Cheapmondo

Came across the Quasimondo and Cheapmondo circuits to excite transformer/rectifier oscillations and tune in snubber and decided to implement it using junkbox parts:

• Mosfet: 05N03L
• Logic level gate
• Ron 4mohm @4.5Vgs Id=55A
• Id max 80A
• "gate driver" 
• transistor PNP 2N3906
• basis resistor 1k
• pulldown 150ohm
• Clock generator 
• 74LS14 hex inverter
• RC feedback
• 1uF
• 1kOhm

Simulated in LTspice (using 0.1uF to get higher oscilator freq and lower sim time)
got some LTspice help from:
https://www.mikrocontroller.net/topic/428100 on how to use schmitt trigger in ltspice
http://electronicsbeliever.com/how-to-sweep-resistance-in-ltspice-with-step-by-step-tutorials/ on how to sweep resistor values

Not pretty but it works well :-)

Here is a 500VA toroid oscillating at 1Mhz.

Here it is dampened out. 

NewClassD NCD1 (re)build. New case and snubber.

Decided to give my aging NewClassD NCD1 a new home. Its been living inside a Doxa 40 Power amp enclosure for 6 years.

I figured i could cram it into a smaller case. I went for the B2109 from Ebay

Had to split the amp alu thermal sink in 2. one on each case heat-sink. I put a 500VA 1x230V 2x36V toroid transformer in there powered trough a 20D thermistor for soft startup. I figured that as normal 500W PC power supplies can live with this in series at all times a ClassD amp might also.  Have no room for a full soft start PCB. The transformer should give me a theoretical Pmax=36V^2/8ohm=162W.

Had some faint noise in the speakers when listening at 50cm. 

Mounted Common mode ferrite filters on power harness into the boards and and on the speaker cable output. Also added ceramic capacitors from speaker terminals to copper tape on lower back chassi. This solved all the hissing noise in the speakers.

Tranformer snubbering

I made a "Quasimondo clone" using stuff in my junkbox. Squarewave generated by 74LS14 and a mosfet that came off a PC mainboard CPU DCDC converter. It is driven with a PNP transistor. and the rest is like the Quasimondo. The exiting works and the transformer rings at 1Mhz.

Here are some results with C_s=150nF Cp=10nF and different R values taken from Rigol DS1054Z. Saved as csv and imported to Libre Office.

Seems 14ohm is the right one. 

Finished 2 channel snubber. One for positive and one for negative supply. 150nF/100V and 10nF/400V film capacitors. Two 30ohm metal film in parallel gives 15ohm.