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To quote Ehien: "At the moment I have LM6172 in my phono stage for auditioning. It is indeed a very fine opamp with superb specs. But the perspective into sonic texture is very different than the ones (OPA2604, OPA2134, OPA637) from BB/TI. LM6172 has great clarity and resolution, but the tonal balance, compared to OPA's is on the leaner side. For me LM6172 is more like what a good solid-state (YBA comes to mind) sounds; while OPA's are more like what a good tube amp sounds. With one exception that bass seems to be a bit weak on LM6172."My comparisons of the LM6172 with OPA2604 and OPA2134 in entirely different conexts gives the same impression BUT there is not very much likelihood that what we are hearing is in fact literally a treble boost. The chip just can't be that non-linear as a function of frequency. It must be something else? Better transient response (well, that's not such an easy answer either, as the ability to deal with a sharp wavefront is also a partial function of high frequency response...).
I am not where my test equipment is, so can't give this a rigorous test. I do recall scoping the loaded output of a Rotel RCD791 with LM6172 in the analogue stages, using a test CD. Result: dead flat sine wave output from the lowest track to the highest. Voltage variance was on the order of millivolts.
So what's up here?
Norman
Follow Ups:
Good to know that we are hearing the same thing. Wouldn't this world be perfect if 6172 has better bass and be slightly warmer? :-)
Hi Norman,Jan Meier, designer at Headwize.com, uses the LM6171 extensively, and likes to bias them into class A using a resistor in the usual manor. According to him:
"This modification resulted in a substantial improvement of sound quality, and can be easily added to the original design. Strongly recommended."
In fact, I have on of Meier's Class A designs--a Corda headamp. It is a very nice LM6171 design (OK, so I modified it a little...). I haven't done any Op Amp switching with it, so can't comment on the LM6171 in any comparative sense.The sound from the Corda headamp is less 'lean' than the output of the discrete preamp in my Bryston B-60, for what that's worth.
Norman
Norman,What 'mods' did you do to the Corda HA-1?
Hi,The answer is simple, assuming there are no Powersupply problems present (inadequate HF bypassing, insufficient Capacitance at LF), that the LM6172 unlike the OPA604 and even the 637 behaves as "straight wire with gain".
All the OPA's you mention have a distinct rise of distortion even in the audio band, the LM6172 remains basically the same up to a few 100KHz.
However, the Powersupply may be very well the reason, as the LM6172 has a much lower PSRR due to it's inherent design, so greater care is needed here than with classic "differential" Op-Amp's.
Later T
so thorsten, with those caveats, would your advice be that if going from older chips such as 4558, it might be the go to stick with the 2604 for a noticable improvement without too much work on power supply etc; and plan on getting max sonic upgrade using 6172's when youre prepared to do some associated work??..im thinking of a teac x-2000 which uses the jrc4558 and considering whats in the box vs sourcing?$$$ etc...because ive got a bunch of 2604/604 that have been sitting around for 10 yrs looking for a circuit to enhance. ive had some previous advice that opa2132 would be an almost direct upgrade..and other advice to go with 2604 and some passive reg via choke in the main power supply as well as electro replacement. same caveats with gain etc in record/replay eq areas. I know this is slightly off thread with regard to your riaa pre, but its doesnt seem to be as cut and dried as choosing particular tubes for particular applications...relatively speaking!! your comments?? (btw whats the url for your tube phono...its gone from the ref at tnt??)
thanks.....cb
Hi,No, I would, especially in CD Players and similar Digital gear allways go for the 6172 and sort the PSU out while I'm there. THis means:
1) 1uF/50V Siemens stacked Film bypass Cap across the supply line, directly on top of the Op-Amp to gurantee stability under all conditions (you can use other brands than Siemens which seems not sold in the US, important is the physical size and low inductance which allows the Cap to bridge the supplies with the shortest possible loop)
2) 220uF/25V or larger value Elna Silmic Powersupply decoupling capacitors close to the chip. Do NOT use Black Gates there under ANY circumstances, trust me you would not like the resulting sound.
3) Schottky Diodes in the Supply
4) Larger value and higher quality (I use Panasonic FC Series - do not use Black Gates if you trust me - Elna Cerafine or Silmic are better but very expensive in large values) Supply reservoir and Regulator decoupling Caps
That's it. Not so bad, is it?
Ciao T
Follow up for Thorsten: Should the 1uf cap(s) go across v+ & v- or as a bypass from v+ and v- to ground?
Thanks...Bob
Thorsten...in my CD player, during loud passages the 6172 sounds as if it overloading (i.e. a distorted fuzzy sound) the linestage of my preamp. Could this be caused by oscillation?Thanks...Bob
Hi, T.
What do you think of BlackGate N series caps? They are much better than Standard series, aren't they?
Thanks, Sasha
Hmmm... Good point. I didn't notice that it has lower (95dB vs. more typical 110dB) PSRR than some other opamps. It does warrant one taking a closer look on PS bypass. Having so much fun using inductor/choke and capacitors for PS filtering lately, maybe I'll apply the same treatment to the phono stage (if there is none yet, I'll check) where 6172 resides. However, I'll be surprise that power supply has more high freq junks than low freq ones and cause the leaness.There have been numerous cases where audio gears measured flat and non-distorted sounded lean or thick. Our ears treat sound wave in a funny way that I've yet to fully understand. Well, I don't really know. Hopefully one day I will.
Ehien
Hi Ehien,Like Thorsten says below, you should take care of both the SSM and PS rails. From experience, LC cell applied directly on DC regulated PS rails sound bad. For me, it removes all the music leaving only sound. I use choke with great effect only as RFI filter between rectifiers and transfo and as pre-regulator between main cap filter bank and DC regulator.
As for the SSM2017, I finally manage to get some feedback about them and they sucks. They are lean and very detailed in some ways, i.e, that kind of souless music that some audiophool crave about. Replacing it with any low-noise op-amp discussed here should remove that leaness. What you need to know, is if the gain will remain more of 5. Most of the time, it should be enough with most op-amp.
Regards,
Daniel TrudeauP.S.: There's a new web site that inclued some mods on a CD player and explain some op-amps sound, as heard by the tweaker.
Hi,I cannot fail to note that owner of the mentioned site "forgot" to make sure he added the Capacitor I racommend (this can be added so that the IC can be plugged in and out together with the cap) and got sonic problems.
For one last time for anyone using LM6172. If you do not add a LOW INDUCTANCE, small form factor capacitor of quite material value (absolute minimum 10nF, it sound however with 1uF!!!) the Chip will at best be marginally stabe and will burst into damped oscillation at the slightest provocation (like a transient in the music). This does not improve the sound at all.... ;-)
Ciao T
I certainly argree with Thorsten's recommendation on the 6172. It is really quite wonderful, if you do as he says and install a non-inductive stacked film cap (I used a .47uf Panasonic stacked film) from v+ to the v-. I've used the 2604 and the AD827 (a few others as well) but the 6172 is the champ so far...IMHO.They should be located as close to the chip as possible.
My 2 cents. Bob
hi,
would the smd panasonic metalised polyphenylene
sulphide film caps be ok?
cheers
dek
Hi,> would the smd panasonic metalised polyphenylene sulphide film
> caps be ok?I have not specifically tried these, so I can only answer from theory, in which case the answer is yes....
Ciao T
cheers thorsten
Hi T,I know that! I didn't say that I totally agree with him. In fact, I always use at least a 10uF 'lytic with a 0.1 X7R SMD ceramic bypass. I'll always wonder why people forget that simple thing. One can add tons of cap. on PS rails to ground, but if one fail to add, like you say, a LOW INDUCTANCE, small form factor capacitor of quite material value, the IC will always see AC difference between rails and be instable.
It reminds me of bad copy of LM78xx that oscillate without a 10uF directly at the input. Or with a different length of trace between the 1uF and is output. Tricky stuff. Better buy real LM or LT. Anyway, they sound bad...
If I remember good, you use Siemens. I have to contact the Canadian Distributor soon, so did you have a specific serie that I should check? Mylar, PP?
Thanks,
Daniel Trudeau
Hi,They are sold quite widely in europe, stacked film Mylar, NAKED CHIPS (no coating, no further plastic cases, metal ends that are solderable without burning the Cap up). They come in lots of voltages and values.
What I like about them - 9nH typhical residual inductance.... That is about 0.5 Ohm at 10MHz impedance....
Ciao T
NT
Hi,Also something to consider, with the 6172 Distortion is dominated by 3rd order harmonics (not that is much of them but still) while with the LM6182 (if applied correctly) the 2nd Harmonics are dominant. Now all this happens below -100db but it is still the best theory I have as to the (arguably small but noticable) differences between chips that are almost idenical with only an additional buffer section on the negative input allowing Voltage feedback.
BTW, I'f may wager, the leanness and thinness is likely more the SSM2017 (because that what it sounds like - incisive, cutting and lean, if with great detail) than the LM6172, it just does "nice up" things like some others do.
How about trying to change all signal relevant resistors to Carbon Types. On Solid State gear, especially Op-Amp sort of stuff I tend to prefer these sonically and how about some Elna Silmic PSU Capacitors which reduce the distortion fed back into the Op-Amp from the Supply rails?
Ciao T
Makes sense to me. Just listening, OPA2604, etc. seem to fuzz/muffle highs and transients a bit.Not that I hear nearly as much difference between these and LM6172 as between a bad and good interconnect...
Norman
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