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Old 1st June 2011, 07:26 PM   #1091
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I don't think there is a reasonable argument that an LM317 regulator would be less than ideal for the sound, considering it isn't physically part of the LDR audio circuit at all. The audio circuit literally just goes through the LDRs. The resistor value of the LDRs is determined by how bright the adjoining LEDs are. What those LEDs are powered by isn't of massive concern (unless it's oscillating quite a lot - which is completely unlikely). There has to be SOME common sense in Hi-fi - there are those on the LDR site that will claim they can hear a difference when those LEDs are lit with batteries, but IMHO they are the same people who replace all the caps in a hi-fi with $$$$$$ Black Gates in their speakers in the hope of improvements - in other words, DAFT!

I'd be more concerned about the drain on the DCB1, but even that is irrelevant, as it is constant amperage (when not adjusting voltage) and a tiny tiny draw.
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Old 1st June 2011, 07:31 PM   #1092
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Replacing caps after 15 years is a money spinner for parts companies - that's all. A leaking or out of spec power supply cap is massively unlikely on a 14 year old Quad.
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Old 2nd June 2011, 08:30 AM   #1093
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Lucas, thanks for reply and a very encouraging one.

What made me think of dried out caps was a degraded sound of lower regions... and the hum. But maybe I'm not the right doctor here, so it's not a even a diagnosis.

For LDR PSU, I'm leaning towards options 1 & 2. What bothers me is another transformer. I'm affraid to add one more possible source of noise. My current R-Core has a separate housing and is not located on the chassis of DCB1...

I've found some ready made modules of LM317 implementation made by asian engineers : LM317 In DC or AC 4V-30V Out DC 2.5V-27V 1A Converter | eBay UK

Looks convenient. But as a diyer I would be more tempted to build my own.
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Old 2nd June 2011, 10:50 PM   #1094
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Regarding hum, isolate signal GND from power GND by 2x star GND arrangements - one for signal, isolated from everything, including the metal case, and one for electrical earth. Connect the signal GND star to the electrical GND by a CL60 thermistor. That should clean things up.

It is definitely complicated by your Russian GND-less supply
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Old 3rd June 2011, 10:14 AM   #1095
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Lucas, I appreciate your suggestion. If I understand correctly, it's meant for the buffer and I intend to implement it.

Though, I'm sure the main issue is in the amp. Yesterday, I've opened it up again, and convinced myself it has a floating (virtual?) GND. No safety earth is coming in, so nothing's connected to it by default. Have to do a research if this particular scheme is helping or causing problems in my setup.

One more off topic. Geopolitical this time. This old "sans safety earth" supply shouldn't be called russian. Nationality has nothing to do with it There are some differences between soviets (almost a historical state of mind), russians and lithuanians (formerly sovietized nations)

BTW, similar supply, but with additional safety implementations is still used in Switzerland and sometimes found is Scandinavian old buildings.

Here, we are moving away from it.
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Old 3rd June 2011, 11:51 AM   #1096
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Hi-tech electronics manufacturers, like Quad, use a different system than is possible for DIYers these days.

We generally use Class 0 Earthing arrangement, where all earths are connected to chassis, and lead out to electrical earth.

Modern manufacturers use Class 6 Earthing arrangement, where they can eliminate the need for an electrical earth by absolutely guaranteeing that it is impossible for the metal case, etc. to become live, even if a wire comes loose, by double insulating everything inside the chassis. We can't easily do that. Nobody does it that way here. Quad can, and it should cause you no problems, unless transformer AC hum noise escapes up the interconnect shields, into the pre-amp and into your signal, which has happened to me.

Sorry for calling your system Russian. I meant Soviet of course. Whatever it is, it isn't ideal. I'm sure glad we've always had a safety earth in the UK though - it saves a lot of lives! If I make a mistake in my Hi-fi and so much as 30mA goes into my body or to earth, a residual circuit device trips the switch, and I am saved a nice big shock (especially working with valves.)
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Old 3rd June 2011, 11:59 AM   #1097
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Having said that, perhaps working on a Class 6 arrangement (like in the Quad) for your pre-amp might be a good way to go for you, as your house has no Earth connection. A ventilated wooden case will help, as it provides your first layer of insulation, so is probably safest.
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Old 3rd June 2011, 01:27 PM   #1098
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It's not that current power instalation is completely unsafe. The fuse blows when there's a loose wire on chassis, the switch trips if there's fault. Earth is connected with neutral, but at one distant point.

Quote:
Originally Posted by LucasAdamson View Post
unless transformer AC hum noise escapes up the interconnect shields, into the pre-amp and into your signal, which has happened to me.
Is it possible that this kind of noise affects only one side? Is there a cure to this? Thermistor?
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Old 3rd June 2011, 01:36 PM   #1099
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OK. I think what I suggested is unlikely to affect one side only. You really need to determine for absolute certainty whether it's your power amp or pre-amp that's causing you problems first. It's impossible to diagnose remotely - sorry.
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Old 3rd June 2011, 02:04 PM   #1100
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Thanks for all information, anyway. It helps to get a full picture of all possible troublemakers.

Yes, you are right, I should make a proper buffer grounding and then look further.

Recap: with my passive pre (2 mono atenuators only), I have got same noise results as with the DCB1 (both channels humming). I've got different results with when no interconnects connected (1 channel noise) to the amp.
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