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Old 22nd January 2007, 08:26 AM   #1
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Default let's start a new project? yeahh!!!

Hi guys!

Here we go!
Since i've seen all this project built on this forum (krell 50, krell 100...and so on...), i would like to start a new one.

hope it will catch up your attention...



I would love, if possible with your help of course, to re-design and up-to-date this project.

For example, i think the bumb control circuit for the loudspeaker (which on this project is made with a relè) and the protections circuit could be made better than this.

There are on the ouput stage, two feedback networks:

one network with a cap and res, and a second with an operational amp.

Is it possible to improve and this last one?
Is it possible to lessen the feedback network without compromising the stability?




I don't know if anybody kows gryphon, but they have designed a Microprocessor-controlled non-invasive "smart" protection system

This is just an idea, to design together a system controlled by a micro that would regulate, in a not invasive way, the soft start and the protection system..



Anyways i really hope to see the post of this project growing up!!!



Best,
Stefano.
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Old 22nd January 2007, 08:36 AM   #2
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this is the pre stage
Attached Images
File Type: jpg preamp.jpg (53.5 KB, 661 views)
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Old 22nd January 2007, 08:39 AM   #3
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and this is the output stage witht the protection system, the bump control and the power supply stage:
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File Type: jpg output.jpg (93.2 KB, 661 views)
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Old 22nd January 2007, 09:05 AM   #4
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does anybody see the file attacched?

Becase i don't see them
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Old 22nd January 2007, 09:32 AM   #5
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the op amp is the DC servo, and returns to the noninverting side of the diff amp, not a problem, since it is outside both the signal path and the negative feedback path. negative feedback is fed back to the input of the amp, which is also the inverting input of the diff amp. there is no compensation in this amp, but the inputs have feedback integrating caps, so there's room for improvement there..... remove the caps across the feedback resistors, and add b-c compensation on the driver transistors if needed.

as far as the protection circuit goes, it already looks "noninvasive", since the detection circuit monitors the output collector current, does not interrupt the drive signal, but trips the relay. it's a simple SOA detector.
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Old 22nd January 2007, 10:02 AM   #6
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About the dc servo:

are there any other way of controlling the dc condition rather than this one?

Basecally that net on the schematic , is a network that by mean a low pass filter takes the output signal and compare it with the ground on the other input of the op amp. Even if the low filter is made with a very low cut off frequency that ideally would control just the dc component of the output signal, as far as i can understand, in the reality it cold interact with the signal and might be a little form of feedback and distortion.



Moreover, about the the bump control circuit, as far as i know, the relè was the first introduced way to keep this issue under control and i think that other design on reguard of this were made during this time.

Is there any different way of controlling the bumb rather than using a relè with a delay?


I didn't understand what you meant about the improvement on the feedback network.
you would take off the capacitor and b-c compensate the amp?

would a compensation be better than the simple rc network?
Wouldn't the amp have an heavier feedback network?
I'm the one that belives that an heavy feedback network just worsen the sound of an amp.
So if i would modify a the feedback it would be to make it ligther than it is now (even if it's already a low feedback network)

Is it not the zobel network on the output a compensation?



Another thing:

wouln''t it be a benefit to redisign the power supply stage for instance with an inductive power supply (pi-greco l-c network) ?


My original purpose when i decided to start this 3d was to modify a very good sounding amp, but old design, with a NO-compromise design.
This means for me to take the compromises away, if there are, made on the original design, and then the carefully choice the component to use on the important parts of the design.

I really hope to see this 3d growing up and catch up your attention.

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Old 22nd January 2007, 10:30 AM   #7
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Quote:
Originally posted by Stefanoo
this is the pre stage
Quote:
Originally posted by Stefanoo
and this is the output stage with the protection system,
the bump control and the power supply stage:
Hi, Stefano

1. preamplifier.
Looks like No Global Feedback, with Volume Control
I can not really understand this one.
I am sure I can do better, with not so many transistors.


2. output stage.
Very nice Inverted Power Amplifier.
Looks like it can be very good!


I have saved both figures: preamp + output
I call them:

070122a_preamp.jpg
070122a_output.jpg

They are in my Stefanoo Folder .. in My documents.


See you manyana.
lineup
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Old 22nd January 2007, 10:32 AM   #8
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perfect....see you manana

...hope this 3d will start up !!
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Old 23rd January 2007, 04:09 PM   #9
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uuupppp!!!

but...nobady is interested?
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Old 23rd January 2007, 08:50 PM   #10
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ok, maybe you don't completely understand feedback..... feedback, especially as it is used in amplifiers, doesn't just reduce distortion, but it sets the overall gain of the amplifier. compensation is used to slow down an amplifier, without compensation you have a large rf oscillator. these are two separate subjects, but they are also somewhat related.....

an amplifier with a differential input stage, even a power amp like this one follows the same rules as an op amp. you have two inputs, inverting and noninverting, and you have an output. there are three basic ways to operate this amp, closed loop with negative feedback, closed loop with positive feedback, and open loop with no feedback.
there are very few applications for operating with positive feedback, and you don't want a 100 watt comparator, so we won't discuss that one. that leaves the negative feedback amp and the open loop amp. we'll go with the open loop amp first. operating the amp open loop, you get whatever gain is present in the amp circuitry, which could be as high as 120db. let's use a 1uV sine wave input signal at 1khz that's .000001V...... at 120db gain that would give us a million volt output, except for a 100 watt amp, we only have +/- 60 volts to work with, so we het a 120V P-P square wave. that's like 99.999% distortion. most preamp outputs have signal levels around .1 to .5 volts, so this amp has way too much gain so how do we get the gain down to a useful level? we could degenerate all of the devices that produce gain in the amp until we have a gain of 30 or so, but it's a very delicate balancing act to match all of the linear regions of all the devices in the chain, and with standard components, you will have mismatches resulting in distortion. so we apply negative feedback to our 120db amplifier. just like with an op amp, we insert a voltage divider at the output, and tap off the desired amount of feedback. let's say we want a voltage gain of 30. so we choose a resistor pair that gives us 1/30 of the input voltage. we'll use 300k and 10k. 300k from output to the inverting input, and 10k from the inverting input to ground. the inverting input will always attempt to maintain itself at the voltage on the noninverting input. so we apply our signal to the noninverting input, and our 120db amp tries to amplify it 120db, but once the voltage fed back to the inverting input goes past what is on the noninverting input, the inverting input "tells" the amp "whoa". so the inverting input limits the output signal so that it tracks the input signal. it tracks the input signal so closely, that if there is any distortion added by the amp circuitry, the inverting input attempts to correct it. so we now have our 120db amplifier "tamed down" to 13.5 or so db, and the inverting input is also correcting for any remaining nonlinearity that it "sees" in the output signal. that's ok for a noninverting amp, but the amp we're looking at in this thread is an inverting amp. almost all of the same rules apply, the inverting input will attempt to maintain itself at the same voltage as the noninverting input. so we now unground the 10k resistor and feed the signal in through it, and ground the noninverting input. the inverting input will now attempt to keep itself at ground, so if the input signal goes positive, it will drive the output negative. the amp is now inverting. if all were perfect with the world, this amp would also have no dc offset, but all is not perfect, there are dc currents flowing in the input elements that will add offset to the output, so we feed back the dc to the input as well to attempt to correct for it as well, but instead of sending it through a voltage divider, we atempt to get all of the dc corrected, so we need a 1:1 ratio of the dc, either on the inverting input (that's the purpose of the existing capacitor,which is now in both the signal path AND the feedback path, or we invert the dc and feed it back on the noninverting input (which is now no longer in the signal path), this is what a dc servo does.

this is getting long, so i'll let you digest this before i describe compensation.........
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