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Old 8th August 2012, 04:08 PM   #41
Bensen is offline Bensen  Belgium
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Quote:
Originally Posted by dadod View Post
It is similar to Miller comp if TMC resistor was connected outside(directly to output) the probe. Here is screen shot with the resistor inside the probe.
Thanks for your comment.
dado
Hi D,

I see that your amp has an open loop bandwidth of only +-200Hz.
I'm currently focussing a lot on this in my design. I'm breaking my head trying to reach an open loop bandwidth op +-10Khz without using resistive loading of the VAS.

Can someone tell me if this is really that necesarry, some people are telling high open loop BW is important. But, most Solid State amps have rather small open loop BW.
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Old 8th August 2012, 04:14 PM   #42
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Try current feedback designs.
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Old 8th August 2012, 04:16 PM   #43
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i saw the diagram. It will not work! It only works when the Collector voltage is higher then the basis voltage. Because of the ripple at the collector, the collector is not always higher then the basis voltage. Besides that the whole current has to pass this transistor that produce lot of heat. After all the power supply has to have a low impedance for AC which is acchieved by the usual Condensator but in this case the impedance is the emitter resistance of the emiter which is too high..
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Old 8th August 2012, 04:29 PM   #44
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Quote:
Originally Posted by Bensen View Post
Hi D,

I see that your amp has an open loop bandwidth of only +-200Hz.
I'm currently focussing a lot on this in my design. I'm breaking my head trying to reach an open loop bandwidth op +-10Khz without using resistive loading of the VAS.

Can someone tell me if this is really that necesarry, some people are telling high open loop BW is important. But, most Solid State amps have rather small open loop BW.
Open loop high bandwidth, low gain, already low distortion with little feedback gives the best result.
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Old 8th August 2012, 09:20 PM   #45
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Bensen View Post
Hi D,

I see that your amp has an open loop bandwidth of only +-200Hz.
I'm currently focussing a lot on this in my design. I'm breaking my head trying to reach an open loop bandwidth op +-10Khz without using resistive loading of the VAS.

Can someone tell me if this is really that necesarry, some people are telling high open loop BW is important. But, most Solid State amps have rather small open loop BW.
This is with the VAS local feedback, no resistive loading of the VAS needed, if you like that more. THD20k is the same as before, but higher at lower frequences.
dado
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Old 9th August 2012, 11:21 AM   #46
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Originally Posted by liching1952 View Post
Open loop high bandwidth, low gain, already low distortion with little feedback gives the best result.
Here we go again.
Show us some low distortion with little feedback.
Just two days ago while working on a design this being a current feedback one I saw how damaging this low feedback myth really is. With the amp in question I found that lowering the loopgain to get wider bandwith and lower feedback causes the amp to have considerable more higher order harmonics from 4th up. TIM is also much higher.
Jlh has proved and shown this before back in the late 70s, if youre going to use feedback, better it be plenty or rather than just dont use it at all. A certain amount of feedback is necessary before the higher order harmonics are lowered so in fact low feedback is the worst you could do as it will cause them to be higher instead of lower.
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Old 9th August 2012, 11:32 AM   #47
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its up to you. Seeing the level here I will not proceed to defent this statement.
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Old 9th August 2012, 05:10 PM   #48
Bensen is offline Bensen  Belgium
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Quote:
Originally Posted by dadod View Post
This is with the VAS local feedback, no resistive loading of the VAS needed, if you like that more. THD20k is the same as before, but higher at lower frequences.
dado
Interesting, the local feedback to IPS is done with the 10Meg resistor if see it correct?
I'm gonna play arround with this a bit.

Greetz
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Old 9th August 2012, 05:40 PM   #49
a.wayne is offline a.wayne  United States
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Originally Posted by homemodder View Post
Here we go again.
Show us some low distortion with little feedback.
Just two days ago while working on a design this being a current feedback one I saw how damaging this low feedback myth really is. With the amp in question I found that lowering the loopgain to get wider bandwith and lower feedback causes the amp to have considerable more higher order harmonics from 4th up. TIM is also much higher.
Jlh has proved and shown this before back in the late 70s, if youre going to use feedback, better it be plenty or rather than just dont use it at all. A certain amount of feedback is necessary before the higher order harmonics are lowered so in fact low feedback is the worst you could do as it will cause them to be higher instead of lower.
OK... Now define how much is low, how much is enuff vs a lot ...


Yeah ...
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Old 9th August 2012, 06:22 PM   #50
dadod is offline dadod  Croatia
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Originally Posted by Bensen View Post
Interesting, the local feedback to IPS is done with the 10Meg resistor if see it correct?
I'm gonna play arround with this a bit.

Greetz
Yes this is R20 10Meg resistor making local FB from the Q15 collector(cascode transistor) to the Q12 base(VAS transistor).
dado
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