John Curl's Blowtorch preamplifier

[anatech]

Hi Lumba,
I have to disagree with you sir. It's far easier to sell products when there are no specifications to guide anyone. You have to agree that it's pretty simple to design something with decent specs and good sonics these days.

Look at this another way. If the specs are not good enough, the interested buyer probably doesn't have enough money anyway!

Hi Bear,

Doh! I mean here's an idea, back to the Blowtorch.

Yes!

Let's go friends, where are the sims?
Where are the real world tests?

I had no intentions of going there. I just felt that John would have an easier time of keeping things focused on what he built and why he did certain things. Never having seen one, I think a look at what made this preamp tick would be instructional.

PS. please take the discussion of reviews and amplifier purchases off to another place? Thanks...

Oh! Fer sure!!!
There are far better places to talk about that.

PPS. Hoping Trevor will help us set up and perform that input/output comparison test, still... <holds breath>

Y'all lost me there.

Hi Joshua,

Also, Tektronix 2465B.

Designing for 100 MHz or better is an entirely different thing. Even the 40 MHz bandwidth of the 3585A is pushing things quite a bit. I just threw that in for a faint hope on these. Mind you, a low noise preamp that would extend the S/N down past the 80 dB limit it now has would be great. Such a preamplifier would work with your 'scope also, but not to full bandwidth.

Oh boy! You speculate about a person you don't know at all.

I think that getting personal about some posts only serves to distract the attention of the thread. Jan was not criticizing you, he was only pointing out how wide a definition can be taken about your earlier comments. His response should be taken as an impersonal comment. Often, we use the word "you" to designate every reader very generally. You (meaning Joshua now) took his examples to be a specific comment on you personally.

It would be nice to keep responses and comments to technical points. I think we have all seen enough personal shots to last us a lifetime, and that's in this one thread only!

-Chris

[Wavebourn]

Originally posted by Lumba Ogir
Hi,
since specifications do not relate to sound quality, only fit (and have been used) to fool the buying public, it would be more honest not to provide any.

I understand Lumba, it is a new joke of your humor again, since it is too brought generalization. Specifications do relate to sound quality. What does not relate, irrelevant specifications, here I agree with you absolutely. Many of them very often are used to mislead potential buyers.

Do you have an idea what specifications may be relevant? Let's try to find together if there are some correlations between sound reproduction quality and specifications? There should be some, I still hope.

Let's take several amps, some of them reproduce sounds nice, another sounds more artificial, measure, compare, then try to figure out correlations. It's the way that is used by NLP to model experiences and strategies of people without needs to know how exactly perceptions and thinking works. Write down everything, then discard steps one by one. If after discarding some step it does not work the step is needed. And so on.

[anatech]

Hi Anatoliy,
The problem is that most people would not understand such specifications. But, I do agree with you. The basics such as output power into both 8 and 4 ohms, plus signal to noise ratio are a good start. These things do pass on meaningful information. THD at three frequencies would be nice as a minimum spec everyone should supply, and at two power levels (low and higher but not just before clipping). Then there are a number of factors that could provide additional, meaningful information.

You know what I'd like to see almost more than anything else? How about a well designed chassis, good minimal soldering work and some way to limit how small or cheaply a heat sink is.

All these things add value to a purchase for the consumer. An anti-garbage law would be very welcome.

I guess we are trying to enforce ethical marketing and selling practices. We have to get back to looking at the intent in any advertising. Have fun with that. Never forget too that most people shop on price.

-Chris

[Wavebourn]

Originally posted by anatech
Hi Anatoliy,
The problem is that most people would not understand such specifications. But, I do agree with you. The basics such as output power into both 8 and 4 ohms, plus signal to noise ratio are a good start. These things do pass on meaningful information. THD at three frequencies would be nice as a minimum spec everyone should supply, and at two power levels (low and higher but not just before clipping). Then there are a number of factors that could provide additional, meaningful information.

Graphs would be preferable, to see how things change in dynamics. For example, speaking of harmonic distortions (I don't mean we have to be limited by them!) it would be nice to show a waterfall, with frequency, output power, and level of harmonics.

You know what I'd like to see almost more than anything else? How about a well designed chassis, good minimal soldering work and some way to limit how small or cheaply a heat sink is.

This specs of course are reflected indirectly on prices, cost of repair, , MTBF, and reliability. What I mean, to find specs that correlate with quality of sound reproduction.

All these things add value to a purchase for the consumer. An anti-garbage law would be very welcome.

What do you mean? Anti-recycling law?

I guess we are trying to enforce ethical marketing and selling practices. We have to get back to looking at the intent in any advertising. Have fun with that. Never forget too that most people shop on price.

I did not have such an intention, however everything you write is very significant and is defined by exploitation conditions. What I meant, simply to find measurable differences between equipments that sound real, and that sounds artificial. Lumba Ogir dismisses all specs as if they don't reflect reproduction quality, while I do still believe that such specs are very possible if to search for them honestly and thoroughly.

[PMA]

Originally posted by bear
[B]

Let's someone test a moderne ultra low distortion audio opamp or two with the square/sine test and let's see the perfection!!

_-_-bear

Bear, you would see nothing in an opamp like THS3001, I can make you absolutely sure.

In fact the DIM100 3.18kHz + 15kHz test is very easy to fulfill for modern really fast devices.

On the other hand, I do strongly agree that there are still issues in sound of very good opamps. The DIM100 is not the explanation, I am very sure.

[janneman]

Originally posted by Joshua_G
[snip]Now, you said I was biased because of I read 1 user's review on this amp.
Obviously you don't know me and my attitude to reviews.[snip]

Sure, but it is reasonable to say that if you hadn't read that review, you would not have bought that amp. You auditioned that amp based on the review you read.

Jan Didden

[Wavebourn]

Originally posted by PMA


Bear, you would see nothing in an opamp like THS3001, I can make you absolutely sure.

In fact the DIM100 3.18kHz + 15kHz test is very easy to fulfill for modern really fast devices.

On the other hand, I do strongly agree that there are still issues in sound of very good opamps. The DIM100 is not the explanation, I am very sure.

Earl R. Geddes and Lidia W. Lee even gave a name to the new metric that can give you a clue, despite they did not discuss frequency dependent measurements.

[PMA]

Thanks Anatoliy, I know their work.

[Wavebourn]

Originally posted by PMA
Thanks Anatoliy, I know their work.

I mean, correlation between numbers and their impact on audibility. In short, Absolute percentages are obsolete. If to weight them against perceptibility some very small mice are much bigger than other big elephants.

[PMA]

Yes, I got it. Also measured spectra at very low levels.