Questions about k8060 & k8084

Kits Audio Hi Fi Projects
1

Hello!
I’ve built an amplifier I use for acousting building measurement (insulation measurement) with n. 12 (4 ohm) fullrange loudspeakers (dodecahedron loudspeaker) with a k8084 preamp. I used 2 k8086 module. Every module drives 6 of the 12 loudspeakers. This 6 loudspeakers are in serie/parallel configuration (three pair in series, every pair made by 2 loudspeaker paralleled) 6 ohm total.
Instead of two 120VA trafo I used two 225w velleman trafo with just a little problem about fuse (both 1A fuse, blew every time turned off the amplifiers - probably caused by higher magnetizing current of bigger trafo). with 1.6A all is ok.

  1. I made some test with pc sound card and pink noise to know max power capability of amps+dodecahedron. Short session (15 sec.) with 3/4 potentiometer and 1 session (7 sec.) at max power. I was outside, in the garden, Temperature was 5° C, heatsinks were cold. After 2 hours I was beginnig last test…sound card connected to amplifiers (pre k8084), NO SIGNAL, I turned potentiometer to max…only much background noise produced probably by pc circuits… and 2 second of big noise like “HUM” and both fuse blew and poth amplifiers blew…
    Before this test, I made 1 hour test with pink noise, half way potentiometer, and 50 watt , 5 ohm resistences in the amplifier outputs…heatsink hot and resistences very very hot, but everything allright.
    Bias was befor setting at 10mw (cold amplifier).
    I changed tip142, tip147 and bc547 , now both amplifier are ok.
    Made new test like before, but without pc, playing pink noise with cd player.
    No problems.
    Have you an idea about what appened ? I’m shure everithing is all right (soldering, components etc…)
    May be pc background noise cause amplifier oscillating???

  2. 200watt isn’t enough. I was thinking to add 2 more k8060 module , 4 k8060 in total and each one for 3 loudspeaker (6 ohm).
    Can every channalel of K8084 preamp drive 2 k8060??

  3. I have read only 1 k8060 for 1 trafo, the only problem is “hum”? In this case I could try… (I used 225w instead of 120w trafos)
    During session measurement with pink noise I have to use every time very high sound pressure level (about 100dB Lp(A)) so hum is not a problem bacause is impossible to hear it .

thank’s a lot and sorry for my English…

alessandro angelini, Italy.

2

Hello, if the fuse is before the large transformer then yes there would be a higher current demand from the transformer, so this should be ok,

  1. im not sure on this one. when you said you turned the potentiometer to max is this the bias adjustment pot?

2)if you add more power stages you may need more pre amp stages, not always necessary though, so you should get away with one preamp driving 2 power stages.

  1. Hum usually comes from the magnetic field around the transformer inducing voltage/current in the rest of the circuit becasue of flux leakage, this can usually be reduced by the positioning of transformers, and using toroidal transformers. and as a general rule of thumb ive always kept power transformers as far away from the input as possible. other causes of hum are ground loops, as far as i understand this is when points in the circuit that are supposed to be at 0v are at different potentials.im not sure using just a bigger transformer would work, plus you wouldn’t be able to cancel out the leakage with another transformer.
3

Hello, thank you for your answer.
I turned the amp potentiometer to max power, not the bias pot!

4

ah i see, whats the voltage input to the k8060? would it be possible the output from the k8084 is too much for it?

5

When both k8060 blew there wasn’t any signal out from pre amp.
Just much background noise from pc audio schede (i used audio from pc but in that moment player software was in stop!

6

I think I will go with a PA amplifier…If a k8060 blow during work it will be’ a problem for me…

7

interesting, if the pot is before the amp at the input it can only really be becasue of the signal in as the amp would be functioning the same as it always would have… a properly built PA would probably suit better if its going to get used alot.