Hi everyone.
I have built a chipamp with a dual secondary tx and it works ok. Now I have two new tx's: I have 240v mains supply.
100va
Prim 0-120v 0-120v
sec 0-25v 0-25v
0=blue
120v=gray
0=purple
120v=brown
I think I have to connect the primaries in series,
do I connect blue to 0v mains,
gray to purple and brown to 240v mains?
Please help someone? I am stuck!
Regards, Lee.
I have built a chipamp with a dual secondary tx and it works ok. Now I have two new tx's: I have 240v mains supply.
100va
Prim 0-120v 0-120v
sec 0-25v 0-25v
0=blue
120v=gray
0=purple
120v=brown
I think I have to connect the primaries in series,
do I connect blue to 0v mains,
gray to purple and brown to 240v mains?
Please help someone? I am stuck!
Regards, Lee.
Yes.... the primary windings are to be wired in series for 240V...
Then for 120V operation you wire them in parallel...
You are correct in your description of wiring primary in series... [START(0v)----FINISH] + [START----FINISH (240v)]
If you wire the primary in series incorrectly....you will blow the mains fuse quickly...
Chris
Then for 120V operation you wire them in parallel...
You are correct in your description of wiring primary in series... [START(0v)----FINISH] + [START----FINISH (240v)]
If you wire the primary in series incorrectly....you will blow the mains fuse quickly...
Chris
... and use a Volt / Ohm meter before you plug it in the wall to check for continuity, etc. ...
I would also suggest a circuit breaker (or fuse) in series with the main windings untill after the "smoke tests" ... 2/3 to 3/4 Amp should be enough, although after confidence is higher, 1.0 Amp quick blow or 0.75 Amp to 1.0 Amp slow blow would work fine (240 VAC / 100 VA = ~ 0.5 Amps, max operating current) ...
I would also suggest a circuit breaker (or fuse) in series with the main windings untill after the "smoke tests" ... 2/3 to 3/4 Amp should be enough, although after confidence is higher, 1.0 Amp quick blow or 0.75 Amp to 1.0 Amp slow blow would work fine (240 VAC / 100 VA = ~ 0.5 Amps, max operating current) ...
Hi Thomo,
build yourself a mains light bulb tester.
It only needs a plug, bulb holder and socket outlet.
It prevents you blowing up new or modfied projects due to wiring errors.
The mis-wiring of the transformer primaries is a perfect example of the protection this method provides.
Wire the transformer incorrectly and all that happens is the bulb comes on full brightness, no damage, no repairs required and not even a fuse blowing.
Build it and use it every time for each fresh start up on modified or new build equipment.
An example of a mistake I made.
I reassembled my power amplifier board to the PSU. Plugged in and switched on. Bulb bright measured the AC voltage at the rectifiers and it was very low. measured the DC voltage at the PCB. even lower. checked the voltage at the primary side. Just 7Vac, all the rest was dropped through the bulb.
More head scratching. Then noticed I had the colours across the terminal block swapped. The DC voltages were inverted in the amplifier and the catch diodes across the output were sucking all the current they could manage. Switched off, swapped wires around, switched on. No damage, not even the 1n4004. They held the DC voltage down to under a volt and protected all the semiconductors and electrolytics.
build yourself a mains light bulb tester.
It only needs a plug, bulb holder and socket outlet.
It prevents you blowing up new or modfied projects due to wiring errors.
The mis-wiring of the transformer primaries is a perfect example of the protection this method provides.
Wire the transformer incorrectly and all that happens is the bulb comes on full brightness, no damage, no repairs required and not even a fuse blowing.
Build it and use it every time for each fresh start up on modified or new build equipment.
An example of a mistake I made.
I reassembled my power amplifier board to the PSU. Plugged in and switched on. Bulb bright
measured the AC voltage at the rectifiers and it was very low. measured the DC voltage at the PCB. even lower. checked the voltage at the primary side. Just 7Vac, all the rest was dropped through the bulb.More head scratching. Then noticed I had the colours across the terminal block swapped. The DC voltages were inverted in the amplifier and the catch diodes across the output were sucking all the current they could manage. Switched off, swapped wires around, switched on. No damage, not even the 1n4004. They held the DC voltage down to under a volt and protected all the semiconductors and electrolytics.
AndrewT: " ... build yourself a mains light bulb tester. It only needs a plug, bulb holder and socket outlet. ..."
Now that's the ticket: this is without a doubt the greatest little DIY transformer wiring tip (or any circuit) there is ... 
( Although that 1n4004 diode can take a lot of punishment without hurting it = several amps at hundreds of volts = No? )
Now that's the ticket: this is without a doubt the greatest little DIY transformer wiring tip (or any circuit) there is ...
( Although that 1n4004 diode can take a lot of punishment without hurting it = several amps at hundreds of volts = No? )
Hi again.
Thanks for all your help so far everyone. I have but one more question....
What is a suitable / recommended CHEAP rectifier suitable for this amp?
I cannot afford schottky or anything like that. Would this do the job?
http://uk.farnell.com/jsp/search/productdetail.jsp?sku=9549765
Cheers,
Lee.
Thanks for all your help so far everyone. I have but one more question....
What is a suitable / recommended CHEAP rectifier suitable for this amp?
I cannot afford schottky or anything like that. Would this do the job?
http://uk.farnell.com/jsp/search/productdetail.jsp?sku=9549765
Cheers,
Lee.
Ignoring inefficiencies, at 100 VA for your transformer, that's about 1/2 an Amp from your local power grid = 220 to 240 VAC, No?) ... if your power grid is 110 VAC, then that's ~1 Amp. (VA ~= volts X amps).
On the output side, +/- 25 VAC is about 4 amps ... which is right close to the upper limit of that diode bridge you have chosen from farnell.com. So, I would look for something a little bit healthier, say able to handle at least 7.5+ Amps or even 10 Amps.
FYI: The 1N4004 is a relatively common diode, not a Schottky type. the '004 indicates the ability to deal with up to 4 Amps, each diode. (This is not universal diode power rule, but does work for the older 1N400x series, usually ... 1N4002 = 2 Amps, 1N4004 = 4 Amps ...) ... So, if you have four of these in series / parallel as used to make a full wave diode bridge, then any two of the diodes will be passing current for a total of 4 Amps through the bridge or 2 Amps through any diode at any instant = a nice 2X safety margin.
Interesting Reference: http://www.geocities.com/bioelectrochemistry/schottky.htm ... the actual discoverer of semiconductor diode type junctions ... just fooling around on the old DIY work bench!
On the output side, +/- 25 VAC is about 4 amps ... which is right close to the upper limit of that diode bridge you have chosen from farnell.com. So, I would look for something a little bit healthier, say able to handle at least 7.5+ Amps or even 10 Amps.
FYI: The 1N4004 is a relatively common diode, not a Schottky type. the '004 indicates the ability to deal with up to 4 Amps, each diode. (This is not universal diode power rule, but does work for the older 1N400x series, usually ... 1N4002 = 2 Amps, 1N4004 = 4 Amps ...) ... So, if you have four of these in series / parallel as used to make a full wave diode bridge, then any two of the diodes will be passing current for a total of 4 Amps through the bridge or 2 Amps through any diode at any instant = a nice 2X safety margin.
Interesting Reference: http://www.geocities.com/bioelectrochemistry/schottky.htm ... the actual discoverer of semiconductor diode type junctions ... just fooling around on the old DIY work bench!
Thanks for your reply, you've been a great help again.
I have some 1n4148's in my drawer, I gather that these will be more than enough to do the job.
Do you think that Schottky diodes will make much of a difference (sound wise)? I remember reading on TNT Audio that in power amps they don't make a huge difference.
Oh, and thanks for the link, quite an interesting read that.
Regards, Lee.
I have some 1n4148's in my drawer, I gather that these will be more than enough to do the job.
Do you think that Schottky diodes will make much of a difference (sound wise)? I remember reading on TNT Audio that in power amps they don't make a huge difference.
Oh, and thanks for the link, quite an interesting read that.
Regards, Lee.
Yes, you are right: http://www.fairchildsemi.com/ds/1N/1N4004.pdf ...
The differences are the maximum voltages = so the 1N4004 is rated to 400 volts.
Its funny how that works ... and I've never had any problems using the 1N4004 with currents up and beyond 4 amps and voltages ~ 50 VAC ... no heat problems anyway. I'll bet I just wasn't getting the full load passed through ... Oh well, fooled again.
" .... Schottky diodes will make much of a difference (sound wise)? ..."
Well, the claim is that they can, but I believe that the Schottky diodes are all rather low voltage devices, not suitable for AC voltage swings above about 20 VAC ... and as long as you have plenty of filter capacitance, it doesn't seem to matter on larger power supplies. (I use plastic snubbing caps in parallel with the electrolytic caps, so the use or not of Schottky's becomes a non issue. I'v also used surplus 2 amp, 200 volt Zeners instead of regular diodes in a bridge = worked just fine and the "fast recovery" features made for an easier time of getting the filtering down to the fine line ... )
The differences are the maximum voltages = so the 1N4004 is rated to 400 volts.
Its funny how that works ... and I've never had any problems using the 1N4004 with currents up and beyond 4 amps and voltages ~ 50 VAC ... no heat problems anyway. I'll bet I just wasn't getting the full load passed through ... Oh well, fooled again.
" .... Schottky diodes will make much of a difference (sound wise)? ..."
Well, the claim is that they can, but I believe that the Schottky diodes are all rather low voltage devices, not suitable for AC voltage swings above about 20 VAC ... and as long as you have plenty of filter capacitance, it doesn't seem to matter on larger power supplies. (I use plastic snubbing caps in parallel with the electrolytic caps, so the use or not of Schottky's becomes a non issue. I'v also used surplus 2 amp, 200 volt Zeners instead of regular diodes in a bridge = worked just fine and the "fast recovery" features made for an easier time of getting the filtering down to the fine line ... )
Hi,
1n400x are good for low power requirements. Pre-amps can easily run on these.
you might get away with these 1A devices wird as a bridge for upto 100W amplifiers or a pair of 50W amps. But they may run a bit too hot.
1n540x would be much better for a power amp.
I have 1n5404 (dual bridges for each half of the dual polarity supply) in a 190W into 8ohm monoblock feeding +-19mF smoothing and they don't even get warm.
1n400x are good for low power requirements. Pre-amps can easily run on these.
you might get away with these 1A devices wird as a bridge for upto 100W amplifiers or a pair of 50W amps. But they may run a bit too hot.
1n540x would be much better for a power amp.
I have 1n5404 (dual bridges for each half of the dual polarity supply) in a 190W into 8ohm monoblock feeding +-19mF smoothing and they don't even get warm.
Holly Cow, Thomo ... the MBR20200 are max. rated 20 amps / 200 volts !!. These will make perfect, very fast, very clean, full wave bridge rectifiers ... for pre-amp, or even mid power amps!! I would "derate" them to ~ about 1/3 power, and still use healthy heat sinks if power requirements exceed ~about 500 watts (=~7 amps @ 70 volts AC into the bridge). For US$25 bucks, a steal!! (Got a source for the rest of us?)
Hi
IMO, it is also important to separate the large charging pulse currents from the transformer and the large amplifier output current pulses(AB operation) in the filter caps such as using multiple caps separated by a small cheap wirewound resistor, like 0.5Ohms or less. Since the cap leads are wires and have resistance, these large different transient currents can interfere with each other. The first cap connected to the rectifier holds charge as a reservoir and the other essentially runs the amp circuit by seperating these two current sources to seperate caps. I prefer the second cap larger than the first.
Proper grounding is always important.
IMO, it is also important to separate the large charging pulse currents from the transformer and the large amplifier output current pulses(AB operation) in the filter caps such as using multiple caps separated by a small cheap wirewound resistor, like 0.5Ohms or less. Since the cap leads are wires and have resistance, these large different transient currents can interfere with each other. The first cap connected to the rectifier holds charge as a reservoir and the other essentially runs the amp circuit by seperating these two current sources to seperate caps. I prefer the second cap larger than the first.
Proper grounding is always important.
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