John Curl's Blowtorch preamplifier part II

[john curl]

Of course, we considered speaker cables as an RF antenna 40 years ago. Look at Otala's IIM distortion papers. I think you will find something there, but in any case we discussed it among ourselves.

 

[Esperado]

Of course, we considered speaker cables as an RF antenna 40 years ago.

I still use to shield my speakers cables and boxes ;-)
The output coil in the amps helps on this, but the output impedance of the amps are not so low as expected at RF, and the feedback loop is an input for RF signals.

 

[DPH]

Do we all have a sudden vehemence for an RC Zobel to ground at the amp's output? There's your low impedance termination.

 

[hitsware]

Real amplifiers don't need it !

 

[jacco vermeulen]

(well at least to me)

I've met the Siltech guys in the previous millennium, can't recall any talk about rf/tl. Their hottest ticket now does something like $8.5k per stereo feet.

(not much use to me anyway, I still do cross-connected hd coax as speaker cable, and am confined to a solitary straitjacket room by the local government)

 

[Kindhornman]

Jacco,
Are you talking about some kind of solid core coaxial cable or what here?

Is the jailer for the straight jacket your Wife!

 

[jacco vermeulen]

Mr. Soibelman, surely you are not accusing me of taking any other form of 'authority' serious.

2 coaxials, inner conductor of one connected to the shield of the other.
http://www.diyaudio.com/forums/soli...l-shielded-cable-input-wiring.html#post782635

 

[Kindhornman]

Thanks. And treat the jailer nicely, it helps.

 

[jacco vermeulen]

Life with a higher echelon eidetic can be intimidating at times.

 

[brianco]

Eidetic images can be weird indeed. Last 'big' one I had (20 years ago) was of a poster stating with the most vivid of letters & background stating that the woman sitting next to me would bring trouble!

............She did - and plenty of it!

Perhaps best in the telepathy thread!

 

[jacco vermeulen]

weird indeed.

If only it didn't make one talk so weird.

( http://www.diyaudio.com/forums/pass-labs/186060-threshold-sa-4e-vs-sa-1-a.html#post2548248 )

 

[john curl]

Bruce Hofer of Audio Precision has a new presentation on 'Designing for Ultra-Low THD in Analog Circuits' this really useful as well as telling many of you as Ed Simon and have: "I told you so!" Get it if you can. It is in pdf format, about 1.6 meg.

 

[scott wurcer]

Bruce Hofer of Audio Precision has a new presentation on 'Designing for Ultra-Low THD in Analog Circuits' this really useful as well as telling many of you as Ed Simon and have: "I told you so!" Get it if you can. It is in pdf format, about 1.6 meg.

Bruce is my buddy, watch out. He doesn't do quantum purification. He is hard core engineering all the way the BS walks.

 

[JayReed]

JC
Is this a new version of the paper with the same title from 2013?

 

[gpapag]

That one was 6.12MB
http://www.ap.com/download/file/747
>Edit. The link at AP site although dated 25 Feb2014, leads to the same Audio Express Nov 2013 pdf
George

 

[DF96]

Interesting that the speaker cables are not viewed as an antenna connected to the amp's output.

It has been known for years that speaker cables can act as an antenna. Radio amateurs have been only too aware of this, as their neighbour complains that he hears a funny noise on his 'hi-fi' some evenings! May be less well known among audio folk, but then there is the danger of over-hyping things.

Real amplifiers don't need it !

Maybe some misunderstanding here?

 

[jacco vermeulen]

That one

There was an update at ap, but apparently taken off-line again.

 

[john curl]

The presentation I was sent appears to be a 'Power-Point' that has a lot less detail, except for some fundamental recommendations not present in the 2013 article in AudioXpress. For example, avoiding 'bulk metal resistors' for hi end audio, etc.

 

[jcx]

I don't know about "avoiding" bulk metal resistors - I believe the commentary is just that they aren't as much better on thermal modulation distortion at audio frequencies as simple comparison of DC Tempco might lead you think

still very good compared to many other types

Bruce's recommendation for ultimate low distortion numbers (way below any suspicion of audibility) are still expensive and uncommon 5 ppm thin film R to see better distortion numbers than the bulk foil at audio

(and some of us "conventional engineers" have seen the presentation in person at AP Audio Master Class seminars)

 

[DPH]

Maybe some misunderstanding here?

It was a humorous response (along with a circuit that purports universal stability) to my comment about a vehement hatred of Zobels (which was also tongue in cheek).

There's enough on Bruce Hofer's article/powerpoint that everyone can have their, "I told you so" moment and miss the rest of the details.