John Curl's Blowtorch preamplifier part II

Status
Not open for further replies.
Jump to Latest
D

DPH

Member
Joined 2008
scott wurcer said:
The stubbornness around not revisiting "the low open loop BW" theories "proven" with tests using primitive, flawed for audio, op-amps is as closed minded as anything I see here.
Click to expand...

One of so many. But then again, audio electronics are *so* much less interesting when you define them as a black box. Too much caring about how the sausage is made versus its taste test.
 
D

dvv

Member
Joined 2004
john curl said:
It is interesting how people operate throughout the decades. It is almost always the same. Did most of you know that experts in the USA maintained that jet engines were impossible, even as the Germans and the British were making them? We like to bury our mistakes in opinion, but the same problem still goes on. Many people are comfortable with what they learned in college, and are open to little more. Oh well.
Click to expand...

Still regarding airplanes, everyboda thougth Geoffrey de Havilland was mad to even propose playwood bodied airlane in 1939, asking how would it defend itself against the Lufwaffe MEs. H said that his plane's power-to-weight was better than anything alse in the sky ad gave the Mosquito a twin engined RR Merlin engines, making the Mosquitoat least 20 MPH faster than the fastest in the sky. It quickly became a legend and did what no other airplane could (e.g. hopping bomb destruction of German dams, etc.).

Just another example of impossible at work.
 
billshurv

billshurv

Member
Joined 2014
Paid Member
Without wishing to sail close to the forum rules the clusterf*ck that was BL was only 50% the fault of the management. The fact that Russia was funding the local communist party to stir up the unions was a help.

Now roll forwards and BMW bought Rover just to get access to the production methods used at longbridge (with big thanks to Honda) and the LandRover 4wd tech.

Hands up who remembers where there was still a mangement canteen on site where they worked. Thank $Deity that has vanished outside of the armed forces and a few dinosaur organisations :)
 
jan.didden

jan.didden

AX tech editor
Joined 2002
linearaudio.net
Paid Member
john curl

john curl

Member
Joined 2003
Scott, apparently you did not read his original AES paper carefully. Perrot says on p. 4 '...The amplifier of J.Lohstroh and M. Otala. Its schematic is rather clean for memory, and the drift (Fig. 6) results mainly from transistors thermal drifts. ' Of course this amp has only 20dB of negative feedback AND a 20KHz open loop bandwidth. So the results are opposite of what you inferred.
 
J

jcx

Member
Joined 2003
John, try searching the paper's text too

the Measurement of a Neglected Circuit Characteristic Preprint 4282 paper's unspecified 'commercial amplifier' "bad" result is simply uninformative - no conclusion re "flat open loop bandwidth" vs "high feedback" can be drawn from what's presented in the paper

this is essentially all the info provided on the amplifiers tested:

...Many measurements were made with an amplifier similar to the amplifier
of J. Lohstroh and M. Otala [2]...

...Measurements of sampled memory were made in the same condition ( a
tone-burst of a 60 Hz sinus signal at ± 6 V pk-pk on a 4_ load ) for 3 amplifiers
using different technologies:
- a commercially available high quality transistor amplifier, with a THD of
-86 dBc at the level of the test signal ( Fig. 8 )
- a triode tube amplifier designed by an audiophile, with a THD of-27 dBc
at the level of the test signal ( Fig. 9 )
- a new transistor amplifier designed for low memory, with a THD of about
-110 dBc at the level of the test signal ( Fig. 10 ).
Click to expand...

so in fact we aren't even told just how 'similar' the 'new transistor amplifier designed for low memory' is to 'the amplifier of J. Lohstroh and M. Otala [2]'

I have searched the paper for all of 'open', 'loop', 'flat', 'gain', 'bandwidth' terms and nowhere is it stated that the "low memory distortion amp" follows Otala's "flat loop gain" prescription

if I were going for the low THD and low 'memory distortion' given 'the amplifier of J. Lohstroh and M. Otala [2]' I would 1st cut the VAS load resistors to gnd, giving more open loop gain at every audio frequency, and potentially decades more error reducing loop gain for signals of few to 10s ms time constants

nothing in that paper precludes that mod
 
Last edited:
scott wurcer

scott wurcer

R.I.P
Joined 2004
john curl said:
Scott, apparently you did not read his original AES paper carefully.
Click to expand...

Frankly John it is my opinion that these papers were written in an era of primitive circuits and very early semiconductor devices both with lots of shortcomings. The fact that none of this has been revisited indicates to me it is no longer relevant and not worth the time. You and your posse seem content to sit around the campfire and relive 40yr. ago over and over and over...
 
J

jcx

Member
Joined 2003
actually the theory, detailed analysis, and excellent performance circuits were available in EE world in the large, often decades before these 'Neglected Circuit Characteristic' "problems" appeared in the "Audio" press and JAES

Philbrick's publications alone cover most "subtleties" of amplifier circuits, then add 'scope manufacturer's attention to settling details, thermal drifts in their input amp's...
 
billshurv

billshurv

Member
Joined 2014
Paid Member
LIGO have announced a 3rd gravitational wave detected. Go science!

What would be interesting for me is to look at the techniques in the precision analog arsenal that have been ignored in domestic audio and understand why, especially if they are used in the pro world. Obviously a lot of that is because you don't really need (for example) high CMRR in domestic setting, but for those chasing the last fractions of 1% performance would seem logical. Unless of course a good story is more important that getting measurably better performance...
 
Status
Not open for further replies.
Top Bottom