John Curl's Blowtorch preamplifier part II

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#90,481
PMA said:
AD825 "sounds good", but has limitations:

- very low OLG so it is good only for low gain like 1 - 10
- quite high noise which makes it suitable only for gain 1x, as a link stage
- not very low distortion

So the only advantage is the JFET input stage. I was playing with this opamp in 2002 and then abandoned it.

If John likes it so much, then I would like to turn his attention into ADA4898
ADA4898-2 Datasheet and Product Info | Analog Devices
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As far as I can see, the '4898 doesn't have the crossover distortion enhancing cap load countermeasure, so John probably doesn't like it 🙂

Jn
 
#90,484
1audio said:
SID: Slew Induced Distortion (I assume your not asking about an old relative).

Slew rate can mean two things. Max rate of change where the internal circuitry is mostly saturated or max rate of change where feedback still has some control. Outside of audio slew rate was figured as 3% distortion at full output converted to V/uS. In practice its really hard to see legitimate audio getting near either limit. Mistracking, EMI, RFI, DAC outputs etc. are another story.
Click to expand...

I forgot what the acronym meant.
 
#90,486
Hi jcx,
so you are really thanking John for being wrong all these years and continuing to mislead on the issue in the face of overwhelming technical analysis, peer reviewed publications AND measured hardware
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Nope. I thanked John for drawing my attention to the fact that the capacitance in the gate to drain might fluctuate with varying signal. Normally I use cascode connections to reduce this problem and I didn't recognise that they didn't exist. I had to have another look at the circuit we were referring to and give my head a shake.

I may disagree with someone mostly, but I will thank them if they point out a mistake on my part. In this case, John might very well be correct. I don't particularly feel like building this circuit and proving his concept one way or another. I have too much on my plate right now as it is.

-Chris
 
#90,489
Destroyer OS said:
I recently got a vinyl copy of Nirvana Unplugged. The CD version has higher dyanmics in the voice, believe it or not... The vinyl has more bass and power in the instruments though.
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Vinyl cut from digital sources has soft top end. I keep saying this. That's why Kurt's vocals are less lively on the unplugged. Too bad! That would have been a great performance to have sourced from R2R tape.
 
#90,490
PMA, thanks for your input, but you forgot to note that the circuit is 40 years old! There were NO 389, 109, or any really complementary high Gm parts available at the time. IF you change the output devices, you have to also change the SOURCE RESISTORS, perhaps, in this case to 10 ohms or so. And then you have to start with higher Idss parts like the SILICONIX J113, and J271 that were available at the time, I made over 100 of these work successfully.
 
#90,491
Robert, the funny thing is despite that, I can understand the conversations with the band that aren't mic'd, much better. I think the vinyl came out better overall, but I don't have any high-res files. The lack of timbre in digital is one of the biggest reasons I like vinyl on just the sonic quality topic.
 
#90,492
john curl said:
IF you change the output devices, you have to also change the SOURCE RESISTORS, perhaps, in this case to 10 ohms or so.
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That's absolutely correct, and use it as self-bias. I was just curious, I do not assume I would optimize the circuit. As you have stated, the circuit is 40 years old and there is almost no reason to use this circuit today. However, an interesting reminder of the circuit design history, thank you for that.
 
#90,497
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#90,498
morinix said:
Vinyl cut from digital sources has soft top end. I keep saying this. That's why Kurt's vocals are less lively on the unplugged. Too bad! That would have been a great performance to have sourced from R2R tape.
Click to expand...

That may have been the case so far, or up to some point, particularly with early digital. Using high quality hi-rez converters, it shouldn't necessarily be a problem forever. They can produce very extended and detailed highs, so no clear reason why vinyl should suffer. Unfortunately, not everybody updates their A/Ds with the best as soon as they become available. Over time that should improve, though.
 
#90,499
I can't confirm that there's any relation to Nirvana's problems from being digital to analog conversion. Frankly I just think the mix is a little low in the vocals, and/or nominalized a little. But the CD may also simply be a little less authentic.

It appears I'm not the only one who liked it, sonically, and no one's 100% whether it was digital/tape either. Wait, actually mine is by Geffen, so it's not that same perhaps.
 
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#90,500
Maybe they compressed and limited the CD in mastering more to make it louder for radio play. If so, that wouldn't necessarily indicate a problem with digital technology, it could be more of a problem with record company executives.
 
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