Single or dual differential? - Page 11

hitsware · 17th November 2003, 04:55 PM

Quote:

Originally posted by Bricolo

what scematic are you talking about?

....

hitsware · 17th November 2003, 05:01 PM

Quote:

Originally posted by PMA
I am sorry I meant 10kHz - 20kHz, as THD is usually worse at higher frequencies.

I don't remember if I did 20k but did do 10k (don't have the analyzer any more). Also (and I think importantly) the distortion was ~same at all levels........mike

PMA · 17th November 2003, 05:17 PM

Pretty confusion - I was speaking about image at Post No.81.

hitsware · 17th November 2003, 05:23 PM

Quote:

Originally posted by PMA
Pretty confusion - I was speaking about image at Post No.81.

That one is in the conceptual stage. Should sound good though.

hitsware · 17th November 2003, 05:27 PM

Quote:

Originally posted by PMA
Pretty confusion - I was speaking about image at Post No.81.

http://www.ne.jp/asahi/evo/amp/J200K1529/report.htm

Oops ....... Somebody did it .....

Bricolo · 17th November 2003, 05:36 PM

Quote:

Originally posted by hitsware

....

The 2SK170 has to be selected, but selected for what? I don't see the reason for it, there's no "matching" required (no dif pair, no multiple output transistors...)

hitsware · 17th November 2003, 05:42 PM

Quote:

Originally posted by Bricolo

The 2SK170 has to be selected, but selected for what? I don't see the reason for it, there's no "matching" required (no dif pair, no multiple output transistors...)

To have it run in the center of it's operating range with the given resistor values.............jfets do vary somewhat

PRR · 17th November 2003, 06:03 PM

> I thought that dif pairs had a very high gain.

Voltage gain to one output is one-half of the same device working grounded-cathode (or whatever).

On another forum I just pointed out that if you have two triodes, cascading them gives 2*Mu more voltage gain than the same tubes as a diff-pair.

Diff-pairs are useful in high-gain DC amplifiers because the diff-pair has near-zero DC offset. They are often useful in audio with NFB because you get two "identical" inputs. They also avoid cathode bypass capacitors which are often problematic.

The diff-pair has half the gain of a single device, but using BJT, Pentodes, or cascoded FETs or Triodes the useful gain is really limited by stray leakage and capacitance, and may be further limited by overall NFB stability consideration.

If you take both outputs of a diff-pair (either two outputs or a current-mirror turn-around), the gain is identical to a single device.

Fred Dieckmann · 17th November 2003, 06:05 PM

"To have it run in the center of it's operating range with the given resistor values.."

Vary the resistor values. Go read

http://www.borbelyaudio.com/ae599bor.pdf

http://www.borbelyaudio.com/ae699bor.pdf

and learn to bias jfets.

john curl · 17th November 2003, 06:31 PM

Folks, please get your ducks in a row about this circuit.
Personally I don't like to use much series resistance in the base of Jfets, BECAUSE it increases the noise of the entire unit. SE is correct, if you want to make an input filter, then put 50-200pf mica or film cap to ground to have a LINEAR capacitance at the jfet input. Then you can reduce the input R to 1K or so.

17th November 2003, 06:05 PM	#109
Fred Dieckmann diyAudio Retiree Join Date: Oct 2002 Location: Spain or the pueblo of Los Angeles	Tail wagging the dog "To have it run in the center of it's operating range with the given resistor values.." Vary the resistor values. Go read http://www.borbelyaudio.com/ae599bor.pdf http://www.borbelyaudio.com/ae699bor.pdf and learn to bias jfets.

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17th November 2003, 05:17 PM	#103
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	Pretty confusion - I was speaking about image at Post No.81.

17th November 2003, 06:03 PM	#108
PRR diyAudio Member Join Date: Jun 2003 Location: USA	> I thought that dif pairs had a very high gain. Voltage gain to one output is one-half of the same device working grounded-cathode (or whatever). On another forum I just pointed out that if you have two triodes, cascading them gives 2*Mu more voltage gain than the same tubes as a diff-pair. Diff-pairs are useful in high-gain DC amplifiers because the diff-pair has near-zero DC offset. They are often useful in audio with NFB because you get two "identical" inputs. They also avoid cathode bypass capacitors which are often problematic. The diff-pair has half the gain of a single device, but using BJT, Pentodes, or cascoded FETs or Triodes the useful gain is really limited by stray leakage and capacitance, and may be further limited by overall NFB stability consideration. If you take both outputs of a diff-pair (either two outputs or a current-mirror turn-around), the gain is identical to a single device.

17th November 2003, 06:31 PM	#110
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Folks, please get your ducks in a row about this circuit. Personally I don't like to use much series resistance in the base of Jfets, BECAUSE it increases the noise of the entire unit. SE is correct, if you want to make an input filter, then put 50-200pf mica or film cap to ground to have a LINEAR capacitance at the jfet input. Then you can reduce the input R to 1K or so.

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