NE5532 preamp noise

tallnutt

Member
2016-10-13 1:38 am
Hi,


I'm working on a replacement preamp and amp for an old B&O. See this post https://www.diyaudio.com/forums/class-d/342430-beomaster-refit-controversial-6.html


I have a TPA3116 based board from Aliexpress, XH-M569, this board had some bad noise issues from an unnecessary opamp on the input, I removed this as suggested elsewhere and now it has acceptably low noise.


I am trying to hook it up to an NE5532 based preamp, aliexpress XH-A901, but it has a terrible whine noise, which is not dependent on volume. I have tried several power supplies an configurations, running both amps on same power and separate power.



Both the preamp and the amp have single line inputs, would it be possible to convert the preamp output to balanced? Would this help with the noise?



Can anyone help with how to eliminate this constant whine noise?


Thanks,


Theo
 

tallnutt

Member
2016-10-13 1:38 am
I don't have schematics for either board. It's a high pitched tone noise, not a hiss.


As an audio source I'm using my phone, but the whine is there whether it is connected or not.



I have tried lots of ways to connect power, common 24V from the same supply and with different supplies.
 

tallnutt

Member
2016-10-13 1:38 am
That was with no volume on the preamp. Different power supplies still give the noise but it sounds a slightly different tone with each. If I use a 9V battery on the preamp the whine goes away, but I need to power it from a supply, preferably the same one as the amp.
 

ubergeeknz

Member
2018-08-31 12:32 pm
That was with no volume on the preamp. Different power supplies still give the noise but it sounds a slightly different tone with each. If I use a 9V battery on the preamp the whine goes away, but I need to power it from a supply, preferably the same one as the amp.
Ok great, probably it is a ground loop of some kind. Either use a completely isolated supply or use a supply isolator between amp and preamp something like

1pcs new dc dc converter 12V to 5V 12V 3.3V 9V 15V 24V regulated isolated dc-dc power module quality goods
AliExpress
 

tallnutt

Member
2016-10-13 1:38 am
Thanks ubergeeknz. don't really want to wait another 5 weeks for a component from Aliexpress! Is there no other way to eliminate this kind of noise? A filter of some kind?


Also, this all needs to go in the same box, so can't have isolated supplies. I could try that isolator, but I have doubts it will fix it.
 
Last edited:

rayma

Member
2011-04-29 8:37 pm
Try an RC filter in each supply line to the preamp. Run the power lines to the amp.
Then connect a 1k series resistor in each power line to the preamp. Then add a 10uF or more
capacitor (observe polarity) from each preamp power terminal to the preamp ground terminal.
 

tallnutt

Member
2016-10-13 1:38 am
OK, so I tried a 1k resistor in series with the +ve to the preamp with different capacitors (0.1uF to 470 uF) accross the +/- power on the preamp side. It made no difference to the whine (which is about 1000Hz), Other than the reduced voltage to the preamp lowering the volume of it a bit.
 

tallnutt

Member
2016-10-13 1:38 am
Mucking around randomly, this is what worked! Connected the amp directly to 24V. Ground of the amp connected to ground of the preamp (same as it was before), then a 330ohm resistor from +24V to the preamp.. no cap, and the whine has disappeared completely. I have no idea why.
 
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Rolz

Member
2016-10-19 1:15 pm
I apologies for resurrecting an old thread , Ive done something similar with the same pre amp running from an smps. The above method/tricks did not work for me. What worked reducing to hum/buzz to almost nothing was to hook earth/ground from the smps (earth/ground from the mains) to the ground of the amps "signal-in ground" (the signal after the pre amp - signal out - and thus before into the amp).

It seems to be working fine, my question is that is this safe? Perhaps ive overlooked something in haste of getting it to work. Its 100% something with these preamps. Ive etched custom pcbs for the pots.. anyway the whole things looks like a mess and im not too keen it catching on fire. Thanks heaps for any feedback.