Very good heatsinking and steady mains would be required. MWP has run a bridged gainclone long term at this voltage. Or you could regulate, a good idea, but LM3886s just are not the easiest way to get 350 watts @ 8ohm.
Another possibility is more bridging and floating some of the amps above ground
Another possibility is more bridging and floating some of the amps above ground
to protect the chips u need to use something like UPC1237HA, and relays, if u read carefully datasheets of these chips many a cases will suggest output protection at 0vRMS input ....
tryshorting ouput with something like 2 V-RMS and wow u ve got couple of blown chips at ur hand.
My recomendation use a protector circuit particularly when u r looking at something like 350 watts RMS
tryshorting ouput with something like 2 V-RMS and wow u ve got couple of blown chips at ur hand.
My recomendation use a protector circuit particularly when u r looking at something like 350 watts RMS
Sorry but you simply can't get 350W RMS in 8 ohms out of a bridged/parallel LM3886 based amplifier.
I have made a bridged/parallel based on LM3886
(see http://www.diyaudio.com/forums/attachment.php?s=&postid=224065&stamp=1061370653)
and even with a regulated supply of -/+ 42 V you will not get to 350 W in 8 ohm, despite how many LM3886 you use.
Remember that paralleling LM3886 gives you extra current and you can go as fare as you want by just adding extra chips. (in theory you should be able to get 1000W in 1 ohm with the right supply and cooling, if you need that)
However you also need some voltage across you load and to get extra you can bridge, but it will only give you max 2x the voltage across your load and you can not take it any further.
With a 2 x30 V AC transformer and a bridged/parallel set-up of at least 4 x LM3886 you get 200-250 W RMS in 8 ohm. And trust me, it is a lot !
Have fun
Thomas
I have made a bridged/parallel based on LM3886
(see http://www.diyaudio.com/forums/attachment.php?s=&postid=224065&stamp=1061370653)
and even with a regulated supply of -/+ 42 V you will not get to 350 W in 8 ohm, despite how many LM3886 you use.
Remember that paralleling LM3886 gives you extra current and you can go as fare as you want by just adding extra chips. (in theory you should be able to get 1000W in 1 ohm with the right supply and cooling, if you need that)
However you also need some voltage across you load and to get extra you can bridge, but it will only give you max 2x the voltage across your load and you can not take it any further.
With a 2 x30 V AC transformer and a bridged/parallel set-up of at least 4 x LM3886 you get 200-250 W RMS in 8 ohm. And trust me, it is a lot !
Have fun
Thomas
tlmadsen said:
Hi!!! I'm reading the post of your 4xLM3886 amp.
Very nice job!!! and very interesting post to read.
Since I started reading in this forum, I'm thinking that my amps (GEMINI XG3000) specifications lies a lot.
The specification is 2x170W in 8ohms or 450W RMS bridged in 8ohms.
Im planning to buy a scope, then i can measure the output and see the really output power.
Also i have a true-RMS meter to do some measurements, but... i cant see V output vs PSU v to see the clipping.
Another thing is that the gemini amp doesnt have big caps. I'm using it to power my sub (RCF 18" 350W). So i think it lacks of psu capacitors.
That's why I want to make my own AMP, and 350W for the 18" speaker.
thanks again!!!
A 6 chip BPA would get you plenty of power and the difference in 250W and 350W is minimal if the 6 chip BPA could supply ample current to the woofer.
Jeff Rowland used a 6 chip BPA to get a very powerful amplifier that sounds VERY good.
Of course not as good as his old stuff
, but good none the less.
Jeff Rowland used a 6 chip BPA to get a very powerful amplifier that sounds VERY good.
Of course not as good as his old stuff
, but good none the less.
zafira1981 said:
If the specification has the letters RMS, then it's quite likely close to that power. If it does not then it can be anything.
Two things you can do that do not need a scope:
1) Measure the supply voltage. My guess is a bipolar 170W RMS amp should need close to +/-70v.
2) Count the output transistors on each channel. A bipolar 170w RMS amp should have at least 6 on each side: three NPN and three PNP. They can also be six NPN if it's an old design. Also check the part numbers to see which are their top spec voltages.
Also have a look at the transformer size. Small transformer size and/or few output transistors, even if voltages are high, mean that the output on lower impedance speakers will not be large.
To see the clipping point you do need a scope.
What is the suply capacitance?
If the transformer is large enough and the bridges are heatsinked, you can go up to uF 20,000 with no need to add anything else. BTW: splitting the supply after the transformer with separate bridges and capacitors can be very effective.
It might be a better idea to use that amp to power the RCFs, instead of the 3886s, if the tests I suggest show the 170w may be right.
But to be completely sure you certainly need a 'scope and an output load. This output has to be heatsinked.
Carlos
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