Peter Walker and his current dumping principle

[jan.didden]

Here is the link

Quad 405-2 upgrades

Stuart

Very ambitious project, very well executed. And by someone who actually understands the current dumping concept as implemented by Walker.
Hats off.

Jan

 

[MarcelvdG]

Using a FET op-amp, you can get rid of the electrolytic capacitor in the DC loop if you want to, see

Redesigning QUAD-405 DC bias loops

Mooly's simulations in that thread look awful because of an incorrect value of R16.

 

[jan.didden]

Marcel, I missed that thread of yours! :-(

Jan

 

[dtrussler]

Very ambitious project, very well executed. And by someone who actually understands the current dumping concept as implemented by Walker.
Hats off.

Jan

There is a lot of good work in the Ludwig/Snook vein on the 405 as you say. My question is about the subsequent evolution of the design and revisiting this evolution without some of the constraints of historic componentry and commercial mindset.

 

[tiefbassuebertr]

In the link below are measurements of an optimized 405-2, this achieves distortion of 0.0025% which is quite respectable for an amplifier with an unbiased output stage, I built some clones in the early 80s and measured the distortion at 0.0018. If the over-current protection is ignored the 405 is quite a simple design using only one opamp and 8 transistors
Quad 405-2 upgrades

Stuart

The value for THD+N don't provide any hints for the audible sound character - go to post #2 under
Choosing of best sounding OP AMPs for the lowest possible THD+N -really the best Way?
The amps with images No 8 and 9 cannot sound good, even if THD+N is extrem low.
Unfortunately the diagram with fundamental notched out for Quad's 405/405-2 I don't find. This curvature would be interesting to know.

Here a test review from an Australian magazine:
Quad 405 / 405-2 Power Amplifier Review - Understated Elegance

I am always looking for amps with same sound character of very hard running amps like Pass Aleph series, but with small idle power consumption. Until now I know only one such amp - its sonic character is close to Pass' Aleph series (Aleph 4):
Horch 3.0 (classic series) go to
HORCH-CLASSIC

The Quad 405 sounds like usual good AB power amps, i. e. good behaviour while reproduction of the mid- and bass range but harsh character in the upper range, unfortunately.

 

[True Sound]

Yes, I know this resource, thanks to point out Linsley-Hoods analysis.

BTW I also read the article about that 'old' Voyager spacecraft, this was 1989, and Voyager is still en route I believe! Incredible!

Jan

I read that too. In 2022 (over 44 years of operation), both Voyagers are in interstellar space. While many of the instruments have been shut down (nothing to report, so why use the energy), approximately half of the instruments are still sending data back to earth. Real-time updates can be found at https://voyager.jpl.nasa.gov/mission/status/.