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Old 1st January 2005, 10:28 AM   #1
SM7UYJ is offline SM7UYJ  Sweden
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Default my first GC monoblocks

My first monoblocks done and working!
PSU in the same box as the amp as you can see. Any sugestions on how to get rid of the slight humm I hear in the speakers with no input signal?
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Old 1st January 2005, 12:49 PM   #2
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Those look very sleek!

Hmm, hum is not a nice thing, that's for sure.

I'm thinking of the proximity of the amp to the power supply. Being that close, there must be care taken to shut up any transfer of hum from the supply to the amp.

It is especially important that the signal wires are away from the transformer, shielded wire if possible, and well grounded. Star ground being essential as well. Of course, an iron plate between the amp and power supply sections would improve upon hum problems as well, but that's not always too easy to implement and isn't really necessary.

Is your input wire running beside the transformer?
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Old 1st January 2005, 01:24 PM   #3
SM7UYJ is offline SM7UYJ  Sweden
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Hi,
As it's rather tight in the box, signal wires (shielded) are quite near to the transformerwires and bridge. Here's a picture of the wiring inside.
As you can se, installing a shield plate is not so easy!
It's no big problem, but it would be nice to get it dead quiet in 'standby' mode. Any experiance with filters to cure this problem?

//Roger
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Old 1st January 2005, 01:52 PM   #4
hifi is offline hifi  Sweden
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Twist the cabling from the transformer to the bridge carrying oppposit phase.

Twist all signal carrying conductors with a ground wire, this will help if it is radiated hum you are picking up. You could also consider a mu-metal screenen around the toroid.

Also every cable pair you want to reduce intereference between cross att right angles.

I saw those recently on an ad on hifimagasinet btw... id you get the cases from conrad?

/ Micke
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Old 1st January 2005, 02:12 PM   #5
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Is your circuit ground connected to the mains earth at all?
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Old 1st January 2005, 03:08 PM   #6
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That was rather incomplete of me to not mention wires at 90° angles and shared earth to signal grounds.

Definitely pass signal and DC power wires across the AC wires at right angles if possible when the wires must come near eachother. This reduces coupling to a minimum.

An earth-grounded signal/amp connection may cause a ground loop with other equipment that might be grounded. Do these gainclones hum when there is no input wire connected?
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Old 1st January 2005, 07:00 PM   #7
SM7UYJ is offline SM7UYJ  Sweden
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Tnx for all replys and advice!
Will try them out as possible with the current layout.

Micke: Cases are 'home made'. Originating from 24V battery chargers. Originaly black but (sorry don't know the english word) 'omeloxerade' (anodisized!?) to silver finish.
For sale, as I'm going to try another layout for the casing.
Have a stereo GC in similar lcases for everyday listening !

Scribble: Yes, grounded att mains. SG for power and signal!

Duo: Aparently easy to forget! I'm a ham radio operator/builder, so quite familiar with shielding/coupling/RF pickup etc, but taught this was more a problem for the radio frequency region!
Looking at other amps, the layouts mostly don'tn adress this or have I been looking at the wrong ones??

Maybe I'm making a chicken out off a............. !?

Sitting at listening distance you can't notice the hum only if you put your ear to the speaker.

Is there any hum in the GC's you've built ?


/Rog
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Old 2nd January 2005, 07:06 AM   #8
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Hej, Roger, radioamatör?

You should identify your grounding. Signal ground should meet the speaker ground, really "sniff" the cable. Then the speaker ground should go to smoothing caps and rectifier bridge. Do you have home brewed pcb's or is it BrianGT's?

A mono GC is totally hum free if you do it right.
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Old 2nd January 2005, 07:22 AM   #9
SM7UYJ is offline SM7UYJ  Sweden
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Hi PerAnders (PA) !
Yes a 'radiamatör' and main interest poweramps for RF.
Have been building power ampf for RF for almost 12 years now - gee...I'm getting old!

Latest project : http://hem.bredband.net/sm7uyj/

The boards are self made, but with similar layout as Brian's cards as you get a symetrical (component placement) nice looking card this way.
I'll try a different layout for my next project to get PSU and signal paths even shorter and more separated.

Will fire up the solder iron today and do some of the suggested advice!
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Old 2nd January 2005, 03:07 PM   #10
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Peraneder What do you mean by "totally hum free". Do you mean ,no hum should be heard at a certain distance or if I put my ear 1 inch from the woofer?
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