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High power amp for low power needs - better result?
High power amp for low power needs - better result?
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Old 18th September 2019, 04:31 AM   #91
bimo is offline bimo  Indonesia
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Quote:
Originally Posted by wg_ski View Post
An amplifier will behave exactly per theory. The trouble is making a complete model for it.
Yes, it is. Several members proved it that measurement result can very close to simulation result. Of course, the implementation is matter, example: good pcb layout, choosing right component type, good wiring, etc.

Only who do not understand theory, said opposite.
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Old 18th September 2019, 11:14 AM   #92
martinsson is offline martinsson  Sweden
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I realize that the linked document regarding feedback is a generic and basic run-trough of how it works, I assume it can be applied both locally and globally, or perhaps both, and even though this is interesting and helps the understanding of how it works I cannot really see the load control part of it beyond a gain stabilizing function.

However, as far as I can understand (and mind you that is not a lot at this stage, so this may be wrong) it seems that a large amount of negative feedback, globally, might act destructive if the load is highly reactive, meaning a big delta from the intended signal at the summing point (as per the schematic in the link), making the feedback circuit work a lot harder than intended or beyond the purpose for which it was designed, if designed for a nice stable dummy load (resistor) for example.

I currently think there are several different parts/processes ina an amplifier that makes up the load control, here is how far I've come, and again, I just starting out here so I may be wrong about this.

1. / To ensure accurate initial signal or transient reproduction we need to have a sufficient current delivery capacity and slew rate (V/microsecond)(although the slew rate may be well above need in most cases), the current need I have been told can be up to five times higher than the basic theory would have you believe.

2. / To ensure accurate signal or transient end or stop we have the output impedance acting as a damper on the reactive signal where a lower output impedance seems favorable. (I'm trying to get to grips with that).

The amount and type of feedback (local/global) or mix there of is the most tricky part for me to understand, since at least on the surface it does not seem wise to "bother" the amp with corrective functions even if it means an increase in efficiency (gain), it should come at a cost of load control, or signal integrity (in the case of extensive global negative feedback) if the amplifier is not designed for it (beyond a dummy load).

This is how far I have come, but I'm sure this is grossly oversimplified and even perhaps plain wrong, and I'm very sure there are a lot more things to consider.

As for the processing and speakers, I have applied sufficient processing in terms of delay and crossovers to comply with what the design requires to operate as intended, both alone and together with the top system.

I'm very pleased with the result, both the integration between the two speakers, and each of their stand alone performances in their respective ranges.

I'm not all that concerned about a dead flat response curve, and I am aware that big variations in the response may be perceived as a lack of load control, sounding heavy, slow or muddy etc. but it is a good point and good to bring it up.

I find that you may kill the joy of the system if apply EQ to aggressively on order to flatten it out, especially in a room, make sure to take care of the most evident problems and leave the rest alone, all speakers have a character, just make sure you agree with it.

I will try to bridge the IP450 and see what happens, I'm not expecting miracles to be honest, and as for the drivers I am aware of their design features, performance and T/S parameter balancing, I chose them specifically based on that.

But it could be good to know that they are a bit on the extreme side, the 200g of moving mass is somewhat compensated for by a 30 in BL (motor strength), the inductance is fairly low for a 3,4kW program capacity driver with a well ventilated 4,5" voice coil (1.8mH) indicating a high efficiency in transferring the current to a force acting on the cone, and more important perhaps wise versa.

It is housed in a highly efficient 6'th order series tuned quarter wave design, meaning that it may generate a lot of back-emf for the amp to handle since there are a lot of secondary forces acting on the efficient drivers diaphragm, most likely way beyond what you may encounter in more traditional designs such as bass reflex (Helmholtz) or a closed box, and so well hence my question regarding load control.

The Labgruppen IP450, although being a nice enough amp, is by my guess not intended to handle a load such as this, and so I found the FP6400 which most likely is designed for this, and so I wondered if there might be an improvement in load control (sound quality) if I sprung for the more powerful amp, that's how it started at least, but I'm learning a lot.

Last edited by martinsson; 18th September 2019 at 11:37 AM.
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Old 18th September 2019, 11:56 AM   #93
edbarx is offline edbarx  Malta
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Quote:
Originally Posted by martinsson
However, as far as I can understand (and mind you that is not a lot at this stage, so this may be wrong) it seems that a large amount of negative feedback, globally, might act destructive if the load is highly reactive, meaning a big delta from the intended signal at the summing point (as per the schematic in the link), making the feedback circuit work a lot harder than intended or beyond the purpose for which it was designed, if designed for a nice stable dummy load (resistor) for example.
Completely reactive loads do NOT dissipate power. So, a totally reactive speaker would not emit sound.
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Old 18th September 2019, 11:58 AM   #94
zjjwwa is offline zjjwwa  Poland
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High power amp for low power needs - better result?
Quote:
Originally Posted by martinsson View Post
I cannot really see the load control part of it beyond a gain stabilizing function.
Try a mental exercise with a calculator in hand.
Imagine that you re-do all the calculations of the voltages in the feedback loop.
But this time, Your load will be constituted of an 8 Ohm load AND a 1V battery in series with the load.
The battery will serve the purpose to try to "upset" or kick off-balance the output of the amplifier (or op-amp, or whatever).
Try to re-calculated what is now "happening" at each of the nodes.
You will most probably come up with interesting results, and notice that it is not at all easy to upset the output voltage of the amplifier.
So, basically, in other words: If you apply an EXTERNAL 1V battery to the output of the amplifier, in series with your 8 ohms load, but the output voltage of the amplifier remains almost unchanged, from this data, you can draw conclusions as to the output impedance of the amplifier.
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Old 18th September 2019, 12:20 PM   #95
sajti is offline sajti  Hungary
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Quote:
Originally Posted by martinsson View Post
However, as far as I can understand (and mind you that is not a lot at this stage, so this may be wrong) it seems that a large amount of negative feedback, globally, might act destructive if the load is highly reactive, meaning a big delta from the intended signal at the summing point (as per the schematic in the link), making the feedback circuit work a lot harder than intended or beyond the purpose for which it was designed, if designed for a nice stable dummy load (resistor) for example.
No. Highly reactive load means big delta between the output signal, and the output current. The amplifier with feedback, will provide the output signal depended by the gain, which is set by the feedback. The question if it can provide the current, or the protection will kick in, or maybe the output devices are fail because of the SOA violence.

Sajti
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Old 18th September 2019, 01:46 PM   #96
zjjwwa is offline zjjwwa  Poland
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High power amp for low power needs - better result?
Quote:
Originally Posted by martinsson View Post
...on the surface it does not seem wise to "bother" the amp with corrective functions even if it means an increase in efficiency (gain), it should come at a cost of load control, or signal integrity
Typical amplifiers actually decrease (not increase) the gain. But it is a bit like trading horses.

For example:
Open Loop Gain (meaning: an amplifier without global feedback, or: the wire going "backwards" as feedback is cut / discontinous) could be 60 dB.
Or in other words:
60 dB = 20 log (V_out / V_in)
3 = log(V_out / V_in)
V_out = V_in * 10^3
V_out = V_in * 1000.
An amplifier with its Open Loop Gain multiplies the input voltage signal by a factor of 1000.
Closed Loop Gain (meaning: an amplifier with global feedback, or: the wire going "backards as feedback is "re-connected" so as to activate the feedback loop), could be 40 dB.
Or in other words:
20 dB = 20 log (V_out / V_in)
1 = log(V_out / V_in)
V_out = V_in * 10^1 = V_in * 10.
An amplifier with its Closed Loop Gain multiplies the input voltage signal by a factor of 10.
Difference between Open Loop Gain and Closed Loop Gain is sometimes called "The Loop Gain":
60 dB - 20 dB = 40dB.
Which basically means: 10^2, or a factor of x100
The output impedance of an amplifier, when you close the loop, will fall by a factor of this "Loop Gain". In our example, the output impedance will become 100 times smaller, when you close the loop.
So basically, you are "trading horses". You "give up" a factor of 100 in terms of gain, but you get a 100 times smaller output impedance instead.
{ I hope I got it right here; A second pair of eyes - please verify }.
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