PSU question

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4

4daudio

Member
Joined 2017
#1
Hope this is in the right place,

I have a couple of BHI 500va single secondary toroidal transformers, 2x 15,000uf NAD caps + 4x 10,000uf cerafines & decided that I should do something with them,

I also have 2x hammond 155b 6mh 2a chokes,

Transformers output 20.5v or 22.2v no load depending on which primary I use so I am in the ballpark for DOZ or JHL 1969 monoblocks,

Thinking 50a bridge - 15,000uf - choke - 2x10,000uf cerafine per monoblock,

Can I get away with the small chokes if I use a soft start for the transformers ?

Thanks.
 
#4
You can put a thermistor in series with the transformer primary to act as a soft start. Nelson Pass does that in his First Watt power supplies. Many diyers building First Watt clones and similar amplifiers have done that, including myself. Usually CL60 thermistor is used but some use even higher resistance thermistors for an even slower start.
 
#5
Speakers will be 8ohm & maybe 6ohm, I will be looking at about 27v & 1.35a idle current going on Rod Elliot's chart as a starting point,
When I find my rectifiers I will load a psu & see what dc voltage I have exactly,

I have some inrush limit thermistors from other projects not sure on the values, never used them for audio psu's before,
also have relays & wirewound resistors hiding in the loft.

Thanks
 
#6
I had a play with psud2 using the esp chart of 1.35A been 75% of max current & allowing for me guesstimating esr of the caps becasue its below what my tester can measure & a rough measurement of transformer secondary resistance with fluke87 in 4.5 digit mode,

I am below 2A & right around 27volt,
I think I will be ok with an inrush thermistors & bypass relay, may have to add a bit more capacitance,

The proof is in the measurement when I hook it up & see how far off my sim is to reality.
 
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