Lightspeed Attenuator a new passive preamp

Okay,
I kind of doubted that noise from LEDs could get through to the resistor side.
Today I was using an OLD 10 turn wirewound pot to control LDRs. It was a little scratchy as old wirewounds can be. There was one spot in the rotation I could go back and forth over and get the same result. What result? Well, you could hear the noise from the sparking in the pot but you could hear it in the speakers. So found that interesting and thought you guys might want to know.
I guess I will try snubbing the LED side and let it be. It doesnt bother me but makes me more aware that power supply matters.
Uriah
 
Just FYI
I suppose you all know that Philips had already a lightspeed included in the electronic organ "Philicorda" in the sixties. It was a 6,3 volt (bike)bulb built into a pedal. The bulb threw more or less light on a LDR inside the pedal by mechanical way (vary the shielding). Sorry my English is limited but I hope you get the idea.
 
Hi

A while ago I built a Lightspeed clone on strip-board, it performs really well apart from a power supply issue.

Two of my walwarts got very warm and started to smoke. I put the first one down to a duff power pack, but now that a second has failed in the same way there is obviously an error in my circuit.

I've checked the regulated +5v supply wiring and it seems fine. The 7805TS regulator remains cool.

:: DatasheetPro :: Download TS7805 datasheet PDF download :: Taiwan Semiconductor Company Ltd. :: TS7800 series 3-Terminal Fixed Positive Voltage Regulator

5vPSU.jpg


Picof5v.jpg


Any ideas? I'm a bit foxed as it appears to work OK...for a while that is.

Thanks :)
 
There is nothing wrong with that circuit you posted. I could only say that maybe the 10uF goes before the regulator but still it makes no difference as far as smoking power packs.
I havent a clue. Maybe you should put a fuse on the AC side of things and see if it blows. Then if it does, put another on the DC side of things and see if it blows. This would tell you if its the power pack or the circuit. If both blow its the circuit if just the AC side blows its the power pack. I suppose you could just measure current in both those places and find the same thing.
----it would take tiny fuses to figure this out, so I think measuring current is a better thing to do.
Uriah
 
Hi

A while ago I built a Lightspeed clone on strip-board, it performs really well apart from a power supply issue.

Two of my walwarts got very warm and started to smoke. I put the first one down to a duff power pack, but now that a second has failed in the same way there is obviously an error in my circuit.

I've checked the regulated +5v supply wiring and it seems fine. The 7805TS regulator remains cool.

:: DatasheetPro :: Download TS7805 datasheet PDF download :: Taiwan Semiconductor Company Ltd. :: TS7800 series 3-Terminal Fixed Positive Voltage Regulator

5vPSU.jpg


Picof5v.jpg


Any ideas? I'm a bit foxed as it appears to work OK...for a while that is.

Thanks :)

Tried batteries? If they go up in smoke then there is something seriously wrong!:D
 
The LED and it's current limiting resistor is just an indicator telling you the unit is powered up.
It does nothing for the audio.
The loss of volume at the speakers as the battery went down tells us that the LDR is reacting to the reduced current supply. As the LED current drops the LDR resistances rise and eventually you have a -6dB fixed resistance attenuator.

The voltage at the input to the regulator is required, not the output of the regulator.
 
The LED and it's current limiting resistor is just an indicator telling you the unit is powered up.
It does nothing for the audio.
The loss of volume at the speakers as the battery went down tells us that the LDR is reacting to the reduced current supply. As the LED current drops the LDR resistances rise and eventually you have a -6dB fixed resistance attenuator.

The voltage at the input to the regulator is required, not the output of the regulator.

Hi Andrew

I know the LED is only an indicator, but I wondered if the excessive resistance in the series resistor was causing a problem in the power pack. I'm guessing not