how can i measure the current my gainclone needs? if i connect my multimeter in series with one of the power rails, i get zero reading and severe distortion on the output.
Truck
12Vx2A = 24 VA.
Anyway, you need big batteries, and worst than that, how are you going to charge that?
The alternator on your car may not handle with that.
Maby you could go with a switching PSU instead of batteries.
You're confusing me! 
Matttcattt said:its going to be a car amp 😀 max voltage is about +/- 14v, i cant aford more batteries.
it doesnt need that big a power supply does it?
my 2 channel gainclone with a +/-12v supply takes about 2A max, which is about 12VA needed? 12x8=96VA. or am i insane?
at 60watts per chip at 24v is 2.5A max, 2.5x16=40A.
re-thinking needed possibly 😀
maybe i could aford +/-24v supplys 🙄
edit: i have 66,000uf on each rail 😎
12Vx2A = 24 VA.
Anyway, you need big batteries, and worst than that, how are you going to charge that?
The alternator on your car may not handle with that.
Maby you could go with a switching PSU instead of batteries.
You're confusing me!
Matttcattt said:
I also tried to measure the current exactly the same way as you tried, and had hudreds of mA reading on multimeter. Of course I had SEVERE distortion on the output. 🙂 There should be some other ways to measure it. Any comment, please?
are the capacitors circled in red electrolytic? can i use electrolytic capacitors? can i use 1000uf ones? i have loads. i am using 4 on one circuit board, can i use one 1000uf capacitor per rail for all of them?
where do the input capacitors go? after the potentiometer? where the blue circles are?
where do the input capacitors go? after the potentiometer? where the blue circles are?
waste of parts and time
Matttcattt,
Something has hit me in my had, I was too confused.
Have you read the datasheet of the LM3875?
With +/-12 volts you get something around 10 watts.
If you bridge two of them, you get 20 watts.
Paralleling you double the current.
So... with 4 chips in bridge-parallel configuration per channel you'll get 20 watts!
It's a big waste of parts, time and money.
These power op-amps are not made to work at these low voltages.
You should investigate the TDA1562.
You'll get around 3 times more power with one chip per channel than with four LM3875s in bridge-parallel at +/-12v.
And it's made to work on single voltage supply.
For these voltages I don't know a chip with more power than this.
It was made for car-audio.
Matttcattt,
Something has hit me in my had, I was too confused.
Have you read the datasheet of the LM3875?
With +/-12 volts you get something around 10 watts.
If you bridge two of them, you get 20 watts.
Paralleling you double the current.
So... with 4 chips in bridge-parallel configuration per channel you'll get 20 watts!
It's a big waste of parts, time and money.
These power op-amps are not made to work at these low voltages.
You should investigate the TDA1562.
You'll get around 3 times more power with one chip per channel than with four LM3875s in bridge-parallel at +/-12v.
And it's made to work on single voltage supply.
For these voltages I don't know a chip with more power than this.
It was made for car-audio.
Carlos,
Your power calculation isn't quite right: when bridging an amp the power theoretically increases by x4 since power = V^2/R
Single ended, assuming an 8R load and +/- 9v output swing....
9v^2 / 8 = 10 watts
As above but bridged to give a +/- 18v output swing....
18^2 / 8 = 40 watts.
When bridging an amp, the output current doubles compared with the single configuration. In the case of the bridged amp above, the peak current is 18v / 8R = 2.25A, which is well within the capabilities of a single pair of LM3886 devices so paralleling isn't necessary.
Bridging is an efficient way of getting high power from low supply voltages.
Regards,
David.
Your power calculation isn't quite right: when bridging an amp the power theoretically increases by x4 since power = V^2/R
Single ended, assuming an 8R load and +/- 9v output swing....
9v^2 / 8 = 10 watts
As above but bridged to give a +/- 18v output swing....
18^2 / 8 = 40 watts.
When bridging an amp, the output current doubles compared with the single configuration. In the case of the bridged amp above, the peak current is 18v / 8R = 2.25A, which is well within the capabilities of a single pair of LM3886 devices so paralleling isn't necessary.
Bridging is an efficient way of getting high power from low supply voltages.
Regards,
David.
Right
David,
You're absolutely right, now I wake up...
But I still think it's much cheaper to use 4 TDA1562s (only one per channel).
Or else it's going to be a huge amp, and the man will loose all the baggage space of his car with the amp and the extra batteries.
And to charge those batteries...
I think he wants a Krell in his car.
David,
You're absolutely right, now I wake up...
But I still think it's much cheaper to use 4 TDA1562s (only one per channel).
Or else it's going to be a huge amp, and the man will loose all the baggage space of his car with the amp and the extra batteries.
And to charge those batteries...
I think he wants a Krell in his car.
Re: waste of parts and time
time: i have loads of time
money: as above 😎
parts: chips, free, others about £1 per amp (about £16)carlosfm said:Matttcattt,
Something has hit me in my had, I was too confused.
Have you read the datasheet of the LM3875?
With +/-12 volts you get something around 10 watts.
If you bridge two of them, you get 20 watts.
Paralleling you double the current.
So... with 4 chips in bridge-parallel configuration per channel you'll get 20 watts!
It's a big waste of parts, time and money.
time: i have loads of time
money: as above 😎
im using the OPA541, not the LM3875. it can run with +/-4v.
These power op-amps are not made to work at these low voltages.
You should investigate the TDA1562.
You'll get around 3 times more power with one chip per channel than with four LM3875s in bridge-parallel at +/-12v.
And it's made to work on single voltage supply.
For these voltages I don't know a chip with more power than this.
It was made for car-audio.
for the third time 
:
are the capacitors circled in red electrolytic? can i use electrolytic capacitors? can i use 1000uf ones? i have loads. i am using 4 on one circuit board, can i use one 1000uf capacitor per rail for all of them?
where do the input capacitors go? after the potentiometer? where the blue circles are?
:are the capacitors circled in red electrolytic? can i use electrolytic capacitors? can i use 1000uf ones? i have loads. i am using 4 on one circuit board, can i use one 1000uf capacitor per rail for all of them?
where do the input capacitors go? after the potentiometer? where the blue circles are?
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Matttcattt said:for the third time
are the capacitors circled in red electrolytic? can i use electrolytic capacitors? can i use 1000uf ones? i have loads. i am using 4 on one circuit board, can i use one 1000uf capacitor per rail for all of them?
where do the input capacitors go? after the potentiometer? where the blue circles are?
Yes, you can use 1000uf electrolytic, but bypass them with 100nf poly or ceramic near the op-amp pins.
I think you only need one input capacitor, after the pot.
okcarlosfm said:
that will save me some money - at £4 per input capacitor 😀 i only need 6, not 16 😀
are the capacitors accross the rails really neccessary? (on the DRV134 on the bridge and parrellel circuit) if they are, what are the ideal components? (type and value)
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