High-end preamp for my GC

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#403
Well, been running the THS4061 op-amp for sometime in my "pavel macura/carlos fm" style pre-amp with a NIGC based on LM3875.

The short conclusion is that this op-amp is better in this application (i.e coupled with BUF634) than the OPA627.

What does the THS4061 do well?
First there is an open window onto music, much more so, believe it or not, than with the OPA627. The OPA627 is very precise, but it is almost shut-in compared with the THS. The THS has more "air" for wnat of a better description.


Second, highs are so much better resolved with the THS. I have a recording where the sound engineers have done their best to make the highs sound splashy. The 627 seems to help the splashiness, the highs being white, unresolved, unpleasant to listen to. Against expectations, the THS4061 actually gave some detail and structure to these same highs and made them more listenable.

Mids seem on par with the excellent presence provided by the 627, while bass is at least as deep and powerful. One area of uncertainty relates to soundstage depth, only because I have been running one channel vs another, but I'll report on this in due course.

I have not tried class A bias yet (with JFETS) and of course the THS is only available in SMT, but I have found, assuming you have the right adaptor, (which is very easy to DIY as a PCB) that working with these SMD's using a thin tip for the soldering iron is no problem at all.
 
#407
Dr.H said:
The short conclusion is that this op-amp is better in this application (i.e coupled with BUF634) than the OPA627.
Click to expand...

I have some THS4081 op-amps here for some time and plan to test them, when I finish other things...
Anyway Ryan, do you use the 200pf cap?
The OPA627 is very picky about PSU bypassing and layout, and with the buffer, even more so.
Every chip must have it's bypassing caps, and on the right place.
Share the electrolythics with the OPA627 and other chips (like the BUF634) and you thow it all away.
Other op-amps may give better results on one circuit and not on another one.
I'm curious to test the THS4081 on my pre, but for now I'm finishing a "bi-amping chip-amp" (not GC😀 ) with a different approach from the norm.😀

PMA said:
Ryan,
we have had excellent sonic results with OPA134PA, you might like to try it instead of the OPA627AP. BUF634T must remain installed in the circuit.
Pavel
Click to expand...

Yes, I like the OPA132 (similar, if not equal) very much.
For me, it's much better than the OPA604.
 
#408
Deadline opamp ?

Texas Instruments have from april in program headphone amp TPA 6120A2, which have probably the best parametres, which I have seen in integrated opamp. I mean, that in next year this circuit will be in all new developed machines of top class. I am asking, if somebody try it now - I have samples still on the way 🙁 .
 
#410
Carlos, inside is probably large chip ( look at output current - 750 mA ), which give output power 2 W ( ! ) - these unconnected pins help to dissipate heat from chip. Noise is by gain two ( ref. to 1 V ) 125 dB, so by unity gain 131 dB ( ! ) - it is not enough for you ? And distortion, SR and BW ? I say again, in the next year will be it everywhere.
 
#411
Yes Upupa, I checked the datasheet and the numbers impressed me.
What confused me is that 5 uVrms output noise (Vn parameter on the table at page 4)...

Anyway, what about the AD815?😉
Not made for audio, is it?😀
But it's inside the best pre I've heard in my life: the Jeff Rowland Coherence.😎
Maby one of these days I'll give it a try...🙂
 
#415
I've seen an Analog Devices app note (some years ago) that had a line stage design featuring the the AD823 (or was it AD820) driving an AD815.

Upupa Epops said:
AD 815 is also excellent ( one my friend had try it ), but TI is better - have much lower distortion and more symetrical SR and mainly more symetrical settling time - look at step response.
Click to expand...
 
#416
jonclancy said:
There are some very interesting threads over on headfi.org with guys implementing this chip in both portable and home applications.
Jon
Click to expand...

Yes, I've seen a thread there, started by a member, asking what people think about this chip, and people started building headamps with this.
Who is that member?
Mr. Per-Anders.😀
 
#417
Best chips

From the measurement, the THS 4061 is the best JFET-input opamp ever, unfortunately it is quite expensive.

The OPA 134 (and similar ones) is outstanding one, if it is not excessively loaded at the output (RL > 8 kohms), so it needs to be buffered. Followed by the BUF 634 it performs very well, if the BUF is set to "extended bandwidth" by programming resistor about 500 ohms between pins 1 and 4.

The TPA 6120 is a CFB amp, so it behaves quite differently comparing the conventional opamps. The datasheet values are given mostly for G=2. In fact, it should be usable for greater gains, too, but it need some experimenting, particularly concerning the resistances at the inverting input. I believe the input-referred noise can be lowered this way.
 
#419
The AD 797 is the one of best choices for the low voltage/low impedance amps, e.g. mike preamps, MC phono input stages. It performs well in the DACs, too. It has very low distortion, although not the best known. The only significant drawback is quite high input bias current and, maybe, quite big input capacitance.
 
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