John Curl's Blowtorch preamplifier

[cbdb]

Much to our detriment. If one thinks that IC's have no place in audio, then what does that say about surface mount electronics?

Considering 90% of the music you listen to has been thru as many as 20 op-amps before mastering, good luck trying to listen to music thats IC free.

 

[KBK]

I listen to a lot of electronic/trance/ambient/acid/reggae/dub, so most/some of it has actually never seen an analog op-amp unless I show it one.

Other than that, it's LP's. Some of which have never seen anything but a tube amp at any given circuit location (Basie, Joe Williams, etc) , until they meet my discrete SS stuff at playback. It's all over the map, at best. I tend to not like the sound of the overly processed 70's-80's stuff, due to those 20 op-amps. We each deal with it as we may. 🙂

 

[PMA]

There is still a question how to get the best sound from the recording. You probably wouldn't believe me, but it matters how you do it.

 

[h_a]

Thanks for your replies!

How about your MOSFET amp and the FQAxxxx's?

My amp? harhar 😀 😀

pcb-artwork for

amp DONE
dc-protection w anti-thumb DONE
PSU DONE

Ordering semiconductors and stuff DONE
Order heatsinks, HEAVY METAL -> IN THE WORKS

Waiting for assembly and fun!!

Thanks for asking, all the best, Hannes

 

[cbdb]

I listen to a lot of electronic/trance/ambient/acid/reggae/dub, so most/some of it has actually never seen an analog op-amp unless I show it one.

Other than that, it's LP's. Some of which have never seen anything but a tube amp at any given circuit location, until they meet my discrete SS stuff at playback.

So you know how all this music was recorded and mixed and mastered?

 

[cbdb]

There is still a question how to get the best sound from the recording.

Agreed, but how much can one more good opamp change the sound? (compared to discrete?) And were back to the "whats best sound mean" debate

 

[KBK]

It would be best to circle around to understanding what is important to the ear - first.

Figure it out..then...Design for that critera- second.

Then try to correlate what we hear in the new designs ...to that ear's desire -third.

And so on.

 

[john curl]

Much of the best audio is relatively op amp free. We don't use just ANY recordings for evaluation, and don't pretend to make ANY recording sound great. However, with the BEST recordings, we find that op amps usually compromise the sound quality. This is true in almost every case. Why do you think we make discrete designs, or even use tubes?
I have monitored IC's for the last 42 years, longer than some IC designers. I have TRIED to make truly exceptional sound with them, and have failed to do so. I am even TRYING to make an exceptional phono stage with all IC's, including Scott Wurcer's AD797. I hope it works out. Measures OK. I do keep trying, but I find that I can barely keep up with tubes, by using elaborate discrete complementary designs. This is why I am so outspoken about the subject.
For example, I didn't see Scott at the CES show. He could not point out to me any really successful IC based amp or preamp even if he had attended the show. I heard some tube equipment that made me envious, even though they were too costly for anyone that I know, and I would have difficulty making the same thing in solid state. However, it might be that Nelson Pass has come close with his approach. You might note that Nelson got 'Poweramp of the year' in the latest 'The Absolute Sound' and I got 'Preamp of the year' in the same issue. Maybe, just maybe, we know what we are doing, and it would be useful for others to take heed.
By the way, Parasound doesn't advertise in either 'The Absolute Sound' or 'Stereophile'.

 

[KBK]

Don't quote me on it, but I don't believe Nelson does, either.

We (at one company at least) do not believe in 'Preaching to the Pew', which means advertising in magazines and places that already know of your existence. A waste of money, IMO. Depending on the given rag, it can be between $5-10k per full page, which can get expensive rather quickly.

 

[scott wurcer]

And if the amps were exactly the same, equally fast, but had 40 dB more DC gain:
That would really make them unsuitable. 100 times lower open loop frequency.
How horrible.

Yes that's exactly where things ended up. Putting a resistor on the VAS to kill the open loop gain "greatly improves" the sound, "why don't we bring out the VAS pin on all our amplifiers? yadda, yadda."

 

[andy_c]

Can anyone steer me to these equations?

Sure. There's links to a bunch of articles by Barrie on this page. The one that's been discussed at length here regarding PIM is the article called Are Op-Amps Really Linear?.

Also, regarding Barrie's view of the open-loop bandwidth issue, he makes some interesting comments in Spicing Up The Op-Amp. Here's the pertinent quote (bold items per his text):

By Barrie Gilbert
So, is there a better way to model an "ideal OPA?" I think there is. As noted in an earlier column, the model that fits reality quite well is that of an integrator. This is only approximated for a practical OPA by using the transfer function:

A(s) = AO/(1+sTO)

The problem with this model, to my mind, is that it introduces two rather artificial parameters: the dc or zero-frequency (ZF) gain AO, and the open-loop corner frequency defined by wO = 1/TO. Neither of these are very important in practice: there will usually be an immeasurable impact on performance when replacing an OPA with an AO of, say, 100,000 with one having AO = 10,000,000, provided the gain-bandwidth product is the same for both OPAs. The artificiality of TO is quite apparent here: it would differ by a factor of 100 between these two cases, without any effect on the ac behavior!

 

[john curl]

Best idea you have put forth all month, Scott.

 

[PMA]

How inherently linear is your open loop structure? (to Scott Wurcer)

 

[scott wurcer]

For example, I didn't see Scott at the CES show. He could not point out to me any really successful IC based amp or preamp even if he had attended the show.

We had several folks there but they avoid the high end rooms. I'm actually working on computer games these days, more money in it.

 

[john curl]

Of course they avoided the hi end rooms. We are all 'crazy'!

 

[PMA]

If working on computer games, does it make any sense to assess high end audio circuits? 😉

 

[KBK]

I just read a bit at the start (industry news area) of January 2009 of stereophile mag.

There's a report on 'Burning Amp.' I'm gratified to see that my efforts over at the Stereophile forum have not been for naught. I have mentioned the reason for the existence of DIYAudio.com and how important it is for the future of High End Audio..on multiple occasions at the Stereophile forum. How the guys here, like John and Nelson Do give away what they can of what they know -- as it is quite important to do so, even in the face of derision, arguments, and fights that we here may get into.

For without that there might not be any 'high quality' audio gear in the future, and to have that future it must be a commercial success and we must help create the next great names in Audio.

Somebody was listening.

 

[scott wurcer]

PMA - Nothing special just an undegenerated diff-pair but lots of gain-BW.


Thanks andy - Barrie says what I thought he said.

 

[scott wurcer]

If working on computer games, does it make any sense to assess high end audio circuits? 😉

Remember as John said my circuits are hobby circuits anyway.

 

[Edmond Stuart]

Yes that's exactly where things ended up. Putting a resistor on the VAS to kill the open loop gain "greatly improves" the sound, "why don't we bring out the VAS pin on all our amplifiers? yadda, yadda."

A degrading pin. A brilliant idea Scott.

Regards,
Edmond.