John Curl's Blowtorch preamplifier

[jan.didden]

Yeah, bad drivers are everywhere

Jan Didden

[Wavebourn]

Originally posted by janneman
Yeah, bad drivers are everywhere

Except Oregon, probably. Drivers there are very disciplined.

[john curl]

Actually, Wavebourn, you are showing your ignorance. CCIF two tone distortion is very important in this case, because the IM difference tone is going to be amplified (effectively) by the RIAA EQ. that can be as much as 40dB. Therefore, a 50Hz difference tone, for example, might be multiplied from .01% to almost 1%. This effect was noted by AMPEX many decades ago, even before my time, with analog tape reproduction. My reference is: J.G.(Jay) McKnight, AES member, and available in the bay area to clue you in.
For those who have some academic background and interest, this problem is why I switched over to complementary jfets, back in 1981, after successfully getting the same noise performance from bipolar transistors for about 8 years, with a patented and proven topology. The open loop performance was 10-100 times better with distortion cancellation due to complementary design, than my earlier effort.
While a paralleled row of fets will give low noise, the inherent distortion is very high, and it will be amplified out of proportion by the RIAA network with some inputs. This is what makes a Vendetta design exceptional, not its nominal noise, which is noteworthy, but not exceptional.
Making negative references to Jack Bybee in this context, just confuses people, and is completely just a random attack on someone, whom you have never met, but I might introduce you to his cousin ( also named Jack Bybee) who is his lawyer, and who lives in Walnut Creek. I have met him and had lunch with him, and he is the guy who will conduct the lawsuit, if it becomes necessary. It has happened before, and the effects were serious.

[syn08]

Originally posted by john curl
I have met him and had lunch with him, and he is the guy who will conduct the lawsuit, if it becomes necessary. It has happened before, and the effects were serious.

I'm scared to death.

[Wavebourn]

Quantum Jurisprudence... Is your 7'th harmonic cancellation by balanced topology claim is backed up by something similar?

[john curl]

No. It is another design problem that keeps repeating itself here. However, it is easy to be less ignorant about 7th harmonic distortion. Just Google: '7th harmonic music' and see what you get. Many here, without engineering degrees, can learn something important, just by doing a little 'research' on the internet.
The second reason for using fets is that their inherent transfer function does not easily allow much generation of 7th harmonic distortion. Not too much 5th either, but they DO put out a lot of 2'nd harmonic and some 3rd.
If you cancel the 2'd harmonic by differential (pair) input, you reduce the distortion considerably, BUT you add 3dB of input noise, and you have to use twice as many jfets.
In fact, to get back to the basic paralleled fet array, you have to use 4 times as many jfets. Think about it!
When you use a complementary jfet array, you can get low noise, and 2'nd harmonic cancellation with only the same number of fets as you might use in a single array. The downside is MORE non-linear input capacitance, because the P channel jfets have more non-linear input capacitance for the same transconductance, and usually a slightly lower peak operating voltage, due to the fact than many p channel jfets made for low noise operation have a lower rated max voltage.

[Wavebourn]

John;
Not being afraid of a lawsuit, I can tell you my opinion that cancellation of the 2'nd order harmonic by diffstages and symmetrical topology is worthless. Been there, done that, discarded as a dead end idea that have no advantages except economy of an energy consumption.

Better results I got by:

1. Approximation: several devices in parallel working on different parts of their transfer functions. One example you've seen: degraded BJT in parallel with MOSFET. However, I used that in output stages, did not try on inputs.

What I tried on input, was:

2. Transistors with bigger emitter areas than usually used there: smaller Rbb, flatter H21 on working currents.

Then, 2 ways to make a single device more happy:

3. Bootstrapped device: more linear transfer function due to smaller variations of a voltage across it's terminals,
4. Output current cancellation by a counter-modulated current source: less distortions due to smaller current variations through the device.

And, of course,

5. Using of more linear devices in combination with transistors, even though they are considered as obsolete and less linear. Yes, I mean vacuum tubes.

[john curl]

Single ended design can sound pretty good, but with fets, it gets a bit 'mushy'. It is better to do single ended with tubes, for the most part. They have lower overall distortion, and what they do have is mostly 2'nd harmonic.
It is possible, but difficult to cancel the second harmonic distortion of a fet by using a certain combination of idle current and a specific value of load resistor. This is because the output conductance changes with idle current and can be made to track with the change in transconductance of the fet(s). It is fussy, but it will work. We, once made a microphone input stage this way (lowZ, not hiZ). Worked OK, but each channel had to be individually adjusted.

[MikeBettinger]

Originally posted by john curl
Joshua, I think the biggest problem is GROUND contamination.

Interesting topic that never gets discussed yet has a profound effect on all things audio... The battery approach is a highend bandaid.

Just an observation.

Mike.

[john curl]

Mike, batteries work, they just are not reliable. However, batteries have something special: They are NOT connected to the power line. Think about it! What could connection to the power line, even with unmeasurable garbage or noise coming from the regulator outputs, do to effect the sound? It has to be the ground, and parasitic caps, etc connecting the power line to it.