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Old 9th June 2010, 11:31 AM   #11
Galgo is offline Galgo  Israel
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Quote:
Originally Posted by gk7 View Post
Attached are spectra from an OPA2604 and a LM4562 I have tested in my DAT recorder (gain of 10 or so I believe). The LM4562 has higher 2nd harmonic (if that is what you wan´t) but higher 5th too. At least it lacks the
unfavorable 7th which the OPA2604 has. No integrated opamp will give you
"tube sound". I cannot confirm that the OPA2604 has predominantly even harmonics (at least not in the sense as a single ended class a circuit would have).
OK (I'll pretend I understood this completely...),

Assuming that I'd prefer to reduce distortions as much as possible from the power amp - and perhaps use an optional TUBE stage which I'd power On/Off depend on the music - could I just bypass the integrated opamp's?
And taking the risk of asking a complete silly Q - what role do they actually have?
If I'll use a decent DAC and good quality Preamp - is there any need at all for these integrated opamps?

Thank you again guys for the information and extreme patience
Gal
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Old 9th June 2010, 11:41 AM   #12
Mooly is online now Mooly  United Kingdom
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Whether you can "bypass" the opamps or not depends on how they are used and configured, and that can only be determined by looking at the circuit. You can't guess on that.

The distortion spectrum produced by circuits is a really interesting subject, and this seems to be one of the reasons why certain designs have that real "musical ability" factor.
Generally "even" harmonic distortion is actually pleasing to the ear, while odd harmonic isn't.
What it means is that if a 1khz signal is fed to the amp, the residual distortion products produced are for example 2khz, 4khz and so on for even harmonic distortion and 3khz and 5khz etc for odd.
That we seem able to "sense" this is remarkable given that the figures are so small anyway, but it does seem so in practice.

I haven't tried the LM4562 in anything yet, as up to now the OPA2604 has performed admirably for me.
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Old 9th June 2010, 12:02 PM   #13
gk7 is offline gk7
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Yes Mooly is right, we would need to know what the opamps are used for. Do you have a schematic of the board you ordered ? I have looked at the datasheet for the TAS5613
and it has symmetric inputs. Probably the opamps are used to convert a usual single ended signal output from a preamp to symmytrical.
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Old 9th June 2010, 12:10 PM   #14
Galgo is offline Galgo  Israel
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I don't have schematics (and probably won't have them soon).
I'll try to get the info from the maker or at least an image of the PCB section.

Thank you for now,
Gal
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Old 10th June 2010, 10:53 AM   #15
apolo is offline apolo  Serbia
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Quote:
Originally Posted by Mooly View Post
Whether you can "bypass" the opamps or not depends on how they are used and configured, and that can only be determined by looking at the circuit. You can't guess on that.

The distortion spectrum produced by circuits is a really interesting subject, and this seems to be one of the reasons why certain designs have that real "musical ability" factor.
Generally "even" harmonic distortion is actually pleasing to the ear, while odd harmonic isn't.
What it means is that if a 1khz signal is fed to the amp, the residual distortion products produced are for example 2khz, 4khz and so on for even harmonic distortion and 3khz and 5khz etc for odd.
That we seem able to "sense" this is remarkable given that the figures are so small anyway, but it does seem so in practice.

I haven't tried the LM4562 in anything yet, as up to now the OPA2604 has performed admirably for me.
Mooly, did you try OPA2134?
Is there any diference between OPA2604 and OPA2134 and how would you describe it? They are both FET input devices. Which one do you prefer?
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Old 12th June 2010, 12:47 AM   #16
Matt BH is offline Matt BH  United Kingdom
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Sorry to hijack,
I use two NE5532s in my low distortion test oscilator. It is way below the floor of my HP334. Not much to boast about, but still very reasonable. I dought if a soundcard job can beat it, unless its a crazy pro external job. Im using an LED and LDR in the feedback loop. Amplitude is a bit jumpy but nowhere near as bad a PTC thermister or lamp.
This thread has me very interested as I would never even considered using an op-amp for audio(valves me, I even removed the things from my CD player), although some of the best kit back in the day used the supposedly terrible 417 to great effect. Some of the best recordings we listen to are through these bad boys or even god forbid a 301.
What I am trying to say is its horses for courses. a bad circuit will be bad and a good un can only be improved (or ruined).

Cheers Matt.
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Old 12th June 2010, 06:14 AM   #17
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by apolo View Post
Mooly, did you try OPA2134?
Is there any diference between OPA2604 and OPA2134 and how would you describe it? They are both FET input devices. Which one do you prefer?
Sorry... you didn't trigger the thread notifier (still under moderation )

I haven't tried the OPA2134 at all.
The OPA2604 and single OPA604 I find really do have something special to offer sonically... they were particularly impressive replacing NE5534's in a DAC used as I/V convertors.
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Old 12th June 2010, 06:52 PM   #18
gk7 is offline gk7
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Just in case it is not known already, an excellent coparison of various opamps:
http://www.sg-acoustics.ch/analogue_...distortion.pdf
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