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Flywheel or LSES Filter?
Which Low DCR PS Filter Should I Choose?
My latest SE DC 6AQ5 stereo breadboard amp project uses an well-filtered , ultra-quiet under idle conditions "flywheel" power supply filter.
Can an LSES ( low storage energy supply ) be as quiet as the "flywheel" for my project circuit.
I explore this idea in the pages below.
One aspect of the filters is explored here : AC ripple at C2 in the filter chain and AC ripple at the speaker terminals.
DT 667 June 2019
Flywheel Filter
My current SE DC 6AQ5 breadboard project circuit uses a "flywheel" type power supply filter.
The filter is : 35mH/2A/.79ohms -> 10uF -> 2H/300mA/7ohm -> 200uF -> a single filter chain for both channels.
The AC ripple at the speaker posts is low : 1.8mVAC per channel in PSUD2 .
The actual measurement is closer to 0-1mVAC at the speaker posts taken with a True RMS DMM.
LSES Filter
I had purchased (2) Hammond 159ZA filter chokes as per Jeff Medwin aka Drlowmu some months ago for future LSES power supply filter experiments.
I was wondering if my (2) Hammond 159ZA filter chokes would be suitable in building a single filter chain for the SE DC 6AQ5 stereo project amp I have been developing.
My concern was if a single LSES filter chain to the finals would have low enough AC ripple to be worth implementing in my particular project.
I honestly don't know what the current "state of the art" implementation for LSES would be in June of 2019 but I recall something about no capacitors over 50uF, so I used those 50uF values in my PSUD2 simulation.
The LSES filter I ran is : 300mH/1A/6 ohms -> 50uF -> 300mH/1A/6 ohms -> 50uF -> a single filter chain for both channels.
IMO, this LSES filter is a high AC ripple type of filter that would need careful implementation to execute correctly. The choice of finals, the mu in particular would probably be another thing to consider.
In my stereo SE DC 6AQ5 circuit, I would need (2) LSES filter chains - one for each channel. Even with that approach, I might need to add more filtering for quiet circuit operation during idle (zero signal conditions).
If I go beyond 50uF per cap, is the filter really a "low storage energy supply" , maybe not in such a case.
Since I am primarily a user of well-filtered "flywheel" power supply filters in my low DCR SE amplifier circuits and not so familiar with the sound of the LSES filters, I will not pass any final judgement.
Computer models are one thing, but "build and listen" on Altec horn systems takes everything to a new level of gnosis.
DT 667
LSES with Hammond 193N Filter Chokes
This LSES filter features Hammond 193N filter chokes for L1 & L2.
The specifications for 193N are : 3H / 500mA / 35 ohm / 600V.
The cost of these Hammond 193N's are $62 at Angela Instruments.
There is another choke rated for 800V, the 193NP with similar current and DCR specs to 193N.
The DCR of the 193N would be considered "mid-fi" but allows for minimum filtering to the finals and low AC ripple at the speaker terminals. I could use the 250VA Hammond ICT without a variac in my circuit and adjust for the extra 33V of B+.
If have read that some guys have used the 193N as an input choke, but it anyone out there reading this has direct experience using this part, please sent an email detailing your experiences.
DT 667 June 2019
LSES with Hammond 193N : 15% Current Step Test
Here is the 15% current step test that shows the settling of the filter. The filter settles at around 300mS. Not as quick as some builders would like but it looks clean for a having a SS rectifier.
DT 667 June 2019