Mpp

[Joachim Gerhard]

I designed a lot of buffers over time. This one was designed for only N-Channel Fet´s and works well. You know, the P-Channel problem.
One question : did you try the 50kOhm differential feedback resistors " one story up ".

[MiiB]

Iam going out now eith my girls..... Will sim that tonight...

if you have some real life results.. Ill make you a nice PCB...

[Joachim Gerhard]

Wow, nice....

[MiiB]

There's a problem with adding the DC-blocking cap before the buffer stage... While it's nice to keep it small..I also raises gain in the low frequencies at the front current stage... this to a degree of app + 40 dB..from at Riaa gain at 10 Hz..at app 80 dB to more than 120 dB.

Don't see much change wit the different mirrors...somewhere i saw an analysis.. that the the difference in current precision between the different types mirrors is only 0.something percent.. So frankly I would settle on at simple 4 transistor mirror.. and maybe have a bleeder to aid in setting the impedance...

Distortion and profile remains the same and so does the amplification...
With 2 x improved Wilson mirrors the resistor in each branch must be lower (app 200 ohm) to get the right working conditions..

[Joachim Gerhard]

Did you try, say a 1MOhm resistor at the input of the buffer after the cap ?
Anyway, i will build the simple 4 transitor Wilson after your advice. This should be as simple as posible or it looses it´s attraction i think.

[MiiB]

Regardless of the mirror-type...I think is a bloody clever circuit...You get enough amplification with super low noise for a MC stage...and only using N-channel fets...add to that a distortion that is decreasing with frequency and as such has lower distortion at 20KHz tnan at 1 KHz..and also that the distortion profile is limited to only 2. order....I bet you I'll sound fantastic.. It also a fast circuit that extends into the MHz area....If nicely implemented...and tuned...I believe It'll be hard to beat...One contender could be My One shot Riaa that bears some of the same strengths...

[Joachim Gerhard]

Lets see if i can make it work. Thanks for praise in advance.

[RCruz]

Now you are really cooking !

Can we learn about the "My One shot Riaa " also ?

[MiiB]

This here seems to work very well.. if the DC cap is placed in front of the buffer... we need the high impedance of the input jfet.. If we add something like a M-ohm we start loosing base...The reason for my trouble was that i already added 100Kohm to gnd.. and thus screwed up the riaa by a few dB..even with 1Mohm you loose app 0.5 db in the base...

One worry is the need for matched resistors in the current mirrors, if just 1 ohm unbalanced we could run into problems...Here again ...practical implementation may show something different.

[MiiB]

Oneshot riaa..