Unipolar vs complementary input stage

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#181
Steve,
You do have a rather extreme viewpoint. Sometimes it helps simply to acknowledge ones extremities and admit that they may not be everyones' cup of tea...or mug of beer as the case may be.
Your somewhat bristly reply to my post is a perfect example of what I'm saying. It's not necessary to be an apostle--or warrior--for the Religion of Transformers. Not many feel the calling, so to speak. Those that do feel the need will come to you--you don't need to go to them.
And certainly not in such an abrasive manner.
You'll win few converts that way.

Grey
 
#183
I suspect if you do a search for me and "LED," you might find a similar number.

I'm thankful for Steve's evangelism. I would never have tried using modern input transformers because of negative experiences with "classic" units if it hadn't been for his repeated urging (and, finally, a group buy he put together). It changed my (audio) life. Call it a successful conversion, if you like.
 
#184
flg said:
Cheap shot??? Pardon me, please, and Grey... A simple search reveals the word "Transformer" has been used 356 times in posts authored by Steve Eddy.
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That's 356 posts out of 4,173 posts. That's what, a whopping 8.5% of my posts which have the word "transformer" in them?

Let's see, a simple search reveals that you've used "JFET" in 55 of your 469 posts. Wow! That's 11.7%! Gee, what sort of aspersions shall we cast upon you based on that? Should Gray think of his hopped up hops buddy whenever he sees you post about JFETs?

Or would that be a cheap shot?

se
 
#185
The point is not for Steve to stop mentioning transformers and certainly not to stop using them. The point is to have a sense of humor and balance about one's eccentricities.
I happen to like wide bandwidth and low feedback, but I try to remember not to forcefully ram it down others' throats. Can't say that I've won any converts, but then I'm content to muddle on building circuits my way. Others don't have to follow or agree. I'm used to piddling about on my own.

Grey
 
#190
john curl said:
improve the JC-1's signal to noise by adding an extra fet buffer.
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I was hoping Mr Curl would be in an informative mood.

(Steve Eddy current is an alias for Mr Ice Rowland)
 

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#199
john curl said:
Bob, why don't you modify your amplifier to do balanced, as well as single ended, depending on the choice and need of the amp's owner? Then we will have a common point of discussion.
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Hi John,

Attached below is the schematic of my input/VAS circuit modified to accept balanced inputs.

As you know, it is normally the case that some sort of buffering is required to perform the differential-to-single-ended conversion for an amplifier with substantial gain, largely due to the need to drive the inverting input. Here I have chosen to pass both differential inputs through a symmetrical discrete balanced JFET buffer. This means that both of the differential inputs can have identical, high values of input impedance and that both positive and negative signals encounter the same signal path for symmetry (unlike the more common approach of just buffering the negative side).

The differential buffer, which I refer to here as a Differential Complementary Feedback Quad (DCFQ), employs two JFETs and two BJTs in a differential arrangement analogous to a pair of JFET-Bipolar CFPs. This arrangement provides a low-distortion, low-impedance drive to the subsequent differential amplifier arrangement of the input/VAS stage.

J3 and J4 form a pair of source-followers that are “helped” by their respective complements Q3 and Q4. Q3 and Q4 are arranged as a differential pair, resulting in much-improved bias stability as compared to the use of two individual JFET-bipolar CFPs. R31 and R32 drop the source voltages down to zero volts.

THD of the DCFQ stage is less than 0.002% under all conditions of positive, negative and differential drive. This arrangement also takes advantage of the good offset matching of the dual JFET, with common variations in Vgs resulting in just a common mode offset that is ignored by the subsequent differential amplifier. If desired, the common mode level presented to the subsequent differential amplifier can be trimmed to zero with R37.

Gain of the amplifier is set to 28 dB, and input-referred noise is 6.9 nV/rt Hz using the LSK389 JFET pairs.

Input common mode rejection is 62 dB out to 1 MHz. This could probably be improved, at least in the audio band, by closer resistor tolerances. The C4-R39 combination plays an important role in maintaining the balance necessary for good HF CMRR.

When a single-ended RCA input arrangement is desired, the negative differential input can just be switched to ground.

Cheers,
Bob
 

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