opa549 as unity gain

[odysseybmx414]

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

 

[odysseybmx414]

hey how are you supposed to post an image?

 

[odysseybmx414]

figured it out

 

[analog_sa]

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.

 

[jaudio]

Why the two buffers?

 

[odysseybmx414]

what do you mean by biasing of the positive input? sry if this is a stupid question

 

[odysseybmx414]

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

 

[carlosfm]

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.

 

[odysseybmx414]

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?

 

[odysseybmx414]

correction: that is not a opa627 its a opa27

 

[carlosfm]

correction: that is not a opa627 its a opa27

Ahh...
OPA134, then. And forget the biasing.

BTW I've just figured out that nasty 200k pot.
Use a much lower value, 10 or 20K.

Also, you better use a resistor after C1 and C3 to ground.
47K is fine.

 

[odysseybmx414]

thank you