Hi all
I'm about to rebuild an old stereo amplifier I've had for years. It's based on two Maplin Mosfet modules (Dave Goodman - 1982 - the 1997 spec version with Exicon Mosfets).
I've got all the parts to build a 500va toroidal based power supply with 4x10,000u/80v Caps, but I don't know if it would be better to do two split supplies each with their own bridge rectifiers and 2x10,000u caps, one for each amp, or a shared supply with two br's and 4x10,000u caps. What's best practice?
Thanks
Stratt
I'm about to rebuild an old stereo amplifier I've had for years. It's based on two Maplin Mosfet modules (Dave Goodman - 1982 - the 1997 spec version with Exicon Mosfets).
I've got all the parts to build a 500va toroidal based power supply with 4x10,000u/80v Caps, but I don't know if it would be better to do two split supplies each with their own bridge rectifiers and 2x10,000u caps, one for each amp, or a shared supply with two br's and 4x10,000u caps. What's best practice?
Thanks
Stratt
How is the existing amplifier set up?
How quiet is the hum and/or buzz at the speaker?
Have you measured the hum and noise at the speaker terminals?
Have you measured the output offset at the (empty) speaker terminals?
When I built it all those years ago I just used what I had to hand; a 32-0-32 2A transformer and a couple of 4700u/80v caps with a 25A br. It's very quiet with little or no offset at the speaker terminals. Just lacks oomph.
Now I have the wherewithal to finish the job properly. I've always been curious to see what difference it will make to have a power supply with enough grunt, but I wasn't sure whether to isolate the dc parts of the supply for each amp.
You might want to use seperate bridge rectifiers for the + and - supplies if your transformer has two seperate secondaries though.
That's what I would have done anyway if I didn't do the separate supply stuff. I'm leaning toward this method.
Thanks
Stratt
I think that should be adequate. There should be no hum with the right grounding scheme.
I'm using a 3U rack type case and I'll be using a typical star grounding scheme with Rod Elliot's safety loop breaker circuit using a 35A bridge rectifier in parallel with a 10R resistor and 100nf capacitor. I'll also keep the power supply over to one side so I can route mains power away from audio circuitry.
Cheers
Stratt
Finished!
So I finished my amp rebuild. It's got two old Maplin mosfet modules that I put together back in 1997. I have no idea where the heatsinks came from.
I've replaced the old 2A 32-0-32 laminated core transformer with a brand new 500va 35 + 35 toroidal. It had just two 4700u 80v power supply capacitors that I've replaced with six 10,000u 80v types, three per side. It has a Velleman loudspeaker protection module (wait and error leds on the front) and a cheapo chinese inrush limit module with a massive ceramic resistor. Switching on is absolutely silent, apart from the satisfying relay clicks. Check out the literal star earth!
I've also put in a chinese 23 step switched attenuator. Note the replacement resistor because of a faulty resistor value.
When I turned it on with speakers plugged in for the first time I thought it was broken. Turned out it was working perfectly; it's just absolutely silent with no signal. Then when I cranked it up I hadn't realised these amplifiers could sound so good with so much grunt!
It's not particularly pretty (probably prettier on the inside!) but it does a good job.
Cheers
Stratt
So I finished my amp rebuild. It's got two old Maplin mosfet modules that I put together back in 1997. I have no idea where the heatsinks came from.
I've replaced the old 2A 32-0-32 laminated core transformer with a brand new 500va 35 + 35 toroidal. It had just two 4700u 80v power supply capacitors that I've replaced with six 10,000u 80v types, three per side. It has a Velleman loudspeaker protection module (wait and error leds on the front) and a cheapo chinese inrush limit module with a massive ceramic resistor. Switching on is absolutely silent, apart from the satisfying relay clicks. Check out the literal star earth!
I've also put in a chinese 23 step switched attenuator. Note the replacement resistor because of a faulty resistor value.
When I turned it on with speakers plugged in for the first time I thought it was broken. Turned out it was working perfectly; it's just absolutely silent with no signal. Then when I cranked it up I hadn't realised these amplifiers could sound so good with so much grunt!
It's not particularly pretty (probably prettier on the inside!) but it does a good job.
Cheers
Stratt
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