John Curl's Blowtorch preamplifier

[Trevor White]

Originally posted by john curl
Trevor, please show me where the 4558 is that much better than the 741 of yesteryear.
Please show proof. Please also show me where IC's, better than the 5532, are used in typical audio equipment.

John, the 4558 is old technology.

What does typical audio equipment mean ?? That could mean anything.

If you mean a cheap DVD or CD player then of course you will only find 4558's in them

The underlying debate here from your side of the camp is that compared to a discrete design, modern high performance op-amps add artifacts to the sound that can't be measured.

regards
trev

[Bob Cordell]

Originally posted by john curl
PMA, such idealism is commendable, but we cannot always make discrete designs. That is why I am working with such op amps today, rather than a completely discrete design on two projects almost ready for the marketplace.
Please understand what I care most about: The existence of SOME FM distortion, comparable to other distortions. That is all that I am concerned about at the moment. The BEST IC's that nobody can afford in production, except hi end designers, may measure nearly perfectly, BUT what about the 741 clones inside of more complex arrays? Or the 4558's or their equivalent, used by SONY and many others, over the years in their CD, and DVD players? What does Mackie use these days? What about a 5532, can we measure something there?
Now, if FM distortion has the same weight as 3rd harmonic or even 5th harmonic on the subjective scale, then so what? However, IF we happen to be MORE sensitive to PIM, more like 7th harmonic, then WOW!

John,

As you know, PIM and FM distortion are one in the same. One is just the integral of the other. The PIM thing has been beaten to death. You've never measured PIM, so how do you know that PIM is less in a discrete design?

Here is an important point. According to theory and measurement, PIM cannot exist in ordinary designs in the absence of amplitude intermodulation distortion. The key, then is to use devices that measure very low distortion in the conventional measurements. That is going to rule out/ weed out 741-like designs that are buried in chips or equipment.

It is almost inconceivable that an op amp that measures below 0.001% THD-20, CCIF IM and SMPTE IM can have any significant amount of PIM.

There is a caveat. I don't think that one can rule out the existence of PIM in designs that exhibit higher levels of conventional distortions, whether those distortions are benign or not. An example there might be vacuum tube amplifiers, where the higher, but perhaps benign conventional distortions would tend to mask an inference of low PIM. There I think the only option is to actually measure it. I have never measured PIM in a tube amplifier, but it might be interesting to do. One might be able to make an argument that tube amplifiers may have significant PIM as a result of the quasi-saturation that high-amplitude low-frequency signals cause in the output transformer.

Cheers,
Bob

[PMA]

IMO it is time to remind very good paper by Walt:

http://waltjung.org/PDFs/SID_TIM_TAA77_P3.pdf

[anatech]

Hi John, all,
I split out the posts relating to test equipment to this thread.

As I am interested in this and I feel that many other people who do have this issue (older test equipment), I'm asking for any help or suggestions in that new thread.

I didn't intend to have that discussion in this thread John, a new thread was my intention all along.

-Chris

[anatech]

Hi John,
This current thread is impossibly long now. Doing any maintenance work is difficult as a result. I am going to lock this thread and begin a new one for you, but not until I return after an appointment I have to keep.

Can you do me a favor then? Let me know where you would like this new thread to start. I'll split at that point, but keep this within 20 posts of this point please.

I feel that this also presents an excellent opportunity to get back on track to talk about the Blowtorch preamp you designed.

-Chris

[anatech]

New thread is here.
This one is locked.

-Chris