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

[Bernhard]

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.

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.

 

[tubee]

If you have good results with it arupg post a sound-report please then i can try that too. I like the THS, even as regular opamp I/V.

 

[arupg]

I am hearing reports that the THS4031/2 isn't a stellar performer in the bass/deep bass dept. This is a bother to me.

Any motivators??

 

[Bernhard]

I am hearing reports that the THS4031/2 isn't a stellar performer in the bass/deep bass dept. This is a bother to me.

a 500 ohm Vishay will be

 

[arupg]

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

 

[ttan98]

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

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

 

[arupg]

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

The Stock AA cap has been replaced for a Vishay 1837 MKP.

 

[Bernhard]

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.

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 ?

 

[banana]

I have bad experience using THS4031 in MFB filter circuit, it oscillates slightly 🙁

Some opamp is not stable when output pin is shorted to its inverting input, even shorted with a cap. The same case for AD797.

 

[arupg]

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)

 

[martin clark]

If you read the AD797 datasheet, it tells you exactly why this is the case, and what to do about it.

Sorry - not jumping all over you personally, just a gentle reminder to people generally to 'RTFM' 🙂

 

[Bernhard]

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.

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.

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??

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.

 

[martin clark]

[Sorry I didnt expect to trip the swearfilter - for '****' please substitute: 'Read the wretched manual' 😉 ]

 

[arupg]

Thanks Bernhard. Will come back with the feedback.

 

[ClausMan]

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

Regards to all

 

[arupg]

Clausman

Thanks for the thoughts and you sharing but the circuit is optimized for +/- 12V DC operation.

Best regards

 

[abzug]

Hello ClausMan, I would like to see close up please, and exact type of OS filter / processor / any odds. Thank you

 

[ClausMan]

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...🙄

regards

 

[Bernhard]

Interesting: INA103 for conversion to single ended.

I have a bunch of INA110 ceramic/gold as alternative for transformer.
Also AD522 but those are

 

[arupg]

ClausMan

Splendid job with the Wadia 27ix pics.....