Clocking the sample & hold externally

LektroiD

Hi, I have finished the sample & hold, but can't seem to trigger it, I have been using a saw LFO to trigger other modules, but doesn't seem to trigger the sample & hold.

I would like to keep everything in time (although I have no sequencer as yet) I'm presuming I need to build a proper clock circuit; where would I find one, or should the saw LFO be OK, and maybe I've made a mistake on the S&H clock in?

Any help appreciated

kkissinger

Sebo · Joined: Apr 27, 2007 Posts: 564 Location: Argentina

Sorry if I'm obvious, but... do you move the switch to the external position?

LektroiD

kkissinger

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

The Sample&Hold circuit expects a positive SQUARE or a PULSE as an input. The sampling is triggerred by the rising edge of the PULSE.

You said that you are using a SAW LFO, a SAW is not recommended for this circuit because there is no schmitt trigger at the input. Check your SAW : if the stiff edge is a falling edge it won't work. If the stiff edge is a rising edge it should work. Try to reverse your saw.

LektroiD · Posted: Thu Sep 30, 2010 10:11 pm Post subject:

I've tried a square wave, but still not strong enough to run, at least the saw made the light flicker, albeit faintly. The Square doesn't even manage that.

I also tried swapping the TL074 with another from stock, just in case the op amp was blown. It seems there's simply not enough voltage coming in to drive it.

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

Normally the clock input is expecting at least 5V (10V is better) to work properly. Normally the LED is shining mid-bright when externally clocked.

LektroiD · Posted: Sat Oct 02, 2010 7:00 am Post subject:

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

LektroiD · Posted: Sat Oct 02, 2010 9:23 am Post subject:

yusynth · Joined: Nov 24, 2005 Posts: 1314 Location: France

The circuit were designed for +15/-15 but can also work for +12/-12 if some resisto values are modified.

In your very case I suggest thtat you replace the 4.7K resistor at the output of the square signal by a 10K, the resistor is labelled R17.

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john trials · Joined: May 12, 2020 Posts: 14 Location: CT

I am having trouble with my sample and hold, too (powering it with +/-15v supply). It samples fine with the internal clock, but with an external clock/gate (0 to +5v gate), the LED illuminates with the gate, but slightly dimmer than with the internal clock.

It does not sample properly with this external gate.

Is there some modification that will get the circuit to sample with a +5v gate? It seems pretty useless if the external clock/gate has to be +10v or above.

The only difference with my circuit is a J102 FET, because I could not get a BF245C.

I'd hate to have to add an op amp gain circuit (3x gain) specifically for the external clock, and rewire the internal/external switch to accommodate this, but that is the only solution that I can think of.

john trials · Joined: May 12, 2020 Posts: 14 Location: CT

Apology.

The Sample and Hold is working properly with an external clock, if the clock is a good signal.

I was feeding the Yusynth Comparator an envelope signal, and using the gate out as a clock for the Sample and Hold. For some reason, the Comparator gate output signal has a strange flicker on the rising and falling edges when running at a slow (<10Hz) rate.

So my Yusynth Comparator is not working properly. The Sample and Hold works fine.

Sorry. My mistake.