Another Wrench In the Works... Inductive RIAA

[wrenchone]

That's why I'm using the circuit configuration I chose - it allows me to use 50 ohm impedance networks. This is much more managable and may be workable without all the extra components to compensate for strays. Time will tell. Fortunately, we have a very good impedance analyzer at work, so I'll be able to really scope out the inductors once they're wound.

[wrenchone]

Just so folks know what to look for, attached is a picture of some ferrite pot cores, one all canned up with shield and PC mount bottom plate, another disassembled so you can see the slightly separated core halves, the bobbin inside them, the bottom plate, the can, and the wavy washer placed inside the can on top of the core so that the ferrite pieces don't get crunched when the can is clinched tight to the bottom plate. These cores happen to be 42 X 29 mm,pretty much the largest size commonly available. There's a host of smaller sizes, for this application those from 26 X 16 mm upward are probably most suitable.

[nicoch58]

I start to build a lcr tube phono ,thorsten design he use the
s&b600 , this one is more simple rispect the tango eq 600 , but riaa is in the 0.3db (0.4) rispect tango 0.2db but this can put the dc bloc caps after the riaa on low value0.1µ

[wrenchone]

That's all very fine, but the entire thrust of this thread is to get away from using those networks. There are several other threads dealing specifically with what you're trying to do. A search will find them.

[Conrad Hoffman]

FWIW, inductors are the most impure electronic component. If you spend any serious time measuring them you'll find that only an air core is linear and can achieve really low THD levels, at the expense of size and internal resistance of course. Mounting is always an issue, as even mounting near a copper ground plane changes the characteristics. I've no doubt that the parasitics can be taken care of in the design, but unless one is trying to build a steep and exotic multi-order filter, using inductors seems like more of a novelty than anything else. And this from somebody who actually likes winding and using inductors!

[wrenchone]

This is why I'm aiming for low impedance network, again, to reduce the necessary inductance as much as possible. Pot cores with a reasonable air gap are pretty linear, especially as they are seeing low current and low signal levels. The pot core geometry is to a large extent self-shielding - adding the cans as shown in the previous picture kills electrostatic noise coupling. Pot cores were used extensively in the telecommunications industry for precision filters, for good reason. At any rate, I'm trying the inductive filters out of curiosity, and choosing the simplest way to do it that I can think of. I, too, work extensively with inductors, but mostly in the grubby power supply realm - a different matter altogether.

[nicoch58]

wrenchone sorry if you thinks that I disturb your work ,I no need info, I try add as I study for a month in all world wide web

if we can trust Bench-Thortsten-Mayer and a lot skilled diy ,this coil works a lot better then RC riaa at last on tube,as they put under x-ray with real misure....only problem is$$$

best

[wrenchone]

I'm fully aware of all that, that's why I'm trying this solution. I might also work as a passive solution, but it would require a hefty buffer with a servo circuit to drive it - hence the feedback approach.