A labour of Love

Hey guys,

Only now at 11 in the night could i make out a very very faint humm from the drivers...

I guess i will have to try and look for the problem..
However, it is nowhere near the previous levels.
Am a bit disappointed with this new turn of events..
However, am still enjoying to the wonderful music it is able to turn out.
Will take it to Arasu's place to try and try to remove the last of the irritating and ever persistent bugs.

All the best. I am sure you will get rid of it soon.

Trust U have made a "STAR" ground ... all circuit grounds to come to a single point on the Power Supply Capacitor Ground.

Dont route allk grounds thru the Chasis... a sure way to get Hum that just wont go...

Also can add a 100 ohm resistor between the Power Amp Input ground to the Power supply gnd.

You may have to cut PCB tracks for this ....

All the best

Amp_Nut schrieb:

Trust U have made a "STAR" ground ... all circuit grounds to come to a single point on the Power Supply Capacitor Ground. Dont route allk grounds thru the Chasis... a sure way to get Hum that just wont go... Also can add a 100 ohm resistor between the Power Amp Input ground to the Power supply gnd. You may have to cut PCB tracks for this .... All the best :)

hmm..usually what people recommend to use between input and power supply grounds is a 10 ohm resistor.,
I haven't tried that..Will try it as a last a resort.

The way i have routed my ground is to take a wire from each of the three capacitor banks and ground them at one single point on the chassis.
I am guessing that thisis what u are advising me against. right?

I have three EI type transformers in my amplifier.
one is a 650VA for my bridged lm4780s and OPA541.
The otehr a 350VA for the paralleled LM4780s and a pair of isolated LM3886.
the last one is a 20VA one for my crossover network.

i have 7 amplifier modules in all.

With 650VA tranny
-----------------
2 bridged LM4780s
1 OPA541

With 350VA tranny
------------------
2 paralled Lm4780
2 LM3886

another point i want to mention is that i have directly grounded the input RCA ground connector to the chassis.

Can you suggest how it should be done to eliminate possible ground loops?

WOW

hmm..usually what people recommend to use between input and power supply grounds is a 10 ohm resistor., I haven't tried that..Will try it as a last a resort. The way i have routed my ground is to take a wire from each of the three capacitor banks and ground them at one single point on the chassis. I am guessing that this is what u are advising me against. right? another point i want to mention is that i have directly grounded the input RCA ground connector to the chassis. Can you suggest how it should be done to eliminate possible ground loops?

Hmmm.... multiple Power Supplies.... hmmm

1. First of all, you are correct... My earlier post should have read 10 ( TEN ) Ohms, not 100 Ohms. Sorry for the Typo.. The purpose of the small value resistor is to discourage a ground loop. Too high a resistor will add an output offset at the speakers.

2. Thanks for your detailed description of the grounding.

Based on the fact there there is only a small amount of hummmm , you have got it almost correct.

I would suggest the following :

a. Remove the local chasis ground at the input RCAs. Run a ground wire from the RCAs to the power supply capacitor ground that feeds the input stage. This I suspect should help the most.

Multiple RCAs should be grounded in their own, dedicated Star connection, with the Star Point on (one) the RCA with handling the lowest input signal level ( if each is for a different sensitivity )

b. Get all your 3 Power Supply capacitor grounds to meet at the -ve of the Input stage power supply capacitor. ( Not directly at the chasis)

From this star point, run a single short, thick wire to a single point/bolt on the Chasis. This should be the Only ground connection on the chasis.

All the Best !

Oops ! I forgot to mention.... I guess that you are Not deploying centre tapped Transformers ?

If Yes, then the Centre Tap must be connected to its local Power supply capacitor ground terminal directly.

The CT should not be connected to the metal chasis.

The metal chasis should be isolated from the ground at all locations, except at a single point, as indicated in my earlier post...

Only now at 11 in the night could i make out a very very faint humm from the drivers...

Oops Oops Oops !

If you can only hear a Faint Hum at 11 pm, and that too, with your ear inches away from the speaker, you dont have a Hum loop at all.

That much of residual hum from the Power Supply is nornal.

Amp_Nut schrieb:

hmm..usually what people recommend to use between input and power supply grounds is a 10 ohm resistor., I haven't tried that..Will try it as a last a resort. The way i have routed my ground is to take a wire from each of the three capacitor banks and ground them at one single point on the chassis. I am guessing that this is what u are advising me against. right? another point i want to mention is that i have directly grounded the input RCA ground connector to the chassis. Can you suggest how it should be done to eliminate possible ground loops? Hmmm.... multiple Power Supplies.... hmmm 1. First of all, you are correct... My earlier post should have read 10 ( TEN ) Ohms, not 100 Ohms. Sorry for the Typo.. The purpose of the small value resistor is to discourage a ground loop. Too high a resistor will add an output offset at the speakers. 2. Thanks for your detailed description of the grounding. Based on the fact there there is only a small amount of hummmm , you have got it almost correct. I would suggest the following : a. Remove the local chasis ground at the input RCAs. Run a ground wire from the RCAs to the power supply capacitor ground that feeds the input stage. This I suspect should help the most. Multiple RCAs should be grounded in their own, dedicated Star connection, with the Star Point on (one) the RCA with handling the lowest input signal level ( if each is for a different sensitivity ) b. Get all your 3 Power Supply capacitor grounds to meet at the -ve of the Input stage power supply capacitor. ( Not directly at the chasis) From this star point, run a single short, thick wire to a single point/bolt on the Chasis. This should be the Only ground connection on the chasis. All the Best ! :)

hey amp_nut
thanks for that detailed reply.
well i ahve posted this query on diyaudio.com and i have got the same repkly from them too.
they too are saying that once i isolate the inpt ground from the chassis things should be fine.
Will give it a try soon as i get home today evening and post an update.