asking for matching.