Phono Pre-Amp design question

> google search found this http://www.analog.com/library/analogDialogue/archives/39-05/Web_Ch6_final_I.pdf

Yes, more of Jung's thoughts, with much supporting data and bibliography.

No, I'd just happened across one in Jung's Audio IC Op-Amp Applications, 1975-1978, with two '5534, first non-invert Gv=~~ 3, second inverting with proper RIAA curve. This too is surrounded by pages of thoughts and cites. While the book is not cheap, it is affordable, and still (near 40 years later!) a Good Read.

Here's a "stove-snap" so you see the general topology. (Best light in my house is over the stove; I cropped the burnt crumbs.) I won't put a good scan up because Walt watches his legacy, and because I don't wish to crack the binding on my vintage paperback.

PRR said:

> google search found this http://www.analog.com/library/analogDialogue/archives/39-05/Web_Ch6_final_I.pdf

Yes, more of Jung's thoughts, with much supporting data and bibliography.

No, I'd just happened across one in Jung's Audio IC Op-Amp Applications, 1975-1978, with two '5534, first non-invert Gv=~~ 3, second inverting with proper RIAA curve. This too is surrounded by pages of thoughts and cites. While the book is not cheap, it is affordable, and still (near 40 years later!) a Good Read.

Here's a "stove-snap" so you see the general topology. (Best light in my house is over the stove; I cropped the burnt crumbs.) I won't put a good scan up because Walt watches his legacy, and because I don't wish to crack the binding on my vintage paperback.

Click to expand...

The interesting difference between this and many contemporary preamps back then is that executing the RIAA EQ in an inverting NF  stage, means the 75 uSec pole can continue to roll off well above the zero at roughly 200kHz seen in the more typical non-inverting topologies.

I've avoided the 200kHz zero in all but my first ('78) phono preamp, but never exactly like that. 

JR

[edit removed TMI  /edit]
 

> difference between this and many contemporary preamps back then is that executing the RIAA EQ in an inverting NF  stage

That's very old. Here's one with inverter NFB for 50Hz and 500Hz but the 2KHz (the troublesome one in non-inverting) is done by loading the cartridge inductance (very common for some years before this).

Yup, the ancients keep stealing our ideas.

Back in the '80s when I published my second phono preamp kit, I used a balanced input, and some guy from TX contacted me saying he patented that???

Seriously, I sent him back a schematic from an old tube phono preamp that used a balanced transformer input.  I ordered a copy of his patent wrapper (the full file including arguments with the examiner.) It turns out the examiners never heard of balanced/differential inputs and was impressed by that. Just more evidence of the inexperience in typical patent examiners.

They say a good prosecutor could indict a ham sandwich, a good patent lawyer could patent a rubber band, the real test involves a trial and a judge.
=====

I've never seen the 75uSec RIAA pole done that way... but I like it early in the audio path to limit the slew rate/gain bandwidth required for the following circuitry.

JR

what are you amplifying? Pioneer with a Shure, or a Thorens with a Ortofon MC driving some K241-D's strapped for 12.5?

> never seen the 75uSec RIAA pole done that way

An early, and hi-profile, microgroove cartridge was the GE. GE actually told you to load it with 6.8K to get the top curve. Fine, as long as you only used GE (or other half-Henry) carts.

Later came Pickering (among others) with the notion of taking the cartridge "flat" by resonating L and C with an R (100K, 33K, later 47K) for a mild 15KC-20KHz 2-pole corner (then doing the slopes in the amplifier).

The rarely-seen but correct correction is to integrate the differentiating transducer, then fine-correct for the historic turnovers. However the input impedance and hiss levels suggest a buffer in front of the integrator, and the integrator should not really rise to infinity at DC, so it becomes as complex as the Bugle 3-stage, for no real-world benefit.

Things were simpler when we clamped a cactus needle on a telephone earpiece on a 78 and got a good high voltage that naturally followed the curve +/-10dB over 150cps-3kc.

PRR said:

Things were simpler when we clamped a cactus needle on a telephone earpiece on a 78 and got a good high voltage that naturally followed the curve +/-10dB over 150cps-3kc.

Click to expand...

Where did you find cactus needles up there in southeast Canada?

Andy Peters said:

PRR said:

Things were simpler when we clamped a cactus needle on a telephone earpiece on a 78 and got a good high voltage that naturally followed the curve +/-10dB over 150cps-3kc.

Click to expand...

Where did you find cactus needles up there in southeast Canada?

Click to expand...

When I was a very young puke, growing up in NJ,  I fell off my bike into a cactus plant next to my driveway... I recall my mother having to pull the cactus needles out of my butt with tweezers. (IIRC they were much too small to play a record with but big enough to sting).

JR

> Where did you find cactus needles up there in southeast Canada?

I'm from away.

As JR says, cactus needles came from Camden NJ, the Victrola/RCA buildings.