Hi guys,
this is my first thread 🙂
I am building a LM1875 dual mono amplifier (it is a cliche I know, but it is what it is) and I have a rough time finding adequate transformer for it.
I live in Bosnia and there are no specialists who produce transformers (as far as I know). Then few days ago I found this toroidal transformer.
It's been taken out from some brand name audio amplifier, but I don't know which one.
Now, on the label it says 2A along with some other info. Does this mean that this transformer can output just 2 amps of current or this means that I need 2Amp fuse for it?
Basically, is this transformer enough for my amplifier... It is about 11cm (just over 5 inches) in diameter and it's 1270g (just over 2 lbs).
When I use it with my LM1875 test amp, music sound great to me. I don't hear any distortion even with volume all the way up.
Thank you.
this is my first thread 🙂
I am building a LM1875 dual mono amplifier (it is a cliche I know, but it is what it is) and I have a rough time finding adequate transformer for it.
I live in Bosnia and there are no specialists who produce transformers (as far as I know). Then few days ago I found this toroidal transformer.
It's been taken out from some brand name audio amplifier, but I don't know which one.
Now, on the label it says 2A along with some other info. Does this mean that this transformer can output just 2 amps of current or this means that I need 2Amp fuse for it?
Basically, is this transformer enough for my amplifier... It is about 11cm (just over 5 inches) in diameter and it's 1270g (just over 2 lbs).
When I use it with my LM1875 test amp, music sound great to me. I don't hear any distortion even with volume all the way up.
Thank you.
I'm not sure 2A is for secondary.
But you can check it: measure secondary voltage and load winding with some safe load. Safe load means that voltage drop with load won't be higher than 5-10%.
I have to say that 33VAC rectified is, of cause, too much for LM1876.
18 VAC rectified can be ok, but that winding may have weaker (thinner) wire, you must check it first.
But you can check it: measure secondary voltage and load winding with some safe load. Safe load means that voltage drop with load won't be higher than 5-10%.
I have to say that 33VAC rectified is, of cause, too much for LM1876.
18 VAC rectified can be ok, but that winding may have weaker (thinner) wire, you must check it first.
Hi stojanbn
The transformer is 500VA. 2 amp x 250V primary implies a maximum of 7.5A for each 33V secondary with all other secondaries open circuit. Or, 13.9A for each 18V secondary with all other secondaries open. But only if the secondary wires are large (ie around 2mm ^2 cross sectional area)
More than enough to power the dual mono.
The transformer is 500VA. 2 amp x 250V primary implies a maximum of 7.5A for each 33V secondary with all other secondaries open circuit. Or, 13.9A for each 18V secondary with all other secondaries open. But only if the secondary wires are large (ie around 2mm ^2 cross sectional area)
More than enough to power the dual mono.
Does this mean the load can be 60W light bulb?
I was planning to use dual 18V secondary for the LM1875. That is how I tested both amplifier and transformer.
18V secondary is a pair of tick white wires and a black one as center tap. Those wires are significantly ticker from other secondaries. It gives 25V rectified.
On the image below You can see those dual supply secondary with ticker wires form the rest od secondaries.
And this is my test setup 🙂
Final version will be with other PCBs for amplifiers and rectifier. Also a larger heat sink will be used.
I guess I will use 2A 250V fuse for primary and 2.5A fuse for each rectified DC rail.
Thank You.
written as that,xformer is rated at 2A at 230Vac , simple as that
so , roughly 460VA
however,without dimensions - even if bolt shown on pictures is M8 ( not M6) , it looks small for 460VA
last picture, where we can compare donut size with size of fuse holders on pcb - it looks more as 200VA or so
in any case - more than good enough for intended use
so , roughly 460VA
however,without dimensions - even if bolt shown on pictures is M8 ( not M6) , it looks small for 460VA
last picture, where we can compare donut size with size of fuse holders on pcb - it looks more as 200VA or so
in any case - more than good enough for intended use
Perfectly correct: there are two indications: 230V 50Hz as a nominal primary voltage, and 250V 2A with a thermal fuse of 125°C.
The nominal primary current should not exceed 75% of the rated fuse current, which means a 340VA limit (at most).
The nominal VA is probably 300VA or 250VA.
Fortunately, for an amplifier it does not matter too much (no safety issues).
If it is underdimensioned, all you risk is sagging during high power episodes
Dimensions (110mm) and weight (1.3 kg) given indicate maybe only 120-150 VA, based on a quick comparison with other units.
Yeah... Either way I think it would be enough for lm1875 dual mono amplifier. With +25/-25V on supply rails, the amp can put out maybe around 25W per channel (maaaybe a bit more as JohnAudioTech measured).
In past several days I somewhat tested the amp setup and performance, and there is no audible distortion even with the volume way up. The sound is loud, punchy and clean.
Anyway, thank you so much guys for your inputs. They all were helpful.
Even a 120VA transformer should be enough for LM1875, right?!
I don't know how much power my amp puts out. It should be around 25 W with +25/-25 V supply rails. JohnAudioTech measured 31 W output with non inductive load (8 Ohm as my speakers) at +25/-25 V supply with same PCB and components. That is the same setup I have for testing purposes. My final PCB will be this one (some components will be different opposed to JohnAudioTech's and my testing amp):
I don't know how much power my amp puts out. It should be around 25 W with +25/-25 V supply rails. JohnAudioTech measured 31 W output with non inductive load (8 Ohm as my speakers) at +25/-25 V supply with same PCB and components. That is the same setup I have for testing purposes. My final PCB will be this one (some components will be different opposed to JohnAudioTech's and my testing amp):
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Hello Stojan, around 50VA per channel will be enough.
You can also read this: Building a Gainclone chip amp power supply.
You can also read this: Building a Gainclone chip amp power supply.