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Old 15th May 2013, 12:07 PM   #1
Frarun is offline Frarun  Poland
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Default PSU noise - distance between blocks - cables length

Hi. I have some distance between power-AMP and Torroid inside my enclosure. I need to use a longer cables between two blocks of PSU. Which one configuration will be the best concerning noise generated by cables:

1. AMP(local small cap) <-----------> BigCaps<-> rectifier<->Torroid
2. AMP(local small cap) <-> BigCaps <----------->rectifier<->Torroid
3. AMP(local small cap) <-> BigCaps <->rectifier<----------->Torroid

I need to note the PSU is inside a small enclosure with preamp and some LCD inside. I observed twice the trashy signs on the LCD. The LCD is mounted really close to the rectifier (and AC cables), and I am not sure now if this can be related to some high current spikes, or something different... Is it possible this PSU cables can impact TTL level on the LCD cables? This is like max 2-3 Ampers only...
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Old 15th May 2013, 12:41 PM   #2
DF96 is offline DF96  England
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1 will be best. 2 and 3 will be roughly equally bad, as both send charging pulses over a long cable.
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Old 15th May 2013, 02:14 PM   #3
Frarun is offline Frarun  Poland
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Thanks. I will go for 1. But could you acknowledge these pulses may induct such high noise/spikes on TTL lines to have impact on 0/1 logic?
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Old 15th May 2013, 03:01 PM   #4
DF96 is offline DF96  England
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TTL is fairly robust but spikes could create trouble. Circuit loops carrying charging pulses should always be as small as possible, and as far from other stuff as possible.
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Old 15th May 2013, 04:23 PM   #5
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by DF96 View Post
1 will be best. 2 and 3 will be roughly equally bad, as both send charging pulses over a long cable.
I very much agree.
The charging pulse circuit must be kept very compact and every effort taken to minimise effective loop area.

A figure of 8 loop as described by Dr Cherry is very effective in canceling the two loops that cannot be reduced to zero area alone.
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Old 16th May 2013, 12:08 PM   #6
Frarun is offline Frarun  Poland
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Exactly what I though. The TTL couldn't not be so sensitive... I have exchanged the TTL cables to be sure this part not failed. But happened again yesterday. I observed once the LCD goes trashy. This happened most likely during some signal connection/disconnection. I get the hard 'knock' in the speakers is such moment (during power-on as well).
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Old 16th May 2013, 01:49 PM   #7
Frarun is offline Frarun  Poland
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AndrewT, I don't know Dr Cherry description. Do you mean the loop between the traffo and rectifiers? It would fit to my example. For reference please look at the picture. As you can see my diodes block are not 'parallel' with the transformer. I mean the diodes and transformer cables do not make a symmetrical loops.

Click the image to open in full size.
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Old 16th May 2013, 04:07 PM   #8
AndrewT is online now AndrewT  Scotland
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I see lots of pairs and quads.
All are close coupled.
If each pair is a flow and return then you have low loop area.
I see one 5wire. Are there separating grounds between signals?Again this could mean low loop area.
I see two red wires at the bottom separated. Where are the returns for these?
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Old 17th May 2013, 02:17 PM   #9
Frarun is offline Frarun  Poland
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The cables colors are definitely misleading. There is no ground between signals. Please have look on the 1'st photo. The thick arrow shows GND. The back arrows shows the signals current. Now I see there is not only a PSU cables optimal location, but signals may be a problem as well.... Two red cables are the +DC for power-amp. 2'nd photo shows more power-DC connections... Insane loops!

Click the image to open in full size.
Click the image to open in full size.

Last edited by Frarun; 17th May 2013 at 02:31 PM.
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Old 19th May 2013, 06:14 PM   #10
gootee is offline gootee  United States
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Routing details are extremely important.

Always keep the power and ground pairs together, everywhere, as close as possible or twisted tightly together if possible. If you have space between them, they make better transmitting antennas. Similarly, any pairs that might pick up interference need to also be tightly twisted together, or else they will make better receiving antennas.
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