OPA-627 or AD-843,845,825 for bass
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Kevin McCready

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I have narrowed my search for the ultimate OpAmp for bass reproduction to: OPA-627,AD-843,AD-845,AD-825.I will be using a Jung/Galo regulated power supply for the preamp of a bass guitar amplifier I am modifying. The three stage OpAmp preamp(input non-inverting, tone control , output inverting, will feed a tube 12AX7 driver/phase splitter for the tube output section. I am really only conserned with the quality of the OpAmps bass as the bass speaker used (15") has a frequency response up to 2500hz, if that. Anyone who has been comparing these OpAmps in their headphone amps I would realy appreaciate your subjective opinions as to which one is the bass king .
Kevin McCready
 
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andrzejpw

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Hi Kevin, and welcome to head-fi:

If someone would correct me if I'm wrong, but I believe that headroom uses the 627/637 in their amps, specifically the cosmic. From what I remember, the cosmic had detailed and deep bass. Anyone want to jump in?
 
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Dev

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AD845 have lower slew rate then another. Maybe it must being offcasted?


And AD811/2 exist also (slew rate is 1600!) . Do you want to examine it closely as well?
 
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ppl

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IMHO the AD_843 has all the other's by quite alarge amount, with the AD-845 being next as well as smooth But the AD-843 is alot better For AC powered Applications and also sounds alot better.
 
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gavinbirss

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Hello,

I would say it depends on your sub consious or consious ability to listen and appreciate even order or odd order harmonic distortion.

The BB opamps are FET or DIFET input where the AD844 to my knowledge uses bi-polar transistors.

Because of the I-V nature of FET compared to Vavles the OPA627 is said to have valve like sound. (produces they same nature of harmonic distortion that a vavle).

I would say that I like the OPA627 but have not as yet heard the AD844. Spec wise the AD844 looks good. (Slev rate and so on).

Gavin
 
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ppl

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The 843 is a FET input Opamp as is the OPA-627. The 843 has greator bandwidth twice the 627's 16 MHz. over 250 V/uSec Slew Rate vs the 50 of the 627. The Specs on the627 are however more than good enought for High Performance Audio but don't think anyone that has Compaired thes two side by side will say the Bass on the 627 is Better than the 843. BTW tangent has a review on these two devices on his site
 
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gavinbirss

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Hello, me again.

It will help if I read correctly.


The AD844 was not in your list.


Well I suppose then the AC coupling (cap) or any other components that will create a low pass filter will, regardless of your choice of opamp influence your bass response.

I have not heard the AD843 but am very happy with the OPA627.
I tried a OPA134 in a circuit with the BUF634T and I think that I was convinced that the OPA627 sounded more true in the BASS end.

Gavin
 
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The AD-844 is a CFB opamp and will require AC Coupling somthing I am not a Fan of. Again the Bass on the AD-843 is alot Better than the OPA-627, Now it is true the OPA-627 sounds alot better than the OPA-132, As it should considering the Price difference so if the Bass on these BB chips sound good to you you will be in for a treat with the AD-843.
 
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