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

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tubee

tubee

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Joined 2004
Hartono said:
Hi Tubee,
regarding using AD844 , and sounding worse over time, is it possible that oscillation might happen ? you mentioned that it sound ok when the circuit first started.
Hartono
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Yes that's an possibility. If i have time will hang my scope on it and see if i can find something. The AD is not getting very warm btw.

Originally posted by ctong
I was also wondering what is the setup in which you made the comparison (sources, preamp, amp, and speakers)?
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Source: CD304MK2 modded, has standard I/V configuration/kwak7 to 7210,7220 and divided reclock to 1541. (also a kenwood tuner and busy with diy TT)
Tubed srpp pre, hybrid poweramp (tube/fet, pio-C coupled) 2 way series filtered ML-TQWT with very old units. Cables: diy with RG58U, speakercable diy braided with different 230V wires.
 
C

ctong

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Joined 2005
tubee,

Thanks for the list. So far I have made the comparisons mostly using SACDs with a modified Sony SCD-C555ES and a modified Denon 2900 (and DIY pass aleph pre, adcom 5400 amp, b&w N803 speakers). I can also hear a difference with CDs but to a much lesser extent. To me SACDs sound much better with 2132 than with 2134. CDs merely sound less offensive with 2132 but not even close to SACDs. Therefore, they might not fully reveal the strength and weakness of an opamp. I am interested in a comparison between THS4312 and opa2132 with a source other than CD (SACD, DVD audio, or vinyl).
 
tubee

tubee

Member
Joined 2004
ctong said:
tubee,

Thanks for the list. So far I have made the comparisons mostly using SACDs with a modified Sony SCD-C555ES and a modified Denon 2900 (and DIY pass aleph pre, adcom 5400 amp, b&w N803 speakers). I can also hear a difference with CDs but to a much lesser extent. To me SACDs sound much better with 2132 than with 2134. CDs merely sound less offensive with 2132 but not even close to SACDs. Therefore, they might not fully reveal the strength and weakness of an opamp. I am interested in a comparison between THS4312 and opa2132 with a source other than CD (SACD, DVD audio, or vinyl).
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Nice gear you have CT!

The THS is not the best choice solely as opamp, for I/V very good in a cdp or on current output of dac from sacd (AD1955?) If you want a good opamp in a Phono, pre or SACD/DVD try the LM4562. I still want some to try too.

Btw forgot what i have on the other side of the room: Marantz SR4300 surround amp, use R-L out as pre to hybrid with main speakers. The diy surround and centerspeakers are hooked on the Marantz. And as source for DVD/SACD a Yamaha multi player. The surroundspeakers looks a little like your 803's(with cherry veneer), but the tweeters radiate 360 degrees through room)

Btw yesterday i discovered the spdif is not the best, dolby prologic (of Marantz) sounds more airy then dolby 5.1 through spdif. Discovered it because a DVD had no 5.1 signal on it, had to create 5.1 from 2.0!
 
tubee

tubee

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Joined 2004
ctong said:



Where do you connect the cap to? There is no ground pin. Do you connect to the in+ pin, which is connected to the signal ground in an IV stage?
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In my cdp one pin is connected to Gnd indeed, so the "tailor made" adapter with chip is only usable in that CDP. The THS is a fast chip with chance of oscillations, best is to decouple as close to chip as possible.
 
C

ctong

Member
Joined 2005
tubee said:


Yes, others say that's because the distorsion is lower. I like bass btw, but in good proportion to the rest. It is also a matter of the right combination of different gear, speaker towards amp, source.
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In my experience lean bass is because of some sort of distortion that makes the midrange and treble seemingly louder (but the measured frequency response is flat). Such opamps usually give you listening fatigue.
 
A

arupg

Member
Joined 2005
Hello All:

I am keen on some circuit ideas for my AUdio Alchemy DITB dac where the dac chip are AD1860 (1 per channel) and the resultant output is simply buffered out to the RCAs using 1 dual OpAmp.

The stock AA DITB came with a OP275 that I swapped for a OPA2134 and now an OPA2107.

I'm told I may get spectacular results if I use the THS4031/2 on a small separate PCB where I do the external I/V conversion and directly take it to the RCA outputs - scrapping the AA DITB's buffer stage altogether.

Can anyone give me some circuit ideas as to how to go about it? Again I'm told to bypass the internal opamp and feedback resistor in the AD1860 dac chips. It would be most welcomed.

Schematics:

1. AD1860 Chip
http://img211.imageshack.us/my.php?image=ad1860vv3.jpg


2. DITB Schematic
http://img61.imageshack.us/my.php?image=aaditbcircuitlo0.jpg



Thanks in advance!!!!!
 
A

arupg

Member
Joined 2005
Thank you Bernhard for the suggestions. Much appreciated!!

Disconnecting Pins 9, 10 & 11 means on the PCB, cut the track.

Terminating Pin 13 to Gnd with a 500 ohms resistor - ok, then how does one hook up the THS4031/2 OpAmp for the ext. I/V. Any circuit ideas? And where (which Pin on the dac chip) does the THS OpAmp gets its feed from?

Sorry to be a bother but must confess am a newbie on this.....
 
Bernhard

Bernhard

Member
Joined 2002
arupg said:


Disconnecting Pins 9, 10 & 11 means on the PCB, cut the track.

Terminating Pin 13 to Gnd with a 500 ohms resistor - ok, then how does one hook up the THS4031/2 OpAmp for the ext. I/V. Any circuit ideas? And where (which Pin on the dac chip) does the THS OpAmp gets its feed from?

Sorry to be a bother but must confess am a newbie on this.....
Click to expand...


Cut the traces and route the trace that was connected to pin 9
now to pin 13 instead ( Pin 13 goes to the output filter/buffer)

No more THS4031/2 OpAmp because the 500 ohm do the conversion.

1mA / 500 ohm gives you 500mV output that is usually ok as most amps are much to sensitive.

If not, you can use a buffer with gain of 4 on the output.
Another chance to play with opamps :rolleyes:
 
A

arupg

Member
Joined 2005
No more THS4031/2 OpAmp because the 500 ohm do the conversion. 1mA / 500 ohm gives you 500mV output that is usually ok as most amps are much to sensitive. If not, you can use a buffer with gain of 4 on the output.
Another chance to play with opamps
Click to expand...


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.
 
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