Thanks
Thanks Andy well i'll add another mode make the connetion between power and signal ground bigger to avoid problems there. True for the feedbackit needs to be taken after the emitter resistors. Well There's no wire jump on this circuit only one will do no harm. I'll do these little mods as i get my pc back waiting for a motherboard replacement to be delivered.
Thanks Andy well i'll add another mode make the connetion between power and signal ground bigger to avoid problems there. True for the feedbackit needs to be taken after the emitter resistors. Well There's no wire jump on this circuit only one will do no harm. I'll do these little mods as i get my pc back waiting for a motherboard replacement to be delivered.
Further mods
I've been looking for transformers around well its a rare thing here. The only one i was able to get was a EI 25-0-25 5A. I'll upgrade the outputs to2 pairs TIP35C and TIP 36C. Think the transformer above is a little bit weak plus am planning two build 2 pairs of these amps each pair will be bridged to one 8ohm 10" woofer. At most i can afford two transformers one per amplifier pair. How bad is a 25-0-25 5A + 2X20,000 uF caps for the job for two amps? Is 5A enough for even one amp?
Thanks
I've been looking for transformers around well its a rare thing here. The only one i was able to get was a EI 25-0-25 5A. I'll upgrade the outputs to2 pairs TIP35C and TIP 36C. Think the transformer above is a little bit weak plus am planning two build 2 pairs of these amps each pair will be bridged to one 8ohm 10" woofer. At most i can afford two transformers one per amplifier pair. How bad is a 25-0-25 5A + 2X20,000 uF caps for the job for two amps? Is 5A enough for even one amp?
Thanks
25-0-25 @ 5A is 250VA.
That is sufficient for between 125W and 250W.
I would recommend upto 170W.
Your 25Vac transformer will give considerably more than +-30Vdc, more like +-34Vdc. This will get you to nearer that 80W into 4r0.
A bridged pair will get about 170Winto 8ohms, so your guess of one transformer for each pair is about right.
But, do you want bass? +-20mF into a pair of 4ohm amps will raise the low response by about two octaves (if you adopt the input filter philosophy I have been promoting) to around F-3db=8Hz and may sound a bit bass light.
That is sufficient for between 125W and 250W.
I would recommend upto 170W.
Your 25Vac transformer will give considerably more than +-30Vdc, more like +-34Vdc. This will get you to nearer that 80W into 4r0.
A bridged pair will get about 170Winto 8ohms, so your guess of one transformer for each pair is about right.
But, do you want bass? +-20mF into a pair of 4ohm amps will raise the low response by about two octaves (if you adopt the input filter philosophy I have been promoting) to around F-3db=8Hz and may sound a bit bass light.
Excellent!
The RMS power of a module with that supply will be ~80W/4Ohm, then the bridged amplifier will give ~160W/8Ohm-RMS.
Your 25-0-25/5A transformer is rated 250VA, that's just excellent for a 160W amplifier.
Supply capacitors (2*20mF) are enough too!
Using TIP35C/36C as output devices is a good idea.
The RMS power of a module with that supply will be ~80W/4Ohm, then the bridged amplifier will give ~160W/8Ohm-RMS.
Your 25-0-25/5A transformer is rated 250VA, that's just excellent for a 160W amplifier.
Supply capacitors (2*20mF) are enough too!
Using TIP35C/36C as output devices is a good idea.
It's my starting technique developed during twenty odd years of hillclimbing and sprinting.Andy L. Francis said:Hey Andrew, you foreran me again!
Have you heard the one:
hillclimbers do it quickly, but sprinters take a little longer!
That would be a great if the forum board would include automatic refreshing during writing a post to avoid posts with identical matter.
Zeus Threat, sorry for the offtopic!
Zeus Threat, sorry for the offtopic!
Sorry Andy, don't know why forenamed you andrew got a colleague at work called andy too maybe it was my mind trying to differentiate the two. Well the transformes has this written on them 25-0-25 5A but 125VA might sound weaker now. How is that VA derived finally am getting lost with it isn't it from the 25V and 5A or something like that?
Hi,
the transformer is a centre tapped 50Vac @ 5A, that makes it 250VA.
The windings could be called up as 0-25-50Vac and if they were separated then you would have 0-25, 0-25 each capable of 5A.
the transformer is a centre tapped 50Vac @ 5A, that makes it 250VA.
The windings could be called up as 0-25-50Vac and if they were separated then you would have 0-25, 0-25 each capable of 5A.
Thanks andrew that sounds more correct to me too, but i don't understand why they printed 25-0-25V@5A/125VA on the transformer when its a 250VA?
Isn't that marking is 125V instead of 125VA?
Probably it's crazy idea because in Mauritius the mains voltage is 230Vac.
What is the size and the weight of the transformer? Could you attach a photo of it?
Probably it's crazy idea because in Mauritius the mains voltage is 230Vac.
What is the size and the weight of the transformer? Could you attach a photo of it?
Thanks for the foto!
Bad news: from the size this is a 125VA rated transformer 🙁
Sufficient for one channel only.
Bad news: from the size this is a 125VA rated transformer 🙁
Sufficient for one channel only.
I agree that looks a bit small for 250VA EI.
I cannot see how they arrive at 5A. A dual secondary could parallel the windings to give 5A total but a centre tapped cannot achieve that.
However, if it is a half winding rating of 125VA per winding then it is a small looking 250VA transformer. Can you weigh it and measure the core width and thickness? That area determines the VA rating fairly accurately.
One transformer rated at 125VA can power between 60W and 125W.
I cannot see how they arrive at 5A. A dual secondary could parallel the windings to give 5A total but a centre tapped cannot achieve that.
However, if it is a half winding rating of 125VA per winding then it is a small looking 250VA transformer. Can you weigh it and measure the core width and thickness? That area determines the VA rating fairly accurately.
One transformer rated at 125VA can power between 60W and 125W.
So it means at most i can get 2.5A per rail which is 50Vac X 2.5A which comes to 125VA. So that 5A is total current per set of windings or am i wrong? Anyway i'll have to stick to two of these for the time being in case i can much later i'll upgrade to 4 transformers with one per amp.
The core looking from top is 5.5cm by 7.5cm.
Height is 4.5cm.
Weight is approximately 2400g or 5.5 lbs
Can you please explain how you acheive to derive an approx VA rating from these figures might need to do it for another transformer i have.
Thanks
Height is 4.5cm.
Weight is approximately 2400g or 5.5 lbs
Can you please explain how you acheive to derive an approx VA rating from these figures might need to do it for another transformer i have.
Thanks
those measurements are the transformer overall size.
you need to look at the inside of the bobbin and measure the core that passes through the bobbin.
2.5kg is heavy, it might still be 250VA.
Try to find the free download for designing an EI transformer.
Anybody with a link?
you need to look at the inside of the bobbin and measure the core that passes through the bobbin.
2.5kg is heavy, it might still be 250VA.
Try to find the free download for designing an EI transformer.
Anybody with a link?
the cross sectional area (width*thickness) of metal laminations that pass through the bobbin.
The wire diameter will help as well.
The wire diameter will help as well.
Zeus, I'm sure that it's a 125VA rated transformer.
There is a ~200VA "EI" transformer laying around here, and measures ~3kg.
http://www.tauscher.com/html/ei_07_e.html
125VA rated EI-transformer measures ~2kg, a 250VA rated measures ~3.5kg.
There is a ~200VA "EI" transformer laying around here, and measures ~3kg.
http://www.tauscher.com/html/ei_07_e.html
125VA rated EI-transformer measures ~2kg, a 250VA rated measures ~3.5kg.
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