Sources of hum.

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#23
Well, I disconnected my filtering, hooked up RCA jacks with the ground insulated from the chasis, this then caused the "helicoptering" and then I hooked up the grounds of both the poweramp and the preamp to little connectors on the backs and hooked them together. This seems to get rid of it, it sounds very nice now, I'm going to give it a listen now to see if it's truly gone for good...
 
#25
Is my amp safe?

I've just finished my JLH for ESL mono blocks, but there is a ground loop problem. Once the input RCA interconnect from the pre-amp is plugged into the power amp hum started. The interconnect cable between power and pre-amp completed the loop.

The way my JLH is grounded as follows;

Mains earth/ground --->chassis/heatsink--->input negative solder tag---->amp PCB signal ground--->signal star ground--->PSU star ground.

The PSU uses one Tor.transformer center tap and two bridge rectifier to two banks of smoothing caps to +ve _ve PSU PCBs and PSU PCBs ground traces to PSU star ground.

I solved the ground loop hum by breaking the connection between chassis ground and input negative solder tag. The rest of my systems are all commercial products, so I assume they are all chassis grounded. Now my question is that how safe are my mono block power amps? I have no other DIY compnonets in the chain.

Thanks in advance!
Chris
 
#27
Hi Joebob,
I built an STK amp recently and it had a nasty hum emanating from the speakers, constant no matter what the volume. I bunched up all the negatives together with the 0 V rail of the PSU and hooked it up to the earth of the house and voila, the hum was all gone.

Vivek
 
#28
AudioFreak,

Thanks for the answer.
The input RCAs are the isolated ones, that's why I had to cut the connection that I made( in the first place ) between chassis and the negative tag in order to get rid of the hum. But there is still no answer to my original question, how safe are my mono blocks in terms of any fault developed later in its normal life span? Will it kill someone who came to contact with the chassis/heatsinks, will the slow blow fuse protect the circuit if the transformer melt down etc etc? The mains ground is only connected to the heatsinks/chassis. The power supply and amp(signal) ground are connected to the rest of the sysytem only by means of the RCA coax cables now.

Thanks,
Chris
 
#29
Chris,

If I understand you correctly, you've grounded the chassis to the main's ground and the power supply and signal ground are electrically floating. This should not be a safety problem as you have the chassis grounded and the power supply is internal and isloated from prying hands. The chassis will not shock anyone as it is at ground potential. I've done this will some of my amps, especially the bridged ones.

With respect to faults and melting transformes, you should have a slow blow fuse in one primary leg of the transformer and one fast blow in each of the secondary legs.

Regards, Robert
 
#30
Fire

Thanks for your reply rljones.

Hi fellows, now my amps have been running for more than 30 hours with no problems so far.
But still what are the possible causes that may make the transformer to start a fire,
overload by other failed components like shorted ones,
transistors grounded to heatsink, blown resistors caps, surge spike, overheated bridge rectifiers ? Please name a few possible potential failure causes/reason.

Thanks in advance,
Chris
 
#31
This is interesting ... in my audio system at home, all the chassis grounds of all the components are connected together via their 110 plugs (into a Tripp-Lite surpressor). All the audio circuits are completely isolated from that, including the grounds on the power supplies, which are connected to the audio signal ground on the DC side of the supply, and the chassis on the AC side. I have no problems ever, no matter what crazy things I do (like taking my ground rod out from the outside to prevent lightning strikes) ;-)

~jon
 
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