GC - gain of 3

miguel2 · 7th February 2005, 01:47 PM

Hi,

I'm running now a OPA549 based GC. It has a OPA627 based preamp with gain of 6.7. After it goes to a OPA549 inverted GC with gain of 3.2. Feedback resistor is 220k (SMD) and input is 68K. With this low gain I have a higher bandwith in the OPA549.
The psu is Pedja's discrete psu for GC, with +/- 22VDC rails. The preamp section also uses this psu, with regulators to get +/- 18VDC.
The sound of this thing is fast, crisp an articulate. For now I would say that it is a bit on the bright side, maybe after burning in it softens a bit. Bass is fast and punchy. I am quite happy with the result. Just need to get rid of the hum. Not much, but audible from the sitting position.

Miguel

demogorgon · 7th February 2005, 01:59 PM

miguel:
how is the opa627 reacting to a gain of 6.7?
are you using multiple opa's? the data cheet say a max of 5 when it comes to gain..

Alcaid · 7th February 2005, 02:17 PM

Quote:

Originally posted by demogorgon
miguel:
how is the opa627 reacting to a gain of 6.7?
are you using multiple opa's? the data cheet say a max of 5 when it comes to gain..

That's wrong. It can handle much higher gain than that. It's stable down to unity, while the opa637 needs a gain of 5 or higher. Maybe your mixing things together.

miguel2 · 7th February 2005, 02:23 PM

The datasheet only mentions the gain of 5 to the OPA637, because this one is not stable for lower gains. The OPA627 has the advantage of being stable for unity gain. This permits to use a cap to reduce high frquency noise to this gain of 1, while keeping audio frequencies at gain of 6.7. This helps to stabilize the power section.

Miguel

demogorgon · 7th February 2005, 02:41 PM

Quote:

Originally posted by Alcaid

That's wrong. It can handle much higher gain than that. It's stable down to unity, while the opa637 needs a gain of 5 or higher. Maybe your mixing things together.

I'v been known to do that from time to time, although thats what i'v read both in this forum and other places.

analog_sa · 7th February 2005, 03:11 PM

Quote:

although thats what i'v read both in this forum and other places.

I'll be curious to know just one single source of your information. Not that i doubt the existence of ignorance and stupidity.

demogorgon · 11th February 2005, 07:19 PM

Quote:

Originally posted by analog_sa

I'll be curious to know just one single source of your information. Not that i doubt the existence of ignorance and stupidity.

It's just one of those things one pick up from time to time, and not remembering where i read it.

I was uninformed. my apologies are yours.

7th February 2005, 01:47 PM	#1
miguel2 diyAudio Member Join Date: Jun 2002 Location: Portugal	GC - gain of 3 Hi, I'm running now a OPA549 based GC. It has a OPA627 based preamp with gain of 6.7. After it goes to a OPA549 inverted GC with gain of 3.2. Feedback resistor is 220k (SMD) and input is 68K. With this low gain I have a higher bandwith in the OPA549. The psu is Pedja's discrete psu for GC, with +/- 22VDC rails. The preamp section also uses this psu, with regulators to get +/- 18VDC. The sound of this thing is fast, crisp an articulate. For now I would say that it is a bit on the bright side, maybe after burning in it softens a bit. Bass is fast and punchy. I am quite happy with the result. Just need to get rid of the hum. Not much, but audible from the sitting position. Miguel

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7th February 2005, 01:59 PM	#2
demogorgon diyAudio Member Join Date: Jul 2004 Location: Behind you.	miguel: how is the opa627 reacting to a gain of 6.7? are you using multiple opa's? the data cheet say a max of 5 when it comes to gain..

7th February 2005, 02:23 PM	#4
miguel2 diyAudio Member Join Date: Jun 2002 Location: Portugal	The datasheet only mentions the gain of 5 to the OPA637, because this one is not stable for lower gains. The OPA627 has the advantage of being stable for unity gain. This permits to use a cap to reduce high frquency noise to this gain of 1, while keeping audio frequencies at gain of 6.7. This helps to stabilize the power section. Miguel

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