John Curl's Blowtorch preamplifier part II - Page 3257 - diyAudio
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Old 12th January 2013, 06:52 PM   #32561
PMA is offline PMA  Europe
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Yeah, I should have said -1. Your are right in the rest as well.
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Old 12th January 2013, 07:23 PM   #32562
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Quote:
Originally Posted by john curl View Post
Richard, it is more than that. It is using the RIGHT part for the job.
That would show up in my (broad) 'performance' catagory.

Last edited by RNMarsh; 12th January 2013 at 07:30 PM.
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Old 12th January 2013, 08:23 PM   #32563
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Then, Richard, you are not explicit enough.

For me, having the RIGHT switch, designed to do that SPECIFIC job meaning current-voltage as good and clean as possible. This usually means gold-on-gold switches, but silver on silver switches can be even better in some circumstances.
Another alternative is some 'typical' switch controlling a set or many sets of relay contacts. There, gold-on-gold is usually best.
This also means to avoid 10A switches to control .001A. This is because gold usually blows off with 2A or more, and you get a more base material that can be easily tarnished, and therefore compromised.
Many here have no knowledge of this. Others just ignore it. Yet it can make a serious difference in listening quality. You cannot necessarily look at a switch from the outside and know its internal characteristics. That takes further investigation and study. Study up everybody! '-)
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Old 12th January 2013, 08:33 PM   #32564
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by gk7 View Post
John did define quality in the post you were answering to. Do you read
your own posts only ?
Is your only goal to make comments like the one
you just did ? Probably quality means nothing to you, but for others it does.
Good accuracy .......
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Old 12th January 2013, 08:42 PM   #32565
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Quote:
Originally Posted by simon7000 View Post
Scott,

I don't think you got my reference to the parable of the blind men and the elephant. Each looked at parts and thought they had the whole.

Making standard measurements of the AP is mostly autopilot. If you don't pay attention to the details you get very pretty graphs of nonsense.

Attached is a THD curve that shows the noise limit and the maximum voltage out of the unit. (It gave me an error message when I tried higher source voltages.)

The second attachment is the best curve of the LM4562 as there is a gain of about 100 be sure to reduce the label values.

I showed you the current source version of the test circuit as shown in the data sheet. Now from prior questions it seems almost no one here can even write the loop equations, which I thought were obvious from inspection.

Trying to get the same view of the Elephant how do you read the limit of the AP trying to display what is shown?

ES

PS I see I forgot to do log on the voltage so the graphs don't look the same!
Ed I'm not here to teach EE101 end of this chapter. If the equations are obvious why can't you write them?
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Old 12th January 2013, 08:52 PM   #32566
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About the setup to increase distortion a good basic explanation is given in the opa134 specsheet http://www.ti.com/lit/ds/symlink/opa134.pdf

101.jpg

This is the relevant part and I hope it reads well. It is easy to see that the input impedance is defined by the input impedance of the opamp. If R1 is included. It is a voltage divider consisting of R1 and R2, which keep the voltage at the inverting input at the voltage at the non-inverting input, which is Vo of the generator. No current flows through R3, except most part of the error voltage. In case R1 is omitted, so for G=1, the situation is identical, since Vo of the op amp is now identical to the Vo of the generator, bar again most of the error voltage.

I think Scotts explanation using the concept of bootstrapping is a bit misleading. Nothing is really bootstrapped as I see it, except for the error part, it is like reverse degeneration. The input impedance seen by the generator is exactly the input impedance of the opamp, plus whatever error voltage has to be sunk. But that is minute.

Nice little experiment for a Sunday afternoon: by replacing R3 with a small pot, one can have a continuously variable distortion component at an opamp output. I did this when I started working with OPA134, just to hear when stuff becomes audible and because I like the smell of rosin core in the morning.
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Last edited by vacuphile; 12th January 2013 at 09:16 PM.
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Old 12th January 2013, 09:22 PM   #32567
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Quote:
Originally Posted by vacuphile View Post
About the setup to increase distortion a good basic explanation is given in the opa134 specsheet http://www.ti.com/lit/ds/symlink/opa134.pdf

Attachment 323428

I think Scotts explanation using the concept of bootstrapping is a bit misleading. Nothing is really bootstrapped as I see it, except for the error part, it is like reverse degeneration. The input impedance seen by the generator is exactly the input impedance of the opamp, plus whatever error voltage has to be sunk. But that is minute.
If you have an input resitor and drive the other end with a replica of the input voltage so the resistance appears much larger to the driving signal I call it bootstrapping as it is in general use.
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Old 12th January 2013, 09:34 PM   #32568
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Originally Posted by gpapag View Post
Avgolemono ! For some fat, tasty soup, a pie or for roast dressing ? Try a bit of oregano or thymus in it.
George
Yesterday just the soup, I wasn't kidding around 1969 while I was at MIT there was a nice Greek community here in Central Square and I miss the comfort food I even made a batch of lamb shanks last month.
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Old 12th January 2013, 09:42 PM   #32569
a.wayne is offline a.wayne  United States
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What , I thought all IC guys were Vegan ......
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Old 12th January 2013, 10:01 PM   #32570
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Quote:
Originally Posted by Esperado View Post
About pots, my question was not so insane: what can-we measure to ensure a pot is a "quality" parts. Of course, i got no answer.
No, or we don't have the same definition of "define". It is like "Right part".
For me, a crucial attribute of quality is that the characteristics are maintained with time, or improve. If a supposed high quality item starts well but then degrades while in its normal operating environment for no other reason than it's just doing its job, then for me the "quality" is not there. Pots fall into this category, as do standard methods of connection.

I would be far happier using a lower grade item which stabilised in its characteristics with time, than a "gold plated" unit which I could be aware was losing its "polish". The tension of hearing, and waiting for the qualities to "go off" is not worth it ...

Frank
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