John Curl's Blowtorch preamplifier

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#5,721
John, ummm, what did I say to set you off? Other than offering to do a listening session with you. I bathe and brush my teeth, so it wouldn't be that awful.

I generally don't like audiophile recordings because the music is so lousy. But there are a bunch of Reference Recordings that I'd happily call the exception. But hey, it's your ears, put on whatever you like, I'll have a good time.
 
#5,722
Please everyone, I'm sorry, but I just don't think that my audio associates should be mocked in my presence. Now, I realize that many of you have strong negative feelings about hi end audio, but please don't burden me with this. I am here to try to help audiophiles make better sounding audio systems. That is the only real reason that I participate. Sometimes I learn from others, but I hope to give more than what I might get, and I will participate more, if I am not continually diverted by uninformed criticism.
 
#5,728
john curl said:
Thanks Snoopy, that was my own personal preamp that was reviewed. However, SY doesn't think much of it, because I have not added a transformer to the output. You can please only some people.
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Apart from the odd tube preamp I wouldn't have thought there were too many hifi preamps with coupling transformers.

Having said that I do know of one solid state preamp that uses transformers in the moving coil section of their preamp.

http://amp8.com/sansui/etc/jpeg/c2301-0.jpg
 
#5,736
Steve Eddy said:


Jeff Rowland has been using them for quite some time.

se
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Actually you are right about that 😉

http://www.jeffrowland.com/Technology/LineLevelTrans.htm

I'm just looking at the benefits but the claims are a bit dubious in this day and age of wide bandwidth, low noise and high CMRR opamps and differential amps.

OK. Very good line level transformers aren’t damaging to the sound. How do they manage the miracle of subjectively improving the sound so dramatically? That is harder to explain definitively – and possibly not fully understood. Let’s start with why recording studios love them so much:

1) Transformers break ground loops. Since the transformer’s primary and secondary aren’t electrically connected, no ground loop currents can flow. Hair- pulling, aggravating ground loop related hum and noise problems disappear.

2) Transformers have ultra-high common mode input impedances (inputs-to-ground), unrivaled by active differential circuits. This is also a result of the galvanic isolation provided by the insulated, shielded primary windings. Direct connection to a differential (balanced) amplifier’s inputs doesn’t guarantee perfectly balanced operation – transformers do.

It should be noted that many studios have been seduced by the low cost and great looking specifications of the solid-state "diff-amps" sold as transformer replacements over the years. The harsh reality is that there is a huge gap between laboratory measurements and real-world performance.

Most studios can’t afford the extravagance of transformers over diff-amps. Nevertheless, there is a rapidly growing cadre of perfectionists in professional audio who are returning to transformers as the ultimate signal interface.

These usability issues should be important to we audiophiles as well, but our list pretty much starts and ends with sonics. Ease-of-use is important to a manufacturer supporting a product, but some of the more radical "tweaks" consider dealing with difficult hook-ups a red badge of courage. They wouldn’t dream of compromising the sound for convenience. Fortunately, line-level input transformers improve the sound as well.
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#5,737
snoopy said:
I'm just looking at the benefits but the claims are a bit dubious in this day and age of wide bandwidth, low noise and high CMRR opamps and differential amps.
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No, nothing really dubious there.

First, can you name any opamps that provide galvanic isolation? 😀

Second, while there are opamps which claim high CMRR, they're very sensitive to source impedance imbalances (some pro gear includes trimmer resistors and capacitors to precisely balance output impedances in order to get the full measure of CMRR provided by electronically balanced inputs).

A transformer on the other hand offers exceedingly high CMRR even when fed from a wholly unbalanced source.

For example, the Jensen JT-11P-1 offers 107dB of CMRR (at 60 Hz) when fed from a balanced source. But when fed from an unbalanced source, it still provides 100dB of CMRR.

However Bill Whitlock of Jensen Transformers has patented an active circuit which isn't as sensitive to source impedance imbalances and has licensed it to THAT Corporation which they sell under the InGenius line.

However even these don't provide any galvanic isolation.

se
 
#5,740
Steve Eddy said:


Well, given that most every piece of high end audio gear out there uses three pin IEC connectors and power cords and a dozen different ways of connecting the safety ground and signal grounds which can cause varying degrees of interchassis leakage currents, I think it is. 😀

se
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I think for that reason some manufacturers are now using some sort of proprietory current mode interface which by its very nature has high common mode and differential mode impedance, so impedance imbalance is irrelevant 😉

I think Krell and Halcro are doing this 😉
 
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