Color Organ

[johnfin]

Can someone tell me what drives the freq. for the scr's. I believe its the caps in series. I would like to lower the freq of the base. Any recommendations.

[redwire]

Re: Color Organ

It's not a great design.
The filters are at the gate of each SCR.
Because the level pots drive the filters, the frequency moves around with the level pot's setting! Can drive you nuts.

Low Band is C1 0.1uF, R5 1k, but pot R1 could be from near zero to 50k at middle.
0.1uF 50k gives 32 Hz. But level pot at 1/4 rotation gives 85Hz, too high for bass drum.
Much bass response is also lost in main coupling cap C9 as it is too small. I would upsize to 1uF.
Low pass filter calculator.

The midrange filters are a low pass and high pass filter. But they move around with the level pots. Lowest frequency range with pot 1/2 way.


I've built similar circuits and they had problems.
The input transformers cooked with higher power audio going in.
There is no snubber across the SCR's so a lot of RFI generated and SCRs short if there are voltage spikes.
It could use a fuse.

[johnfin]

Re: Color Organ

I agree. Do you have a schematic for a decent 3 channel unit?

[redwire]

Re: Color Organ

To me this circuit looks much better, using active filters that behave the same as the level controls are moved around. About the same parts count.

Schematic from: chemelec color organ, and has PCB layout.

[stj]

Re: Color Organ

is this "organ" what used to be known as a "sound to light" unit??

[redwire]

Re: Color Organ

Yes, a sound to light converter. Also called a 'light organ'.

Original "color organs" go back to the 1700's as mechanical light shutters on a harpsichord.

The color organ name stayed when around for psychedelic 1960's, a popular to make electronics build, using thyratrons, then SCRs, driving mains lighting like Christmas light strings.

When disco hit in the 1970's they took off in popularity.

Velleman K8017 sound light kit very similar but only has a microphone input.

eBay kit has PIC doing the work, drives low voltage LED strips, remote control.

[stj]

Re: Color Organ

use chinese SSR's instead of thyristers.
then you get 0-point switching and less dead lamps.

[redwire]

Re: Color Organ

I often wondered why light organs use SCR's with the resulting 1/2-wave pulsing DC to the lights. It must be in-rush currents burn out lamps?

$4 Fotek SSR's with TRIACs would make it easier, and full-wave would give all the light's brightness.

I blew many 10A 600V SCR's, when a 7W 120VAC incandescent Christmas light burns out, it seems to have a lot of inductance and takes out the SCR.

[stj]

Re: Color Organ

scr's and triacs need snubber components across them - i used to make sequencers for fairground operators.

[johnfin]

Re: Color Organ

I replaced C9 with a 1us but it did nothing. That is a filter for all lines. I want to change the cutoff to the base so the low scr only fires with very low tones.

[redwire]

Re: Color Organ

Sometimes the low end isn't even making it to the bass channel filter - C9 being small or the transformers T1/T2 having poor LF response.

To lower the bass channel's frequency, increase C1 (you can add your old C9 in parallel to get 2x0.1uF=0.2uF).

[johnfin]

Re: Color Organ

I added a .1 and and .56 in parallel to C1 and it helped but it still picks up stray signals that are not in that spectrum. Strange. Its better though. I built one over 35+ years ago in high school that had a half dozen parts and worked PERFECT. 3 channel with SCR's, 3 pots and that was it. Wish I still had it.