John Curl's Blowtorch preamplifier

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#7,942
Badge said:
KBK, I love the lightspeed sound, but the basic attenuation rate and ability to work with a variety of different loads must be addressed.
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You are probably right, I've never taken much more than a cursory look into the thread, but the idea managed to get my attention.

Most (OK, all) resistive materials have a considerable amount of self noise, and any energy reflective point that will rear it's head in a non-linear fashion under transient load, is off my list. The problem being, that the nature of resistance as applied to the idea of electrical function, at this time and to my knowledge, cannot escape this.

For example, has anyone tried to paralell the devices for a difference in mass loading (signal vs effect and device) and then potentially a more linear transfer/pass?
 
#7,945
reinhard said:
Use a high quality resistor in series and the blue alps as shunt to ground.
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That is misconception: the shunt element is equally important as the series one, if not more.

Mixing different resistive types for both branches is not a good idea either.

When I used quality series resistor and Noble pot for shunt, the pot by itself actually sounded beter to me 😉
 
#7,951
KBK said:

Most (OK, all) resistive materials have a considerable amount of self noise, and any energy reflective point that will rear it's head in a non-linear fashion under transient load, is off my list. The problem being, that the nature of resistance as applied to the idea of electrical function, at this time and to my knowledge, cannot escape this.

For example, has anyone tried to paralell the devices for a difference in mass loading (signal vs effect and device) and then potentially a more linear transfer/pass?
Click to expand...

A resistor in thermal equlibrium with its environment has noise predictable from first principles. There are mechanisms to get more but not less.
 
#7,955
Now, some can understand why the Blowtorch cost so much. We didn't compromise and used these TKD pots. They got so expensive, later, that this made us not want to make any more units, as well as the extra cost of the cases over time. This is why the CTC is not made anymore.
 
#7,956
hermanv said:
Obviously I was unclear, I meant to reply to fredex who asked: "How can we know it's not all in our heads?" Answer: because with a known good (live) sound, almost anyone can hear a difference.

No visitor to my home nor during my visits to another's home has there been confusion about whether or not a live group was performing in the other room. For this test, suddenly everyone seems to have golden ears. So when you say it's a bit beyond cryoed PCBs and supply rail fuses is the problem inclusive of those issues?
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(Not to get lost back a ways, but I only get to read through the posts about once a week... )

...but you could get quite confused as to if a live group was playing here on this system, since quite often a live group has been playing here, the system doing the real-time monitoring, and the instruments being run "direct" through the system.

Ok, it's a "cheat" of sorts, but it would fool anyone from over in the "next room" without any trouble...

There's a good bit of difference between a recording made live "straight up" and almost anything put out commercially - that has to be taken into account too.

Now, as far as "symphonic levels" are concerned?
You're gonna be surprised.
I've measured a symphony orchestra, with full choral singers in the Troy Savings Bank Music Hall (google it), an 1890's construction fwiw, and the max levels at the front of the first balcony were <100dB.!!

Imho, the main thing that holds back the typical playback situation (all other factors being held approximately equal) is simply the size of the room - which relates to the reverberation time and field instensity. Nothing more.

I've heard a first rate system in a room that someone locally built that is like a small barn in size - the effect of the overall sound due to the room size is quite surprising and pleasantly so. And, it is not at all a dead room! But you do not sense the reflections.

_-_-bear
 
#7,957
Quick, cheap and essentially as good as you can get for a pot Trimmer . Adjustment is a little tedious but in reality most people don't adjust for every cut. And for a modest investment ($12 ea) you can have a baseline to compare to.

The optocoupler controls are interesting but have very high distortion and a voltage sensitive non-linearity that's pretty easy to measure. I decided they were too questionable to use. And tracking between two is very difficult. You can get very low distortion with them in an AGC circuit (oscillator) but you need to be very careful to keep the voltage across them almost zero.

I got a sample of these Pot a long time ago and they seemed to be almost on a par with the Vishay solutions. Single gang only however. But 30 detents are available so a pair may be viable for a non-geek.
 
#7,958
Here is a discussion on the effect of the bypass resistors on the TKD.

http://www.audiocircle.com/circles/index.php?PHPSESSID=1p2krk7g0469p0ec6n45ra6n35&topic=54068.20

I had no idea this was posted anywhere (so I don't feel so bad anymore-there was obviously intent to share), I came up with the solution on my own via logical analysis of the issues involved in the 'idea' of a pot (or, that type of execution of a variable branched divider). The very idea tells you flat out that there is going to be a dynamic noise/distortion consideration that will need taming. The rub-is to do it without damaging signal.
 
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