1-The servo has the cleaner reference because it is actively adjusted (superior).
A passive trimmer offset adjust lets more shirt, ripple, and unwanted trash
into the music than a servo would (inferior).
2-Most amps should work with 1 - 2 mV offset shouldn't they?
Not just Japanese amps?
I have 60 to 70 year old American amps that work just fine.
Nope let's say 50 years old, but they are tube amps.
3-Anyway, you're saying the 30 old Japanese stuff still works
fine because they have the servo, which compensates
for the age and drift of passives.
4-Holy Smokes OS, how do you design this stuff so quickly?
5-Some of the above, but have most of the other circuits
optimized to the point where changes won't be significant.
YES -Now I'm going to crank up my stereo, tune my axe, grab an amp
plug in and play some Jazz, Rock, then blues.
I'm not very good, but I have a damn good time. :)
1- Yes - some just use a cap , some resistors .... a "dirty" , halfarsed
"git er' done" type of thing .... 😀
The servo is an "amp within an amp". Just as the main amp rejects dirty
power , the servo is just a "baby" amp sitting within. It will take the
already cleaned power from the zener regulators and clean it more.
The TL072 is a tiny "Wolverine" amp in a chip with it's own 80-100db
ripple rejection.
2- A lot of them don't need much , Valve amps set behind an output trafo -
some (older) transistor amps sit behind a capacitor.
NO servo needed .... here.
A 1970 - 2010 direct coupled BJT/FET amp better have low offset -
woofers are expensive. Some work with >50mv offset , most are <10mv
without a servo. As the DC blocking cap ages or the semi's age - dirt ,
humidity , offset changes ..... 🙁
Servo will always be looking (and looking) to correct what is DC -
20-30years down the road.
3- Yes , those old servo 70's amps .... most are not blown ! Just
put some new 4700uf/ 63V supply caps in your typical 50W 1975
sansui/kenwood/pioneer and the amps work.
plus - regrease the outputs , change other auxiliary caps.
4-I took a break , this will be the first of about 4 more to keep
em' busy😎 .
5- spook , symasui , wolverine , kypton V/C ,CFA-x - all "golden".
Sometimes just a resistor tweak to compensate for a different
transistor (or application).
YES !! I " level the living room landscape" ( with some shine or wine) ,
on occasion. Lot's of good music takes on a whole new character at
>200W !!
OS
So too is this place, DIY Audio, which is why I enjoy it so much and you
gents do such a good thing here. It's all about trying and tasting these things
and just finding what works for us. We are all different have differences
in hearing sensing etc yet are Gung Ho getting these things to make some
fricking Music.
Now I'm going to crank up my stereo, tune my axe, grab an amp
plug in and play some Jazz, Rock, then blues.
I'm not very good, but I have a damn good time. :
😎🙂
Yes...but one way or another, it interfere with the main feedback of the amp, phases at low frequencies etc. Bob Cordell had well defined its specifications. Saturation margin, authority, HF evils due to the limited open-loop gain and bandwidth, noise and internal offset of the ICs.
It require a great care in design, as everything else.
On my side, i tend to prefer to use two OPAs for the purpose.
Btw, OS, did you read my suggestions here : http://www.diyaudio.com/forums/solid-state/248105-slewmaster-cfa-vs-vfa-rumble-2.html#post4275409
Not only did I go to your site and read (most of it) , but I yanked the servo
on my present servo'ed amp to A/B with and without.
Between what my simulations say and what I hear , servo lore is just that -
(unwarranted paranoia).
Besides , some of the most expensive audio
I have seen (below) ..... just a single stage non-inverting servo.
PS - they do use a good one - OPA2134. "sound plus" 🙄🙄
That is the same as my favorite "spook" - and I KNOW that works !! 😱
The ND simulated with 1/3 the THD - might be the better VAS ...
(old nad 25ppm / new ND 8ppm).
But , it also has 15db better PSRR that my original NAD (bonsai's SX amp).
Servo is not degrading anything - that's for sure !
OS
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It seemed that one of the points that Bob Cordell was trying to make was that the opa in the servo should also be quite, low noise as it was in effect part of the audio chain and not outside having no effect on the sound. For the difference in cost between a cheaper non audio opa and one meant for audio applications isn't it worth it to spend a little more money? Can we have a comparison of the output distortion numbers with only a change of the opa in the servo position and see if this holds true or is just an opinion of sorts that has no true effect?
I can throw my whole slew of op-amp models into the simulation and
NO change in that <10ppm THD20k.
I can remove the op-amp - also , no change. Same holds true for 20HZ.
That OPA2134 would be a "drop-in replacement" for the TL072 , BTW.
PS - that "sound plus" is just TI marketing fluff to rip off audiophools.
OS
shame on you and then you come out with.
contradiction? 🙂
i was surprised to see the elektor/doug self pre-amp 2012 to use so many ne5534a opamps. and a few lm4562 is key spots.
yes your junk 5532 technology. i built a pre in college using 5533/4, it sounded good to me then. os what do you use as a pre-amp?
so how much improvement of your fav opamp vs the ole 5534?
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I have seen lots of sansui top end designs that use a njr4558 as the servo, in those days they were claiming dc coupling as the best way to do it.
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I called it a "junk" op-amp because many here feel it is so.
For me , if it works reliably - it will do. 🙂
OS
For me , if it works reliably - it will do. 🙂
OS
sitting on your fence 🙂
reliable sound or operational longevity?
only doug self has the balls to still promote this cost effective part for audio usage.
i do want to try out a opa(2)602 for sq however.
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I think this was the suggestion of a few including B. Cordell.
http://www.ti.com/lit/ds/symlink/opa604.pdf
I see the price for single units of $2.50 or less.
http://www.ti.com/lit/ds/symlink/opa604.pdf
I see the price for single units of $2.50 or less.
+1
In fact the only thing that afraid-me with TL071 & co is their tendency to invert their polarity when too much saturated.
My curiosity was more about my idea of the input filter dumping the diamond. and your reaction about the two branches of feedback.
Nice ! For my DAC buffers and EQ's . 🙄
"Fiddy" Cent TL072 for my servo is fine for me. Just hit a
300W peak whil'st listening to triumph - my servo matters not here. 😀
Just when I think I've heard it all - the "spook" put a shiver down
my spine yet again. (aptly named).
OS
Just don't saturate them ( and design so a saturated condition would not
cause too high resulting offset).
This is what I don't like about a direct servo connect - a servo failure
would send the amp to the rails !! 😱
Series resistance at my servo out , if high enough , will even make
a shorted servo produce just a few volts main output offset -SAFE !
"input filter dumping the diamond" translate that - and ... I will answer.
Back to work on the "Dvssa" (ND) 😀 .
OS
I could still buy half dozen TL's for the same price. 🙄
Ooooh , the "cheepness" of it ! "Audio scrooge" ... hah !
OS
the metal wrap can also add some thermal inertia; helping to minimize effects of short term temp changes.
mlloyd1
mlloyd1
I understand OS' comment and yours. It gets to the point of
such diminishing returns it isn't worth the effort changing for changes sake.
This is not just me, but pioneers in industry, for example Dr. Edwards
Deming. I heard it from the horse's mouth where he explained it showing
results of a derivative, for optimizing a system. The parabola resulting and
that the slope (measured as a tangent[90 degrees]) as long as you are close
to optimization moving along that small space...lets say +- 2 degrees maybe
5 degree from optimum or so... might not yield many benefits versus the effort/cost.
Of course you can continue...but then you might be invoking Mr. Murphy
and all of his laws, correlarrys (sp) and other challenges.
A set of things called Murphy's Law.
If it's invoked your screwed, so better to let it rest.
added:
Careful OS, what are you kid's going to say over the holidays?
He made this cheapshirt gifts that if he'd used the better part...
and as my baby is fond of adding:
Whhhhaaaaaaa Humbug!
I think I need another dose of playing to think right again.
Ok gentlemen, slow blues in G, a storm is brewing.
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not with me, i am happy with a ne5534, other's well, every one can chose what they want to use, that is the beauty of it all.
ne5534a = sounds good to me and Doug Self.
I wonder if some of my old Signetic parts are aged enough now to be used for my ears.
I can find lots of NE5534's in my E-waste.
When I've used these "oldies" , they all worked - reliable.
But they are not "audiophile" approved.
300$ new soundcard , you won't find NExxxx - but OPA/lme49710's.
Or , even a chip isn't good enough , A 150$ burson's discrete
will stuff any stocking (except scrooges 😀 ).
Just being sarcastic. 🙄
Edit - after reading a "CFA is worthless for audio" comment , I don't really believe D Self's opinion.
OS
When I've used these "oldies" , they all worked - reliable.
But they are not "audiophile" approved.
300$ new soundcard , you won't find NExxxx - but OPA/lme49710's.
Or , even a chip isn't good enough , A 150$ burson's discrete
will stuff any stocking (except scrooges 😀 ).
Just being sarcastic. 🙄
Edit - after reading a "CFA is worthless for audio" comment , I don't really believe D Self's opinion.
OS
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