Could someone model this circuit for me? See attached, just the amplification circuit itself. Classe got two transistors backwards (Q106 and Q107) and I suspect stability is iffy. This isn't a typo / oops in the schematic. I confirmed it on the circuit board.
Also, based on the input buffer circuit, is this truly balanced? It appears to be in looking at the circuit board (i.e., mirror imaged layouts per side) but I see opamps at the input, which normally mean it isn't.
(I'm a newbie here)
Also, based on the input buffer circuit, is this truly balanced? It appears to be in looking at the circuit board (i.e., mirror imaged layouts per side) but I see opamps at the input, which normally mean it isn't.
(I'm a newbie here)
There is a tutorial where you can learn to do this yourself here Installing and using LTspice IV (now including LTXVII). From beginner to advanced.
You can replace the MJE340/350 by KSC3503/A1381 and short the Q107.
The C110 instead of grounding bring it to the base of Q110. Adjust the value to have it just stable, then fix a triple of that value.
The C110 instead of grounding bring it to the base of Q110. Adjust the value to have it just stable, then fix a triple of that value.
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Related discussion is here :
https://www.diyaudio.com/forums/solid-state/366705-schematic.html#post6502889
https://www.diyaudio.com/forums/solid-state/366705-schematic.html#post6502889
What do you really want to model?
Setup schematic and set operating modes?
This is a very simple amp designed without understanding or with errors in a service manual. They mistaken with transistors markings and their placement in functional nodes.
Choosed Q111 and Q112 aren't good to be first current amplification stage.
They try to cascode LTP, but make this very ugly, it will be much better to cascode LTP's current source.
LTP load are ugly. They've dropped at least 30-40 dBs of performance.
VAS trannies aren't good to be top pick, bias modes aren't optimal.
So amp are good to be labour work at third-fourth age of engineer graduation but can't be defended as magister work.
Yeah, there are definitely some obvious improvements to be made. Firstly, they're using the same large TO-264 transistors for the drivers as they are for the outputs. That's common in really big amplifiers with an EF triple, but it makes no sense if the amplifier only has a single set of output devices. Something like a KSC3503 / KSA1381 or MJE15034 / MJE15035 (sorry if I butchered a part number) would be better choices, depending on the power level. Higher Hfe, lower input capacitance and lower cost.
They're cascoding the LTP (or at least trying to), but they haven't even bothered to put a current mirror on it.
There are a few other things that I need to stare at for a little longer to see if they're more goofy circuit design or a badly drawn schematic.
It's one of those designs where I really scratch my head because I can't for the life of me figure out what the designer was trying to do.
FWIW, if you are a beginner taking the time to learn how to use LTSpice is one of the best things you can do for yourself. It's a bit daunting at first, but it's an incredibly powerful piece of software if you learn how to use it properly.
They're cascoding the LTP (or at least trying to), but they haven't even bothered to put a current mirror on it.
There are a few other things that I need to stare at for a little longer to see if they're more goofy circuit design or a badly drawn schematic.
It's one of those designs where I really scratch my head because I can't for the life of me figure out what the designer was trying to do.
FWIW, if you are a beginner taking the time to learn how to use LTSpice is one of the best things you can do for yourself. It's a bit daunting at first, but it's an incredibly powerful piece of software if you learn how to use it properly.
The inputs are perfectly balanced an instrumentation amp is formed with 3op and input impedances are equal and if the resistors are of high precision the performance is top.
everything is high impedance and unnecessary resistor noise is added in 2 places, but the line level is not that sensitive to it.
For the discrete part others have pointed out problems.
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35k inline? It will hiss as a snake...
While it isn't a kind of sophisticated copy-paste protection it's really as bad as possible.
They even put electrostatic discharge protection by diodes. But usually they not fast enough without some kind of input filter. Even 1kOhm/1nF RC will greatly improve protection properties and dropdown unnecessary HF interference.
Just practice with PA systems. Unpleasant hiss at pauses or silent track fragments.
Can be calculated directly keeping in mind +26 dB amps gain, ~110 dB sensitivity of horn loaded compression drivers and main hearing sensitivity bump at 1-3 kHz.
But really not a main issue with this amp.
Within one page. A guy asks a question, and within one page the thread derails in something totally unrelated to the request and people bragging about how they know much better.
Awful.
Jan
Awful.
Jan