FOverture5

For the three and more legged things
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Nick
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#16 Re: FOverture5

Post by Nick »

It makes the inside of the amp safer if live and neutral are reversed, entirely possible with some mains plugs, even without incorrect house wiring. Dont think it makes any difference to the amp.
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little eddy
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#17 Re: FOverture5

Post by little eddy »

So I have embarked on my exploratory journey through the desert sands.

My vehicle of choice, a dilapidated Sony ta-212 upgraded with a new engine (600VA), transmission (30 sandwatts/channel) and cooling (probably not enough) will hopefully get me to my audio destination. But lack of navigational skills and travel budget constraints have meant I will initially avoid route F5.

I was drawn to this article on the LM3886, (as I used in my 'cheap-as-chips' amp). http://www.circuitbasics.com/design-hi- ... er-lm3886/

So I have ordered a couple of the following pcbs as they incorporate both the Zobel and Thiele components omitted in many designs. I will change nearly all of the individual components in line with my calculations after following the above guide.
LM3886 pcb.jpg
Initially will build with a gain of 21 so can test as a single stage solution.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#18 Re: FOverture5

Post by simon »

Interesting link, I'll have to have a proper read of that site when I have more time.

He's made the pcb design available, but you've ordered some different ones if I understand correctly? If so which ones and from where?
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#19 Re: FOverture5

Post by little eddy »

I looked for a link to buy his PCBs but with no luck. So the ones I bought are from slease-bay. But at less than £5 for an assembled board quite reasonable but obviously not branded parts. Should take all of the recalculated components - will know over the next couple of weeks.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#20 Re: FOverture5

Post by simon »

It took me a second look but right at the top there's a link to the schematic and PCB in EasyEDA. Looks like you should be able to click on "buy" somewhere but I can't see it, but I think you can generate the gerbers - 5 no. boards are $23 at PCBWay, or $28 for 10. Plus shipping and customs. Cheap as chips really. But expensive compared to complete amps from China.
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#21 Re: FOverture5

Post by little eddy »

Progressing slowly but b****y cold in the garage.
With sockets small.jpg
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
little eddy
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#22 Re: FOverture5

Post by little eddy »

The capacitors look a bit bigger!
Before and after small.jpg
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#23 Re: FOverture5

Post by little eddy »

All looking a bit industrial but I knew those plc termination blocks would come in handy some day.
DIN Terminals small.jpg
With two parallel 300VA transformers and 80,000uF of caps, need to get some bigger input fuses because 2.5A slow-blow ones popping like candy!
Rectifier and filter small.jpg
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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ed
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#24 Re: FOverture5

Post by ed »

I recommend a thermistor between the primaries on the transformers....I use cl60s but anything similar should work
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#25 Re: FOverture5

Post by little eddy »

ed wrote: Fri Mar 23, 2018 2:33 pm I recommend a thermistor between the primaries on the transformers....I use cl60s but anything similar should work
Stuck in Sunderland looking a a 'Stadium of Light neon.

Thanks will have a look at the F5 schematics when I get back as know they employ thermistors. Is this necessary on non class A amps? I believe the max temperature for the LM3886 is 150C.

I thought the type refered to a temperature threshold but the data sheet suggests a bit more investigation needed.

I haven't seen thermistors used with the LM 3886. Had ordered some 5A slow blow fuses so will see how it goes.

EDIT. Just seen F5 PSU schematics and uses the same CL60. Looks easy to incorporate. Thanks Ed. But the scheme still uses a 1.25A fuse where I'm blowing 2.5A for fun when 80,000uf is not unusual.! Also see the F5 schematic has a thermistor in the 0V line.

Also need to get a larger or less sensitive class of MCB in the garage consumer unit! Should have thought 4A was going to be an issue. Anyway it's an excuse to move to the kitchen to test.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#26 Re: FOverture5

Post by ed »

I'm not sure now what you're doing with this power supply...I mentioned it because the thermistor effect is generic if used in the primary, i.e it restricts the inrush current at switch on and gives the fuse a fighting chance.

I have 120000 uf in all my mosfet amps and so far haven't wasted a fuse on 300 watts, but as I say I didn't pay close attention to your supply so you might need something more robust.
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#27 Re: FOverture5

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The point of the thermistor is it reduces the turn-on surge into the transformer. When cold (at turn on) its high resistance, so inrush is reduced, as current flows, it warms up and the resistance drops and is low under normal use.
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#28 Re: FOverture5

Post by little eddy »

I have the 2 transformer primaries in parallel. Each has the split 120V windings in series as per an earlier schematic. Have bought 2 so 1 per transformer to minimise volt drop. Some schemes have them in the 240V supply, others between the two 120V windings. Does it make any difference?
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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#29 Re: FOverture5

Post by Nick »

No, use one in series with each pair of primaries in series, one per transformer.
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little eddy
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#30 Re: FOverture5

Post by little eddy »

Well you learn something everyday.

I can remember squirrel cage motors with 'embedded' thermistors that fed a control relay, thus I thought they were used in control circuits, rather than in-line.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
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