I bought this amp a while ago, and I constructed it with ALL the recommended Velleman components, including the Heat Sink and the correct Transformer. After building I tested the bias on the trimmer pot and set it at the correct setting. I tested the whole system and it worked. I used a self-built crossover for improved bass and it delivered great sound. After one or two hours of low-powered work, the two 0.47Ώ 5W resistors (named R19 and R20 on the board) onboard the amplifier blew out. At first I thought the problem laid with the resistors and I replaced them with new ones The same happened. I replaced the resistors again and double-checked all my soldering connections. The problem persisted and I bought a new amplifier. As this happened again on the brand new amplifier I once more checked my soldering on the new amplifier. Still the resistors blew, so I thought it might be the transformer, and replaced this as well. The problem continued, with the exact same resistors blowing out again.
Could anyone help me please? I spent a lot of money on this system already, and bought nice speakers and everything, but I can’t get this thing to work! I’m getting desperate, and will try anything to get this thing to work!!!
Difficult to say what might have gone wrong. This amp is extremely stable and reliable, a real classic circuit. As you have the same problem twice, the problem is definately not related to the amp, but to the construction, hook-up or use. Did you perform the test with the lightbulb prior to using the amp ? Did you perform any modifications, even minor ones, to the circuit ? Do you have the same problem when you remove your filter circuit (maybe it is oscillating) ? Is the impedance of your speakers too low ? What are the + and - DC voltages ? Is there a DC offset at the speaker terminals ?
should i have the amp connected when testing with the light bulb? can it maybe be the trim pot? the transformer voltages are 30 volts dc, exactly like it should be.
but the thing that bugs me most is the fact that it worked perfectly but suddenly it gave problems. and i removed the input with the filter and the speakers but it still blew…
HELP! I have Exactly the same problem. It sounds like it could be a build problem. I’ve just started my 5th attempt on my own PCB board following the circuit diagram.
I made no modifications to the boards and their were no problems with the soldering. Now one thing I will add is that I connected my cambrige audio torroidal to the board which is a lower voltage and I had a sound at least one i could hear from a few rooms away but still way underpowered. I bought 2 x 120VA 2x30V Vigortronix power supplies and I tested each circuit and the white large resistor first blew up, then on the second board some other resistors blew.
I did I multimeter test on the Vigortronix supply and both measured at 35V on the multimeter, could this be the problem?
I’m hopelessly stuck too and can’t keep afford to buy all these velleman boards (4 so far) I feel like giving up on this project and just looking for ANY advice someone could give me please. I’m sure the first post on this board would sure appreciate it.
(Items that blew:
1st board - R3 (3K3)
2nd board - R19 and proably R18 (5W 0.47)
3rd / 4th simply no audio (light displayed - thats it)
p.s. I emailed the vigortronix company and got the correct wiring diagrams for the inputs)
Please HELP ARRRGH! lol A bit of music would be nice. Thank You!
Ok, so I’m back on this train. I’m wanting to try this again, but I’m bloody sceptical. I’ve bought a brand new transformer for this amplifier, and it’s specs are as follows:
Heatsink I have is very similar to this one: electronics123.co.za/Main.as … geNumber=1
with holes I drilled myself according to measurements. The previous amplifier (finished build) fit perfectly on there, so I’m positive it’ll work. Forced cooling can also be arranged, I want to drive a subwoofer so the noise isn’t an issue.
Now, I want to know how I can go about making sure that problem doesn’t arise once more. As mentioned before, the amp worked well for a day or two, and then blew the 5W resistors. I bought a new amp, and it did the same. I replaced the transformer, but to no avail, and then I dropped the project. So now I have the transformer and heatsink and the will to try again! I’m a bit more experienced than last time, so I’m positive. Any hints/tips? I’m going to be using static-free equipment and static-prevention tools all the way, and I’m making sure to not ground anything that shouldn’t be grounded and everything.
EDIT: Can the blowing of the 5W resistors be attributed to the wrong setting of the trimmer pot? I don’t remember setting it as it should be, and if at all possible, can this be the reason the resistors kept popping?
If that was indeed the problem, I’m literally going to kick myself. LITERALLY. I remember setting it to about 30mV, with the manual asking for 10mV. Man, I feel like an idiot.
I feel like giving up on this project and just looking for ANY advice someone could give me please. I’m sure the first post on this board would sure appreciate it.