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Old 8th January 2009, 02:48 PM   #1
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Default Video Op Amps...?

Talking to my 'tech' friend about the benefits of upgrading op amps in the output stages of CD players (such as the LM833 to NE5532 change I made in my Philips CD620), he wondered if video op amps have ever been considered for upgrade use in audio applications?

After having a wee search through here I didn't come across any mentions of them and I'm just wondering why they have been ignored?

Excuse if there is a blatently obvious reason... they cost a fair bit more, so cost vs benefits perhaps? Or is there a more technical reason they're not considered?
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Old 8th January 2009, 03:38 PM   #2
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Default video versus audio op amps

Video chips are viable for audio. I like the AD811 for example.

It may not be suitable for upgrading an existing product since it is a high bandwidth current feedback amp. There are a number of possible problems that could lead to oscillation.

Internally, the LM7171 is current feedback amp with a buffer on the inverting input; so it is a voltage feedback amp with the speed of a CFB amp. (It can be a drop in replacement for VFB amps, if the circuit can handle the high bandwidth.)

I think there is a subjective preference. I "imprinted" on video amps and think they give a realistic sound. Others might say that they are harsh or noisy and that audio amps are more musical. It is really hard (or at least faulty) to make generalizations since the application of the amp can affect the sound quality so much.
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Old 8th January 2009, 04:58 PM   #3
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Default Re: Video Op Amps...?

Quote:
After having a wee search through here I didn't come across any mentions of them and I'm just wondering why they have been ignored?
They haven't. I have a Micromega DAC1 which uses the LT1227 for the unbalanced analogue outputs.

I think the circuit needs to be designed to take video opamps. I tried the pin-compatible OPA627 in place of the LT1227 but noticed they got very hot (they did work, though). I had adjusted the DC-offset to 0.0 mV with nothing connected to the outputs (outputs of the DAC1 have no DC-blocking caps). Once I connected my headphone amp the DC offset jumped to > 130 mV (despite the fact that the headphone amp does have DC-blocking caps at the input).
The offset-shift after connection was gone when I reinstalled the LT1227.

BTW, my headphone amp actually had some oscillation-issues with the DAC1 in combination with short interlinks that I fixed by adding some HF bypassing on the headphone amp (unhappy marriage (oscillations) ).
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Old 8th January 2009, 05:57 PM   #4
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I for one prefer using video opamps when using such devices for audio. I find them to sound more transparent than normal audio ones. Some measures have to be made if the video opamps are much faster and make sure they arent oscillating. While experimenting between various opamps I noticed that the ones I prefered all had faster settling times and this was always the case with the video opamps. Some of the commercial highend gear do go this route but mid Fi usually stick with the normal audio ones. Video opamps arent necessarily current feedback, look at ad826, ad827 and ad829.
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Old 8th January 2009, 09:12 PM   #5
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Default looking at the thread

felt like making a joke .....

imagine one amplifier that in the ltp stage uses a video IC as mentined above ..... then for drivers use a TDA8177 (clasic vertical television amplifier ) and then for outs something like BU508 ir even better S2055
(dumper diode included ) !!!!!

ha ha ha this will be called amplivision ha ha ha
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Old 8th January 2009, 10:01 PM   #6
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Default Re: Video Op Amps...?

Quote:
Originally posted by bleachershane
Talking to my 'tech' friend about the benefits of upgrading op amps in the output stages of CD players (such as the LM833 to NE5532 change I made in my Philips CD620), he wondered if video op amps have ever been considered for upgrade use in audio applications?

After having a wee search through here I didn't come across any mentions of them and I'm just wondering why they have been ignored?

Excuse if there is a blatently obvious reason... they cost a fair bit more, so cost vs benefits perhaps? Or is there a more technical reason they're not considered?

There seems to be an obsession with very high bandwidth audio amplifiers.
So long as the amp reproduces audio frequecies faithfully I cant see any point in having a wider bandwidth.
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Old 8th January 2009, 10:11 PM   #7
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Alot of the video opamps have very large gain specs and IMHO would best be reserved for phono stage applications. This is particularly true for moving coil inputs.
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Old 8th January 2009, 10:37 PM   #8
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Thanks for all the replies so far, has been very enlightening...!

In general, the only reason my electronic engineering mate brought up video op amps are for the faster settling times and better slew rates. Going with what homemodder said, to me I'd expect the better specs in those areas to translate to better transparency... but ones persons transparency and realism can always equate to someone elses trashy, harsh and noisy! ...And of course, what's on paper might not work out so well in different real life uses.

"More musical" to many people seems to mean what I class as warm, a very British thing apparently.
I have a Denon PMA-255UK integrated amp that was apparently tuned for that "warm British sound". I, on the other hand want to try and undo that (Elna Tonerex capacitors need to get ripped out lol!)

Of course, the extra bandwidth of a video op (up to what 50MHz?!) is hardly going to improve a CD recording that's freqeuncy response ends at 20KHz!

As I'm learning, in these fields everything is subjective and down to very personal taste in most cases...

There is of course all the problems of trying to place a video op amp into where an NE5332 once sat in a CD player even if on the surface it looks like a pin-for-pin replacement (have been reading a pdf about the differences in implementation between voltage feedback and current feedback op amps) but nevertheless, it's something else worth knowing about!

The AD826 looks interesting, has anyone had any experience dropping one of these into where something like an NE5532 was? There are also what gets called 'Precision' op amps that seem to offer better than audio grade op amps specs in settling and slew, but not as 'fast' as video op amps.
Most op amps are reasonably priced to buy and try... I think I really need to do that more to practically see what happens!
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Old 8th January 2009, 10:41 PM   #9
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Quote:
Originally posted by bleachershane
"More musical" to many people seems to mean what I class as warm, a very British thing apparently.

I use an ECC83 mixer for getting my warm sound.
Us guitarists love the valve sound.
But I also use the valve mixer on my disco and get good feedback from audiences about it.
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Old 8th January 2009, 10:48 PM   #10
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I too am a guitarist, and completely understand the love of the 'valve sound'.

I just find that I prefer having my music presented to me when I'm listening through my system with all the harshness warts and all that might be inherent in a recording, rather than trying to slightly gloss over what might be a trait of a recording with syrupy warmness...

At least, that's what I think I think LOL
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