you could try to remove a few turns of wire from the transformar that you have..
you would need to remove the wire until you find the middle point.. and count how many turns are...
and then you wouln need to revove a few more truns until you have about 45V ac max or less and then put the other secondary back..
43/50 * number of turns that you numberd in the secondary that you unwind
that is how many turns should have each secondary for it to have a 43V ac output
if you know how many turns a secondary hav and haow many it must have you can find how many you wolud need to remove from the no 2 secondary ...
i hope you understand what i am saying
the voltage rise is 1.41 times minus 1.5V,
i said up to 45Vac becatse this would give a 62Vdc but when the amp is running at high volume this could drop up tu 3-4-5V
my english sucks,i know
you would need to remove the wire until you find the middle point.. and count how many turns are...
and then you wouln need to revove a few more truns until you have about 45V ac max or less and then put the other secondary back..
43/50 * number of turns that you numberd in the secondary that you unwind
that is how many turns should have each secondary for it to have a 43V ac output
if you know how many turns a secondary hav and haow many it must have you can find how many you wolud need to remove from the no 2 secondary ...
i hope you understand what i am saying
the voltage rise is 1.41 times minus 1.5V,
i said up to 45Vac becatse this would give a 62Vdc but when the amp is running at high volume this could drop up tu 3-4-5V
my english sucks,i know
so you are only 13...and this is your first amp that you try to build..
i also sugest you do a little more reserch before start building..
you need a 45V ac max, yes,you could use what ever voltage you wnalt, up to 45V ac , and it must be dual..
you also must check to see that it has at least 500W for stereo in 8 ohm operaton and almost double.. for 4 ohm..
i have a 400W for mono and i use it in 4 ohm,and it works fine..
yaou may also whant to make sure that you have original transitors.. because fake ones blw up in you face..(they burn out)
i used 3 paires for the output.. but i think that it could work only with 2 paires..but i used 3 ...you could use 4 but it would be a wast of many..because 3 originals will work just fine..
i also sugest you do a little more reserch before start building..
you need a 45V ac max, yes,you could use what ever voltage you wnalt, up to 45V ac , and it must be dual..
you also must check to see that it has at least 500W for stereo in 8 ohm operaton and almost double.. for 4 ohm..
i have a 400W for mono and i use it in 4 ohm,and it works fine..
yaou may also whant to make sure that you have original transitors.. because fake ones blw up in you face..(they burn out)
i used 3 paires for the output.. but i think that it could work only with 2 paires..but i used 3 ...you could use 4 but it would be a wast of many..because 3 originals will work just fine..
For the M250 you want a 2x40V transformer. The voltage after rectifying to DC is typically (AC voltage * 1.414) - diode loss of about 1v. So a 2x40 transformer, or 40-0-40 transformer would be ideal. You want at least a 300VA one I would think. Make sure to get some decent capacitance - I have just bought 2x15000uF 80V capacitors on eBay for a little under £13.
If you already have your 2x35V transformer, it will work, you just won't get the full 250W out of the amplifier.. probably more like 100W-120W or so.
I see that you're 13 and I won't discourage you since I was about 12-13 when I started seriously messing with electronics myself
But you do need to read up on things when dealing with high power circuits like this, or you're liable to end up with a large bang, a lot of smoke, and wasted money. There is a lot of good reference material online now, a lot of which is on Rod Elliot's site at http://sound.westhost.com
A useful trick, is to buy some 10 ohm 10W resistors, and use these in place of the fuses when you first power the amp on. If the resistors get burning hot, there is a fault in the circuit. Similarly, for when you wire up the transformer, build a "lamp lead" so if you get anything wrong, the current will be limited, and you won't cause a big bang and a fire.
Just to add - Farnell and RS are indeed good, but can be expensive. Rapid Electronics is good for some less fancy parts, and a bit cheaper with shipping. Forget Maplin - they're useless these days for anything but the most basic of stuff.
If you already have your 2x35V transformer, it will work, you just won't get the full 250W out of the amplifier.. probably more like 100W-120W or so.
I see that you're 13 and I won't discourage you since I was about 12-13 when I started seriously messing with electronics myself
But you do need to read up on things when dealing with high power circuits like this, or you're liable to end up with a large bang, a lot of smoke, and wasted money. There is a lot of good reference material online now, a lot of which is on Rod Elliot's site at http://sound.westhost.comA useful trick, is to buy some 10 ohm 10W resistors, and use these in place of the fuses when you first power the amp on. If the resistors get burning hot, there is a fault in the circuit. Similarly, for when you wire up the transformer, build a "lamp lead" so if you get anything wrong, the current will be limited, and you won't cause a big bang and a fire.
Just to add - Farnell and RS are indeed good, but can be expensive. Rapid Electronics is good for some less fancy parts, and a bit cheaper with shipping. Forget Maplin - they're useless these days for anything but the most basic of stuff.
I finished building the M250 a couple of days ago, was my first amplifier and I'm quite happy with it. I just got a question about the setting of bias current. I try it with a light bulb in series with the ac line, I can't reach the recomended setting of 1.8 mA, the amp iddles at 1.92 mA across T3 and when I want to reach 1.8mA the light bulb goes a lot brighter so I left it just in the threshold. Is it normal for the amp to be correctly biased to draw much more power or I have made a mistake ? Is the first truly analog design I build so I'm not to familiar with bias setting in an amp, I'd apreciate any help, I tryied to research on the web but failed to find a good explanation about how to set the bias, just specific instruccions for diferent amps.
I Haven't actually Built this Amp as I use another amp that I built many years ago. But I did design a PCB For it.
Curious, Are you using the PCB I Designed?
Did you also make the DC Protection Board?
** I would definately Recommend it for protection of your Speakers.
I am also not sure What effects your 42 volts will change, compared to the suggested 55 volts.
But A few Questions for you.
Are you using a GREEN LED as Recommended on the Schematic?
Different Colored LED's have Different Voltages.
And even the same colors can have some voltage variations.
This could result in why your brightness goes so high.
The higher Brightness Could be Also that you just have just used a "Bright LED". So the higher Brightness Might be Normal.
One Last Comment:
As long as your Output Transistors Stay Fairly Cool when the Amplifier is running for long periods of time with no actual sound being amplified, It Should be OK.
Curious, Are you using the PCB I Designed?
Did you also make the DC Protection Board?
** I would definately Recommend it for protection of your Speakers.
I am also not sure What effects your 42 volts will change, compared to the suggested 55 volts.
But A few Questions for you.
Are you using a GREEN LED as Recommended on the Schematic?
Different Colored LED's have Different Voltages.
And even the same colors can have some voltage variations.
This could result in why your brightness goes so high.
The higher Brightness Could be Also that you just have just used a "Bright LED". So the higher Brightness Might be Normal.
One Last Comment:
As long as your Output Transistors Stay Fairly Cool when the Amplifier is running for long periods of time with no actual sound being amplified, It Should be OK.
Road test passed
I buitlt the M250 to replace the power amp section of an old Peavey Mark III Bass Guitar head, I've been playing with it for about 2 weeks and I'm really happy with it, it has a good bass response. On the first gig I noticed that the heatsink was getting too hot so I made a hole in the cabinet and installed a fan I gutted from a non working PC power supply and now it works completly cold.
I hevent built the dc protection yet but I'll for sure as soon as I have a few days off, good speakers are expensive.
I buitlt the M250 to replace the power amp section of an old Peavey Mark III Bass Guitar head, I've been playing with it for about 2 weeks and I'm really happy with it, it has a good bass response. On the first gig I noticed that the heatsink was getting too hot so I made a hole in the cabinet and installed a fan I gutted from a non working PC power supply and now it works completly cold.
I hevent built the dc protection yet but I'll for sure as soon as I have a few days off, good speakers are expensive.
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