On my resent amplifier project on TH-cam, I used a switch mode power supply, mostly due to price and size. I know many people will think this is a bad idea, me also, but in tests I found no noise issues at all. Voltage is much more stable than a standard power supply. I used a +/-40 volt output which off load was in fact 42 volts but on full load of 85 watts into 8 ohms both channels driven of clean power the voltage only dropped to 40 volts.
Good quality switchmode supplies can certainly be used but aren't that cheap. With their fairly good regulation, they make the dynamic power close to the continuous output power. Dynamic headroom is always welcome.
Adding my tuppence worth: As they're cheap I would place 10KpF caps across each bridge diode - keeping diode switching noise down. As always great video, I'm looking forward to your JATAmp's completion :)
Thanks for the walk through John. I have seen a lot of comments regarding the Power supply, I would suggest to try out the amp and add what is necessary to the supply according to the outcome. People are suggesting a lot of things and it could be that they are not necessary.
John thank you for including the power supply. Tube amp power supplies seem simple compared to SS power supplies. Having a + and - rail plus ground gets complex. This video gives some clarity to that complexity. This design will work for other power supplies, depending on the requirements of the circuit. Thanxz
I like the small bypass caps at the power supply too, wouldn't consider them optional unless power conductors are kept very short, otherwise they may radiate the powerline RF the cans failed to eliminate.
For a transformer may i suggest AnTek. for a 25-0-25 check out the AS-2225. its a 200VA model, should be good for about 80Wx2 depending on efficiency, losses and all that jazz. prices aren't bad either.
I have a question . Can I use 18V 250VA toroidal transformer with Vishay 400V 35A diode bridge ? I want to power 5 x LM1875 & 1 X LM3886. I am building a 5.1 hi-fi system. Will 250VA be enough?
You can use a choke input filter (LC) to weaken the requirements on the transformer VA rating and get much lower load regulation. But the choke will be pretty big.
Yes, chokes are the way to go. Very common on low current HV tube amp supplies but almost never seen on LV high current solid state amplifier supplies.
Just food for thought. I have juist built two 100 watt transistor amps. I´ve powered them, with two switched power supplies from eBay- It works quite well
Tjhe speakers are connected to the end transistors via a relay that is energised about 10 seconds after switching on thereby eliminating any plops from the speakers.
You will get around 40W@8ohm with 2x25VAC, with the 1943/5200 I would try 2x30V AC min 300W. I had older SimaAudio, which was only 50W@8, but with 2pairs big Motorola out tranies and 500W toroids per channel and 33000u per rail on each channel it could drive 2ohm load no problem close to 200W - Martin Logans, Maggie's no sweat. Clean, dynamic, transparent, very similar in design to Prof Leach amp.
Howdy. Some comments. If one is to get 2 x 50W the current after the filter cap.s should be around 2 A mean value. Yes. However if one measures the current after the rectifier it is way larger. It could about 3,5 A root mean square. This rms value is the one to be used rating the transformer. I would recommend as much as 200 VA. The transformer should be type approved as a shock protection class 2 device (protective separation). One should use an all-pole breaking mains switch for two reasons. In case of an insulation breakdown in the transformer breaking only one pole could leave the chassis at live potential when the amp. is fed from a non-grounded outlet. And breaking both the live and the null provides faster growing of the total breaking gap resulting in faster quenching of breaking arcing. This reduces the risk of a plasma explosion in the switch. And for the same reasons both the live and null should be equipped with their own fuses. Regards.
Why not consider to use a couple of 90w isolated switching power supplies from notebook computers with outputs like 18.5v, and switching boost them with dc-dc converters at 150kHz, to 32 - 50v? I have been using them single ended for class D amps with no perceptible power supply noises, and could see no reasons for them not to work for class A or AB applications. If works, it would be lighter, and cooler.
Hello john. Excellent video.. look when you talk about watts you confuse the words. Sometimes you say volts and others say watts for the same thing. Thanks
please do a complementary Feedback Output stage because self douglas tought us that they perform much better. (have you read his book about apm design? i know ist a bit Long with 600 pages but I think ist really interesting
How do the Car music system have no humming inspite of using same power supply of battery to power both the audio amplifier & Bluetooth/Usb receiver module whereas when use the same connection using a transformer it has lot of high frequency humming when the Bluetooth module is connected?
That is a class D amplifier, and the spec does say 420 Watts into 8 ohms with a bridge output or two channels at 210 Watts into 4 ohms. The voltage at the rails need to be +/- 41 VDC.
If you do a kit, please give your nod to the best transformers, carcasses, and you got one buyer already. but I will need a mere 6 channel 100w per channel for bi-amping the towers Im building.
i have really cheap 5.1 surround amp with remote like $35. and it makes a noise! the volume covers it up but on mute you can hear it. its kind of a hum or buzzing. is this its nature or could i fix it. im really into improving things! like buying nice speakers for it and maybe rebuilding it.
John Can you not make a video about making a proper ground connection to the chassis. Some is doing it before the rectifier, to my mind it is better to make the connection after those rectifier From where is the ground best to make the connection? What if there are several power supplies?
eeeh careful now you connect + and - to make the dual 24 - 0 - 24, dual is a bit tricky. it has to be the correct + and - Blue and red Find the schematics. You better check the voltage out put when you do what you do. It is like you make a single 48 volt output but uses the connection of the 2 lines as ground. If you only get 24 volt you have done it wrong, you got to get 48 volt That will be your 24 - 0 - 24 if you connect the negative as ground the 2 lines will be in the same phase, they have to be the opposite phase of each other. The problem is if they are in a same phase you have doubled the current. The circuits may not work as intended.
The transformer is way overrated for a stereo 50w amp, but can be used. The load would be light for it and load regulation good. I think you meant 26a at 24 v as you would parallel the two secondaries. Transformers don't have "negatives" but you can join the two secondaries together so they are series for 24-0-24.
Here is all of the information that they offer, thanks John 625VA Toroidal Transformer 117/234V to 2 x 24V or 48V at 13 Amps www.surplussales.com/item/_TP/aa56252-024.html www.surplussales.com/Transformers/Pdfs/Actuant_Amveco_1-14.pdf www.surplussales.com/Transformers/Pdfs/Actuant_Amveco_18.pdf • Primary: 117/234 volts 50/60 Hz • Secondary: 24/48 volts • (two 24V @ 13A or one 24V @ 26A or one 48V @ 13A) • Apparent Power: 625 VA • Weight: 9.5 lbs • Dimensions: 5.5"DIA x 3.2"H • Factory New Surplus • Manufactured by Amveco Magnetics • Alt. P/N: AA56252
Tbonyandsteak+ Thanks, I told them I'm new at this and all I need to know is what 2 wires to tie together to get a 24-0-24 and they could have just said to tie a neg to the other pos or tie the 2 negatives, but the company wouldn't explain it and told me to look at the PDF's. I left all of the information on this transformer in the comments from the company. Could someone please look at this, I would greatly appreciate this, thanks I'm happy I asked, I was under the influence that AC didn't matter about pos and neg and thought that they only wrap one wire bent over then cut it when they're done @ 24v then have it again to get another 24v and they color code the wires so you don't have to test the continuity and make sure you don't have the same wire
That IS a beefy toroid. You're right about there being no + or - and about the center tap winding being one wire, double wound and cut to make the 2 secondaries. The issue (as Tbony mentioned) is getting the phasing right. This is determined by the direction of the windings. Same direction=same phase=double voltage (48-0-48@13A). Opposite direction=180phased=double current (or 24-0-24@26A) A quick power up trial with your multi-meter should set you straight. Twist 2 different coloured wires together and probe across the untwisted wires. If it's 48VAC, switch ONE of the twisted wires for the same colour untwisted one and you should see 24VAC.
I was searching for transformers a short while back, and also about a year ago for another project, and much to my surprise, getting close to what you desire has become one big chore nowdays. Please, if you can, and know where we can find, provide some info where to find monoboard, stereo, and maybe strapped compatible transformers. When I was a kid, most supply houses had any kind of transformer your imagination could conceive, and had it in stock, or a couple days wait. They all had catalogs from several brands, thousands of kinds, all available. What Has Happened nowdays? Maybe I forgot how to search for transformers?
Just make it yourself. Making a transformer is pretty interesting experience. You only need to find a core. Maybe from some broken variac, or an old TV. Of course you can buy a new core, but this may be even harder than find a ready-made one. Come to us in Russia, I know a few manufacturers who sell transformers and cores ;)
Believe me, I have already studied this area, make self. The toroid winders are far too expensive to buy. They can be home made though, but only someone like me, who has a machine shop could make one. Making an older style laminated core type has it's problems. Mainly producing the laminations. And even if you can, I could if I wanted, getting the right quality consistency of the raw material is an issue. Then another issue, joining the laminations so they do not vibrate, or come apart and vibrate. That definitely takes experienced personal, and good methods. A problem though, making one self, is that unless you make it as well as a major manufacturer, and that is most unlikely, you will end up with the transformer producing self noise at levels that are unacceptable. This noise may not matter if one is making a door bell, which was the reason I wanted a transformer a year ago, but in electronic applications, noise can make many circuits non functional. I have considered manufacturing transformers if they actually are difficult to come by.
@@BiddieTube if you need only one or two transformes you don't need an expensive winding machine, you can do it with your hands. This requires some practice though. Concerning the quality, I must say that all transformers that you can find in modern electronic equipment are pretty crappy. The main goal of any manufacturer is to make the product as cheap as possible. They usually pick a smaller core and thinner wire, wind less turns, don't use a shielding winding (you rarely need it though), etc. You definitely can find a good transformer, but it will be SO expensive! I just want to say that it is not a rocket science. Do some simple math to get the core size and the number of turns. Take a core made of steel with high flux density. Wind the wire neatly (it may take a few days). Voilà! You have a transformer which is better than 90% of the commercially available rubbish.
I am building small amplifier with vintage transistor (ac187/188k) and I got a power transformer for it but I am worried because open circuit voltage after rectification is 19-20v DC and original circuit in radio that this circuit is from runs on 16.8v DC no load... So can the same circuit run on 20v idle or will it cause problems with bias or transistor breakdown ? And how would I reduce open circuit voltage if possible ? I don't want to buy another transformer because this is more of a learning project for me.
I have no idea not knowing the circuit. I would error on the side of caution. You may find the supply voltage will drop with just idle current draw. You can put a few silicon rectifier diodes in series with the supply since they have a voltage drop of about .6 volts and check what the idle voltage is. If it is too low, just remove one until you get around 17v.
Hi John, have you tested toroidal transformer efficiency in real word, compared with Ei transformer ? Toroidal transformer with the same power rate with Ei, cost triple more. It is not just interference distortion reason. Do these transformers have far gap in efficiency ? Thanks for your great videos.
Biggest difference is the quality of the core and winding, so you can have good EI. With toroids you can have lower stray inductance. Generally toroids are build to better quality. My Pilitron audio toroids are quieter, run cooler and are more efficient than similar EI used in Far East made equipment. Tim de Paravicini of EAR, an electrical engineer by education uses 1000W core for 700-800W transformer in his designs. All my Japanese 'made' equipment have transformers which are average in quality - they run very hot comparing to more Hi-end pieces and usually are undersized.
Simple supplies are nice and work well, but they generate a lot of noise at line frequency harmonics in the mains. Of course you can get away with this for a roll your own amplifier, but you would need to add some filtering if you were going to sell this commercially and wanted to meet FCC/CE conducted radiation requirements, so it's a good thing you won't be including the power supply with your kit! ;-)
I've only seen heavy filtering and common mode chokes on switching supplies that must keep the noise out of the mains. The typical receiver or power amp that uses a standard line frequency transformer often has simple filtering such as an across the line cap.
You're right. I made an LT SPICE model using your schematic and sized the transformer to put out 420VA with +/-25V voltage rails. There is a small amount of distortion of the input current from the LISN, but it starts falling off at 40 dB per octave at 1 kHz and isn't even close to what you would see from a solar inverter. I guess the just the leakage inductance from the transformer (I assumed K would be between 0.97 and 0.99) in conjunction with the capacitance across the line is more than sufficient to resolve any issues above 150 kHz where conducted emissions are tested...
ats89117 the bridge rectifier is the source of the noise - the Harmonic content is based off the 60 Hz, and well within our audible range - but yes well below the 150kHz corner of the fcc EMI specs, but are we not concerned about what might be offensive to our ears? What did you measure as Harmonic content above 60 Hz?
@@KissAnalog I had a PC with cheap power supply that would sent back into AC lines 120Hz - if I connect the frequency counter it read 120Hz. Didn't have FFT analyzer back then. So, yes there's a lot of junk flowing around in the mains. As for the switching noise from diodes in regular bridge rectifier - that is interesting to explore. Is this the reason for Schottky diodes in power supply.
pliedtka Schottky diodes have a lower voltage drop so are more efficient. Capacitors that are too big can cause high peak currents and if they are too small they can cause high ripple voltage.
Line voltage stepped down, rectified and filtered is regulated enough. You can consider choosing the right voltage output transformer the regulation step.
Regulation means you would have to pick a transformer with a higher voltage at the same current for the regulator dropout headroom which means the transformer would be a higher VA rating. That means a larger and more expensive transformer. You also have to design a regulator that can handle the load from the amplifier(s) and dissipate heat. The continuous power would be the same as the dynamic power. I'd rather it not be regulated and have the extra dynamic power since music is not high a level continuous signal (unless you like the bass type stuff).
Thanks John for this series on a discrete audio power amplifier design. I just joined your Patreon to lend support. Also can recommend AnTek for good supply of Toroids. Keep up the good work!
For universal power supply that has lots of options , linear with an absolutely excellent illustrated assembly guide. Extremely easy to assemble. There’s a discussion form to ask for help if you run into trouble at DIYAUDIO.COM diyaudiostore.com/collections/printed-circuit-boards/products/universal-psu
3:00 IM DESIGNING MY PREAMP POWER SUPPLY AND I HAD NO IDEA THANK YOU FOR THIS!!!!!
I don't skip ad on ur video
Thank you john.... Plzz
... Can't wait to see the final amp..
The mains capacitor is useful to remove pops from the switch. The contacts inside arc and you get a loud pop in the speakers.
It's main purpose is to shunt away the switching noise before it gets back onto your mains, making other electronics in your house very unhappy.
On my resent amplifier project on TH-cam, I used a switch mode power supply, mostly due to price and size. I know many people will think this is a bad idea, me also, but in tests I found no noise issues at all. Voltage is much more stable than a standard power supply. I used a +/-40 volt output which off load was in fact 42 volts but on full load of 85 watts into 8 ohms both channels driven of clean power the voltage only dropped to 40 volts.
Good quality switchmode supplies can certainly be used but aren't that cheap. With their fairly good regulation, they make the dynamic power close to the continuous output power. Dynamic headroom is always welcome.
For the size yes. For the price? Idk man.
Adding my tuppence worth: As they're cheap I would place 10KpF caps across each bridge diode - keeping diode switching noise down. As always great video, I'm looking forward to your JATAmp's completion :)
Thanks for the walk through John. I have seen a lot of comments regarding the Power supply, I would suggest to try out the amp and add what is necessary to the supply according to the outcome. People are suggesting a lot of things and it could be that they are not necessary.
John thank you for including the power supply. Tube amp power supplies seem simple compared to SS power supplies. Having a + and - rail plus ground gets complex. This video gives some clarity to that complexity. This design will work for other power supplies, depending on the requirements of the circuit. Thanxz
I like the small bypass caps at the power supply too, wouldn't consider them optional unless power conductors are kept very short, otherwise they may radiate the powerline RF the cans failed to eliminate.
For a transformer may i suggest AnTek.
for a 25-0-25 check out the AS-2225. its a 200VA model, should be good for about 80Wx2 depending on efficiency, losses and all that jazz. prices aren't bad either.
I'll check that out. I've seen Avel and Hammond transformers so far.
this is the website. www DOT antekinc DOT com
I have a question .
Can I use 18V 250VA toroidal transformer with Vishay 400V 35A diode bridge ? I want to power 5 x LM1875 & 1 X LM3886. I am building a 5.1 hi-fi system.
Will 250VA be enough?
You can use a choke input filter (LC) to weaken the requirements on the transformer VA rating and get much lower load regulation. But the choke will be pretty big.
Yes, chokes are the way to go. Very common on low current HV tube amp supplies but almost never seen on LV high current solid state amplifier supplies.
Thanks for the walk thru, John. Good stuff.
Just food for thought. I have juist built two 100 watt transistor amps. I´ve powered them, with two switched power supplies from eBay- It works quite well
Tjhe speakers are connected to the end transistors via a relay that is energised about 10 seconds after switching on thereby eliminating any plops from the speakers.
You will get around 40W@8ohm with 2x25VAC, with the 1943/5200 I would try 2x30V AC min 300W. I had older SimaAudio, which was only 50W@8, but with 2pairs big Motorola out tranies and 500W toroids per channel and 33000u per rail on each channel it could drive 2ohm load no problem close to 200W - Martin Logans, Maggie's no sweat. Clean, dynamic, transparent, very similar in design to Prof Leach amp.
Howdy. Some comments.
If one is to get 2 x 50W the current after the filter cap.s should be around 2 A mean value. Yes. However if one measures the current after the rectifier it is way larger. It could about 3,5 A root mean square. This rms value is the one to be used rating the transformer. I would recommend as much as 200 VA. The transformer should be type approved as a shock protection class 2 device (protective separation).
One should use an all-pole breaking mains switch for two reasons. In case of an insulation breakdown in the transformer breaking only one pole could leave the chassis at live potential when the amp. is fed from a non-grounded outlet. And breaking both the live and the null provides faster growing of the total breaking gap resulting in faster quenching of breaking arcing. This reduces the risk of a plasma explosion in the switch.
And for the same reasons both the live and null should be equipped with their own fuses.
Regards.
11:43 Better add RC snubber to prevent ringing. PSRR won't work well at a higher frequency.
Your teachings are great. What’s your honest opinion about surround sound amp brands: Yamaha aventage vs pioneer elite?? Thanks
Why not consider to use a couple of 90w isolated switching power supplies from notebook computers with outputs like 18.5v, and switching boost them with dc-dc converters at 150kHz, to 32 - 50v? I have been using them single ended for class D amps with no perceptible power supply noises, and could see no reasons for them not to work for class A or AB applications. If works, it would be lighter, and cooler.
Hello john. Excellent video.. look when you talk about watts you confuse the words. Sometimes you say volts and others say watts for the same thing. Thanks
please do a complementary Feedback Output stage because self douglas tought us that they perform much better. (have you read his book about apm design? i know ist a bit Long with 600 pages but I think ist really interesting
How do the Car music system have no humming inspite of using same power supply of battery to power both the audio amplifier & Bluetooth/Usb receiver module whereas when use the same connection using a transformer it has lot of high frequency humming when the Bluetooth module is connected?
What do you think about TDA8954 is claiming to be a 420w amp
That is a class D amplifier, and the spec does say 420 Watts into 8 ohms with a bridge output or two channels at 210 Watts into 4 ohms. The voltage at the rails need to be +/- 41 VDC.
If you do a kit, please give your nod to the best transformers, carcasses, and you got one buyer already. but I will need a mere 6 channel 100w per channel for bi-amping the towers Im building.
i have really cheap 5.1 surround amp with remote like $35. and it makes a noise! the volume covers it up but on mute you can hear it. its kind of a hum or buzzing. is this its nature or could i fix it. im really into improving things! like buying nice speakers for it and maybe rebuilding it.
Hey John, can you make a recommendation on a good transformer that you would want to use. and I'll buy one for you, and one for me. thanks mike
Hi Mike. Thanks for the offer! Let me poke around the interwebs to see what is available and perhaps fine tune what I should get.
cool
Thanks for the video.
A Companys Densen went to the ekstrem with Battries, No noise from the net and Lot of Amps.
I am bit worried choosing transformer
John Can you not make a video about making a proper ground connection to the chassis.
Some is doing it before the rectifier, to my mind it is better to make the connection after those rectifier
From where is the ground best to make the connection?
What if there are several power supplies?
JohnAudioTech+ I bought a toroidal transformer it has 4 wires 24v + 24v @ 13amp or 48v @ 26amp so I could connect the negatives to make a 24-0-24?
eeeh careful now you connect + and - to make the dual 24 - 0 - 24, dual is a bit tricky.
it has to be the correct + and -
Blue and red
Find the schematics.
You better check the voltage out put when you do what you do.
It is like you make a single 48 volt output but uses the connection of the 2 lines as ground.
If you only get 24 volt you have done it wrong, you got to get 48 volt
That will be your 24 - 0 - 24
if you connect the negative as ground the 2 lines will be in the same phase, they have to be the opposite phase of each other.
The problem is if they are in a same phase you have doubled the current. The circuits may not work as intended.
The transformer is way overrated for a stereo 50w amp, but can be used. The load would be light for it and load regulation good. I think you meant 26a at 24 v as you would parallel the two secondaries. Transformers don't have "negatives" but you can join the two secondaries together so they are series for 24-0-24.
Here is all of the information that they offer, thanks John
625VA Toroidal Transformer 117/234V to 2 x 24V or 48V at 13 Amps
www.surplussales.com/item/_TP/aa56252-024.html
www.surplussales.com/Transformers/Pdfs/Actuant_Amveco_1-14.pdf
www.surplussales.com/Transformers/Pdfs/Actuant_Amveco_18.pdf
• Primary: 117/234 volts 50/60 Hz
• Secondary: 24/48 volts
• (two 24V @ 13A or one 24V @ 26A or one 48V @ 13A)
• Apparent Power: 625 VA
• Weight: 9.5 lbs
• Dimensions: 5.5"DIA x 3.2"H
• Factory New Surplus
• Manufactured by Amveco Magnetics
• Alt. P/N: AA56252
Tbonyandsteak+ Thanks, I told them I'm new at this and all I need to know is what 2 wires to tie together to get a 24-0-24 and they could have just said to tie a neg to the other pos or tie the 2 negatives, but the company wouldn't explain it and told me to look at the PDF's. I left all of the information on this transformer in the comments from the company. Could someone please look at this, I would greatly appreciate this, thanks
I'm happy I asked, I was under the influence that AC didn't matter about pos and neg and thought that they only wrap one wire bent over then cut it when they're done @ 24v then have it again to get another 24v and they color code the wires so you don't have to test the continuity and make sure you don't have the same wire
That IS a beefy toroid.
You're right about there being no + or - and about the center tap winding being one wire, double wound and cut to make the 2 secondaries. The issue (as Tbony mentioned) is getting the phasing right. This is determined by the direction of the windings. Same direction=same phase=double voltage (48-0-48@13A). Opposite direction=180phased=double current (or 24-0-24@26A)
A quick power up trial with your multi-meter should set you straight. Twist 2 different coloured wires together and probe across the untwisted wires. If it's 48VAC, switch ONE of the twisted wires for the same colour untwisted one and you should see 24VAC.
I was searching for transformers a short while back, and also about a year ago for another project, and much to my surprise, getting close to what you desire has become one big chore nowdays. Please, if you can, and know where we can find, provide some info where to find monoboard, stereo, and maybe strapped compatible transformers. When I was a kid, most supply houses had any kind of transformer your imagination could conceive, and had it in stock, or a couple days wait. They all had catalogs from several brands, thousands of kinds, all available. What Has Happened nowdays? Maybe I forgot how to search for transformers?
Just make it yourself. Making a transformer is pretty interesting experience. You only need to find a core. Maybe from some broken variac, or an old TV. Of course you can buy a new core, but this may be even harder than find a ready-made one. Come to us in Russia, I know a few manufacturers who sell transformers and cores ;)
Believe me, I have already studied this area, make self. The toroid winders are far too expensive to buy. They can be home made though, but only someone like me, who has a machine shop could make one. Making an older style laminated core type has it's problems. Mainly producing the laminations. And even if you can, I could if I wanted, getting the right quality consistency of the raw material is an issue. Then another issue, joining the laminations so they do not vibrate, or come apart and vibrate. That definitely takes experienced personal, and good methods. A problem though, making one self, is that unless you make it as well as a major manufacturer, and that is most unlikely, you will end up with the transformer producing self noise at levels that are unacceptable. This noise may not matter if one is making a door bell, which was the reason I wanted a transformer a year ago, but in electronic applications, noise can make many circuits non functional. I have considered manufacturing transformers if they actually are difficult to come by.
Agree
Last I looked, there was a good range of toroidal types available new. Other than that, shop the surplus market though pickings are slim.
@@BiddieTube if you need only one or two transformes you don't need an expensive winding machine, you can do it with your hands. This requires some practice though. Concerning the quality, I must say that all transformers that you can find in modern electronic equipment are pretty crappy. The main goal of any manufacturer is to make the product as cheap as possible. They usually pick a smaller core and thinner wire, wind less turns, don't use a shielding winding (you rarely need it though), etc. You definitely can find a good transformer, but it will be SO expensive! I just want to say that it is not a rocket science. Do some simple math to get the core size and the number of turns. Take a core made of steel with high flux density. Wind the wire neatly (it may take a few days). Voilà! You have a transformer which is better than 90% of the commercially available rubbish.
Discrete audio amplifier project
PART 1 th-cam.com/video/0m3Ztf8yvOY/w-d-xo.html (Introduction)
PART 2 th-cam.com/video/r-w376O9YZE/w-d-xo.html (Supply voltage, Transistor SOA)
PART 3 th-cam.com/video/u9op-CBlhw0/w-d-xo.html (Input stage)
PART 4 th-cam.com/video/7_OQvmzU6S8/w-d-xo.html (Current mirror)
PART 5 th-cam.com/video/iv8sg_qswVE/w-d-xo.html (Finish input stage)
PART 6 th-cam.com/video/M04kBwGDOig/w-d-xo.html (Power supply design)
Thanks for making the list! YT held it for review. I also have a playlist for this project.
I am building small amplifier with vintage transistor (ac187/188k) and I got a power transformer for it but I am worried because open circuit voltage after rectification is 19-20v DC and original circuit in radio that this circuit is from runs on 16.8v DC no load...
So can the same circuit run on 20v idle or will it cause problems with bias or transistor breakdown ?
And how would I reduce open circuit voltage if possible ? I don't want to buy another transformer because this is more of a learning project for me.
I have no idea not knowing the circuit. I would error on the side of caution. You may find the supply voltage will drop with just idle current draw. You can put a few silicon rectifier diodes in series with the supply since they have a voltage drop of about .6 volts and check what the idle voltage is. If it is too low, just remove one until you get around 17v.
@@JohnAudioTech thanks man.
Hi John, have you tested toroidal transformer efficiency in real word, compared with Ei transformer ?
Toroidal transformer with the same power rate with Ei, cost triple more.
It is not just interference distortion reason. Do these transformers have far gap in efficiency ?
Thanks for your great videos.
Biggest difference is the quality of the core and winding, so you can have good EI. With toroids you can have lower stray inductance. Generally toroids are build to better quality. My Pilitron audio toroids are quieter, run cooler and are more efficient than similar EI used in Far East made equipment. Tim de Paravicini of EAR, an electrical engineer by education uses 1000W core for 700-800W transformer in his designs. All my Japanese 'made' equipment have transformers which are average in quality - they run very hot comparing to more Hi-end pieces and usually are undersized.
Nice explained #discreteoptical
Simple supplies are nice and work well, but they generate a lot of noise at line frequency harmonics in the mains. Of course you can get away with this for a roll your own amplifier, but you would need to add some filtering if you were going to sell this commercially and wanted to meet FCC/CE conducted radiation requirements, so it's a good thing you won't be including the power supply with your kit! ;-)
I've only seen heavy filtering and common mode chokes on switching supplies that must keep the noise out of the mains. The typical receiver or power amp that uses a standard line frequency transformer often has simple filtering such as an across the line cap.
You're right. I made an LT SPICE model using your schematic and sized the transformer to put out 420VA with +/-25V voltage rails. There is a small amount of distortion of the input current from the LISN, but it starts falling off at 40 dB per octave at 1 kHz and isn't even close to what you would see from a solar inverter. I guess the just the leakage inductance from the transformer (I assumed K would be between 0.97 and 0.99) in conjunction with the capacitance across the line is more than sufficient to resolve any issues above 150 kHz where conducted emissions are tested...
ats89117 the bridge rectifier is the source of the noise - the Harmonic content is based off the 60 Hz, and well within our audible range - but yes well below the 150kHz corner of the fcc EMI specs, but are we not concerned about what might be offensive to our ears? What did you measure as Harmonic content above 60 Hz?
@@KissAnalog
I had a PC with cheap power supply that would sent back into AC lines 120Hz - if I connect the frequency counter it read 120Hz. Didn't have FFT analyzer back then. So, yes there's a lot of junk flowing around in the mains. As for the switching noise from diodes in regular bridge rectifier - that is interesting to explore. Is this the reason for Schottky diodes in power supply.
pliedtka Schottky diodes have a lower voltage drop so are more efficient. Capacitors that are too big can cause high peak currents and if they are too small they can cause high ripple voltage.
thank you. but any kind of voltage regulation is not necessary ?
Not overall, there will probably be some regulation onboard for the front of the amp.
Line voltage stepped down, rectified and filtered is regulated enough. You can consider choosing the right voltage output transformer the regulation step.
Regulation means you would have to pick a transformer with a higher voltage at the same current for the regulator dropout headroom which means the transformer would be a higher VA rating. That means a larger and more expensive transformer. You also have to design a regulator that can handle the load from the amplifier(s) and dissipate heat. The continuous power would be the same as the dynamic power. I'd rather it not be regulated and have the extra dynamic power since music is not high a level continuous signal (unless you like the bass type stuff).
i see. so, if we are into bass, then it will be helpful to have regulation a bit.
Where would a regulator get additional current from? If I wanted more current I'd use a bigger transformer and more filter caps.
Thanks John for this series on a discrete audio power amplifier design. I just joined your Patreon to lend support. Also can recommend AnTek for good supply of Toroids. Keep up the good work!
Thanks for the support! I will consider Antek when I get serious about purchasing.
Smaller capacitors are faster
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