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Old 4th Apr 2022, 10:24 am   #1
robinshack
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Default Sound to light converter, my second build.

Back in 1973 I built the Practical Wireless sound to light converter.
https://worldradiohistory.com/UK/Pra...PW-1973-04.pdf
is first part of four.
My version was for stereo (just doubled up all except psu) and included the light dimmer option as well.
A lot of parts were bought from John Birkett, at Lincoln. His "1A unmarked triacs" were very cheap...and worked fine. The 6 way, plus power switch bank complete with buttons was also from him, 25p I think! I bought two.
I used 8 pole miniature (Jones or Cinch) connectors for mains feeds to the 3 75W reflector spotlights mounted on one board to sit either end of the sideboard near the stereo speakers. My "hi fi" was a Philips cassette player/recorder with matching speakers, together with a Garrard deck on wooden plinth with cover. The cassette speaker cable output fed into the STL (sound to light) and then straight out to the speakers. Thus the STL was in parallel.

The STL audio filter circuits had bass (red), middle (green) and treble (blue) channels feeding the triacs which were individually dimmable by the 6 left hand pots on the front panel, using unijunction transistors. The 2 right hand pots being the sound level controls, left and right. Thus the amp volume could be adjusted independently and the STL also to compensate for different speaker levels.
The switch bank Right hand button was mains power on-off. All buttons were latching, no interconnect.
The 6 buttons to the left were each an independent override of the STL circuit. This was so that each channel colour could be adjusted with the lamp "on" at whatever maximum brightness level you wanted to preset.

Overall, this system worked extremely well. Each set of 3 spots were angled up at slightly pointing to different positions along the of top of wall/edge of ceiling that overlapped.
So good was the colour effects, one dark night, our lounge curtains were almost fully closed and I was playing Pink Floyd "Echoes" track. We lived in a bungalow with a field opposite and a path at the right hand side of it. Suddenly a very loud banging on our front door. It was our neighbour, Don, very out of breath. He had been walking his dog on this path and whilst returning had seen these flickering colours and had ran back to tell us our house was on fire! Honest!

My desire now is to build a new STL, as the original is too big to fit into my "new" hifi rack. Part stripping does seem to be a shame, so I intend to start from scratch. I think I have all the parts in stock. Just the switch buttons (my wanted thread) that are a small problem. Unfortunately, I must have given away my original second switch bank as I cannot find it. Would have been so useful.

I attach some pictures of the original unit. You may notice I used single 741 as I didn't have the dual ones specified. The triacs are those 2 rows of 3 on left hand end, mounted in push fit heatsinks on aluminium angle. The drivers with pulse transformers are at the right hand end. The unijunction transistors and associated components being mounted on a busbar above the 6 dimmer pots. The mains transformer top got broken when I took it apart several years ago to look inside.
The unit has been on a shelf in my garage since around the early 1980s and was quite filthy. It was built in 1973, when I was around 21.

I do HOPE my construction standards today will be a bit tidier and safer than the original. But it WORKED WELL!
I will update as my work hopefully progresses.
Rob
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Last edited by Cobaltblue; 4th Apr 2022 at 10:34 am. Reason: title
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Old 4th Apr 2022, 10:29 am   #2
robinshack
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Default Re: Sound to light converter, my seond build.

More pics. Last 2 are a triac board from a junk sale. Just ordinary dimmer/speed controls with bipolar driver transistors. Will most likely be used in a modified condition in my new build STL. It is unknown condition, 50p I think from a junk sale. The triacs are 500piv 12A.

Rob
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Old 7th Apr 2022, 4:07 pm   #3
dave cox
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Default Re: Sound to light converter, my second build.

It seems to be possible to buy high brightness coloured LEDs

dc
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Old 7th Apr 2022, 4:32 pm   #4
robinshack
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Default Re: Sound to light converter, my second build.

Hi Dave, I know nothing about the requirement of dimmable leds and if this basic triac circuit would be suitable, bearing in mind the constant variations of the music driving them?
In our kitchen refurbishment we had dimmable leds fitted, just a wall switch rotary one.
Thanks, Rob
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Old 8th Apr 2022, 12:40 am   #5
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Default Re: Sound to light converter, my second build.

A standard triac drive won't successfully drive mains LED globes as in the sound to light unit.

You need a trailing edge triggering circuit - lot of messing about.
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Old 6th May 2022, 3:58 pm   #6
dave cox
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Default Re: Sound to light converter, my second build.

Agreed, mains LED's would be a pain.
However, dc drive with a 'switching current source' would work, plus you don't have to mess with mains voltage / triacs etc.
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Old 6th May 2022, 8:53 pm   #7
robinshack
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Default Re: Sound to light converter, my second build.

Thanks for the ideas. However, I intend to keep it original, as I still have the original spotlights, though some colours are a bit flaky.
Currently been collecting everything together. I think I have it all now.
I did try using a paper template for veroboard layout of the input and filter section, but it is just too tedious. Far easier I think to actually place parts and work things out as I go, cutting the tracks last of all.
Rob
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Old 14th May 2022, 5:19 am   #8
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Default Re: Sound to light converter, my second build.

That schematic is almost the same that Popular Electronics published as an article in the late 60's or early 70's, IIRC.
I actually have the one I built back then.
They are a lot of fun.
Mine fit nicely in a 10" x 4"x 6" aluminum cabinet with mass room to spare.
One of my very first projects.
It used audio output transformers as the pulse transformers.
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Old 14th May 2022, 3:08 pm   #9
60 oldjohn
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Default Re: Sound to light converter, my second build.

Quote:
Originally Posted by robinshack View Post
A lot of parts were bought from John Birkett, at Lincoln. I think I have all the parts in stock. Just the switch buttons (my wanted thread) that are a small problem. Unfortunately, I must have given away my original second switch bank as I cannot find it. Would have been so useful.

Rob
I would try phoning JB as his family may be able to help, I would think he has plenty of "end of line stock" still available. You may just be lucky.

PS replied here because I am unable find the wanted thread.

John.
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