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No global feedback V TO I converter THD: < 0.001%
No global feedback V TO I converter THD: < 0.001%
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Old 31st August 2014, 01:27 AM   #1
sonnya is offline sonnya  Denmark
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Default No global feedback V TO I converter THD: < 0.001%

Hi all.

I could not sleep tonight.

I am in the process of doing a frontend for driving my TSSA V1.7 in Balanced/bridged mode.

For this i have developed a front end which convert a given voltage to current with as low distortion as possible without the use of global feedback.

I ended up having less than 0.001% THD. Which i think i okay.

This low distortion we have in the enhanced diamond buffer but also in the currentmirror. The currentmirror normally lays around 0.025%

A note to the V/I converter:
The currentmirror is only that good if driving into a virtual GND node. In other words into an inverting opamp - discrete or chip solution.

Of course there is more to the circuit than shown here.
  • You need a good current generator with high PSRR and low drift
  • U1, U2, U3, U4 is a dual package to lower DC drift
  • The powersupply (+/-15VDC) should be a low noise high PSRR type

I hope your all like it.
Attached Files
File Type: pdf enhanced diamond buffer.pdf (14.5 KB, 214 views)
File Type: pdf bl_drive front end v10.pdf (22.7 KB, 180 views)
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Old 31st August 2014, 11:28 AM   #2
sonnya is offline sonnya  Denmark
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Any comment? :O/
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Old 31st August 2014, 12:05 PM   #3
MiiB is offline MiiB  Denmark
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useable for something...
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Old 31st August 2014, 11:15 PM   #4
manso is offline manso
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The cfp in drive front end will probably make distortion worse rather than better.
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Old 31st August 2014, 11:18 PM   #5
woofertester is offline woofertester  United States
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Any way to make it a power transconductance amp? I am looking for a reliable 50W/8 ohm transconductance circuit.
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Old 31st August 2014, 11:36 PM   #6
soekris is offline soekris  Denmark
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No global feedback V TO I converter THD: &lt; 0.001%
Quote:
Originally Posted by sonnya View Post
Any comment? :O/
Why the current mirrors ? A simple resistor is a V-I converter, if the driver is low impedance then you don't even need the diamond buffer....
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Old 7th September 2014, 10:37 PM   #7
sonnya is offline sonnya  Denmark
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Quote:
Originally Posted by manso View Post
The cfp in drive front end will probably make distortion worse rather than better.
Hi ... I have been offline for some days... Sorry.

No actually, the distortion falls of. Secondly it stabilizes the idle current in the diamond buffer.

The idle current ratio is then set by R12,R13 versus R14,R15.

In this case x5.6. There is a little loss so we end up with ~x5

Believe me the distortion is very low. Driving a 1K load 4Vp gives you below 0.001% without global feedback.
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Old 7th September 2014, 10:45 PM   #8
sonnya is offline sonnya  Denmark
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Quote:
Originally Posted by woofertester View Post
Any way to make it a power transconductance amp? I am looking for a reliable 50W/8 ohm transconductance circuit.
You would have to scale up the currentmirrors and make a mirror feedback to a resistor network. That is possible.
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Old 8th September 2014, 05:50 PM   #9
31697B is offline 31697B  Thailand
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Looks very interesting to me. Thinking about it more......

THx-RNMarsh
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