Aleph Mini-Me

Here's a variant on Grey Rollin's Aleph Mini.

I've added a protection network at the input to prevent some dumbjohn from shuffling across the carpet and dusting the input via ESD.

I changed the input diff pair to the Zetex p-channel devices to reduce the capacitance at the input.

The current source at the tail of the diff input pair has been changed to a "ring of two" source to eliminate the need for selecting the mosfet feeding the diff pair tail.

The mosfets in the diff pair will still need to be closely matched - the degree of match will dictate the output offset of the amplifier. I want to avoid the extra complication of a servo circuit by instead closely matching the input diff pair. This has worked well for me in other projects.

I have chosen to load the diff pair drains with a current mirror rather than resistors.

I pretty much left the Aleph modulated source and the drive current limit alone, except for optimizing the value of aleph current sense resistor for symmetric +/- current drive.

The feedback network was modified to avoid having to use a series electrolytic cap in the feedback network.

Transistors were changed from MPSA18 to high gain devices currently available from FCH/On Semi.

I've added two options for compensation so that I can optimize the phase margin at zero crossing frequency.


The resulting circuit simulates well, and I have gone out for PCBs so I can build up a sample and see how it sounds...
 

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Here's a a simulation with THD results from 0.1V input and 0.75V input. Of course, for a limited open loop gain circuit like this one, the THD will track the input voltage.
 

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Waiting for boards... I just finished a new layout that moves the power devices to opposite sides of the board to spread things out out the heat sink. Since as a result, the board is now narrower, I should be able to mount the PCB directly on the heat sink, saving some space inside the chassis.
 
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Just popping in to say thanks for showing your new thoughts and design. I don't remotely have the skills to analyze the circuits (yet), but I've started to understand a few of the building blocks. Seeing new ways to tinker with existing ideas allows me to notice some of the commonalities and patterns to better understand "how this stuff works".

:cheers:
 

PRR

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Joined 2003
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> Maybe it is common for everyone to shut down for a week.

China Holidays: 2021 Public Holidays & Festival in China
Chinese New Year: 2021: Day: Feb 12 -- Holiday: Feb. 11 - 17
"1st day in 1st lunar month, usually in Jan. or Feb.
"The grandest traditional festival in China, the longest public holiday;
"Annual family reunion, eat dumplings, set off fireworks"

Especially for tech workers who may be working far from home and family, this is the one holiday long enough to travel halfway across the country, hug grandma, kiss the new kid, and load up on dumplings.

Like if your kid went off to work at Google, but without US-customary vacations, you'd expect the kid to return to Milwaukee last week of December to be with family and decent beer.

At this moment it is the day after the holiday, so workers should be back in body, but maybe not 100%.
 
All,
sorry to briefly hijack the thread with this question...
Has anyone done a MiniA with all Jfets? In particular I am thinking to adapt the LU1014 I just found and 2sj74 I have around for the differential. I like to keep rail voltages low +/- 12-15 V or as low as they need to be. All I need is 1-3w of power into 8ohms.
Has anyone done that?

I know a guy his name is Zen Mod...if anyone has done anything 'Pass' he knows about it... ;):D
 
Boards are in house as of yesterday. Strangely enough, both versions of the board arrived simultaneously, though they were ordered a few days apart. Delay on the first board possibly due to non-std red solder mask plus 2 oz copper.

I'm stuffing one channel of the 2nd revision board. Expect some delay, as I'll have to drag out my matching setup for the input mosfets.