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Old 11th May 2013, 03:49 PM   #41
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by Mooly View Post
If you download the program this .asc file of your preamp (unzip the folder) will run straight off.

You can see the amp is inverting. The response extends to many Mhz. Bottom end is poor due to the 0.047uf cap.

I forgot to add the decoupling cap after the 1K resistor which will slightly alter the AC characteristics... but I'll leave that for you to add

If you get stuck then ask.
Thanks for simulating
I'm an old type pencil and paper Engineer (started Engineering in 1969 ) and "old dog learns no new tricks" but it's nice to see that simulation confirm classic design performance.
Just one small detail, "0.047uF" was a typo, corrected in the following answer to:
Quote:
Sorry, I intended to write 0.47uF, which would have a cutoff frequency below 10 Hz.
1uF is fine, of course.
so if you want to re-simulate with 0.47uF , fine.

Maybe this old dog should practice some Spice, after all.

As a side note, original Spice was available way back then ... but we run it in an IBM1620 computer
Click the image to open in full size.
No monitor, of course
Curves/answers were drawings made out of asterisks " * " on a blanket size sheet of paper *or* long lists of numbers.
Not exactly user friendly
So it was ***much*** faster to simply use one of these:
Click the image to open in full size.

Thanks again

EDIT: did we have a *mouse* way back then?
Of course!!, what did you think?
....................
We called it "Mickey", it used to live behind a bookcase and we fed it cookies

Last edited by JMFahey; 11th May 2013 at 03:57 PM.
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Old 11th May 2013, 05:22 PM   #42
Mooly is offline Mooly  United Kingdom
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Here you go with a 0.47uf cap. Around 13Hz for the -3DB point.

Second shot is with a 2N3055 Nice gentle roll off outside the audio band... who need filters
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File Type: jpg Capture3.JPG (140.4 KB, 118 views)
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Old 11th May 2013, 06:10 PM   #43
JMFahey is offline JMFahey  Argentina
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Thanks again.
Even with 2N3055 , "flat within the audio band".
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Old 11th May 2013, 07:19 PM   #44
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wow! !!! :-)
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Last edited by Mosquito; 11th May 2013 at 07:26 PM.
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Old 11th May 2013, 09:39 PM   #45
JMFahey is offline JMFahey  Argentina
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Hi Mosquito, thanks for simulating, but you used a 1K load, too low for this simple preamp.
It expects around 10K or higher.

It still works, of course, but you lose gain and PP excursion with it.

PD: Santa Fe? Dónde?
Un abrazo.
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Old 11th May 2013, 10:02 PM   #46
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Hi, yes , just wanted to see what if... an extreme worst case load.
Santa Fe ciudad, humidity, low atmospheric pressure, and .. mosquitoes!
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Old 13th May 2013, 01:40 PM   #47
Jempie is offline Jempie  Indonesia
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hi i see the output is inverted, must is change this.
or just play inverted or change the + to - and - to + on the output
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Old 13th May 2013, 02:05 PM   #48
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Jempie View Post
hi i see the output is inverted, must is change this.
or just play inverted or change the + to - and - to + on the output
You can't really swap the outputs because of the grounds. An inverting amp (and many are) isn't a problem although some claim to be able to sense absolute phase.

Try an experiment. Listen to some music and then reverse both speaker lead polaritys and listen again. Can you tell any difference ?
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Old 13th May 2013, 02:59 PM   #49
Jempie is offline Jempie  Indonesia
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Mooly, correct me if i'm wrong does the signal is inverted?
If i messure + = - is this normal in the design?

Thx
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Old 13th May 2013, 04:24 PM   #50
Mooly is offline Mooly  United Kingdom
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All it means is that as the input voltage rises, the output voltage falls and vice versa. Forget signals and AC. Think about it at DC. The base of the transistor is biased to some set voltage by the resistor network. If the voltage at the base is "altered" the collector voltage alters too. Base voltage goes up, the transistor conducts more, the collector volts fall. Base volts fall, the transistor conducts less, the collector voltage rises.
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