hum in aleph 30

jos

Member
2002-04-01 4:29 pm
I have built 2 monoblocks based on the aleph 30 schematic. The voltage is +/-23v.
I have used for each monoblock + and - 30000 uF. Offset is 30mV. I get a ripple of 180mV on the plus and 180mV on the minusside. I have tried everything changing the central earth point, moving the transformer. Does anybody has any idea or is 180mV simply too much
Jos
 
I use the same values.I did not made any measurements,them is audible only very close to me speakers.Accoding to simulations I have made, the 180mV is normal with 30mF caps. Try to increase this value- not very cheap or add choke.I did it.The toroid cores I got in computer service shop ( from power supply) for free (not at all, this guy got a bottle of home made spirit).
 

WayneS

Member
2002-03-24 11:44 pm
Dallas
Jos,

How do you know that the hum is caused by power supply ripple ? Did you try to run the amp with no input connected to see if the same hum results ? If not, try it out. If the hum goes away, you almost certaily have a ground loop which is causing the hum rather than the PS ripple. The amp should be fairly quiet on its own but still has a amall amount of hum - you have to hold your ear to the speaker to hear it though so it is not a problem at all for listening.

The problem is, to "get rid" of PS ripple, you need an infinite capacitance. Multiplying your caps by 10 will give you 1/10 the ripple (+or-) and that would give you 20dB less ripple.

I'd also put forth the problems I had in my amps as possibilities, but that is just too perverse :).
 
Koy ...and all others

... in my last multipler i used high quality caps for my multipler and much more than in rod eliots schematic:

40000 uf in the front end and 10000 in back end, four 1000uf-ers in the middle part. - for each monoblock!
All BC cpacitors. the 10000ers in backend are bypassed with mkp`s and styroflex`s. I know, it`s much more than in rod eliot`s schematic, but nevertheless cheaper than hundred thousands of capacitance.

With this psu the speaker is absolutely quiet in absence of any input-signal.

I did not hear any differences in sound between multipler and big capacitances except of the small hum, using big capacitances.

has anyone else made experiences with the capacitance multilpler?

Ralf
 

jos

Member
2002-04-01 4:29 pm
I have just added 39000UF per rail , the ripple dropped to 50mV but the hum is still the same. You can hear it clearly at a distance of 3 meter. Sensitivity of the speakers is under 90. Disconnecting the amp from the rest does not improve anything.
I have used the 3 ohm resistor (R0) to ground, moved the transformer, added caps. Still the same amount of hum. I use 220 W toroid transformers per channel.
 
Hum in Aleph 30

Jos,

I think you have a different sort of hum cremlin lurking in your mono blocks.

Are both channels making the same noise?

Recommend you have a close look at your boards, there maybe an assembly fault.

An earth trace touching where it should not causing an earth loop!

I would also test for all the voltages, particularly around the input pair and current source, or even the orientation of components or and check you bias, it may be too high which could account for hi hum levels.

The first time I turned on my Aleph 3, it draw 6 amps bias and humm..ed a lot but did not break

Just thinking of possibilities .

best of luck

macka
 
hum in Aleph

I had same problem.As I told Jos he might think about a PI filter on the supply rails,V+ and V- try something like 10000/4.7mH:10000 in extra to the main big capacitors of the PSU.Remember that caps radiate noise,and a wire just across might take hum pulses and carry it to the circuit!!!!
I do use the Pi filter,and over a 97dB sensivity speaker it is almost inaudible...
 

jos

Member
2002-04-01 4:29 pm
Thanks nar,
I did all try that, but it did not get any better. The hum is still the same whatever I do. I use the layout of Mark Finnis, just changed it a little bit because I have 2 sinks on the side per channel. I checked the voltages, the sound is oke except for the hum.