Little Dot I+ Tube Rolling - Page 26 - Head-Fi: Covering Headphones, Earphones and Portable Audio

PatOMalley · #**376** (**permalink**) 07-09-2009, 01:22 PM

the LM4562 is a fast opamp @ ~55megahertz. The OPA2228 I have is about 33 and you can sense the slowing up on the OPA. I think the LM is fast enough to get out of the way. But with this speed, so I have found in reading about these opamps, the speed causes oscillation unless you add some capacitance to the power pins. Then tieing to ground draws the noise to ground.

Now with a sharp set of caps you might like the OPA since is softens the bite. But with a nice set of schmoozy tubes like the 6J1 or Mullards then the fast LM can unravel all the details and dynamics while retaining whateve character the tubes have. Big win/win.

morfic · #**377** (**permalink**) 07-09-2009, 06:40 PM

I Agree, the Mullard EF92 (small shield, large shield, same thing) are nice tubes, until i heard the EF91 Mullards, those were my favorites on the MkII.

morfic · #**378** (**permalink**) 07-14-2009, 08:01 AM

RightMark Audio Analyzer test: comparison

Still not sure why differences between *tubes* are so subtle on the I+.
I feel i hear more difference on opamps, still prefering the LME49720.
But take a guess which is the stock LME49720 and which LME49720 is the modified one, just labeled (A) and (B), just as a fun reference i included The stock 6J1 and "The Russians", also less easy to distinguish from each other and the EF91, compared to how easily things are picked out on the MkII with the same tubes. Even frequency response changes on the MkII visibly, not just audible.
I can hear the differences you describe with ease on the MkII, i wonder if the differences being larger on MkII is what makes me have a harder time on I+.

PatOMalley · #**379** (**permalink**) 07-14-2009, 05:14 PM

I do not know the difference in the speed of those opamps but the LM4562 is 50mhrzt and the OPA2228 is 33MGRTZ. I expect they might look similar on a scope but they do sound different in application.

I got my new Russian 6J1 and they sound more bass heavy than my Amperex aka Mullards. I do hear those differences. Having spent time with both the stock and new 6J1s I really don't see any reason to search out any better. I do think modding that opamp made a big difference.

morfic · #**380** (**permalink**) 07-14-2009, 06:27 PM

I need to give the modded opamp some good listen/comparison to unmodified, since it's in amp it hasn't been out, so working from memory, well, that never works

I also edited the previous post, i didn't type it exactly how i meant it, opamps i can actually pick out easier, i meant tube differences are harder to pick up on on this amp compared to the MkII.
While i agree with the differences in sound you describe between tubes.
I enjoy my Russian 6J1P-EV also, with the EF91 just being a much better synergy with my HD600, i use "The Russians" when i crave a little more oompf on low end.
And so NOS is never an issue for me, i have PLENTY of 6J1P-EV (from '71 to '84, they all sound the same, with the '84 looking brand spanking new), and a good amount of EF91s.
The rest is just few here and there to have heard a couple.

I finally did pick up some 408A, just to see if maybe those are easily audibly different.

All in all i am impressed how well this amp even drives my HD600 at gain 7, although i will go back down to Gain3.5x, last night i put the D1001 back on the I+, and with the modded opamp, EF91 and gain7, i listened to music at ~5/100 on scale o_O

morfic · #**381** (**permalink**) 07-19-2009, 07:45 AM

Ever notice the cap size National shows on the LME49720 spec sheet, in the riaa preamp circuit it's 47uF, just a smidgen higher than what we are using.

PatOMalley · #**382** (**permalink**) 07-19-2009, 03:22 PM

47uF? Like where? On the opamp? I am using .1uF

morfic · #**383** (**permalink**) 07-19-2009, 04:27 PM

I know we use .1uF, i see national use higher values in their datasheet too. Just makes me experiment happy

I think i will build a cmoy and measure it against the I+ and MkII as it progresses, one thing i noticed while reading about cmoy and LM4562 is that this opamp needs the decoupling caps to not oscillate, so even if i never did a comprehensive listening comparison between the LME with and without decoupling caps, i can be sure it's the right thing to have them, i just now wonder about 1uF and 47uF, since all three values are used in the spec sheet.

PatOMalley · #**384** (**permalink**) 07-19-2009, 05:02 PM

I think if you use a foil cap you are in good order. Thing is that a .1 or 1uF foil cap is huge in comparison to an opamp. Then use a stacked film and you are back in the game size wise. With the exception being the non polar .1uF Blackgates ... which look to have dried up.

So I guess the choice may be a 47uF electrolytic or a .1uF stacked film.

lazpete · #**385** (**permalink**) 07-21-2009, 07:31 AM

Dear fellow head-fiers.

After reading pretty much all there is on the Little Dot I+, there is one on the way! Red LED and all.
Went for the stock model.

Close to where I work, is a big electronic store, and I could use som help in finding the correct op amp alternatives among them all.

I paste a link to the EU store, in english, and was hoping some kind person could point me to a couple of good op amps.

Heres the link
https://www1.elfa.se/elfa~eu_en/b2b/...do?tab=catalog

Thx a bunch in advance!

Lasse