Easy-to-build I/V stage

[Elso Kwak]

Re: Is discrete transistor I/V conversion an option at +/-5(five) Volts

Hi everyone!

(Hi Elso - This thread seemed more appropriate for a discussion of my I/V conversion)

I have been recently looking at op-amp I/V conversion for my single ended output AD1865N-K project. I am currently using the internal opamps and attempting to shunt HF to ground in the form of a first order filter (To cut a long story short.. I am loading the input of the opamp with capacitance- making it unstable!)

I am looking at my options... I only wish to use +/- 5 (five) Volt supplies.

Can Jocko's zero feeback discrete I/V converter be adapted - I would love to give it a try?

How can I first order filter with an opamp for my AD1865N-K.

Your thoughts please...

Hi Oli,
Just fill in the values for a first order filter in FilterPro.
Your choice: the crossoverfrequecy.
With a unity gain stable opamp it should work.
Just the first part of my scheme.
My best guess at Jocko's circuit you will find here:

http://www.diyaudio.com/forums/showthread.php?postid=201512#post201512

 

[tschrama]

Hi,


I think this could be a discrete easy-low-voltage IV-stage. The CFP does a great job lowering the input impedance and lowering the distortion. Needs to adjust the input Vdc .... it's just a circuit I had for a while now.... finaly a reason to post it..

What do you think Elso?

IS Jocko still around? It challences your circuit for low input R I think, but that might not be sooooo important........


Regards,
Thijs

 

[Oli]

Have you actually built that?

Have you actually built that?

 

[tschrama]

Have you read my earlier posts ...........




Offcourse I din't build it, nor tested it, nor listened to it... ... I put it in circuitmaker... for what it's worth: it simulated relative good, very good, compared to the other circuits..


Regards,
Thijs

 

[Oli]

Filter Pro does not allow it!

Elso,

Using filterpro I cannot build the first section in isolation

Have a go and you will find it will not work!

Is this simply a case of f=1/(2*pi*R*C)

 

[Oli]

Honesty is the best policy

Thanks for your honesty tschrama.

Amongst other options I might give it a try and let you know how it sounds.

A stupid question... Where do you connect to your circuit for a voltage output?

 

[tschrama]

Actually good questions... it's a little less straigth forward than the more simple single BJT version ... Voltage out is between R4 and R2 ..needs a output coupling cap too ....


Greetz,
Thijs

 

[Oli]

A final question- about filtering....

Thanks.. So if I just connect to the junction at R2-R4 and a.c. couple this with a suitable non polar capacitor I am in business?


A final question, then I must go...

I am using a non-oversampling setup and I wish to use a first order filter (at say 200kHz) to remove excess r.f. garbage from the signal chain and affecting my power amplifiers. Will your circuit accept a simple RC filter at the output or should it go elsewhere?

 

[x-pro]

May be this could be of some interest. I did design and build this circuit in 1994 and it worked very nicely. I suspect it could be easily adapted for more modern DAC's.

x-pro

 

[Oli]

Thanks!

Operating voltage is high for my requirements- but worthy of study.

 

[jean-paul]

X-pro, is that a MF schematic ?

 

[x-pro]

X-pro, is that a MF schematic ?

No. This circuit was never in production AFAIK. (And I would never publish somebody else's circuit anyway - this one is my own design from 1994).

x-pro

 

[Elso Kwak]

Re: Filter Pro does not allow it!

Elso,

Using filterpro I cannot build the first section in isolation

Have a go and you will find it will not work!

Is this simply a case of f=1/(2*pi*R*C)

Hi Oli,
I am sorry never tried a first order filter with FilterPro. I did not work indeed.
Yes I guess your formula is right. I calculated 270pF with a 3k feedback resistor.

 

[tschrama]

I've just posted a versions with output cap and HF roll-off cap. This would give you the disered -3dB at 200KHz (or about).

Do you really think your amplifier responds to 200KHz? If so, -9dB at 400KHz is not a large attenuation ... I think you could easely put a fc at 40KHz.

Regards,
Thijs

 

[rbroer]

X-PRO,

Is there a specific reason to connect R12 to the base of Q2 ?

Couldn't R12&R6 be just one resistor between the current source and sink ?

You seem to use a LED constant current source, as well as 2-transistor constant current sources. Any reason why you didn't use LED ccs throughout ?

 

[x-pro]

Now I don't quite remember why I did connect R12 there. Perhaps then it did make sense . However with LED current source there is some reason: in the output follower quality of the current source is not that important, and it saves 2 transistors... .

x-pro

 

[tbla]

is this the output stage from the exposure cdplayer...?

 

[x-pro]

is this the output stage from the exposure cdplayer...?

As I've posted earlier, this design never went into production. And I never worked for Exposure .

x-pro

 

[Oli]

Thanks Tschrama- perhaps 40kHz is better

Tschrama,

Thanks for the modified cicuit. Perhaps my 200kHz choice is a little inappropriate- How could I modify component values for a more sensible 40kHz cutoff?

I desire a suitable voltge output from this circuit (e.g. 3V peek to peek). Do I have to adjust any resistor values to get this from the current output of the AD1865?

 

[Oli]

Thanks Elso for trying!

Amongst other methods I'll give it a try!