Which dual opamps should I try for I/V conversion?

[carlmart]

I have played around with i/v opamps in my Adcom GDA-600 which uses PCM63 dac chips.
my favourites are
OPA1642 dual fet
LM6172 dual bipolar
LM6171 as I/V single bipolar followed by OPA1641 single fet for filter/buffer stage on a brown dog adaptor
They are relatively cheap and in this application stable.
Remember to check the new op amps to see if they are oscillating see Mooly's excellent thread
http://www.diyaudio.com/forums/anal...u-have-checked-see-its-stable-havent-you.html

The LM617X needs some additional parts, doesn't it?

 

[cdsgames]

I am not very familiar with opamps...and I have a question that might be silly.
We are trying to implement a summing circuit for DACs with 5.8Vpp output (2.0 Vrms)

However datasheet requires up to +-12V for the opamp. My question is whats the minimum +- that I can use..can I use 8V ?

 

[Calvin]

Hi,

Carlos @18:
The very fast THS403x and THS413x are certainly well suited for this application.
I liked their sound better than with slower more conventional OPAmps.
Still though the simple discrete feedback-free circuits sound more authentic to my ears.

jauu
Calvin

 

[carlmart]

You mean discrete opamps?

In any case, I think a dedicated supply just for the output amp, something like a Sulzer or Salas, might make a great difference.

 

[abraxalito]

We are trying to implement a summing circuit for DACs with 5.8Vpp output (2.0 Vrms)

However datasheet requires up to +-12V for the opamp. My question is whats the minimum +- that I can use..can I use 8V ?

Most opamps will swing closer to the rails than 3V so a 3V headroom from the rail is plenty (assuming no demanding loads are being driven). So you'll be fine with +/- 6V (12V total).

 

[Calvin]

Hi,

no, I´didn´t mean discrete OPAmps.
Wether discrete or integrated OPAmps they still suffer from global feedback - making them ´slower´ than required.
I meant EUVL´s Zen and Sen IV converters or grounded base (grounded Gate) circuits like the JockoHomo and alike.
The first are well suited to DACs without offset bias current (TDA1541, PCM170x), the latter are more elegant with DACs with offset bias current (TI´s PCM179x series, ADI´s AD1955)
In any case the transistors are only used as ´current buffering´ impedance-matchers under openloop conditions.
Thereby they work very linear (low THD with a nice spectrum) and very fast.

jauu
Calvin

 

[ekidnah09]

The LM617X needs some additional parts, doesn't it?

The datasheets give some information regarding feedback capacitance, power supply bypassing and driving capacitive loads.
In the Adcom the circuitry was suitable for direct drop in with some extra power supply bypassing and a change to the feedback capacitance.
But I did try it before making those changes and they worked fine so no added components needed.
The LM6172 and LM6171 are voltage feedback and the datasheet has specifications for +-5volt supply also.

 

[dazzz]

Somebody tried to use
LT1057 for I/V conversion

I'm currently using one of my projects the LM4562 in the i/v stage
I have a couple LT1057
I am considering replacing
So
lt1057 VS lm4562 in i/v stage

Try or not to try ?

( in the comparator / buffer stage i use the lt1364 And is amazing)

 

[chris719]

LT1057 looks pretty bad for I/V conversion. I don't see any reason to use it, ever, basically. It's a relatively slow, noisy JFET input op-amp that doesn't even have distortion specified in the datasheet. It's not even cheap.

LM4562 is good, but if you must tinker you could try ADA4898-2.

 

[dazzz]

LT1057 looks pretty bad for I/V conversion. I don't see any reason to use it, ever, basically. It's a relatively slow, noisy JFET input op-amp that doesn't even have distortion specified in the datasheet. It's not even cheap.

LM4562 is good, but if you must tinker you could try ADA4898-2.

thanks Chris
for the detailed answer

Best regards David Az