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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 17th February 2018, 09:02 PM   #11
john curl is offline john curl  United States
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OK everybody, let's look at a PRACTICAL preamp circuit that was made for 95% of the audio users. Please note the caps, (input, feedback, output) in the phono stage to start. Check out their time constants and how their DA might add up. But that's not all. There is the rest of the circuit. AND what did they use? Scott's AD712 of course, one of the IC's recommended by me at the time to the designers of this preamp. Just to rub it in, the phono stage has 3 aluminum caps in the circuit, even though the AD712 is laser trimmed for lower DC offset. This is what we try to design OUT with a single servo with a single Mylar cap in the servo.
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Old 17th February 2018, 09:16 PM   #12
gpapag is offline gpapag  Greece
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John Curl's Blowtorch preamplifier part III
Ed thank you for the two posts
I used my soundcard and run some tests (10kOhm load, 1uf caps, 48.340Hz and 320.068Hz dual test tone).
Good noise floor but I could not locate distortion indications using this dual tone or Scott's twenty tone test signal.

In the next days I will make another dual-tone test file with 46.875Hz and 317.139Hz.
These are at exact FFT bin centres closest to prime numbers 47 and 317 (for 48kHz sampling, and all the standard FFT sizes from 65536 samples and above).
I will also adjust load resistor to match capacitor’s Z at one of these two frequencies, may be at both.

One question please regarding your remark on square wave testing.
You said that with the capacitor, the leading edge of the SQRW goes higher than the no cap SQRW, therefore this will produce audible results.
On the other hand, with the cap, the area under the curve becomes smaller. Will this has an opposite audible effect?

On my setup, with the caps the LE goes up about +3dB, while the area under the curve reduces by about 40%

George
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Old 17th February 2018, 09:39 PM   #13
simon7000 is offline simon7000  United States
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George,

I think it is the peak amplitude that is perceptable. Will discuss with a fellow who knows more about this when we get together next time.
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Old 17th February 2018, 09:47 PM   #14
simon7000 is offline simon7000  United States
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Quote:
Originally Posted by scott wurcer View Post
On capacitors I'm only interested in finding the cheapest ones that work, creating an encyclopedia of what does not work has little interest to me.
The cheapest capacitor is no capacitor. But othewise a polypropylene when used as a DC blocker that is good for a factor of ten below your corner frequency. Using ones for equalization my choice would be polystyrene but not the ones I have seen of recent offshore manufacture. Not sure what they do wrong but the "D" as measured is higher than equivalent mylars. The not inexpensive or ridiculous Relcaps are what I have used.

Last edited by simon7000; 17th February 2018 at 09:58 PM.
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Old 17th February 2018, 09:55 PM   #15
Max Headroom is offline Max Headroom  Australia
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A more representative test might be to change input cap of a slightly 'dirty' amplifier/buffer stage and look for 'magnified' consequential changes, after all this is the usage condition that inspires subjective findings.
It might be that AP or soundcard loopback test is too 'clean' to show up real world changes due to capacitor types.

It seems that there is underlying behaviour of materials that causes change in behaviour of other materials and these behaviors are interactive...ie some materials 'play nice' together, some do not.

As an example I placed my mixture on the bottom bridge of my friends electric guitar after his Friday night show.....this quite profoundly changed the acoustic sound of this guitar and for the better.

With the mix in place the guitar sounded more ordered, more powerful and cleaner, reverting to standard condition the clarity and sense of 'power' was reduced and the guitar sounded 'out of tune' in comparison.
The amount and location of the material is too small for mass/mechanical damping to explain the subjectively very agreeable subjective changes, and with the result that Mike begged me to keep the experimental sample for trials in upcoming shows.

Audio systems are the sum of all parts, testing components in isolation may show changes that are below the accepted hearing limits, testing in actual/typical usage may reveal consequential changes that are indeed readily audible.

Dan.

Last edited by Max Headroom; 17th February 2018 at 10:16 PM.
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Old 17th February 2018, 09:56 PM   #16
simon7000 is offline simon7000  United States
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George,

Am I missing something, I don't see a load resistor on the right input to the shell (ground.)
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Old 17th February 2018, 10:27 PM   #17
Markw4 is offline Markw4  United States
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Quote:
Originally Posted by Max Headroom View Post
As an example I placed my mixture on the bottom bridge of my friends electric guitar after his Friday night show.
Dan, What you have provided has no useful meaning, probably to anyone here, certainly not to me. Why not take a picture of the bridge showing the material location and amount? Why not get your guitar player to record his guitar with and without the material into a sound card?

If you let us see and hear what you are talking about, it might mean something. To say that a sound is 'ordered' doesn't mean anything, I never heard of that description of a sound before. You might as well be saying, "blah, blah, blah..." there is just no useful information to understand what you're talking about.
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Old 17th February 2018, 11:19 PM   #18
TheGimp is offline TheGimp  United States
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Doesn't the 10K input impedance of the soundcard swamp the 100K resistor connected to the cap?
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Old 18th February 2018, 02:32 AM   #19
simon7000 is offline simon7000  United States
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Originally Posted by TheGimp View Post
Doesn't the 10K input impedance of the soundcard swamp the 100K resistor connected to the cap?
Not if there is an input capacitor to the A/D.


Scott,

You offered to show how 2 sines (I'll use the wrong name to avoid humor) can produce a third passing through a CR stage using Laplace transforms. I think I know what you have in mind and why it varies from reality. So if you would post your arithmetic...
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Old 18th February 2018, 02:41 AM   #20
Max Headroom is offline Max Headroom  Australia
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Quote:
Originally Posted by Markw4 View Post
Dan, What you have provided has no useful meaning, probably to anyone here, certainly not to me. Why not take a picture of the bridge showing the material location and amount? Why not get your guitar player to record his guitar with and without the material into a sound card?
On the string side of the bridge, underneath the strings.
When we meet up later in the week I can take pics and record some sounds.

Quote:
If you let us see and hear what you are talking about, it might mean something. To say that a sound is 'ordered' doesn't mean anything, I never heard of that description of a sound before. You might as well be saying, "blah, blah, blah..." there is just no useful information to understand what you're talking about.
It's a bit like super stable clocking in a digital audio system.....lousy clocking causes audible 'instability' and sideband noises that can be digital data signal dependent and this can cause an audible signature that can be dynamically varying.
Moreover analog signal contained noise can drive further noise production in intrinsic noise prone systems.

It seems that analog (and mechanical) systems can exhibit a 'jitter/noise' behaviour and attendant signature that can be altered or 'reclocked' at will.
If you go back and listen again to those Dropbox files you might pick up on this.

Dan.

Last edited by Max Headroom; 18th February 2018 at 03:07 AM.
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