Hello all. I just recently decided during lockdown to learn some basic electronics. I then found I just had to build myself an amplifier of some kind. I then found this Instructable: https://www.instructables.com/id/Make-your-first-Serious-Amplifier/ I have copied it as far as I can but am now stuck. I have followed the original version but used a blank pcb used some other ideas from someone else who has made this (at the bottom of the website). Basically I am stuck as to where the connection goes to V+. Also what happens at the potentiometer and the front switch. Can anyone help? This is a pic of where I'm at, but I don't know if it will help:
The two connectors in the centre of the pic are where the lines from pin 10 (V+in) and pin 1 (V+) come to. I don't know where these connect to tbh. Any help very gratefully received!
The two connectors in the centre of the pic are where the lines from pin 10 (V+in) and pin 1 (V+) come to. I don't know where these connect to tbh. Any help very gratefully received!
If rebuilding what you have is unsettling, you'll have to at least be able to partition it into sections conceptually. Maybe dont connect the amplifier V+ (pin 10) to the power supply V+ just yet. The two connectors were suggested by the original designer for a purpose...
Do you have any test equipment on hand? If you have a DMM, that would help you to assure the power supply part is working - before connecting it to the amplifier part.
The most feared result of first power-on is smoke/fire, or an audible "pop" - and that's it. If you have no test equipment (like a Variac... DMM...), you may have to build something to help you out. If you've nothing beyond the parts used to build the amplifier on hand, it's going to take some real creativity to limit the AC current going into your power supply portion, for first power-on debug. (something like a 110V, 15W lightbulb wired in series with the AC line to the power supply part)
"AC line" - I shudder to even suggest those words to a noob probably without an AC line isolation transformer. Be_Super_Careful when messing with the AC input part of your project. Uh, "Wife is calling" so I gotta go at this point. Good luck with your new amplifier build.
Do you have any test equipment on hand? If you have a DMM, that would help you to assure the power supply part is working - before connecting it to the amplifier part.
The most feared result of first power-on is smoke/fire, or an audible "pop" - and that's it. If you have no test equipment (like a Variac... DMM...), you may have to build something to help you out. If you've nothing beyond the parts used to build the amplifier on hand, it's going to take some real creativity to limit the AC current going into your power supply portion, for first power-on debug. (something like a 110V, 15W lightbulb wired in series with the AC line to the power supply part)
"AC line" - I shudder to even suggest those words to a noob probably without an AC line isolation transformer. Be_Super_Careful when messing with the AC input part of your project. Uh, "Wife is calling" so I gotta go at this point. Good luck with your new amplifier build.
Thanks so much for your replies. I have made a dim bulb tester (that works ��
so I can test it up to a point. My version is a mixture of the original one and the first person that made a version of it (bottom of Instructable site page) so this is probably where I’ve got confused (easily done). I have a multimeter but no other testing equipment. I think if I’d followed the original poster’s version with separate psu and amp, I’d be fine ��
so I can test it up to a point. My version is a mixture of the original one and the first person that made a version of it (bottom of Instructable site page) so this is probably where I’ve got confused (easily done). I have a multimeter but no other testing equipment. I think if I’d followed the original poster’s version with separate psu and amp, I’d be fine ��
Great! So if the power supply section (even though it's on the same board) passes your "dim bulb" tester, you should be able to test it for its voltage value using your multimeter. You should know from the instructable what voltage to expect - and it should appear at the terminal for power supply V+ on your board.
I assume the power supply V-, or "ground", is also available on that connector as a separate terminal.
I assume the power supply V-, or "ground", is also available on that connector as a separate terminal.
> where the connection goes to V+.
It's not a stupid question. It is a very lame build instruction. About 90% right, which is enough to confuse. I think today's ??? is that the two power rails are called one thing on one drawing and another thing on another drawing. A builder with 2-3 builds done will probably figure this out. For a first-timer, this is not enough help.
Here's my mark-up.
It's not a stupid question. It is a very lame build instruction. About 90% right, which is enough to confuse. I think today's ??? is that the two power rails are called one thing on one drawing and another thing on another drawing. A builder with 2-3 builds done will probably figure this out. For a first-timer, this is not enough help.
Here's my mark-up.
Attachments
Well now I'm a bit more confused I have measured the voltage from my transformer and I'm getting 18v from the yellow and red wires. According to the data sheet for this transformer, the secondary coils should be red/yellow and blue/green, so this okay. But which pair do I twist together and connect to the rectifier? This is my transformer:Security Check
Thanks so much for the help so far
I have measured the voltage from my transformer and I'm getting 18v from the yellow and red wires. According to the data sheet for this transformer, the secondary coils should be red/yellow and blue/green, so this okay. But which pair do I twist together and connect to the rectifier? This is my transformer:Security CheckThanks so much for the help so far
If you connect yellow to blue and then measure the AC voltage from red to yellow/blue you should get 18 volts. Measure from red to green and you should see 36 volts.
If the last test gives near to zero volts then reverse the blue and green connections so that you measure 36 volts end to end. The centre joined connection then becomes the 0 in 18-0-18
If the last test gives near to zero volts then reverse the blue and green connections so that you measure 36 volts end to end. The centre joined connection then becomes the 0 in 18-0-18
Try and understand the reasoning... the transformer has two 18 volt windings which if connected in series give 36 volts in total however because these are AC voltages we also have to get the phase correct.
If the phase is incorrect we are still always able to measure 18 volts from the centre point to either end but when measured end to end the voltages cancel. In that case we reverse one of the windings.
Lets start from the beginning and be sure each pair of windings is identified correctly
1/ With the transformer OFF and NOT connected to the mains measure the resistance from the RED lead to each of the other three in turn.
Only one of those three leads should have continuity and it will be a low ohms value. That lead and the RED lead form one winding.
There should be no continuity (so an open circuit) to the other two leads from this pair.
2/ The pair that are left should read a similar resistance to the first pair just identified above. This is the second winding.
This second pair should also have no continuity to the first pair.
3/ Now switch your meter to AC volts and measure the voltage of each pair of windings we have identified. Both should be similar and around 18 volts.
4/ If the windings are connected in series they should add and give 36 volts end to end. If they don't then swap just one pair around.
(Also make sure the ends are clean bare wire and not covered in insulating varnish which can give misleading results)
If the phase is incorrect we are still always able to measure 18 volts from the centre point to either end but when measured end to end the voltages cancel. In that case we reverse one of the windings.
Lets start from the beginning and be sure each pair of windings is identified correctly
1/ With the transformer OFF and NOT connected to the mains measure the resistance from the RED lead to each of the other three in turn.
Only one of those three leads should have continuity and it will be a low ohms value. That lead and the RED lead form one winding.
There should be no continuity (so an open circuit) to the other two leads from this pair.
2/ The pair that are left should read a similar resistance to the first pair just identified above. This is the second winding.
This second pair should also have no continuity to the first pair.
3/ Now switch your meter to AC volts and measure the voltage of each pair of windings we have identified. Both should be similar and around 18 volts.
4/ If the windings are connected in series they should add and give 36 volts end to end. If they don't then swap just one pair around.
(Also make sure the ends are clean bare wire and not covered in insulating varnish which can give misleading results)
Are you absolutely certain that the green and blue wires are scrapped back to bare copper?
It sounds crazy but this can be somewhat difficult to achieve. Be 100% sure you have the insulation scrapped off. Use sandpaper to do this.
If there really is no continuity between those two wires (the green and blue) then just for completeness see if there is any continuity between either of them and the other pair. There shouldn't be but lets cover everything.
It sounds crazy but this can be somewhat difficult to achieve. Be 100% sure you have the insulation scrapped off. Use sandpaper to do this.
If there really is no continuity between those two wires (the green and blue) then just for completeness see if there is any continuity between either of them and the other pair. There shouldn't be but lets cover everything.
Well it sounds for all the world that the unit is faulty and the winding is open circuit... which is something I've never encountered or even heard of happening as a fault mode. No continuity and no voltage output are conclusive proof though.
Don't go deliberately bending the wires but have a look and see if there looks to be any fracture where the leads comes out of the core... like would happen if it had been waggled back and forth many times.
(Primaries can become open for various reasons but never secondaries with their thick wire)
Don't go deliberately bending the wires but have a look and see if there looks to be any fracture where the leads comes out of the core... like would happen if it had been waggled back and forth many times.
(Primaries can become open for various reasons but never secondaries with their thick wire)
Right. Well, I went off and had my lunch, thought this can't be faulty as it's straight out of the box and hasn't been fiddled with or anything, so it can't be faulty, especially as you've said you'd never heard of such a thing. So I test both pairs again and lo and behold, 19v on both pairs. So WTF? I don't understand it but am going to get another multimeter anyway as I don't trust this one now! I'll test them again in a bit just to make sure!
right then... so its looking good.Its very important to be sure that not just the transformer leads but also the meter probes are clean.
When you tested the secondary for resistance and got an open circuit then the next instant step to take (well what I would do anyway
) would be to quickly short the meter probes as confirmation the meter is good.If that was OK I would remeasure again and if still not getting the expected result I would then see if the meter read a short circuit if the probes are placed on the same bit of wire (probes just a few mm apart).