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4558 and TL072 question
4558 and TL072 question
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Old 3rd April 2006, 01:32 PM   #21
anatech is offline anatech  Canada
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4558 and TL072 question
Hi lndm,
You might be further ahead to replace them with a buffer. They serve two purposes. One is to isolate the previous circuits from loading due to capacitance or just plain resistance. The second is to provide a low impedance output to better drive the previously mentioned loads. S/N may be improved with a low impedance output as well by shunting picked up noise.

-Chris
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Old 3rd April 2006, 10:12 PM   #22
lndm is offline lndm  Australia
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Just a single example, I cut back through three buffer stages on a mid priced CD player to find the stage before loaded with 3k. My pre Zin is 100k, marvellous. I would expect others to check before doing.
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Old 4th April 2006, 12:49 AM   #23
anatech is offline anatech  Canada
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4558 and TL072 question
True Hi lndm,
But under certain circumstances your output impedance just went from a couple hundred ohms to 3K. If you pick up some noise the couple hundred ohm shunt is gone.

I don't understand three buffers unless they were part of a filter stage, that is very common.

-Chris
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Old 4th April 2006, 01:31 AM   #24
Eva is offline Eva  Spain
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It's normal to see people swapping op-amps when they don't have the mileage and the knowledge to see further in the audio chain. Obviously they can't tweak things of whose existence they don't know.
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Old 4th April 2006, 01:34 AM   #25
lndm is offline lndm  Australia
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Well anatech, there was a chip I didn't identify that had audio. It fed into a 3k resistor to ground and into an op amp connected as a unity gain buffer. This fed both a headphone stage and another unity gain buffer. This then fed a discrete transistor stage -> RCA's.

I think at the time, perplexed, I thought it was a little ridiculous. Then I decided I would just assume these stages were there to mask some grain or something.

Anyhow, I much preferred the after result.
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Old 4th April 2006, 01:40 AM   #26
anatech is offline anatech  Canada
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4558 and TL072 question
Hi lndm,
That's what I figured (you were happier with the sound) and that's fine. The transistor stage was probably for muting the signal. Relays work better. Most of your improvement likely came from excluding these from the signal path. I'd still want something in there for muting.

-Chris
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Old 4th April 2006, 01:46 AM   #27
lndm is offline lndm  Australia
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Yes. If I remember (don't have it now), it did become a little clicky between tracks or something. This is something I consider less important than the sound quality. And yes, I do play it by ear sometimes. It doesn't always make the most sense, but I understand there are always going to be obscured factors that I may or may not see.

Usually (not always) I find simplicity works. It often gives me a clue when I can't think of anything better, and it often works for me.
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Old 13th April 2006, 02:55 AM   #28
Hector Ruiz is offline Hector Ruiz  United States
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I agree with anatech. I have also serviced SSL 9000 series consoles here in the metro New Orleans area (Balance Recording Studio and Trent Reznor's NIN Nothing Studio). SSL used many single opamp NE5534s in the signal chain. One 'trick' that they incorporate is placing a 10k resistor between the -15 volt supply and the 5534's output terminal. I believe this forces the opamp's output stage into Class A operation. I wouldn't try this with a dual opamp due to the heat dissipation native to Class A operation. Another interesting 'trick' is that the inerstage coupling method was two back-to-back polarized electrolytics, with their (+) leads joined together. At this common anode junction, a DC biasing scheme formed by a two resistor voltage divider developed about +2 volts on anode of the electrolytic caps. This helped to keep the electrolyte chemically "alive" (thereby lasting longer) and helped minimize distortion associated with large-value electrolytic coupling capacitors.
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Old 13th April 2006, 09:35 AM   #29
djk is offline djk
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Running two 10K pull-down resistors will only add 0.045W of dissipation to a dual opamp.
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Old 13th April 2006, 01:11 PM   #30
anatech is offline anatech  Canada
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4558 and TL072 question
Pulling down the output of some op amps may improve them, but don't mess with good ones that way.

Besides, there are a ton of op amps in a console. It would take a long time to do all of them. There was an article on this but I can't remember who the author was. Take it with a grain of salt.

Pro audio easily succumbs to it's own fads.

-Chris
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