NAP-140 Clone Amp Kit on eBay

[penmarker]

I think it is safer/better to start with a low wattage bulb, either a 28W, or 40WThat looks like you need further investigation.
It might be an overloaded resistor that has changed value.

There's some contradictions regarding how much the value of the bulb should be, but I think as long as the filament bulb doesn't glow rapidly you should be good to go.

You're right, I'll need to check on it again. However, I'm noticing this wire I'm using as speaker terminals and transformer input terminals are very brittle and break off easily if I move or flip the board too much. They also blacken easily like soot and wouldn't absorb solder tin afterwards.
I'll be doing another overhaul when I have my new board.

I wrote that years ago in this thread, but it's obviously hard to read through it. It's very big now, so I'll repeat it for all people building this kit:

You should never power up this board with the power transistors!

First power-up should be with the drivers only. The circuit works fine on drivers only and output floating (no load)
That has several benefits:
1. If something burns, it will be cheap.
2. If nothing burns, but still the circuit is not working, you'll have generally more time to troubleshoot and measure before it fails permanently... In the worst case, something cheap will overheat and burn.
3. You can verify the whole circuit works - check output offset, check bias spreader work by turning the trimmer and measuring the voltage change between the driver transistors bases.
4. Leave the bias at something like 2V between base-to-base of the drivers. Then, add the power transistors and turn the trimmer up (by now you'll now what is the up direction) until current flows in the output resistors (5-7mV across). That's it!
Play some music.

Thank you very much, I don't remember seeing this in this thread.
So to be perfectly clear, it is safe to power on the circuit without the power transistors TR11-12 2SC2922?

 

[Ruwe]

Thank you very much, I don't remember seeing this in this thread.
So to be perfectly clear, it is safe to power on the circuit without the power transistors TR11-12 2SC2922?

Yes, these two. It is safe. I've done it when I was playing with this circuit. Leave the power resistors (the path is needed), remove only the transistors. Without them the amplifier works, the feedback is still there, just there isn't much power to drive a speaker. It should play well with headphones, maybe (haven't tried), especially higher impedance ones.

Without the output transistors consider this circuit as a very basic op amp. With the power transistors - consider it an op amp with current boost.

If you decide to adjust the bias in the ball park without the output transistors, aim for less than 2V base-to-base of the drivers. I think 2V might produce too much quiescent current when you attach the power transistors. Transistors types also matter... Something around 1.8V should be OK. I kind of remember this number, I guess that's what I was using some time ago as a starting value.

 

[AndrewT]

There's some contradictions regarding how much the value of the bulb should be, but I think as long as the filament bulb doesn't glow rapidly you should be good to go................

There are no contradictions in my head.

I know that if I select a bulb wattage that is too low then the worst that can happen is that the bulb lights up and only a few volts are applied to the transformer primary. The voltage output from the secondary will be much lower. NO DAMAGE. No contradiction.

 

[Bigun]

there are some solder points that had peeled off from the board, doesn't look very pretty. I think it's because my soldering iron is too hot. I'll need to invest in variable temp stations.

The problem of lifted traces is usually an iron that is not hot enough. This forces you to keep the iron on the joint far too long. You actually want a hot iron, get in quick and get out quick. If you are desoldering ensure you have a small bead of fresh solder on the tip before you touch the joint - it acts to transfer the heat to the joint whereas a 'dry' iron sometimes doesn't. Hot irons are good irons so long as they aren't charring the flux. A nice new temperature controlled iron is a great idea, a nice gift for youself. I struggled with cheap irons from the local hardware store and then bought myself a nice solder station and it's wonderful, the quality of the tip is significantly better. But it was expensive (Weller WES51 or similar).

However the faulty channel has a 30mV± DC offset while the ok L channel has about 1-5mV± offset. Is it too much of a difference?

Contrary to others, I don't see that as indication of a serious problem at all. I've build many amps where DC offset starts out the wrong side of 50mV. Yes, you can be extra careful when you match parts before installing them but sometimes the design it'self is not dc-balanced because it specifies resistor values at the input and in the feedback path that match onto readily available values and they are not the right values to get zero offset. I don't consider 30mV a problem at all, and in my opinion it's perfectly safe for use with any set of speakers.

 

[penmarker]

There are no contradictions in my head.

I know that if I select a bulb wattage that is too low then the worst that can happen is that the bulb lights up and only a few volts are applied to the transformer primary. The voltage output from the secondary will be much lower. NO DAMAGE. No contradiction.

That sounds like a lower wattage bulb is safer than a higher wattage. Most of the mentioned bulbs in this thread were 60W.
At similar wattage, does it still matter whether they're energy efficient bulbs (LED/Halogen/CFL) or incandescent bulbs?

The problem of lifted traces is usually an iron that is not hot enough. This forces you to keep the iron on the joint far too long. You actually want a hot iron, get in quick and get out quick. If you are desoldering ensure you have a small bead of fresh solder on the tip before you touch the joint - it acts to transfer the heat to the joint whereas a 'dry' iron sometimes doesn't. Hot irons are good irons so long as they aren't charring the flux. A nice new temperature controlled iron is a great idea, a nice gift for youself. I struggled with cheap irons from the local hardware store and then bought myself a nice solder station and it's wonderful, the quality of the tip is significantly better. But it was expensive (Weller WES51 or similar).

My soldering iron is actually very hot. The metal turns red when left idle for too long. It's very handy for large areas like speaker terminals, but for soldering on PCB I'd actually have to keep turning it on and off to avoid it from overheating.

I've been looking at the TS100 iron
TS100 Digital OLED Programable Soldering Iron Station Embedded Interface DC 5525 Built-in Acceleration Sensors with STM32 Chip NEW MODEL - - Amazon.com
A friend who does cables is using it and his feedback is positive. The threads in EEVBlog reflects that as well.

Contrary to others, I don't see that as indication of a serious problem at all. I've build many amps where DC offset starts out the wrong side of 50mV. Yes, you can be extra careful when you match parts before installing them but sometimes the design it'self is not dc-balanced because it specifies resistor values at the input and in the feedback path that match onto readily available values and they are not the right values to get zero offset. I don't consider 30mV a problem at all, and in my opinion it's perfectly safe for use with any set of speakers.

I've boxed up the amp and been running them for a day plus or so, it runs well, I don't notice much difference compared to its stock form. I must admit I am somewhat tone deaf.
I tried hearing for different before-and-after things but once I start noticing something, it scratches that part of my brain that questions whether its true or confirmation bias. But it does sound like the speakers had 'disappeared' better now.

 

[audio_tony]

For a solder station I feel your money might be better spent on something like one of these:

The most important thing to ensure with these cheaper irons is that you can obtain replacement bits.

I have two irons that I bought from Maplin - they were around £50 each - and they have lasted me for years...

Stahl Tools SSVT Variable Temperature Soldering Station: Soldering Iron: Amazon.com: Home Improvement

Electronix Express 0603DZ99 Soldering Station, Features Continuously Variable, Power Between 110-130V, 1.5 mm Pointed Tip: Amazon.com: Home Improvement

Velleman VTSS5U Low-Cost Soldering Station 50W 150-480degC: Amazon.com: Home Improvement

Soldering Iron Station with extra heating element &5 tips 937D - - Amazon.com

EDIT to add: Also look at the Tenma" brand as their stuff seems pretty good too.

 

[thimios]

I think one of the best.

 

[mrWagner]

At similar wattage, does it still matter whether they're energy efficient bulbs (LED/Halogen/CFL) or incandescent bulbs?

You can't use LED light and most probably CFL either. Not sure about halogen, but I think it works.
LED and CFL has their power supply in they body so they don't work like a resistor. Traditional (incandescent) light bulb works kind of as a simple resistor. So if too much current is being drawn through the resistor, then higher and higher voltage is dropped on it, so less gets to the transformer. Secondary voltage drops also and also less current it can draw. Plus the more current goes through the bulb, the hotter it becomes and even higher its resistance becomes. So at low currents it nearly works as a short. (Not really short, but lot lower than at line conditions)
Size of the bulb depends on the amp. This amp consumes little current at idle, so you can use a small bulb. But if you try to power up a big A class amp with a 60W bulb, then it will constantly glow as it requires lot more current all the time.

My soldering iron is actually very hot. The metal turns red when left idle for too long. It's very handy for large areas like speaker terminals, but for soldering on PCB I'd actually have to keep turning it on and off to avoid it from overheating.

What type of iron are you using? There should be a way to control it. It is not normal to overheat. Maybe the tip is too high temp type?

 

[gaborbela]

That sounds like a lower wattage bulb is safer than a higher wattage. Most of the mentioned bulbs in this thread were 60W.
At similar wattage, does it still matter whether they're energy efficient bulbs (LED/Halogen/CFL) or incandescent bulbs?



My soldering iron is actually very hot. The metal turns red when left idle for too long. It's very handy for large areas like speaker terminals, but for soldering on PCB I'd actually have to keep turning it on and off to avoid it from overheating.

I've been looking at the TS100 iron
TS100 Digital OLED Programable Soldering Iron Station Embedded Interface DC 5525 Built-in Acceleration Sensors with STM32 Chip NEW MODEL - - Amazon.com
A friend who does cables is using it and his feedback is positive. The threads in EEVBlog reflects that as well.


I've boxed up the amp and been running them for a day plus or so, it runs well, I don't notice much difference compared to its stock form. I must admit I am somewhat tone deaf.
I tried hearing for different before-and-after things but once I start noticing something, it scratches that part of my brain that questions whether its true or confirmation bias. But it does sound like the speakers had 'disappeared' better now.

Hi
Just use regular light bulb that has the req. resistance also the correct wattage. The energy saving light bulbs 13W=60W that not going to work properly neither the LED type. If you do not found a 60W you can go with 40W/channel at these amp.
Make sure for main fuse use fast blow type or at least do not over size it.
Once you set up the amp you do not need to worry, these amp runs well, just check the Iq after warm up with the cover on. Remove the cover and test the Iq one side, after do the same the other side with out music. Based on my experience and other plp. feedback do not go over 25-28mA bias after warm up. These amp tend to sound better at (low)that bias. Enjoy your amp!

 

[penmarker]

For a solder station I feel your money might be better spent on something like one of these:

The most important thing to ensure with these cheaper irons is that you can obtain replacement bits.

I have two irons that I bought from Maplin - they were around £50 each - and they have lasted me for years...

EDIT to add: Also look at the Tenma" brand as their stuff seems pretty good too.

I think one of the best.

What type of iron are you using? There should be a way to control it. It is not normal to overheat. Maybe the tip is too high temp type?

Thanks for the advice on soldering irons. My iron doesn't have a controller, its the type that you just plug straight into the wall socket. It's a high wattage iron which I had neglected to check before purchasing. It must be 40W plus or something, its written on the packaging but that's long gone now.

You can't use LED light and most probably CFL either. Not sure about halogen, but I think it works.
LED and CFL has their power supply in they body so they don't work like a resistor. Traditional (incandescent) light bulb works kind of as a simple resistor. So if too much current is being drawn through the resistor, then higher and higher voltage is dropped on it, so less gets to the transformer. Secondary voltage drops also and also less current it can draw. Plus the more current goes through the bulb, the hotter it becomes and even higher its resistance becomes. So at low currents it nearly works as a short. (Not really short, but lot lower than at line conditions)
Size of the bulb depends on the amp. This amp consumes little current at idle, so you can use a small bulb. But if you try to power up a big A class amp with a 60W bulb, then it will constantly glow as it requires lot more current all the time.

That's a good explanation, thank you.

Once you set up the amp you do not need to worry, these amp runs well, just check the Iq after warm up with the cover on. Remove the cover and test the Iq one side, after do the same the other side with out music. Based on my experience and other plp. feedback do not go over 25-28mA bias after warm up. These amp tend to sound better at (low)that bias. Enjoy your amp!

Thanks very much, that's very helpful. For now the amp is running well and I'm going to run it for maybe a few more days before listening to it critically. I'm still bugged by the DC imbalance between the two channels and I might just buy multiples of the transistors so I can match both channels.
Also I do think at least one of the transistors went out of spec after the transformer mishap because the bias V at R12 will only reach 7mV with the trimpot all the way clockwise.

 

[gaborbela]

My experience with my own clone but I read the same from other source the LTP transistor one has to be 5% lower at hFE than the other to get close 0.0##VDC on the speakers terminal. From the schematic the one is inside.
If you can not adjust the bias please check all the resistors also, eye ball the two if they are the same.

 

[mrWagner]

Thanks for the advice on soldering irons. My iron doesn't have a controller, its the type that you just plug straight into the wall socket. It's a high wattage iron which I had neglected to check before purchasing. It must be 40W plus or something, its written on the packaging but that's long gone now.

I have a 50W iron without a controller, but I have different tips.
Different tips will heat up to different temperatures. I think you can also do that.

 

[AndrewT]

for a Mains Bulb Tester you must use a filament type bulb that has a strong PTC character. Carbon is no good.
The most common type is Tungsten filament.
It does not matter whether the gas inside is a near vacuum, or nitrogen, or carbon dioxde, or any of the noble gases, or any of the halides.
The advantage of the halides is allowing higher operating temperature, or longer operating life, or a combination of both. That higher operating temperature gives a slightly higher ratio of hot:cold temperature related resistance and that is a slight advantage for this current limiting duty.

Do not use LED ,or any of the fluorescents. That has been posted dozens of times, READ the Forum !

Get a tungstem filament bulb and preferably in a big range of wattages from around 20W upto 150W.

 

[MarkS]

You can get a very good soldering result, even on pcb boards with no solder resist, provided you have a temperature controlled tip soldering iron with a tip size proportional to the job requirement which will seldom be the default tip supplied, a proper sponge to wet clean the soldering iron tip between each soldering operation and real tin+lead solder of 1mm, or less, in diameter.

Lastly but most important, always remember to heat the work and not the solder.

Hth.

An externally hosted image should be here but it was not working when we last tested it.

 

[penmarker]

Had some friends over for some coffee and movies, and showed them the amp too. Played some music and such, everyone seems to agree that it sounds very good or at least as good as their own amps. I mentioned to them about the bass being not too low reaching or anemic, and they said "Seeing how you don't have subwoofers, the bass sounds fine to me."
Well it turns out my daily driver in ear monitors has boosted bass and I've been accustomed to them for a few years by now.

Wew lad.

 

[mrWagner]

I recently bought a zerozone nap140 pcb and I have a question about DC drift at the output.
I used bd139/140 instead of ZTX, bc546b for input, bd139/140 for driver and 2n3055 for power transistor. Protection part left out.
Fired up with 2x30VDC, input shorted, 8 ohm resistor load. Measeured the 0.22R resistor and set the bias to be 3mV, so around 14mA.
The problem is the output DC. It starts at around 6-8mV, and slowly (1 min) goes up to 15mV. As soon as I touch the VAS bd140, the voltage drops to 12mV (in 1 second). Strangely if I touch the VAS bd139, nothing happens. If I also touch the input transistors top, it drops more back to around 10mV. They don't seem hot, but then why would they drop? Is there a way to decrease the DC and also reduce the heat drift?
Does it drifts so much for others also? I'm afraid if I put it in a box the heat may go up and the drift increases lot more.

 

[AndrewT]

The VAS device sets the current through one side of the input pair.
Thus it's temperature changes the current in that input device.
The input pair change parameters as their temperatures change.

Both of those effects will change the output offset.
The board layout and the circuit design were never optimised to attenuate temperature drift effects.

 

[iceman3]

naim nap 40 clone has rail voltage at output

naim nap 40 clone has rail voltage at output. i don't know what i did wrong but, both kits have the same problem. one of them burnt my speaker before i realized what happened. i tried adjusting the trimmer ,but nothing changed. i removed all of transistors they are fine. any help?

 

[mrWagner]

Any way to decrease the DC by default?
Use more different HFE input transitors?
Changing resistors?

 

[AndrewT]

naim nap 40 clone has rail voltage at output. i don't know what i did wrong but, both kits have the same problem. one of them burnt my speaker before i realized what happened. i tried adjusting the trimmer ,but nothing changed. i removed all of transistors they are fine. any help?

You created two problems that led to speaker damage.
a.) you forgot to always power ON via a Mains Bulb Tester
b.) you forgot to test thoroughly before connecting any speaker.