John Curl's Blowtorch preamplifier

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#13,962
May I ask what you consider a successful speakers for reference purposes?
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The speakers that I am most familiar with, i.e. they belong to friends of mine so I have an opportunity to listen to them on a regular basis, are the Dali Megaline, Kharma Exquisite, and Wilson Alexandria. They are all well-designed, well-built and well out of my reach but they share an outstanding ability to resolve the finest nuances and details.

I would love to hear the Blowtorch in one of these systems to see how it compares to the Aesthetix or the Einstein. I've already heard enough pre-amps that measure first-rate but sound second- or third-rate.

John
 
#13,963
PHEONIX said:



Hello John,

With things that I build I have found that unless you use a proper full range monitoring speaker which is set up properly that you are waisting your time when it comes to evaluation. By proper full range monitor I mean a minimum of a 3 way speaker, bass driver , mid range and tweeter, anything less than this is not good enough for evaluating a product that needs to sound good on most systems. I dont think that two way speakers cut the mustard for evaluation purposes, and its very easy to be fooled into thinking your product sounds good only to find it does not translate the same way into other peoples systems.

With full range speakers you can here things that you cannot possible here on a two way speaker , because it is more revealing.

By the way I agree with you on the impact that passives have on the sound of amplifiers.

Regards
Arthur
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so, esl is certainly out?
 
#13,964
AndrewT said:
is that overshoot due to self inductance of a spiral wound resistor? Would wirewound and metal film be equivalent in this case?

Would carbon film also have some self inductance if spiral cut?
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1) exactly, overshoot due to self inductance of wirewound resistor, 6R8/5W.
For lower resistance resistors, like 0R22, the inductance is lower, BUT ratio of inductance to resistance and relative overshoot are getting higher

2) the 8R2 carbon resistor used shows almost exactly shape of current step used for measurement of resistor voltage (impedance) response.
 
#13,968
I am now using the TO-220 size MP930 from Caddock.
Also, MP821/820 I have used.

If max 3A is enough, I would go bulk metal foil.

All above are non inductive.



Sigurd


QUOTE]Originally posted by PMA
I would like to know what kind (technology, manufacturer) of Re emitter resistors in power output stages are recommended (0.1R - 0.22R values). IMO they make a big difference. Their inductance contributes to stability/instability in a high degree, as well as PCB tracks to/from them. [/QUOTE]
 
#13,969
PMA said:
...........the 8R2 carbon resistor used shows almost exactly shape of current step used for measurement of resistor voltage (impedance) response.
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carbon composition without any spiral in the construction presumably.

What effect does the spiral have on metal film and carbon film?
Are there too few turns to have significance?
 
#13,971
Here's the equation for air core inductors, in uH.

I would expect that the permeability of the resistor body is not too different from air.

L = (r^2 * n^2)/(9r + 10l)

Where r is the radius, n is the number of turns, and l is the length in inches.

Which gives about .084uH for a resistor 1/4" long by 1/10" in diameter, and with 10 turns. In most cases I would say this is not enough to worry about. At 1MHz XL would be .5 Ohm, but I think 10 turns is a lot compared to most of the smaller resistors I've seen.
 
#13,972
We use a simple film (maybe carbon) power resistor that works pretty well. I used to use non-inductive wirewounds, but Bob (of CTC) found these cheap resistors were actually better.
I don't know if these low value resistors are 'spiraled'. I would doubt it, because that technique is used to INCREASE resistance, and why bother?
There is a special spiraling used in quality resistors that has a serpentine look about it, that is apparently nearly non-inductive. You just have to look at a picture of it to understand it.
 
#13,977
PMA said:


1) exactly, overshoot due to self inductance of wirewound resistor, 6R8/5W.
For lower resistance resistors, like 0R22, the inductance is lower, BUT ratio of inductance to resistance and relative overshoot are getting higher

2) the 8R2 carbon resistor used shows almost exactly shape of current step used for measurement of resistor voltage (impedance) response.
Click to expand...


What was the measurement circuit? Source, excitation, measurement equipment?

Jan Didden
 
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