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Old 22nd September 2012, 08:45 AM   #11
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hello again arty

unlike the tda1557 chip that you proposed initially, the lm1875, much like an op-amp, gives you access to the +- inputs and can therefore affect both the DC and AC gain and conditions in an general loop with an other regular op-amp. However, i can not make sense of your design. Please forgive me for not taking the time to suggest corrections or propose an alternative but i would suggest that you study further the subject by consulting any reference text on op-amp design.
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Old 22nd September 2012, 10:06 AM   #12
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Quote:
Originally Posted by Arty View Post
Even if it is possible, can it improve a generic poweramp?
Any Solid State poweramp is an opamp. Most of them use Alan Blumlein LTP (he also pioneered stereo & ultralinear topology) and some sort of internal feedback.

Actually opamp is an analog computer that can be used to implement mathematical equation y=kx. If blocking DC it is an audio "generic poweramp".

Feedback is the key idea of an opamp.

It comes form the days when only tubes were in used and tube characteristics are not stable. The idea was to implement feedback that depends on stable parameters of passive components so analog circuit behaves predictable within long period of time despite the the tube wear off.

No it is almost impossible invent something new in analog schematics nowadays ( I would say impossible). The best way to implement opamp is using standard noneinverting implementation (better BW and extra).

Most exciting DIY sounding gear for home use I would define as a SET parafeed + horn (or line array). In case you are looking for some solid state DIY Goldmund Mimesis 3 Clone project might be interesting

Goldmund Mimesis 3 Clone, World's Best Amplifier!!!!
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Old 22nd September 2012, 03:27 PM   #13
balerit is offline balerit  South Africa
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see a 12v amp, looking for chip

"I would go for the TDA1557. I have designed a pcb for it and my first prototype had loud clicks on the speakers when switching it on so I added a power on delay part to the circuit to pin 11 to allow the amp to settle before the amp powered the speakers. I also designed the pcb with an opamp buffer as a preamp so no need for a separate preamp. It's a great sounding amp."

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Old 22nd September 2012, 05:33 PM   #14
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well it looks like i have to do some experimenting, what i done sofar was use TINA.
I used the spice model of a uA741 as the "power amplifier",
and used a TL081 as the "high quality opamp" and as the "differential amplifier".

Simulation showd that the uA741 starts falling in amplitude over 10Khz or so.
But when used with the active feedback it was allmost identical as if i used a tl081 only.

So i will try to build a circuit with the block diagram i came up with, using tda 2050 as poweramp and some better opamp as the source of the feedback signal and the difference amplifier.
Actualy the aim is to force the poweramp chip driving a speaker to produce a signal as close to identical as possible as a quality opamp driving a high impedance load, by feeding the poweramp with a feedback signal that is the difference between the poweramp and opamp outputs.

And if it does not work, then it will just blow up
will see. got some heavy welding to do on my small log trailer, afterwards i will have more time to findle with it. Naturaly it may end up as a disaster, still it bugs me if it can be made, or not.
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