John Curl's Blowtorch preamplifier

[Edmond Stuart]

Very good Edmond, you get a gold star. You are only off by a factor of 2 or so, due to the amplitude loss across the fet follower, itself. Fire up the simulators gentlemen, and get me an exact value. Cap value changes are OK, as well

BTW John, I was not only 'a factor of 2 or so' wrong, rather a factor of 4.
BUT.... it has nothing to do with the fet followers.
It's R39=33k (of the servo) that spoils the balance. In this case the correct value of the input series resistor is ~15k5.
Without that evil R39 and using two identical input buffers, the input series resistor should have the same value as R40, 3k83 (3k43 was a typo).

 

[PMA]

Back to the trees; is this low, or high distortion?

 

[syn08]

Don't get your hopes "up" too high, it could be a temporary thing, Mr Ovidiu.

[OT]
Resistance is futile. You will be assimilated.
[/OT]

 

[SY]

BTW, has JC ever shown a schematic? No! One more reason to not drop a schematic.

Short memory. The JC-1 was up yesterday. John didn't actually post it (he doesn't have a way of hosting it), but he sent it to me to post. This wasn't the first one I put up for him, and there's another one coming a little bit later.

 

[Sigurd Ruschkow]

To me it is low enough. Nice harmonics envelope, too.
Low or high is a matter of reference.

What happens if you load it a bit harder?

Do your models of the MOSFETs simulate distortion correctly?


Sigurd

Back to the trees; is this low, or high distortion?

 

[Edmond Stuart]

Back to the trees; is this low, or high distortion?

1. Since when is CMRR not a 'tree'? Also, it's not up to you who determines whether CMRR is an unimportant issue.

2. This distortion sim of the IPS is meaningless without simulating the (non-linear?) input impedance of the OPS as well.

3. Almost every mid-fi amp scores quite well at 1kHz. So, I'm not really impressed. Besides, you should also look at worst case conditions: above 10kHz or so, where the real troubles start.

 

[Edmond Stuart]

This REV F is missing +IN/-IN input resistors (R + R//C), that carefully balance for impedance mismatch.
.......

So what are the exact values of these missing components? Or even better, show us a schematic, so I can verify if the IPS is indeed carefully balanced, instead of wasting my time on an incomplete schematic.

 

[john curl]

Actually, Edmond, I scaled the input impedance to 50K, instead of 100K. Now, what value do you get?

 

[Edmond Stuart]

Short memory. The JC-1 was up yesterday. John didn't actually post it (he doesn't have a way of hosting it), but he sent it to me to post. This wasn't the first one I put up for him, and there's another one coming a little bit later.

Stuart, I didn't know that. Instead, I thought that someone has reverse engineered the JC1, because the schematic came (misleadingly) from another website (yours in fact). Besides, why didn't JC drop the schematic by himself. If I can do it (see below) he can do it too.

 

[Edmond Stuart]

Actually, Edmond, I scaled the input impedance to 50K, instead of 100K. Now, what value do you get?

Suppose that R82=43k, I get 6k73 (then the input impedance is 49k73, almost 50k).

 

[PMA]

3. Almost every mid-fi amp scores quite well at 1kHz. So, I'm not really impressed. Besides, you should also look at worst case conditions: above 10kHz or so, where the real troubles start.

No, they do not do at 80Vp, and they have high order harmonics.

 

[PMA]

Do your models of the MOSFETs simulate distortion correctly?

[/B]

This is the weakest point, also for slew rate analyze. Just enough for rough estimation. I like these circuits, they have nice behaviour with low components count, elegant and clever.

Not a boost of current mirrors and CCS. Active CCS and mirrors have their dynamic behaviour, when I designed my preamp and compared, the resistor biased, highly degenerated version was the best and that one was actually produced.

 

[Edmond Stuart]

No, they do not do at 80Vp, and they have high order harmonics.

Okay, not 80V, but you and I were talking about distortion in the first place. In the mean time, I've simmed the front-end of Self's blameless amp. As you know a very simple amp and by some considered as mid-fi.

At Vo = 41Vpk (not Vpp) and 1kHz, I get 0.5ppm (when doing it your way). Almost all 3rd harmonic. As you see, 'slightly less' than the JC1.

If I simmed it the correct way, i.e. also connect the OPS to the VAS, then I get 0.8ppm, mainly 2nd and 3rd harmonics. The 7th harm. is 8ppb.

 

[SY]

Besides, why didn't JC drop the schematic by himself. If I can do it (see below) he can do it too.

There's probably a lot of things you can do that I can't, either.

Anyway, here's the latest from John.

www.syclotron.com/old_2200_.jpeg

 

[PMA]

Edmond, why do you mislead with Vp-p? I had 80Vp, i.e. 160Vp-p.

41Vpeak is here:

P.S.: this is about nothing. These parameters, in such level, are unimportant and inaudible.

 

[Sigurd Ruschkow]

I like these circuits, too. They are elegant in their simplicity.
Borbely uses this design, too. For both line and power amps.
See attachment for his Millenium power amp.

MKV-models of MOSFETs give more accurate distortion simulations, AFAIK. Not many around, though.
andy_c or syn8 made some for output MOSETEs.



Sigurd

This is the weakest point, also for slew rate analyze. Just enough for rough estimation. I like these circuits, they have nice behaviour with low components count, elegant and clever.

Not a boost of current mirrors and CCS. Active CCS and mirrors have their dynamic behaviour, when I designed my preamp and compared, the resistor biased, highly degenerated version was the best and that one was actually produced.

 

[syn08]

andy_c or syn8 made some for output MOSETEs.

andy - not me.

 

[Edmond Stuart]

Edmond, why do you mislead with Vp-p? I had 80Vp, i.e. 160Vp-p.

41Vpeak is here:

P.S.: this is about nothing. These parameters, in such level, are unimportant and inaudible.

1. Me, misleading? Quite the opposite I would think. I wrote Vpk, meaning the peak amplitude as you probably know and to avoid any confusion with the peak to peak value, I added 'not Vpp'. Apparently for people like you, not clear enough. I'm deeply sorry.

2. It's becoming an annoying habit of you by suddenly declaring it as 'unimportant' whenever I drop comments you dislike. Moreover, if it's really that unimportant, why you have simulated the distortion anyhow?

3. I insist that I'm not impressed by your figures, as even the blameless front end (in terms of distortion) performs better.

 

[syn08]

P.S.: this is about nothing. These parameters, in such level, are unimportant and inaudible.

I agree. Using unbleached cotton insulated, solid silver wiring is way more important (and audible).

 

[Edmond Stuart]

I agree. Using unbleached cotton insulated, solid silver wiring is way more important (and audible).