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Old 4th January 2003, 07:10 PM   #31
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: IV-Converter

Hi,

Quote:

Kuei Yang Wang, is your schematic a <B><I>working</B></I> circuit?
If Burr Brown writes accurate application notes - yes. You can simply check their app note for the common base circuit, it's pretty much electronics 101.

As said, I would not use this type of circuit myself for any number of reasons, however if anyone wants a zero feedback, fully complementary I/V converter using the OPA660 is the best bet, plus you get your own buffer on chip too, so it is a single chip soplution for a feedback free I/V conversion.

Yet I too have not much against feedback,if applied apropriatly and in apropriate circuits, again, it is not WHAT you do that matters, it is HOW you do that matters.

Sayonara
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Old 5th January 2003, 01:14 AM   #32
jkeny is offline jkeny  Ireland
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Default simple i/v

Now I'm interested - in building this I/V stage with OPA660 - simple enough even for me - can anybody advise on how a TDA1545 with about 3.3V Vref can be connected - I'm not very fluent in circuitry but followed T's description of circuit for 0V Vref (TDA1541)

John
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Old 5th January 2003, 01:27 PM   #33
Previously: Kuei Yang Wang
 
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Default Re: simple i/v

Hi,

Quote:
Now I'm interested - in building this I/V stage with OPA660 - simple enough even for me - can anybody advise on how a TDA1545 with about 3.3V Vref can be connected - I'm not very fluent in circuitry but followed T's description of circuit for 0V Vref (TDA1541)
This will not be so straightforward. First of all, the common mode Voltage of the TDA1543 will cause offset and the voltage compliance of the OPA660 ios too limited. It would require an unusual arrangement of Powersupplies to start with, namely +8.3V/-1.7V, then the base (pin 3) needs to be connected to Vref. This will ten give 3.3V DC offset on the output, requiring a coupling capacitor or some other form of DC nulling. Sounds like a lot of hassle..

Sayonara
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Old 5th January 2003, 10:47 PM   #34
jkeny is offline jkeny  Ireland
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Default simple I/V for TDA1545

Quote:
This will not be so straightforward. First of all, the common mode Voltage of the TDA1543 will cause offset and the voltage compliance of the OPA660 ios too limited. It would require an unusual arrangement of Powersupplies to start with, namely +8.3V/-1.7V, then the base (pin 3) needs to be connected to Vref. This will ten give 3.3V DC offset on the output, requiring a coupling capacitor or some other form of DC nulling. Sounds like a lot of hassle..
Oops, that's a shame - I was looking forward to trying it out - maybe I can use LM431's to set power supply voltages to 8.3/-17V and use back to back elctros on output (or would film caps do the job?)

Thanks for the help

John
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Old 10th January 2003, 02:07 AM   #35
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I don't know how Jocko's circuit works. I just know that I have one in my CD player. I have never heard any CD player sound better.

Jocko sez it does not use feedback, cuz feedback is not needed.

Did anyone think of asking him about it?

/rg
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Old 10th January 2003, 07:51 PM   #36
Nicke is offline Nicke  Sweden
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Quote:
Originally posted by ronjg
I don't know how Jocko's circuit works. I just know that I have one in my CD player. I have never heard any CD player sound better.

Jocko sez it does not use feedback, cuz feedback is not needed.

Did anyone think of asking him about it?

/rg
You can look for a more simple version here:
Jocko´s I-V stage

It sounds great...

Nicke
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Old 12th January 2003, 12:20 PM   #37
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Default OPA660 in the I/V conversion

Hi Kuei Yang Wang,



Quote:
With -4mA Peak current from a TDA1541 the I/V conversion resistor should be sized so that the typhical output Voltage compliance is not exceeded or a +2mA compensating current should be injected into the TDA1541 Output. This is done easiest by using a 2k4 Resistor from a Well filtered +5V supply via a further 100ohm/1,000uF Filter section.
Can you give details for a newby as I am?
Using the OPA660, is it necessary to compensate the 2mA current?
What about using an LM234 as a current source?

Ciao.
Marco
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Old 12th January 2003, 12:27 PM   #38
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Default Re: OPA660 in the I/V conversion

Hi,

Quote:


Can you give details for a newby as I am?

What do you mean, DETAILS? You have in essence the whole circuit in description, only need to draw it out. What more DETAILS?

Sayonara

PS:

1) Yes
2) No
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Old 12th January 2003, 12:58 PM   #39
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Quote:
Yet I too have not much against feedback,if applied apropriatly and in apropriate circuits, again, it is not WHAT you do that matters, it is HOW you do that matters.
Fully agree. In fact there is no life without feedback. This holds for electronics as well. The debate about feedback in electronics is as old as there are electronic amplifying devices around. The large internal feedback of a triode was the reason for developing tetrodes and later on penthodes.

Concerning the IV stage with an op-amp: What counts is the slewing capability of the input stage without going into saturation and the open-loop corner frequency to handle the fast transients coming out of the DAC. Some BB app notes put a large cap directly at the output of the DAC to tame this. Unfortunately this impairs the noise gain of the amplifier.

Maybe a pair of J-Fets or even an ECC88 as the input stage of a discrete op-amp is better option for the input stage in an IV converter with “feedback”


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Old 12th January 2003, 01:29 PM   #40
mlloyd1 is offline mlloyd1  United States
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Hmmmm... Check out the Borbely Audio site's All FET DAC

mlloyd1

Quote:
Originally posted by Pjotr
.....Maybe a pair of J-Fets ... is better option for the input stage in an IV converter with “feedback”
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