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  #16  
Old 24-05-17, 05:54 AM
davidsrsb davidsrsb is offline
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The human eye is very poor at seeing picture distortions. The specs are set at a level that allowed the BBC to cascade many amplifiers without causing problems.
Supply decoupling is more likely to affect the regulators than the opamps and the regulators are dealing with wideband rectifier noise
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  #17  
Old 24-05-17, 01:34 PM
Bigman80 Bigman80 is offline
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Originally Posted by S-Man View Post
And could you correlate the measurements with picture quality?

I suspect it will be quite hard to meaure any differences with typical DIY test gear and in a phono stage (which is the op's application).

BTW Bigman - you should be very careful indeed if you are thinking of using the Sparko with dc coupling as the 1st stage of an MC amp!
It's going into the second stage. I am looking for a super quiet Opamp to create the gain in the first stage.
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  #18  
Old 24-05-17, 01:36 PM
Bigman80 Bigman80 is offline
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Originally Posted by davidsrsb View Post
Analog Devices are making fairly cheap parts like the ADA4897-2, with remarkable specs. 1nV/rtHz and 230MHz GBw and only 2.4nV/rtHz at 10Hz. This is enough to compete with unobtanium 2SK170 designs in MC preamplifiers. These make the discrete opamps look a bit limited
I'll look into these. Thank you David
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  #19  
Old 25-05-17, 12:01 AM
Julf Julf is offline
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Originally Posted by Bigman80 View Post
It's going into the second stage. I am looking for a super quiet Opamp to create the gain in the first stage.
A discrete one is probably not the best choice for super quiet.
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  #20  
Old 25-05-17, 03:21 AM
Yomanze Yomanze is offline
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Originally Posted by Julf View Post
A discrete one is probably not the best choice for super quiet.
I do find it an interesting phenomenon that there is this assumption that 'discrete is best', but there are some distinct advantages to opamps such as shorter signal paths, better thermal tracking etc. It's sobering indeed to open up some LFD gear & see some of it built around a pair of opamps with a gigantic power supply, not much else, but it's the circuit tuning that makes the difference here.

Pedja Rogic put it well when designing his chip amp: "It takes some time to understand this simple fact about modern linear power amp chips design: the chip is not the limiting factor. It can be anything. The limit is design around it."
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  #21  
Old 25-05-17, 05:43 AM
davidsrsb davidsrsb is offline
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The premium opamp makers are using much better semiconductor processes than the discrete part brands use. The last companies to make high grade audio discretes were Zetex, Rohm and Toshiba. The Japanese makes are all gone and Diodes Inc doesn't do much now.

The opamp makers are not developing these parts for the HiFi indstry but for VDSL and video. They just happen to be useful.
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  #22  
Old 25-05-17, 08:40 AM
audiopile audiopile is offline
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we take leftovers

That is a real issue for the audio industry - we are such a small pond that the device industry very rarely has developed anything specifically for audio use. This has also meant that the change in applied tech/production in some industry we aren't aware we are siphoning parts from - can cause a Toishiba or Motorola to drop a part for lack of demand.
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