My 200 Watt K8060 seems to distort. It’s Sometimes OK but all of a sudden it distorts i cant figure out why. I’ve just installed a 30V-30V, 160VA transformer from maplin (N04BA). It started after i used a 4ohm speaker at what was probebly 20 Watts, it started to distort even with a very quiet volume. As you turn the sound up the level of distortion stays the same just the entire sound just get louder. Also when i turn the power off the Amplifier the power stays on at a constant volume for about 15 Seconds and the distortion quickly fades away and becomes clear again untill it turns off. Can anyone shead some light on this, could 4700uf 50V Capasitors fix this? :?
Changing the smoothing caps will not solve this problem.
Is the bias current correctly adjusted ?
How about the DC level, do you measure any DC at the output ?
Did you check the board for any mechanical problems (solderings, connections, PCB tracks and pads) that might cause troubles e.g. due to heating ?
I’m quite sure, the soldering is fine, i was previously using a 12v PC power supply and it was fine, im still looking into better heatsinks but i made sure i didn’t push the amp too far and i kept it so i could feel it was only warm, im not sure about the Bias because i dont get a propper reading on my multi-meter, also out of curiosity how does the Bias settings actualy work, what does it actualy set.
Oh also i find when i remove the input i sometimes get a squeaky pulsating noise for about 5 seconds, why could this be?
Hmm i’ve just realised that the distortion seems to be some sort of radio signal. i seem to get interference when i touch any input; my mp3 player, mobile phone mp3 player, laptop output. I tried using farrite rings on the cables but it dosn’t seem much of a difference.
I was wondering that if i put a Pre-Amp before the line to the main Amp would it be able to cut out the interference?
It is doubtful that this will solve the problem. Did you use properly shielded wiring troughout your assembly ?
Try connecting the GND of the circuit with a 100p cap. to the enclosure, if it is a metal enclosure
i used to build a lot of cheap amps and sound systems when i was younger and tested with this sort of stuff. i found that if the power cables was anywhere near the input signal there was a lot of distortion. try shifting the power cables. another thing i did was install a 2.2uf cap in parallel with the base of the input signal. it dramatically increased bass and removed a lot of the buzzing/humming sound.
Is it working correctly with 12 volts?
I have just built one of these kits with a 47k pot and mono jack to try it with my guitar through a 4ohm 12" speaker. All seems good but I am getting a lot of humming from it and not a lot of volume. The velleman amp on full volume is quieter than my 20watt guitar amp on a relatively low setting. Why have I lost volume? I have two 4700 Audio grade caps on the board, 72 volts between + and -, the bias is possibly a little high (curse these digital multimeters!). the whole assembly is in the metal housing of my marshall VS100 amp using the transformer that is fitted in that. I would like to connect the ground on the Velleman circuit to the housing but what is the 100p cap mentioned in this thread? 100 pico farad?
Please note that this is a power amp, there is no pre-amp (sensitivity: 600mV for full output, guitar pickup: a couple of mV…)
A guitar pickup has very low output and needs a pre-amp. Furthermore, it requires exact impedance matching, to assure correct frequency response.
The hum is most likely due to poor shielding, a hum loop or a too high input impedance.
100p = 100 picofarad.
Thank you for the help. I have connected the K8060 to the marshall pre-amp board as required, tidied the wiring and connected the ground. humming is greatly reduced and volume is “through the roof”. A superb, clean sound. I have some ferrite rings somewhere, should make it even better. Regards, Jules
As the speaker is connected with a jack plug, would a 4 ohm resistor across the socket terminals so that it is in circuit should the speaker be disconnected, save the amp from damage, or is it best left open circuit in this instance? Obviously not running without a speaker is the best solution but I was just wondering if I can safeguard against a lead being pulled in error. Thank you.
As the speaker is connected with a jack plug, would a 4 ohm resistor across the socket terminals so that it is in circuit should the speaker be disconnected, save the amp from damage, or is it best left open circuit in this instance? Obviously not running without a speaker is the best solution but I was just wondering if I can safeguard against a lead being pulled in error. Thank you
Open circuit should not damage the amp.