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Old 8th December 2012, 12:42 PM   #391
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by JohnGeneva View Post
Hi Guys, I went over Alex PCB design and schematic and R10 looks like inadvertently it was put on signal ground instead of -45v. Was this a mistake?
It is an error... well spotted... and it does indeed connect to the negative rail.
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Old 8th December 2012, 12:55 PM   #392
Mooly is offline Mooly  United Kingdom
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Originally Posted by JohnGeneva View Post
If so, what value should I put for the feedback resistor as per post 385.
The feedback resistor is still 22K, its just the take off point that was open to interpretation/discussion.

Remember the exact point at which this resistor connects in regard to the physical layout, is the exact point which is used as a "reference" for the signal.

Ideally it should be on a spur like this.
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Old 8th December 2012, 01:52 PM   #393
AndrewT is offline AndrewT  Scotland
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as detailed by D.Self.
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Old 9th December 2012, 11:36 AM   #394
Mooly is offline Mooly  United Kingdom
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Two short video clips showing operation of the triac relay delay (post #389 in this thread) in operation,

Simple Universal Speaker Delay Using A Triac
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Old 20th June 2013, 12:36 AM   #395
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Default Revisions for the amplifier "designed for music"?

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Hi Mooly. In a recent thread by Maouna you gave us a quick preview (i.e. the above distortion profile) of a revised form of your amplifier design. This is quite a development and no doubt you are pleased with it, as anyone taking up the design for a project will be if you care to detail what you have been up to.

I'm all err..."ears" to hear a little more about this quite interesting and commendable achievement, if I may say. That is an exemplary SPICE distortion "profile"!
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Old 20th June 2013, 07:29 AM   #396
Mooly is offline Mooly  United Kingdom
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Hi Ian,
it's all still very much "on the drawing board" so I don't want to give to much away at the moment but its evolutionary rather than revolutionary. Two pairs of dual die lateral FET's per channel with the VAS using two paralled small signal devices. An unusual feature I have been experimenting with in simulation is "distortion profiling". This allows via one variable resistor for the basic level of distortion of the amp to be increased (yes increased) while still maintaning that same FFT profile, while another variable resistor transfers the feedback from the normal takeoff point to earlier in the driver stages allowing the output stage to run more "open loop". The servo modifies a high precision reference voltage used for biasing rather than the servo providing the total bias voltage as in the original.
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Old 20th June 2013, 08:46 AM   #397
mcd99uk is online now mcd99uk  United Kingdom
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Originally Posted by Mooly View Post
Hi Ian,
it's all still very much "on the drawing board" so I don't want to give to much away at the moment but its evolutionary rather than revolutionary. Two pairs of dual die lateral FET's per channel with the VAS using two paralled small signal devices. An unusual feature I have been experimenting with in simulation is "distortion profiling". This allows via one variable resistor for the basic level of distortion of the amp to be increased (yes increased) while still maintaning that same FFT profile, while another variable resistor transfers the feedback from the normal takeoff point to earlier in the driver stages allowing the output stage to run more "open loop". The servo modifies a high precision reference voltage used for biasing rather than the servo providing the total bias voltage as in the original.
Mooly,

I understand you want to keep things secret but...

Your project sounds very interesting to me. I will be following this. Hopefully, you will provide us with an asc file to run in due course.

What sort of advantage do you see in the paralleled VAS devices? Do you find that the overall cob is lower this way? What sort of current are you running in this stage?

One last question, how do you set up Ltspice for you distortion profiles? We both ran a circuit for danny92 (I think). You ended up with an FFT looking totally different from what I got.

Paul
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Old 20th June 2013, 11:29 AM   #398
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Originally Posted by Mooly View Post
.... An unusual feature I have been experimenting with in simulation is "distortion profiling". This allows via one variable resistor for the basic level of distortion of the amp to be increased (yes increased) while still maintaning that same FFT profile, while another variable resistor transfers the feedback from the normal takeoff point to earlier in the driver stages allowing the output stage to run more "open loop". The servo modifies a high precision reference voltage used for biasing rather than the servo providing the total bias voltage as in the original....
Well, this still sounds as mysterious as any other description I've yet heard for distortion profiling, FFT tweaking etc. Good luck with this and keep us posted. After all, it is part of the main game here of improving our personal music listening enjoyment and your approaches always seem to me to be well focused and concieved.
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Old 20th June 2013, 12:07 PM   #399
Mooly is offline Mooly  United Kingdom
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Originally Posted by mcd99uk View Post
Mooly,

I understand you want to keep things secret but...

Your project sounds very interesting to me. I will be following this. Hopefully, you will provide us with an asc file to run in due course.

What sort of advantage do you see in the paralleled VAS devices? Do you find that the overall cob is lower this way? What sort of current are you running in this stage?

One last question, how do you set up Ltspice for you distortion profiles? We both ran a circuit for danny92 (I think). You ended up with an FFT looking totally different from what I got.

Paul
Hi Paul, the VAS stage runs at a fraction over 8ma in total. The parallel VAS is more of an experiment at the moment but seems to give good results.

I tend to run all the sims based on Bob C's excellent Spice tutorials in his book but run them over a longer period, at least 80ms (looking at the last 20ms) and try and take out the main R/C time constants (usually input and feedback electrolytic caps) that cause trouble with sims by replacing them with a DC offset voltage of identical value to that present in a sim of the full circuit with the caps.

Quote:
Originally Posted by Ian Finch View Post
Well, this still sounds as mysterious as any other description I've yet heard for distortion profiling, FFT tweaking etc. Good luck with this and keep us posted. After all, it is part of the main game here of improving our personal music listening enjoyment and your approaches always seem to me to be well focused and concieved.
Thanks Ian, and yes, its all about the music in the end
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Old 1st July 2013, 01:18 PM   #400
masood is offline masood  India
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dear sir,
why transistors become heated and destroy when input of an amplifier is not shorted?
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