Yet another amp - simple inverted with 10x gain, mosfet output stage - diyAudio
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Old 15th June 2011, 08:28 PM   #1
sonnya is online now sonnya  Denmark
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Default Yet another amp - simple inverted with 10x gain, mosfet output stage

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.
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Last edited by sonnya; 15th June 2011 at 08:30 PM. Reason: added details
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Old 15th June 2011, 10:10 PM   #2
juma is offline juma  Germany
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Lovely amp except for very low Zin - not many preamps can deal with 1k...
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Old 16th June 2011, 07:01 AM   #3
sonnya is online now sonnya  Denmark
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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.
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Old 16th June 2011, 07:40 AM   #4
WuYit is offline WuYit  Sweden
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..or from a DAC.
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Old 16th June 2011, 07:45 AM   #5
sonnya is online now sonnya  Denmark
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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.
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Old 16th June 2011, 07:45 AM   #6
sonnya is online now sonnya  Denmark
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I would not go higher than +/-25V on the rails.
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Old 16th June 2011, 07:53 AM   #7
juma is offline juma  Germany
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Quote:
Originally Posted by sonnya View Post
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)
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Old 16th June 2011, 07:58 AM   #8
WuYit is offline WuYit  Sweden
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Quote:
I would not go higher than +/-25V on the rails.
Me neither.

SE can drive it.
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Old 16th June 2011, 08:00 AM   #9
sonnya is online now sonnya  Denmark
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Quote:
Originally Posted by juma View Post
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"??
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Old 16th June 2011, 08:01 AM   #10
juma is offline juma  Germany
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I'm just kiddin' you, relax...
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