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Old 18th September 2002, 01:59 PM   #1
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Default Easy-to-build I/V stage

I have had several requests for my I/V board. SInce they are now all gone, here is something you guys can throw together to hold you over until I build some new ones. It is close (distortion is -70 dB vs. -80 dB; input Z is 5 ohms vs. 0.1 ohms).

Hey, you really didn't think I was going to give you the good one for free did you? [joke]

You may need to tweak the current slightly of either CCS to get the collector of Q2 to a decent voltage. And also R4 to get the emitter of Q2 at exactly 0.0 V. (You guys need something left to try by yourselves.....I'm not going to do it all for you.) [joke]

Jocko
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Old 18th September 2002, 02:14 PM   #2
dice45 is offline dice45  Germany
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Jocko,
why must that output coupling cap be so huge? 100µ? Does the circuit only work with 2k5 output load?
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Old 18th September 2002, 02:31 PM   #3
sonnya is offline sonnya  Denmark
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hi hi hi hi hi hi hi!!!!!



Jocko .. nice circuit!

Sonny
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Old 18th September 2002, 03:09 PM   #4
mlloyd1 is offline mlloyd1  United States
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NICE! Thanks Jocko. Looks like I have something to play with over the weekend.
Hey, I must have missed that you had boards for this. I though your DAC boards didn't include IV conv, right?
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Old 18th September 2002, 03:24 PM   #5
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1.) Why so big?

I picked the part closest to me on the work bench.

2.) Other values work too. I use around 4K.

3.) I had some old I/V boards laying around since '89. Some one asked if I had anything to go with the DAC board, and the next thing you know, they were all gone.

New ones......eventually.

Jocko
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Old 18th September 2002, 05:02 PM   #6
sonnya is offline sonnya  Denmark
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will q2 or q4 not go into saturation?

Sorry i ask.. but..

Sonny
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Old 18th September 2002, 05:21 PM   #7
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Wink IV Converter

Hi Jocko,
Nice to see you back. I thought you had left us.
I see a common base amplifier between to current sources or should I say between current source and current sink?
My problem is I don't like common base amplifiers....
All the best.
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Old 18th September 2002, 05:24 PM   #8
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If you carefully adjust the current, it will work.

Yes, it is a common-base. Not an RF engineer, eh? I am, so I do.

Jocko
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Old 18th September 2002, 05:52 PM   #9
sonnya is offline sonnya  Denmark
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Yes.. times go fast!

Sonny
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Old 18th September 2002, 06:52 PM   #10
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Default Re: IV Converter

Quote:
Originally posted by Elso Kwak
My problem is I don't like common base amplifiers....
May I ask why?
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Old 18th September 2002, 06:54 PM   #11
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Jocko, why do you need the current source Q4? Isn't this circuit like on-off, to much gain to be useful? Feedback???
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Old 18th September 2002, 07:15 PM   #12
artnyos is offline artnyos  United States
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Default Collector voltage

I would put the 2.49K(R1) resistor on the other side of the 100uf cap(C1)and adjust R3 to get 9 volts or so across R1. You will have real difficulty getting a stable DC votage at the junction of the collectors of Q2 and Q4 without some resistive load to ground at that node. Now please don't beat me up Jocko.....


Art
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Old 18th September 2002, 07:23 PM   #13
Nicke is offline Nicke  Sweden
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Looks nice.
I will try it soon.

Nicke
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Old 18th September 2002, 07:48 PM   #14
sonnya is offline sonnya  Denmark
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Artnyos is right.. but your circuit is elegant and simple!

Way to go Jocko Homo!

;O)

Sonny
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Old 18th September 2002, 07:55 PM   #15
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The reason is the distortion is much worse. I measured it.

The voltage doesn't have to be that stable.......just stable enough to set a decent operating point.

There are more complex variations, but you guys are going to have to figure them out for yourselves. This is just a starting point to prove you don't need op-amps to make a decent I/V stage.

Jocko
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