Schade Common Gate (SCG) Preamp

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#962
manniraj said:
@ra7 are you looking for these sockets - https://www.amazon.com/dp/B0778TFL39?psc=1&ref=ppx_yo2ov_dt_b_product_details. I got these to test the jfets but seems like we can use even the to220 mosfets too.
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As mentioned, those will not fit the fat pins on a TO-220.

These will work, but you need to cut them up. I use wire cutters to cut through the 4th pin then to clean up the jagged edges.

https://www.amazon.com/ZYAMY-2-54mm-Female-Straight-Connector/dp/B0778F2MLW
 
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#963
Vunce said:
Hi George,
Your last post was wonderful! It painted a picture that penetrated my thick head.
Thanks!
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The "magic" block on my diagram in post #950 is essentially a variable width door that can open and close faster than the highest possible frequency in the program material. It stays nearly closed (set for a watt or two of output power) but can open faster than the amp can make power, providing just enough headroom to avoid clipping.

I built a working prototype back in 2008, but lost interest. I have recently dug out the old circuit board, but I can't find the code I wrote for the controller chip yet.

If I have to start over, I will either go with an all hardware circuit, or attempt to use a high powered Arduino compatible CPU board. I need an A/D that's at least 16 bits preferably with a sample rate of 1 MHz or faster.
 
#964
Tubelab - there is something funny about your link.

At least on my machine - it goes somewhere other than AMAZON.

Must be something about DIYAUDIO

If you copy the link, being careful so you do not engage the link, you can get to where you intended it to go
 
#965
If I recall comments from Nelson Pass accurately this topology brings together two quite linear stages that reduce the influence of the chosen devices; common drain and common gate. So what drives the choice of the devices as it would appear quite a nuanced decision by comparison with perhaps a common source stage?

Secondly, given the typical preference given to Jfet devices is there anything to be `gained' by using jfets instead of mosfets?
for example Linear Integrated systems offer LSJ74 & LSK170 and the corresponding duals... (Aside from the `low cost' comment in the original mission statement)...
 
#966
Great question. The p-channel choice was based on what I had on hand and were plentiful at the usual sources. Several other devices could be substituted without much affect on the sound because it operates in follower mode.

The gain FET is much more important and I tried a number of devices, nearly all the usual suspects, including JFETS. The few properties the gain device should have are: ability to sustain about 40V and 10 mA at the minimum, lowish capacitance, and good sound of course. A schematic with lsk170 and some listening impressions are here.

The smaller devices struggle to drive VFET gates directly but might be fine driving, say, Papa’s 2022 FE. The STP30N10F7 sounds really good and meets all the other requirements. I tried a lot more FETs but that device is yet to be dethroned. Measures really well too.

I am working on an output buffer that could drive headphones and that will open up smaller devices in the gain position.
 
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#974
 
#976
Compact Toroidy
 

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#978
Yes, I have some but they are almost gone again.

In other news, I have been working on some circuits that will drive headphones. Actually, the current circuit also drives my Etys just fine but I am curious to hear what could be achieved with a powerful follower.
 
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