Simple Class AB - Linsley-Hood 1970

[Mark Tillotson]

I looked at the IMD for the JLH1970 and compared this to a Blameless at close to 1W rms into 8R out into 8R with 19kHz+19kHz input.

In the attached images the horizontal cursor has been placed as close as possible to -80 dB to compare the old with something a decade or so later.

Everything above 50kHz or so is unphysical, the speaker acts as a very effective low pass filter in that regime, as does the ear, and in fact the air in between them at the higher MHz ranges!


Plot the 50kHz range only for meaningfulness I would say.

 

[mjona]

I have to get one in the days to come, a clamshell first generation, as I have to dismount anyway, I will look more closely to see if I find an affiliation with JLH.

I see the reference to JLH in the stereophile review where there is a comment about the driver stages of the Brio operating in Class A.

There is no connection with the JLH design only the supposed thinking which you might like to examine for yourself.

There was an earlier review at the time I owned a Brio - where the designer was quite open that his development work was inspired by a circuit published decades earlier. I believe this was the Practical Wireless "Texan" - basic detail of which you can see at A Paul Kemble web page - PW Texan amplifier and the PE Rondo.

 

[Ian Finch]

Yes, the clamshell (original model) Brio and the Texan are the similar designs, both based on an opamp input stage which is limited in voltage swing by the opamp supply rails. Their output stages are therefore a CFP or Sziklai design which is configured to provide the full voltage swing between 25 or 30V supply rails, as well as its usual current gain. You won't find much in common with any of JLH's published amplifier designs there.