THEORY OF OPERATION
Refer to the Schematic and Block Diagrams.
The design of this Electronic Reverb is based around the SAD-1024 Bucket Brigade Integrated Circuit. This IC is a 1024 stage shift register which functions as an audio delay line. Two square wave clock signals sample the audio signal and shift the weighted voltage level 512 times.
A 5KHz low pass filter (IC-5, Dual BiFet Op-Amp) is used to pre-filter unwanted switching information caused by the shifting within the SAD-1024. To further filter out the high frequency range caused by the sample and shift process, IC-5 acts as an additional 5KHz low pass filter used at the Register’s output.
The delayed audio is then mixed with the original audio and is channeled to the Right and Left output terminals. This signal is fed into the input mixer to enhance the reverberation time.
The special effects are produced by modulating the basic clock frequency with a low frequency produced by a sine-wave oscillator (IC-1, 741 Op Amp). By varying the frequency, amplitude, and integration time into the basic clock frequencv, a wide variety of tones are produced.
Problems With Our Electronic Reverb Project Board.
We’ve been getting feedback on this item from various, sources (repair centers, stores, customers, etc.) Here are some hints which should help you and your customers:
Change capacitors C1 and C4-from 47 IF/35V (272-1018) to 470. MF/50V (272-1046).
Adjustment of R42 is extremely critical. R42 should be adjusted so that TP1 and Pin 2 of IC4 read approximately 4-6 volts. -
Check to see if clock signals are present at Pins 3, 8, 10 and 14 of IC4 and at Pins 1, 2, 12 and 13 of IC2. If there are no clock pulses, the SAD-1024A chip (276-1761) is probably bad.
We’ll be getting updated instruction sheets for this Project-Board out soon. In the meantime, pass these tips along to your customers (And check each Electronic Reverb for these points before returning them for repair!)
Copyright by Bill Bytheway, K7TTY February 2012