[gaetan8888]

Hi Gaetan,


     Yes Class-A is correct, I originally used the resistor trick a long time back, found that even a simple Bjt,Led,resistor current source sounded much better, also a drawn current of 5ma,a buffer and nested feedback really improved this chip for a voltage gain stage.



Colin

Hello Colin

I've modified the analog addicts phono preamp. Using a ccs but the ccs resistors value are approximative.

Is, in my image, it is like you said and resistors value ok for 5 ma ?

Thank

Bye

Gaetan

[rha61]

hi

after trying a lot of AOP ( ad825 , 5532 , 627 , 2604 , 2132 , ad845 , 8620 , ths4062 and 8066 ) in CD players output stages or input buffer  in preamps , i've got the best results with AD826 and THS4032

Alain

[VYnuhl.Addict]

Hi Gaetan,


     For the CCs, I assume you are using a Green Led?, in that case a 270R resistor will suffice for a little over 5ma. Also, the 2k from collector to output is not really neccessary as this is a high impedence junction as it is and offers little and is absolutely not neccessary for any sonic benefit, ive tried with and without and never noticed a difference in the slightest. For ythe opa627, negative rail biasing is best, it makes much more sense if you take a gander at the datasheet and simplified schematic as to why you will want to pull current from the Upper half, youll notice from the schematic that the positive rail half is in the same drive configuration as a diamond buffer which is very sonically good, now there is the advantage on running 1/2 single ended which in the opa627 is the upper half, the lower half is a standard EF... For the CCS use a very low capacitance bjt, my favorite for opamp biasing is 2sc2705, 1.5pf cob, and connect to the negative rail exactly as you have drawn with the pnp in the schematic....If you have any questions feel free to PM me, as I dont want to hijack the LM thread ...


Colin

[gaetan8888]

Hello Colin

Thank for your help, I will do as you suggested.

Bye

Gaetan

[gaetan8888]

Hello

I have read again some texts of Doug Self and
found somethings interesting about the LM4562
in his web page "Designing With Opamps"

It seem that the distortion figures tets in the
Nat.Semi. data sheet are done with a shunt
feedback circuit, giving better figures with less
common-mode distortion in the input stage and
less distortions at HF.

The Doug Self LM4562 distortions tests done
with a series feedback mode circuit do have
much higher distortion at HF compared with
a circuit using shunt feedback mode. And the
distortions should be higher in a real life use
with musics and transients.

Since some circuits and most phono preamp circuit
use series feedback mode, maby it is explain the
certain amount of edginess in the top-end for the
LM4562.

Bye

Gaetan

First image are LM4562 in series feedback mode
circuit test. Second image are LM4562 in shunt
feedback mode circuit test.

[daredevil_kk]

Hi Gaetan,

Have you tried the metal can series for the LM4562HA. It seems like Mark and couple of guys from DIYaudio swear by it. They feel that it is a more refine version. I also wonder how they perform as a non-inverting unity gain buffer as compare to the other configurations.

BTW, does anyone knows if it is a good idea to skip the buffer at the cdp output(4.5kohm) as there is a unity gain buffer after the attenuator.

KK

Can't wait to get my hands on my Soraya.

[AKSA]

Hi KK,

Welcome to you, and Colin, and Gaetan, to the forum!

Today I auditioned the new Soraya (update 2009 version as discussed) in a good friend's system, with Squeezebox, Burson Buffer, and VSonics.

Stunning, exceeded specifications, I can continue without any worries at all.  Compared to the older model it offered more resolution, much better layering of instruments, and huge bass articulation.  I'm over the moon, results better than expected....

Colin, you there??  Are you in for a surprise!   

Cheers,

Hugh

[VYnuhl.Addict]

Hugh!,


     Im here now , haha, I emphatically agree, I cant find a fault with it thus far in any way shape or form at this moment, from the Lows to the highs to the Soundstaging, natural, very 3d and most importantly non fatiguing whatsoever...My Jaw dropped with the 50w prototype, at 100w(retail version) its at its best in terms of resolution and drive...This was all conceived during Hugh's outpouring of madness, it required a pogo stick to keep up with the speed of his changing ideas!,


Colin

[AKSA]

Hi Colin,

You are certainly being charitable here, but I'm really pleased you like it too, and I cannot overstate the contribution in practical and creative ways that you have made to my audio madness in years past.

It is a great shame we live on different continents.......  thank you sincerely.   

Cheers,

Hugh

[VYnuhl.Addict]

Hi Hugh,


     Non-Charitable, its a culmination of taking the conventional amplifier, finding the weaknesses and finding a practical and hopefully simplistically elegant solution the weaknesses.Also its driven by a mad passion to experiment with new ideas rather than to re-introduce an old design with minore parts changes which can be often at the small corner of empirical differences.  Ears are essential here, as we have both found, the well known area of measurement does very little to dictate sound "quality", so the Ears are both a first and last defense while we all still retain something to call hearing . As always its great to try and correlate what we measure to what we hear, truly and utterly impossible with straight THD exams, the biggest difference being IM and how the Thd unfolds across the band with music which still gives creedence to the rightfully sought after monotonically decreasing figures 1khz and up. Slew Rate too seems to play a pretty good indicator surprisingly, and then this is affected by many parameters,choice of frequency compensation, gain, nfb-db, Ft and Phase Shift within the amp. Tells me, while Tube amps had acheived their peak of the Art, SS amps still have creative life in them..Hugh, your going to need to set up a Soraya HTX review page pretty soon! ..


Colin