Yet another amp - simple inverted with 10x gain, mosfet output stage

sonnya · 08:30 PM

Hi all.

I was in the mood for modifying an old amp i made ~10 years ago.

Change R9 to set idle current - 500R -> 0.5amp.

It does not need any compensation.
It is stable into capacitive load.

The openloop gain is not that high, but the harmonics fall nicely of.

CLG is 20dB
OLG is 82dB

And the amp will be able to compete with an gainclone amp regarding size.

Bandwidth is >350KHz.

juma · 15th June 2011, 10:10 PM

Lovely amp except for very low Zin - not many preamps can deal with 1k...

sonnya · 16th June 2011, 07:01 AM

You can drive it from a jfet buffer like in this paper:

http://www.tkhifi.com/div/Erno_Borbe..._articel_2.pdf

Or you can choose a good cheap opamp like: LME49721M to drive. Both types have no problem with the 1K Zin.

WuYit · 16th June 2011, 07:40 AM

..or from a DAC.

sonnya · 16th June 2011, 07:45 AM

Yes precisely. And use the DAC's internal volume control.

The feedback network the needs to be changed. But basicly the Resistor R11 should be shorted and R10 need to be changed to match the output to 0dB from the DAC currentsource.

sonnya · 16th June 2011, 07:45 AM

I would not go higher than +/-25V on the rails.

juma · 16th June 2011, 07:53 AM

Quote:

Originally Posted by sonnya

You can drive it from a jfet buffer like in this paper:

http://www.tkhifi.com/div/Erno_Borbe..._articel_2.pdf

Or you can choose a good cheap opamp like: LME49721M to drive. Both types have no problem with the 1K Zin.

I wouldn't drive it from complemetary JFET buffer - it sounds inferior to SE and SE can't drive it.
And if we choose an OpAmp as buffer we might as well use the LM3886 or OPA549 as amp.

So, stop offering bad solutions and change the amp so that Zin=10k or more (without added complexity)

WuYit · 16th June 2011, 07:58 AM

Quote:

I would not go higher than +/-25V on the rails.

Me neither.

SE can drive it.

sonnya · 16th June 2011, 08:00 AM

Quote:

Originally Posted by juma

I wouldn't drive it from complemetary JFET buffer - it sounds inferior to SE and SE can't drive it.
And if we choose an OpAmp as buffer we might as well use the LM3886 or OPA549 as amp.

So, stop offering bad solutions and change the amp so that Zin=10k or more (without added complexity)

What do you mean when saying "stop offering bad solution"??

juma · 16th June 2011, 08:01 AM

I'm just kiddin' you, relax...

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15th June 2011, 10:10 PM	#2
juma diyAudio Member Join Date: Nov 2005 Location: Zemun	Lovely amp except for very low Zin - not many preamps can deal with 1k...

16th June 2011, 07:01 AM	#3
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	You can drive it from a jfet buffer like in this paper: http://www.tkhifi.com/div/Erno_Borbe..._articel_2.pdf Or you can choose a good cheap opamp like: LME49721M to drive. Both types have no problem with the 1K Zin.

16th June 2011, 07:40 AM	#4
WuYit Banned Join Date: Oct 2010	..or from a DAC.

16th June 2011, 07:45 AM	#5
sonnya diyAudio Member Join Date: Oct 2001 Location: Denmark	Yes precisely. And use the DAC's internal volume control. The feedback network the needs to be changed. But basicly the Resistor R11 should be shorted and R10 need to be changed to match the output to 0dB from the DAC currentsource.

16th June 2011, 08:01 AM	#10
juma diyAudio Member Join Date: Nov 2005 Location: Zemun	I'm just kiddin' you, relax...