John Curl's Blowtorch preamplifier part II

[dvv]

Here are a couple of measurements from 'Stereophile' of the speaker I am now using, including the tweeter:

By graphs, not very linear, by sound, I have no idea.

 

[vacuphile]

And what loudspeaker would you recommend, Jan?

Why not something like this:





Not quite as flat as the JBL, but not far off, and not bad for using off the shelf drivers. The directivity pattern is unmatched by anything other than MBL's, I gues; it is almost like a 5/8 inch point source in the front half.

Tom Danley recently remarked about the virtues of having a point source, and I can't agree more. For stereo imaging and loudspeakers magically disappearing, this is what you want. Unfortunately, a 5/8" tweeter is already pushing the limits a bit, and what you see from the directivity pattern is mother nature at work with a 5/8" diaphram. In spite of this off axis roll off at > 10KHz, there is virtually no way of telling which way the speaker is pointing towards you.

I have almost sorted out the IP on this speaker, which I hope to start auditioning this fall in the US. Jan Didden is partnering up for this part of the trajectory. So, hopefully soon in this theatre ...

 

[john curl]

Homemade too, Vacuphile?

 

[bcarso]

I don't work for JBL any more, so I have no 'inside' way to get one. '-(

Me neither. Toole says he is going to put M2s in his living room and remarkably his wife is in accord.

 

[SY]

Homemade too, Vacuphile?

Imagine that, on a diy audio website!

 

[john curl]

Sounds like 'proud papa' syndrome to me. Better to have objective measurements done by others.

 

[john curl]

Toole can get them at cost, I would bet.

 

[john curl]

Does anyone remember 'Beranek's law of loudspeakers? '-)

 

[Triodethom]

Does anyone remember 'Beranek's law of loudspeakers? '-)

And that differs from building your own electronic how ? Just asking . That syndrome manifests it self in so many interesting way does it not ?

 

[vacuphile]

Homemade too, Vacuphile?

I have a workshop. The fr measurement was done together with Jan Didden in the anaechoic room of the Delft Technical University. R&D financed with loudspeaker related licencing income from Harman. Purpose is to find producer.

That's how homemade it is.

 

[dadod]

Especially if the stabilized main channel is more than just another IC, there is almost always a place to inject the correction signal from the servo, obviating the need for a differential servo. If for some reason you absolutely need a noninverting integrator, in addition to the sensible suggestion of a following inverter, one can resort to the Deboo integrator topology, with positive and negative feedback---but the resistors have to be well-matched.

I don't know the history of differential servos with two capacitors, but I suspect it's something that was less than well-thought-out, and then started being copied without a lot of examination.

Brad

Douglas Self clearly disagree with the choice of the Deboo integrator topology over non inverting integrator with two capacitors in his Audio Power Amplifier Design, sixth edition.
Damir

 

[john curl]

My first custom loudspeaker: From 52 years ago.

 

[john curl]

Non inverting (2 cap) integrators have a problem with pole splitting.

 

[john curl]

No wonder that my $28K gift speaker to me is so criticized. You guys are going into competition! '-)

 

[dadod]

Non inverting (2 cap) integrators have a problem with pole splitting.

Not so much according to Self, and not critical resistor matching.

 

[fas42]

Again... all this evidence and anecdotal evidence points to the fact that many listeners probably really do prefer audio that (looked at in absolute terms) is compromised.

I like amps that have a certain distortion spectrum... it makes CD's sound majic

Some like vinyl, so they start with a compromised source but make the most transparent amps they can. Apparently the results can be spectacular.

Dare we now add that those that like SA-CD are inadvertently introducing another variable with the noise... and that wide band systems will react to that noise unpredictably... but the audible results might be, lol, you guessed it, majic Think on this... what is a super tweeter doing when fed all this out of band noise.

Fortunately, this is not right . I have heard plenty of systems that do weird things to the sound, trying to make it sound more palatable, and they fall into the "add more sugar or spices until the bad stuff goes away" camps. This is quite unnecessary, but is an "easy solution" if one doesn't want to do it "the hard way", .

Totally clean reproduction exposes the "magic" of the recordings - absolutely nothing has to be added to make it happen ... except, expertise, - but, it appears that it's going to take a while, a looong while, for this concept to sink in ... .

 

[john curl]

I would listen to Bob Cordell if I were you.

 

[bcarso]

What I've done for a servo most recently: a conventional inverting op amp integrator, driving a differential pair with lots of lumped emitter R. Each collector sinks current from a Wilson mirror internal to the overall gain stage (if you get the polarity wrong despite all, just swap the collectors ). Things are trimmed so the two collector currents are about equal, so noise in the tail current of the pair is nulled (and isn't much to begin with). At the moment the op amp is a bog-standard LF411 but could easily migrate to another JFET amp like the OPA134. This is stabilizing a gain of 100 discrete JFET input amplifier (with series feedback to the source with a stiffish divider) with the 75us RIAA rolloff in that stage. I am about to complete the rest of the breadboard, having gotten another chunk of the Twin Industries ground plane + pad-per-hole board.

Brad

 

[vacuphile]

No wonder that my $28K gift speaker to me is so criticized. You guys are going into competition! '-)

John, you bet! I am always most happy to look somebody elses gift horse in the mouth

 

[Esperado]

I would listen to Bob Cordell if I were you.

+1