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Old 19th April 2010, 03:45 PM   #3161
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Quote:
Originally Posted by georgehifi View Post
I've played with every concievable passive pot, Bournes, Alps Blue Velvet, Alps Black Beauty, Penny&Giles, Dact Switched resistors, and transformers.
Nothing has beat the sound of a series/ shunt LDR arrangment in the attachement, it has no contacts in the signal path, I believe that is the secret.
The only stipulation that all these passive controls including the series/shunt LDR need I believe is,
1: Low source impedence (cd player) <200ohms
2: High input impedence (amplifier) > 50k.

Cheers George
In my opinion, the Lightspeed is the greatest improvement you can make to a high end stereo for only $450.00! I have a pair of McIntosh 240 tube amps which I opened up, and took the gain pots out of the signal path. I run the tape outputs from my preamp into the Lightspeed when I play records as this bypasses the volume, balance, tone, and other contorls on the preamp. I run a dual control attenuator through a single control attenuator so I have master volume, and balance. The Lightspeed, and that simple modification to my amps made a huge difference. Listening to music is much more fun and engaging now.Click the image to open in full size.
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Old 19th April 2010, 08:25 PM   #3162
udailey is offline udailey  United States
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Bins
I think its your grounding. However if its not your grounding, your supply looks fine. Maybe you have a cold solder joint or such. It is very possible that the noise comes from the wall wart. Try a 9V battery. Use alligator clips. Clip it to the rails right after that 7810. Maybe the noise goes away. If not, make sure you dont have the signal ground and earth ground mixed in the lightspeed and never connect signal gnd to the 0V.
Uriah
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Old 19th April 2010, 09:53 PM   #3163
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Quote:
Originally Posted by binspaul View Post
Hi George,

I am using the light speed MK II version. The supply circuit is based on uA7810 & uA7805. It is feed from a simple 12V DC wall wart adapter.

Best regards,
Bins.
I use a 470uf before the 7805 the a 100uf after then a .1uf . I do not earth the neg rail to signal ground, it floats with the neg of the wall wart.

Cheers George
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Old 20th April 2010, 01:24 AM   #3164
alazira is offline alazira  United States
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Quote:
Originally Posted by binspaul View Post
Hi George,

I am using the light speed MK II version. The supply circuit is based on uA7810 & uA7805. It is feed from a simple 12V DC wall wart adapter.

Best regards,
Bins.
Hi,

I would dump the 7810. It is not needed. Indeed, it probably needs more headroom than the 12V input, which may be the problem. If you want to use both then find a 14V+ wall-wart. The 7805 works fine w/ 12V input.
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Old 20th April 2010, 04:08 AM   #3165
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Hi George,

I will remove that 7810 section and will try with the 7805 section alone. Since my cabinet is made up of wood, I will try with an explicit signal ground point. As you suggested earlier, I will also cover the LDR's with aluminium foil to avoid RF interference.

@Uriah: The supply ground and signal ground are not mixed up. Any way, I will check once again. I will also check for a cold joint....

Will impedance mismatch be an issue ?

Best regards,
Bins.

Quote:
Originally Posted by georgehifi View Post
I use a 470uf before the 7805 the a 100uf after then a .1uf . I do not earth the neg rail to signal ground, it floats with the neg of the wall wart.

Cheers George
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Old 20th April 2010, 05:02 AM   #3166
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Quote:
Originally Posted by binspaul View Post
Hi George,


Will impedance mismatch be an issue ?

Best regards,
Bins.
I wouldn't think so. I'd say it's more the wooden case.
Also try not earthing the negative side of the supply, let it float.

Cheers George
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Old 20th April 2010, 05:47 AM   #3167
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Hi George,

The negative side of the supply is not earthed as shown in the supply schematic which was posted earlier. It is actually connected to the DC supply socket's outer terminal. So, I think the light speed ground is the place to check for the noise issues:

1. RF Interference - Can this be avoided using aluminium shield around the LDR's (The shield will also be connected to the LDR's common ground point) ?

2. Ground - Can I take the RCA ground's to a final earth point and ground it explicitly ?

3. Cold Joints.

Best regards,
Bins.

Quote:
Originally Posted by georgehifi View Post
I wouldn't think so. I'd say it's more the wooden case.
Also try not earthing the negative side of the supply, let it float.

Cheers George
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Old 20th April 2010, 09:59 AM   #3168
Tolu is offline Tolu  Germany
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Hi Bins,

just take an aluminium case and all sorrows are gone!

Or use at least shielded NF-cables from/to the cinch sockets!
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Old 20th April 2010, 11:41 AM   #3169
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Hi,

The interconnects that I am using is having RF shield. So, I don't think it is not the source for hum... I think the supply lines, transformers etc inside the mono blocks can also be a reason for the hum. I will try an aluminium casing instead of wood to tackle this issue. Also the RCA pins will be start grounded.

Best regards,
Bins.
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Old 20th April 2010, 01:32 PM   #3170
udailey is offline udailey  United States
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I just plugged in one of my oldest Lightspeeds and was using it most of the day yesterday. I get the same noise you are describing. Well, I assume its the same. Its mounted in an open frame so anything could get in there. I have used it at 3 different residences in 2 different states and have the same buzz in my speakers. Its for sure the Lightspeed and its for sure my choice in power supply when I built that one. Still sounds incredible but its a junky little Rohm switching power supply. I blame my noise on the fact its a switching supply.
I think you should give the 9V battery solution a try. Its super easy. RF interference probably wouldnt sound like hummmm.
Uriah
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