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Old 27th May 2002, 09:30 PM   #11
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lowfi,

if I understood this correct your amp doesnīt hum when not connected to your preamp, right?

If so, what happens when you connect a cd player directly to your amp? Does it also hum?

If not have a look at your preamp and whatīs connected.
Do you have a tuner connected? Disconnect the antenna and try again. If itīs gone now you need a filter to avoid dc-coupling to the antenna (donīt know the englisch name right now)

happy trying,

william
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Old 27th May 2002, 10:03 PM   #12
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william
yes, it hums when the cd player, and another preamp is attached. it is fairly quiet with the interconnects attached, open-ended. i'll keep trying to hunt it down. so close!!!!!

scott
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Old 29th May 2002, 02:12 AM   #13
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Try connecting all your AC powered equipment to the same
power strip connecting to the same AC wall out let. Remove
the all center ground return's ( the center ground on AC cord).
You can purchase cheater plugs-connectors that gives you the
option of connecting these grounds. This normally this solves
most 60Hz hum problems.

The biggest problems comes from AC home runs to you AC
house circuit breakers box. Also, cable TV boxes, cable modems
and computers in a system can inject 60HZ hum. These components must have ground return isolation.

Remember that hum is caused by circulating ground currents paths and missing grounds connections.

Good Luck
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Jim W.
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Old 29th May 2002, 04:00 AM   #14
fcel is offline fcel  United States
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I've read that Halogen lamp's transformer on the same circuit breaker as the amp will cause hum. Do you have one of those lamp connected nearby that's always on?
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Old 29th May 2002, 04:38 AM   #15
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well,
this is the problem, it is very quiet with nothing at the inputs. it's when a pre or cd is hooked to the inputs that the hum is loud. i went to a different circuit and plugged it all in with the same results. if you haven't yet, take a look at the "amp. oscillation" thread i started just before this one, it may help to understand the full scene that i have going on here.

it's really strange, and i don't have the knowledge/experience/tools to really analyze this, that's why i'm hoping someone out there can show me the light.

thanks!!
scott
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Old 29th May 2002, 08:51 AM   #16
swede is offline swede  Switzerland
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Hi,

Well, if the hum appears when you connect the amp to a source, it IS a ground loop (unless you have another amp that hums with the same source).

Without any input connected, try and temporarily connect the ground leads together at the input terminal (using a screwdriver, paper clip or just anything that leads). If you hear a hum, it IS a ground loop.

One solution to this (as I fixed it on my Leach Amp) is to avoid the loop. On the Leach Amp each (mono) board has two ground connections. One for the input stage/signal and one for the output. These grounds are separated on the board with a small resistor. What I did (which was recommended on Prof. Leach's web-site) was to disconnect the signal ground on one board from the ground post and connect the grounds together on the input post, letting the input stage on one board have the same ground reference as the other board. My hum disappeared right away.

Is the hum there when you have only ONE input connected, or is it there ONLY when you have TWO inputs connected?

Best regards,
//magnus
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Old 29th May 2002, 08:55 AM   #17
swede is offline swede  Switzerland
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By the way,

Just the parts to build an Aleph cost some hundred euros/dollars, which is more than what a (not so) decent oscilloscope cost. I got my 20Mhz Leader scope for free.

Try and get a scope, crappy or not. It will sure help you in your future projects as well.

Best regards,
//magnus
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Old 29th May 2002, 10:13 AM   #18
bawang is offline bawang  Malaysia
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Default Hummmmm!!!!!

Hmmmmmm, sounds exactly like my problem with a 3 channel Leach Amp. Hummed only when ANY source is connected (preamp, CD player etc), absolutely silent without any input (input floating). Have tried everything that is suggested by Prof. Leach but to no avail. May have to do a total rebuilt just to satisfy myself that everything has been done correctly. If only I have the time.......
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Old 29th May 2002, 05:23 PM   #19
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Have you tried this, the star ground connects to input ground and then ground it to chasis and then finally to mains earth
star- input- chassis-mains.
If you need further explanation try reading douglas self homepage on the topic of grounding. The method used is describe clearly with drawing at the page and also the reason that this method is used.

Also, i haven't seen the aleph ps but in general don't used the star grounding at the power caps, something to do sharp spikes due to charging or discharging. Read this somewhere
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Old 29th May 2002, 07:25 PM   #20
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you know,
before, when all was quiet, is used 14awg stranded wire from the inputs to earth. now i have 22awg wire, is the gage THAT critical? i'm at work now, but i'll try DSelf's method with as large dia wire as possible.
thanks for that tip, D Self's site is excellent.
cheers,
scott
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