Author Topic: The ol' I/V and op-amp controversy  (Read 7620 times)

Gen. Dreedle

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Re: The ol' I/V and op-amp controversy
« Reply #15 on: August 06, 2012, 12:04:44 PM »
Another guy who believes everything his simulator tells him.

http://www.diyaudio.com/forums/digital-source/217459-dac-i-v-convertion-very-low-distortion.html#post3116901

Of course, I can not see the schematic, so I am not judging its performance. Just the silly notion that a simulator can predict distortion, to this level.

Translation: build the friggin' thing, pal, and then tell us about its distortion.
"Major Danby, sir."
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"Take him out and shoot him."
"Sir?"
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MystereoN

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Re: The ol' I/V and op-amp controversy
« Reply #16 on: August 06, 2012, 01:01:35 PM »
Quote
Of course, I can not see the schematic...
Never argue with a fool,
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Gen. Dreedle

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Re: The ol' I/V and op-amp controversy
« Reply #17 on: August 07, 2012, 07:32:57 PM »
I still don't see anything magical about it. Common-base folded cascode. Guess I am too stupid to see anything magical about how the cascode stage is biased.  I just know it is a place that can make the HF do weird things.

Maybe that is what I always failed to do............simulate it first!

"You don't have a simulator, and if you did, you would be too stupid to make it work."

Yeah..................right on both counts.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

Gen. Dreedle

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Re: The ol' I/V and op-amp controversy
« Reply #18 on: January 26, 2017, 09:57:16 AM »
Real long story short..................

Someone made a private reference, to a certain poster, over at The Pub. Seems to be a sharp guy, that has posted lots of good stuff. Took a look at his site, and one thing stood out.

He has a section on I/V stages.

One of the circuits was a discrete gizmo, similar to what I came up with, back in '89 (or whenever). One thing curious about it: it only had 0.25 V out, for 2.5 mA in. So, it needed a 20 dB amp, after it. Well, to my convoluted way of thinking, that kinda sorta defeats its purpose. This chap felt that raising the gain hurt distortion.

Well, ok................his circuit, not mine, and since it is a free world............

Now, by pure coincidence, I came up with a newer version of the I/V. Around 30 years to think of a better way to do it, maybe better parts (unless you want to make a JFET version, which I never would, despite my heavy reliance on JFETs), SMT, CAD PCB s/w, and a lot of other stuff, here is what it looks like:



(Yes, that is a Beavis and Butt-head mouse pad. Yes, there are mistakes in the layout. Yes, I left off the rail bypass caps. Stop carping!)

So, how does it work?

Well, here is the distortion. First, in % THD, and next in dB down:





So, with a 1 mA input (like you would get from that nasty old AD1862), and you want 2.5 V, it is less than 0.02% THD, and all the harmonics are down 80 dB. Good enough to use, without any tweaking.

And the input impedance............



Roughly 1.75R, and it is flat. OK, I did not calibrate the measurement, but so what.......................good enough to use.

Draw your own conclusions.

If enough folks ask, maybe I will make some more PCBs.

Not for sale to Ireland. (Not sure where that came from, but someone accused me of that before. So, why change now?)

Oh...............did this on +/- 12 V. Designed it to work on higher voltages, which is why some of the LEDs were passed over. Ran it on the designed 18 V rails, and it measured the same. (Because the gizmo it is going to get stuck in has 18 V rails.)

All for now................
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

MystereoN

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Re: The ol' I/V and op-amp controversy
« Reply #19 on: January 27, 2017, 06:48:50 AM »
Looks nice and I belief it sounds nice too....is this dark violet color?
Yes, this older gentleman know what he is talking about.
A lot of opamp based I/V on his site and other interesting circuits, too.
Never argue with a fool,
they will drag you down to their level,
then beat you with their experience!!!

Gen. Dreedle

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Re: The ol' I/V and op-amp controversy
« Reply #20 on: February 06, 2017, 08:59:12 PM »
The guys who make it call it purple.

Picky, picky, picky.......................

oshpark.com
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"