John Curl's Blowtorch preamplifier

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#17,203
stinius said:
Guys what about skipping the guitars and ballet and discuss something interesting, and going back to the volume control.
Not talking about the resistors and Bybee, but how to do it and where to put it.

JC is putting the volume control before the line driver.
CH is putting it after the line driver, and is using a Variable Gain Transimpedance or a variable Gain Transconductance circuit.
According to Ayre it’s a Variable Gain Transimpedance (VGT)
According to Stereophile it’s a Variable Gain Transconductance (VGT)

As far as I know that is two completely different VGT’s

So my first questions would be: where is the best place to put the volume control and second is VGT a variable gain transimpedance or variable gain transconductance.
Click to expand...

These are all fancy names for variable degeneration. In a fully
balanced zero feedback circuit such as BT and Ayre, it is a no
brainer. It should have been done years ago.

There are numerous disadvantages in putting the vol control before
the pre amp and a quick simulation of feeding the pre amps IP
stage with increasing impedance will show significant non
linearities produced by capacitive modulation of the IP devices
loading the source resistance..2J74's are particularly bad in this
respect.

Using variable degeneration has advantages of:
- optimising linearity for any gain setting
- allows very high IP Z
- optimises dynamic range and reduces noise at lower volumes.

What's there not to like about it? 🙂

cheers

Terry
 
#17,206
Joshua is right. It is a personal choice, rather that any real advantage how we decide to make the input attenuator. I have done both, over the decades. Did my first degenerated volume control in 1973, for the Grateful Dead. Made more advanced mic channels with a similar feedback scheme for IHEM in 1974. So what?
 
#17,207
Edmond: "I still hate Beethoven, an annoying bore."
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If you could tune in on the level where his music comes from, you would experience something quite different. LISTEN, for instance, to his 5th pianoconcert the 2nd movement. Not listening with the mind and trying to interpret everything you hear; not YOU must do the listening but just let the LISTENING happen without YOU interfering. It does not happen all the time and sometimes only a few seconds, but the intensity of such an occurence is overwhelming; it is not transferable nor can it be explained to someone else. It just happens.

Reminds me of Jan Akkerman (well known Dutch guitar player) who seeks for this one moment when he plays, where everything falls into place. According to him it occurs every once in a while.

Enjoy ...

Franklin
 
#17,212
Hi Pavel, enjoying the weather too I assume. I understand you listen to a lot of classical music and must know Beethoven's works pretty well.

I'm still looking for a work recorded years ago by the English Chamber Orchestra from Henry Purcell's Dido and Aeneas. Was distributed on LP at that time but I've never seen a CD version. Any suggestions?

Regards,

Franklin
 
#17,216
Actually, it is nice of many of you to help your associate in criticism of me and what I stand for, to open up the right part of his brain.
I know, it sounds strange to a 'logical' person but music is best appreciated with the right side of the brain, but it is often suppressed in getting an advanced education. It is interesting what happens when you suppress the right side from dominating momentarily, so that you cannot appreciate the nuance that underlies the musical notes. It is a main factor in appreciating subtle differences in music reproduction as well, and frees the absolute demand for an intellectual reason for differences. It is good to sometimes go with the flow.
 
#17,217
John, I could take this discussion to a philosophical level, but that is not the scope of this thread or forum. However I understand and share most of your points of view on this and other topics discussed in this thread.

I try to be as open minded as I can and have personally found that taking another route - in spite of what others think or have thought to be the right one - has lead to many interesting findings, as you yourself have experienced.

This is an interesting thread with lots of good stuff on audio design to ponder on and learn. Many are contributing and despite the difference of approach or findings, I think there is the desire for a common goal to achieve better audio designs.

Regards,

Franklin
 
#17,218
It is sometimes important why there are philosophical differences between individuals. Talking 'nuts and bolts' or differences in signal topologies will not show this, explicitly. I waste most of my hours here disagreeing with 'philosophy' rather than definable or quantifiable factors.
The left brain, right brain factor is VERY IMPORTANT to understand why some people can HEAR differences, and can accept that some things cannot be analyzed directly, but still can be audible.
 
#17,219
courage said:


Reminds me of Jan Akkerman (well known Dutch guitar player) who seeks for this one moment when he plays, where everything falls into place. According to him it occurs every once in a while.

Enjoy ...

Franklin
Click to expand...

Hi
I met Jan Akkerman and Thijs Van Leer in Amsterdam in the mid 80’s
Nice people. I was on a tour with a US band “Sir Douglas Quintet” and we did a gig at Paradiso and they both were there. They planned a reunion of Focus and wanted me to do the live sound.
 
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