Need advice from all I/V Aficionados using the THS4031's

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Bernhard

Bernhard

Member
Joined 2002
arupg said:



So, in reality, I'm back to square-one; the OpAmp. Kindly explain how do I benefit by doing a passive I/V and then OpA buffer since I require a healthy 2.5V output or more to drive thro' a passive pre and the pwr amp.
Click to expand...

The opamp buffer is much less critical as it carries the bandwith limited music waveforms.
By comparison, the I/V opamp has to deal with high slew rates of unfiltered 352,8 kHz staircase signals: 12 V/µs.
Settling time: 250 ns.
 
T

ttan98

Member
Joined 2006
arupg said:
Thank U for the confirmation.

Just another thought - what is the harm in me trying the THS4032 in the present OpA slot that is a buffer in the AA DITB circuit?
The AD1860 will do the I/V internally in this case.

Please take a look at the link:

http://img61.imageshack.us/my.php?image=aaditbcircuitlo0.jpg
Click to expand...


you use high quality resistors throughout, what about the coupling cap. at the output of the AD1860?
 
Bernhard

Bernhard

Member
Joined 2002
arupg said:


Just another thought - what is the harm in me trying the THS4032 in the present OpA slot that is a buffer in the AA DITB circuit?
The AD1860 will do the I/V internally in this case.

Click to expand...



In that case you use a super opamp for the buffer but a "who-knows-what-is-inside-that-DAC-chip" opamp for I/V conversion.
Any more questions ?
 
A

arupg

Member
Joined 2005
Let me once clarify the ext I/V route as per your suggestion.

You said : Cut traces for Pins 9, 10 & 11 and take Pin 9 trace & route to Pin 13. Take a 500 ohm resistor & terminate from Pin 13 to Gnd.

Now, how do I use a buffer to get a good Gain (the higher the better) to drive my passive pre, in turn the power amp? From which Pin do I take this?

And would you recommend something like OPA637 here??


Sorry about bothering with too many ques. (newbie!! in this so pls excuse)
 
Bernhard

Bernhard

Member
Joined 2002
arupg said:


You said : Cut traces for Pins 9, 10 & 11 and take Pin 9 trace & route to Pin 13. Take a 500 ohm resistor & terminate from Pin 13 to Gnd.
Click to expand...

You cut those three traces and the trace that was connected to pin 9 must now be connected to pin 13 plus the resistor from pin 13 to ground.

arupg said:

Now, how do I use a buffer to get a good Gain (the higher the better) to drive my passive pre, in turn the power amp? From which Pin do I take this?

And would you recommend something like OPA637 here??
Click to expand...

Before you start thinking about a buffer with gain, maybe try the tracecutting first and see if you like the sound.
I think that will not take more than 10 minutes.
And give us some feedback here.
You will have less output voltage but the exixting buffer will still drive your passive preamp.
You can also use 1000 ohm, that is still acceptable.
 
C

ClausMan

Member
Joined 2004
Hi,
never posted before, but I think I should share some testresults regarding I/V conversion opamps, my advice is this: go for lowest distortion and high slewrate, try opa842, ad8045 or ad9631...

Wadia 27ix use opa642 (=opa842) as iv for pcm1702 and everbody who have heard it recognise it as one of the best sounding dac´s.

In my own krell kps30i and a friends kps20i we have tested opa842 up agains opa627, ad8610 and opa134. It was clearly superior with a much better definition mid and high and very analog in sound...

Only drawback is they need +-5V.

Attached is a picture of one of the two dacboards from a Wadia 27ix I had in for repair (most serious piece of epuipment i have ever seen, with a large margin...), hires is available on request:bigeyes:

Regards to all
 

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C

ClausMan

Member
Joined 2004
Hi,
anyone interested in high res images for download from here:

http://www.ezyphotoshare.com/view/4699
http://www.ezyphotoshare.com/view/4700
http://www.ezyphotoshare.com/view/4701
http://www.ezyphotoshare.com/view/4702
http://www.ezyphotoshare.com/view/4703
http://www.ezyphotoshare.com/view/4704
http://www.ezyphotoshare.com/view/4706

psu is current source and allmost everything is locally regulated and carefully bypassed. Notice the filtering for the shuntregulated dacs...

sorry about the dust...:rolleyes:

regards
 
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