Ok it's this one, but C13 is also named C1 in another schematic...
Edit : No problem to choose C1= 0,01 uF = 10 nF = 10000 pF? F-3dB = 160 Hz
Any "suggested best parts" for this value ?
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Ok I think I'll go with styroflex 10nF like these ones 10nF 10000pF 2 5 630V Styroflex Polystrol Film Capacitor Folien Kondensator | eBay
Sorry for triple post
Sorry for triple post
Ok I think I'll go with styroflex 10nF like these ones 10nF 10000pF 2 5 630V Styroflex Polystrol Film Capacitor Folien Kondensator | eBay
Sorry for triple post
Styroflex should be best but not all make/model are good sounding.
I would go for a safer bet with NOS ERO KP1832:
8X Roederstein Kondensator KP1832 9 5nF 1200V 2 Axial | eBay
Really interesting, George.
I would use an OPA827 if stable, though, it would have a timbre more similar to LM318's one.
In its "original" configuration, with the LM318, the FE (with a good but somewhat "less extreme" BOM, to be honest) was sounding very well but was clearly inferior to George's excellent sounding "myEvo". To our surprise, the same FE with the ADA OpAmp in place of the LM318s outperformed the Evo on all parameters.
In audiophile's terms, the OpAmp change is definitely a HUGE improvement!
This says something about the opamp change but, sincerely, the comparison between the My_Evo and FE is not fair if they're not using the same components...particularly when one of them is using Z-Foils and the other not....
Thanks, I save your link, Styroflex are almost NewOldStock... I think I'll do some tests
From Modulus-86 Rev. 2.1: Composite amplifier achieving 0.000067 % THD.
It would be interesting to know why Tom chose the LME
The LME series has vanishing low distortion figures, I'm sure Tom choose them mainly for this reason, along with an extensive measurement comparison.
But the My_Ref is a different beast which needs even more care for the use of an Howland Current Pump.
Stability is a more important goal than vanishing low distortion.
And BTW distorsion is already vanishing low with LM318
Have a look at the "rev.A" mod. With it, the FF comp. via pin 8 is no longer required. That's what made it possible the use of different OpAmp (beware, not anyone!!).
Inviato dal mio GT-I9100 utilizzando Tapatalk
It was NOT meant as a comparison between them, Dario!
Being impossible to quickly swap the OpAmps to compare them on the same amp, we have used the Evo as a common reference.
Inviato dal mio GT-I9100 utilizzando Tapatalk
I still don't get it... With rev.A mod there is still R43 and C34 between pin 8 and output.
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Dario! That's really something telepatic.. as usual with You
I do use the OPA827 in the Evo, presently.
And while I like what I hear -- it is not the same quantum leap like that with the FE board+ADA4627.
The basic character remained more or less the same, indeed.
The OPA827 had brought a bit of extra smoothness, or in other words it has taken a bit of that hard edginess that I did not like in my Evo; which is very likely a combination of the Cerafine power filters and the Mundorf main caps;
(It's not principally due to the LM318; in other builds it was possible to get a very smooth result, with the classic LM318 configuration)
The OPA827 really has an extra warmth in the midbass region; but still a quite forward, very clean, quick, open, and stable big scene. (~like before)
In the same time, listening to it I start to miss the extra 'correctness' of the LM318 in the bass region..
Oh, and it is a chip which do oscillate in the direct replacement. Slightly, but still. Had to change a bit the compensation.
Had I started with this replacement in the FE, maybe I would not have ended up here, talking about it..
Below it is the square wave response with OPA827, direct;
second shot is after that the comp. cap adjusted (to 100pF)
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The same with ADA4627 in the FE board: (I did not link these measurements yet)
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sure. But, with the chips we are talking about, the amp is stable and works well also without them (that is, they can be omitted).
Yet again, as already remarked by George, do not try to do the same without the "rev.A" mod!
How much run-time on the OPA827?
It will change by a not small margin in some tens of hours...
Most of that warmth and bass emphasys (or less control if you want) will go resulting in a very neutral presentation which remains harmonically rich.
ADA4627 will remain a bit dry.