Need help reading an amplifier schematic

madjay

Member
2016-04-28 10:18 am
Hi.I found this 2000w pmpo diagram that can deliver 1000w rms @2 ohms.There's a part in this diagram that I don't understand.There's a path names as bridge input.(left side of the image).Can I know what it is and what it does.Does it use to bridge the amp?Any help would be deeply appreciated :)
k6EtFH.jpg
 
Bridge input is an inverting input that can be used alongside an identical amplifier. If you input the same signal to Bridge input on one amplifier and S input on another, the outputs from the amplifiers will oppose and allow bridge mode. Giving four times the power.
The bridge schematic is not correct as 120k into 33R will not work.
 
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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
OK :) if its what you want.

Its one seriously big amplifier, 28 output devices for a stereo amp, heatsink that's suitable, PSU that's suitable.

Why are so many of the resistors paralleled with something much higher in value ? What that all about.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Without wishing to hurt anyone's feelings about the design, it really looks like someone has copied an existing, very ambitious, design but substituting a limited range of old generic parts.
All those paralleled resistors to trim values suggests to me the designer is slavishly trimming E12 values to substitute for E24 in the first design or (unlikely) those are literally what he/she used to get best results in their prototype. Either way, this makes it a suspect design and the outcome for DIY rather doubtful.
Personally, I'd look elsewhere unless you have the time to sort through the components for better suited types and more sensible values - then check by proper simulation.
 
Ian, I'm not so sure (but your theory does sound compelling). Mine is that they could be there (the paralleled resistors) to allow for non-explosive degradation in performance would that the lower resistance (higher power dissipating) resistor fail. Especially with film resistors.

But yah… most likely it is slavish measured-resistance trim.

On another hand, the 'bridge' input (being shunted to virtual ground by a 33 Ω resistor) might actually be what is desired, since this is also the negative feedback loop. Could be that that is necessary to tame-the-gain of another amplifier's OUTPUT. Chaining this one to the output of another arbitrary amplifier of not-necessarily exact design. Dunno. Could work. Kind of interesting flexibility.

GoatGuy
 
Thank you so much.Do you think this is a good amplifier.I tried so hard to find a good amplifier diagram and this is the one i found.Do you have any recommendations for me?Im looking for something that can deliver 1000w or more @4 ohms.

The biggest issue is the driver section. NO way those MJE drivers are going
to drive those low beta TO-3's down to 2R.

Another issue is the use of slow 340/350 for the current mirror and Cascode.
The input stage topology is poorly implemented.

I'm so tired of these so called "1KW" idiot designs that a google search
turns up. It is dangerous to try to produce that much V/I with a "idiot design".

PS - for that much power (below) ..... parallel about 7-8 pair Sanken
(2SC3264/2SA1295).
on the example circuit - TO-3P drivers will handle any load or # of pairs.

OS
 

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Agree 100% that this thing is far from what it promises. The output devices will not handle +/-00 volts, let alone looking at their SOAR.

The 33 ohm resistor in the feedback is just wrong.

That absence of protection circuitry is also a major concern. If you start playing with power levels like this, you almost need to start with thermal and protection design!
 

madjay

Member
2016-04-28 10:18 am
Yes.. I also agree that there are some issues with the diagram I showed earlier.When it comes to schematics it's hard to believe anything Google shows in random websites.I'm still trying to find a good diy diagram(and not very complicated one)Don't wanna spend too much on this is either.I have completed a 300W amplifier that sounds wonderful so I wanted to try something with higher power.