John Curl's Blowtorch preamplifier part II

[PMA]

Sounds like true DIY

 

[morinix]

Sy,
One of life's lessons I learned earlier on was that you have to look at parity of price in the audiophile world. I brought a very well designed product to the CES and Stereophile shows and was admonished for setting my selling price to low. This was an eye opener to me. I thought that I had priced the product well to sell based on cost and profit margins but the product was just to good to sell at my price point. I was upsetting the apple cart so to say, the speaker sounded much better than many that had prices 10 times the price and dealers did not want the product in their stores, it would have gutted their higher end product sales. Also it is a matter of perception. If you made and many have a product better than say an Apple product and attempted to sell it at a lower price point people seem to feel that the product must be inferior if the price is lower.

A friend once told me that his first job was to sell ball point pens. He packaged the pens in two ways, as a low cost pen and at a much higher cost in a different package. The cheaper model that was identical to the expensive model languished on the shelf and the expensive pens sold well. Perception is a large driver of consumer choice, I will not make that mistake again.

Can't this be circumvented by direct marketing? I know that such a path requires some heavy lifting but are the rewards not worth it?

 

[Kindhornman]

Morinix,
Today direct marketing is something that is much more common but back when I did what I was doing it wasn't really very prevalent. With the loss of so many audio dealers I don't even see how you can even sell through those channels any more? Perhaps there are a handful of real audio dealers left in Los Angeles and a few major cities like New York but most have just disappeared. I plan on doing all my sales through direct sales at this point. The only other option seems to be to tie into a celebrity and use the Dr. Dre marketing model, selling product based on name recognition and forget about sound quality which I am not interested in doing. I have to say I was in the book store the other day and even in the audio section they didn't even carry Stereophile anymore, just a few titles more to do with home recording and for musicians only. Not one audio magazine in sight! The store was Barnes and Noble!

 

[morinix]

Morinix,
Today direct marketing is something that is much more common but back when I did what I was doing it wasn't really very prevalent. With the loss of so many audio dealers I don't even see how you can even sell through those channels any more? Perhaps there are a handful of real audio dealers left in Los Angeles and a few major cities like New York but most have just disappeared. I plan on doing all my sales through direct sales at this point. The only other option seems to be to tie into a celebrity and use the Dr. Dre marketing model, selling product based on name recognition and forget about sound quality which I am not interested in doing. I have to say I was in the book store the other day and even in the audio section they didn't even carry Stereophile anymore, just a few titles more to do with home recording and for musicians only. Not one audio magazine in sight! The store was Barnes and Noble!

I'm there. I'm living this. I think Europe and Asia are still running on a slightly more traditional audio business model. Asia has rapid growth in affluent classes. My wife has been to Germany and the UK and she said she has seen traditional vinyl shops quite often. As for here? well, online marketing. Unconditional return policy and give so much value that the customer will not want to take you up on it because there is no better value out there. It's a dirty job, but.....

 

[morinix]

Heck! all this marketing stuff! it just gets in the way of good engineering.

 

[31697B]

How do you generate such a signal? If I can generate it, i'll measure it.

-RNM

Now FFT has come up again, it reminds me of the last time it surfaced on this thread.

On the issue of the perfect reversibility of the transform between time and frequency domains, I many posts ago made the rather contrived joke that this was only true if one would have the mathematical formula for random noise. I still can see it flying over all heads. The point was of course that the statement of perfect reversibility is only true for discrete FFT. This may have some relevance for audio measurements, since it requires sampling of the measured signal, with an unavoidable associated loss of information. Also, a discrete FFT only produces data, to get information out requires trade-offs.

I mention it again because of what Pavel and Dick are posting. Thought experiment: what is the FFT of a Kaiser Wilhelm sine? With this I mean a sine with a spike on the upper-half (not to be confused with its mirror image, the wineglass sine).

Edit: I remember Scott posting at the time of the last discussion on some measurements that were developped to, if I remember correctly, identify a peculiar kind of one sided crossover distortion. Pretty much a Kaiser Wilhelm situation if my memory doesn't play tricks on me, but I didn't have time to read it with sufficient attention at the time. Could you please post again?

 

[tomtt]

didn't even carry Stereophile anymore, just a few titles more to do with home records only. Not one audio magazine in sight! The store was Barnes and Noble!

The barnes and noble in calabasas sells out of audio mags all to soon.

You might have arrived between last sale and next delivery ....

 

[Kindhornman]

tomtt,
Didn't know they had a Calabasas in Kansas! The Kardashian's probably bought all the copies or is that Justine Beeber?....

 

[31697B]

A decent PC, something basic in a sound card (I use an M-Audio 192), basic software like AudioTester (you can get fancier signal generation capability if you want to create oddball stimuli, then use the FT analysis in Audiotester to measure the output). A simple analog interface box to get levels and impedances correct for what you're measuring. Really, that's all you need. This has enormously better capability than the ultra-expensive stuff I used to work with when I was at Nicolet.

I have 4 similar products plus a few others to measure harmonics with --> Not counting an A-P (sys one/dual domain), scopes and assorted meters and bridges, plug-ins:





[/ATTACH]

 

[1audio]

Here is an idea I have been thinking about- It would be very possible to either generate or capture a long random noise file. The longer the better. Then play the file through a system and capture the output. Ideally simultaneously so sync is not an issue. It would test every possible transient and verify its output. Any deviation would be an error and the difference could be quantified along with the transient noise that triggered it. It would be a pretty through test of analog fidelity. You would want a noise file that represents the crest factor of the music you intend to use. The digital equivalent is a "Bit Error Rate Test". For an analog system you would need to correct for any frequency response/phase errors.

 

[31697B]

Cool. lets try it and learn what happens. I have a General Radio wide band random noise gen around here somewhere.

-Richard

 

[mikelm]

Here is an idea I have been thinking about- It would be very possible to either generate or capture a long random noise file. The longer the better. Then play the file through a system and capture the output. Ideally simultaneously so sync is not an issue. It would test every possible transient and verify its output. Any deviation would be an error and the difference could be quantified along with the transient noise that triggered it. It would be a pretty through test of analog fidelity. You would want a noise file that represents the crest factor of the music you intend to use. The digital equivalent is a "Bit Error Rate Test". For an analog system you would need to correct for any frequency response/phase errors.

This sounds like a great test and I would like to use such a test but I have couple of questions:

What softwear could be used analyse the differences between the original & amplified signals.

I wonder what the best method could be to "normalise" the two signals with regard to amplitude & phase so that a precise comparison could be. made. ( or do we think the amplifier dwell time would be insignificant ? )

edit: I imagine that many amps will add some non random noise into to mix so I think an A minus B FFT analysis would be very useful.

 

[1audio]

The flat delay through the chain would be simple to correct for. Frequency and associated phase response would require more active correction. It could be done analog or digitally.

I would make a 20 minute track so theres lots of variations. Then use something like a DAW to invert and add. The residual should highlight any differences. Read about using audio diffmaker here FLAC vs WAV Part 2 Final Results - Blogs - Computer Audiophile to get an idea of the comprison phase. Audio diffmaker may be a very good tool for this. Audio DiffMaker

 

[tomtt]

to either generate or capture a long random noise file. The longer the better.

indeed ...

tomtt,
Didn't know they had a Calabasas in Kansas!

most likely more than one

seems some are milking this -

Calabasas Pumpkin Festival

The Kardashian's probably bought all the copies or is that Justine Beeber?....

they may have.

since britney spears moved to thousand oaks,

(and took the paparazzi with her)

the kardashians own the place.

howie mandel, nikki sixx, the jackson bros. and steven spielberg,

are here in public, quite often, yet they are now 'old school',

and don't get as much attention ...

```````````````````````````````````````````

as for justin, he has competition -

https://www.google.com/search?q=cod...s=org.mozilla:en-US:official&client=firefox-a

``````````````````````````````````````````````````````````````````````

looks like amanda bynes is gettin some unflattering extra 15 min. -

#imnotcrazytho

 

[mikelm]

The flat delay through the chain would be simple to correct for. Frequency and associated phase response would require more active correction. It could be done analog or digitally.

I would make a 20 minute track so theres lots of variations. Then use something like a DAW to invert and add. The residual should highlight any differences. Read about using audio diffmaker here FLAC vs WAV Part 2 Final Results - Blogs - Computer Audiophile to get an idea of the comprison phase. Audio diffmaker may be a very good tool for this. Audio DiffMaker

Thanks Demian,

I'll check out the links

mike

 

[SY]

I have 4 similar products plus a few others to measure harmonics with --> Not counting an A-P (sys one/dual domain), scopes and assorted meters and bridges, plug-ins...

Yes, I have quite a bit of fancy R&S and Tek gear at my disposal, much newer than most of that stash. But for plain vanilla audio measurements (the sort which will rapidly determine whether a box of gain will be audibly transparent), the simple computer/sound-card/analog interface is what I turn to.

 

[DF96]

On the issue of the perfect reversibility of the transform between time and frequency domains, I many posts ago made the rather contrived joke that this was only true if one would have the mathematical formula for random noise. I still can see it flying over all heads. The point was of course that the statement of perfect reversibility is only true for discrete FFT.

FFT is necessarily always discrete; it converts time domain samples into frequency domain samples. Continuous Fourier transforms require analytic or analogue methods - but are then fully reversible too.

The Fourier transform of random noise (in the time domain) is (IIRC) random noise in the frequency domain. However, windowing may be a problem as for full accuracy you need to do it for ever. Reversibility is not lost with a finite time, though - all that happens is that the input sample (for a finite time) gets turned by a double transform into a periodic function with period equal to the original sample period. As you have no knowledge of or interest in the input signal outside this time you simply truncate and look at one period.

Playing random noise through a system will give you lots of data but almost no information. With a good system almost all the difference will be due to filters (not 'delay'). Remaining differences will be rather difficult to interpret - perhaps some sort of modelling and data fitting might help but I suspect all it would do is confirm (within experimental/sampling error) that nothing strange is happening. Playing a long PRBS will give a bit more information: control engineers have been using this method to characterise industrial plant for decades.

So noise testing has two problems:
1. any difference may be difficult to explain
2. lack of difference may be due to you not exciting an amplifier weakness - would need to repeat with a different noise pattern but you could never guarantee completeness (like software black box testing)

 

[jacco vermeulen]

for plain vanilla

A Madell/SMTmax curve tracer handles 2.5A at 20V, not really accurate, sold for >$350.
Cheaper means a Leader LTC-905 that can be connected to a scope, 50 bucks and up, but measures not higher than at 0.1A

Just got me the last of Locky's curve tracer boards, ~$90, handles 2.5A, USB connection and screen size options for the blind.
(also saves on hauling of a 50lb boat anchor with a 4''x5'' screen)

 

[gpapag]

Some participants here had an early overdose of top range instruments.
As for me (deep down in the mud), I would be in heaven had I have a 500MHz dual trace oscilloscope with a Yout, and 2 pairs of good probes (the card I already have).

Noise testing has been discussed again with enough linking. What more info is needed ?

Thought experiment: what is the FFT of a Kaiser Wilhelm sine? With this I mean a sine with a spike on the upper-half (not to be confused with its mirror image, the wineglass sine).

I googled for it and what I found is enough to explain the absurdity of the proposed waveform

Give me a woman who truly loves beer, and I will conquer the world. -- Kaiser Wilhelm II (1859-1941)

George

 

[simon7000]

Also please separate particular hardware implementations from the algorithm. No problem generating a digital sine wave and displaying the FFT to, let's see, double precision is about -300dB. In practice it's more in the ~ -200dB's.

At first I misread this to mean you were able to generate sine waves at -200!

Of course you meant the discrete numeric values in computational use.

Just for a reality check a 10 ohm source resistor has 104 pV/rt Hz of noise so for a 1 Hz bandwidth 300 db above that would be 104,000 volts! Now how you would get a 1 Hz bandwidth is a bit of an issue.

Of course for a 100 kHz bandwidth the noise would be 32.9 nV so with only 200 dB of range you would need only 329 volts out.

So a "practical" generator with a more typical 50 ohm output at 15 volts would be limited to 166 db with a noise bandwidth of 100 kHz.

Now to find an A/D converter with 27 bits of accuracy at 200 kHz to analyze this in a single sample would be a nice find!

In practical measurement technique digital scopes are aimed at fewer bits and higher speeds. Audio A/D's at more bits and lower speed, but I have yet to find better than 22 bits at 200 kHz and that was a discrete design.

So the approach I have been using is to reduce the need for such accuracy by using bridge or other techniques.

Now there are lots of useful stuff you can do with what are today basic simple measurements, but trying to get it all at once is asking for too much.

ES