• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Merlin's new hi-fi valve preamp book is released

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#42
I'll withhold most comment until my review in Linear Audio appears, though I think anyone who has read the things I've written will be able to guess my impressions.😀 However, one question keeps popping into my mind- with the availability of tools like the AP (whence the excellent and useful distortion vs level and distortion vs frequency plots are derived), why are the distortion spectra shown as screen caps from a Rigol scope? They are difficult to read and interpret, and frankly look much poorer than what an AP or even a sound card plus ARTA or VIRTINS can give. Given the rigorous engineering approach taken, there must be something I'm missing...
 
#43
SY said:
with the availability of tools like the AP, why are the distortion spectra shown as screen caps from a Rigol scope?
Click to expand...
The AP1 doesn't do FFT, and it's runing on an old Windows 95 machine that is unlikely to cope with any modern software. The Rigol is what I had on the desk. I'm not sure what you're trying to 'read' from the FFTs though? They are only meant to show relative harmonic levels, not absolute values.
 
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#44
I just received a copy and read the first few pages. Really easy to follow and very well written, totally recommendable so far.

Loved the guitar preamp book, and am so sorry I missed the out of print psu book. If someone's got it and is willing to lend it... 😀

Thank you Merlin. Congrats for your site and books. Best of luck with your new one.

Cheers,
Fran
 
#46
The AP S1 comes in several flavors; there's the pure analog ones, and there's the 'S1 + DSP' ones which DO FFT and such.

But I share SY's sentiment, spending lots of time and effort on getting the graphs for Linear Audio come out crisp and clear.
Even with a Rigol, exporting the data and graphing with 3rd-party graphing software gives you much greater control.

OTOH, the current graphs in the book add some nice retro-look appearance 😉

Jan
 
#48
Merlin, spend several hours this weekend reading your book. It's much more than 'just' a preamp book - it has a lot of interesting ideas, methods, tricks and good advice. I love it.

(Sorry SY not wanting to steal your thunder ;-)

BTW I guess you're hard at work on the Tube Power Amp book?

Jan
 
#51
Just got mine through Amazon. I really like the background intro. I'm trained as a chemical engineer and know the math and have been an electronics hobbyist for nearly 40 years, but I found things I hadn't considered before right at the start where "current" is defined, and later with a conceptual description of complex numbers that's a lot clearer than the version I learned in school. Nice.

BTW, I have a professional interest in the book itself, as I work for a manufacturer of high-end commercial digital presses and have visited many book printers and even designed a few production systems for them. It would have been nice to have a title on the case of the book, but I suppose that would have been extra $$$. As is it's kind of amusing to see that the dust cover was localized to 'merican ("tube") while inside it's all about valves 🙂

I also like the touches of light humor, which if you will pardon my stereotyping seems like a British habit that we could use over here (especially this election year...)
 
#55
geezertron said:
Just got mine through Amazon. I really like the background intro. I'm trained as a chemical engineer and know the math and have been an electronics hobbyist for nearly 40 years,
Click to expand...

Not a chemical engineer here, but chemist and follower of the chemical industry stocks for 40+ years -- it's a good thing Merlin didn't write our Organic Chemistry text (Morrison and Boyd, still have it) or I would have been a doctor complaining about Medicare reimbursement.
 
#56
there must be something missing

SY said:
I'll withhold most comment until my review in Linear Audio appears, though I think anyone who has read the things I've written will be able to guess my impressions.😀 However, one question keeps popping into my mind- with the availability of tools like the AP (whence the excellent and useful distortion vs level and distortion vs frequency plots are derived), why are the distortion spectra shown as screen caps from a Rigol scope? They are difficult to read and interpret, and frankly look much poorer than what an AP or even a sound card plus ARTA or VIRTINS can give. Given the rigorous engineering approach taken, there must be something I'm missing...
Click to expand...

Hello All,

I went to Amazon and purchased the book. The author seems to have a good feel for valves and some strong opinions to boot.

Amazon has some sample pages of the book posted.

http://www.valvewizard.co.uk/DHFVP_sample.pdf

Take a look at Fig. 2.11 on the second page of the above pdf. Figure 2.11 is one of those Rigol oscilloscope FFT plots that SY was scratching his head about.

I looked up the data sheet for a Rigol DS1102E oscilloscope, this oscilloscope like most oscilloscopes is a 8 bit instrument. Doing the math, 8 bits gives us 256 steps from minimum to maximum range, each step is 0.3906%. This means that the maximum resolution (at best) is 0.3906% or about -68db at the bottom of the range.

Looking again at Figure 2.11 on the right side counting down 10db per division from the top the noise floor is right at the -68db that we would expect for a 8 bit instrument. Now at the 3K Hz peak in the curve counting down from the top of the plot to the peak we are about 26db down. -26db is about equal to 5% noise + distortion not the 0.008% referenced by the author.

What appears to be missing is precision and accuracy.

DT
 
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#58
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Stoked. Easter reading sorted.

Sent from my GT-I9300 using Tapatalk
 
#59
Hello Merlin, and All as there is interest,

I am reading the distortion testing procedure you layout on page 230 of your new book.

Please share if you will the procedure that you use to connect and operate the Rigol DS1102E oscilloscope. From text in you book it sounds like the AP-1 has an output (sans the 1K Hz fundamental) that connects to channel 1 or 2 of the DS1102E oscilloscope.

I have a Rigol DS1102E oscilloscope and a Keysight U8903B Audio Analyzer sitting on my bench. I am interested in running tests on similar tube circuits. (SRPP and Half mu circuits)

Thanks
DT
 
#60
Ordered my copy today.

My copy of the Guitar an Bass preamp is getting very "dog eared" from extensive use. I'm doing a 2 channnel with footswitch GIT amp now with a Fenderish Clean Channel and Merlins fav. High gain Preamp as the LEAD channel. All 6SL7 rather than 12AX7 with a PP 6V6 power amp based upon my Baby Huey HiFi Power Amp. Will do a thread over at Instruments and Amps for that eventually and let you know how it turns out.

The problem with Digital CRO's and distortion analysis is that even thou' they do FFT they are limited by the 8 bit digitisation. Anything below about -40dB you are not going to see.
I have that same Rigol CRO.

Cheers,
Ian
 
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