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Old 15th October 2005, 07:58 PM   #1
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Default opa549 as unity gain

hey does this look good and should i make any changes to this schematic im planning on building this to see how good it works
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Old 15th October 2005, 08:02 PM   #2
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hey how are you supposed to post an image?
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Old 15th October 2005, 08:06 PM   #3
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figured it out
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Old 15th October 2005, 08:31 PM   #4
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I find it difficult to see the point of such a circuit but work it will. It might be a good idea to provide biasing to the positive input of the chip.
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Old 15th October 2005, 09:09 PM   #5
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Why the two buffers?
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Old 15th October 2005, 10:29 PM   #6
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what do you mean by biasing of the positive input? sry if this is a stupid question
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Old 15th October 2005, 10:31 PM   #7
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the two buffers is for extra current boost i have 10 of HA3-5002 and i have 5 opa27gp's ive tried the 27's in a preamp for my bridged opa549 and i like the sound it has more definitive bass and nice mids and also it makes the highs not harsh on the ear
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Old 16th October 2005, 01:47 AM   #8
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Quote:
Originally posted by odysseybmx414
figured it out
You are on the correct path for the OPAs, because they work (and sound) much better at low gains.
But I would not use unity gain, or you will be limited to the voltage rails of the gainstage. Is something around 10 Watts ok for your application?

Here's some suggestions, or the way I would do it:

- Remove C1, the buffers U2 and U3, C3, and C4.
- Bias the OPA627 to class-A at around 10ma.
- Reduce the gain of the OPA627 to 5 and use a gain of 4 on the OPA549.

You'll have a very transparent amp, but beware, do not try to smoothen things out by 'over-engineering' because the problem may come from the components before the amp: pre and/or source.

PS: a gain of 21 on the OPA627 is way too much, for use with line-level sources.
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Old 16th October 2005, 02:04 AM   #9
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would it be ok if i used something i already have such as: OPA602,opa27,opa134,opa177,op07,max437? if so which is the best choice?
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Old 16th October 2005, 02:05 AM   #10
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correction: that is not a opa627 its a opa27
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