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Old 9th April 2012, 04:22 AM   #21
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Quote:
Originally Posted by Conrad Hoffman View Post
Maybe replace the switch with a jumper. When you open and close the jumper, do you still have the click? That should narrow things down. If you don't. try softening the edge of the switch pulse with a small resistor and cap, maybe 50 ohms in series and .01uF to ground. Also, disconnect the switch pulse and pulse it to be sure you don't have a cross coupling issue elsewhere, like through ground.
I think you're on the right track but I suspect the 5532 is oscillating because of the capacitive loading of the SSM chip. A series 47 ohm resistor should decouple it if it is indeed oscillating. With the SSM out and just a switch it may settle down the 5532 (if it's oscillating) and give a false result. Best test is a scope.

Personally I don't like high value resistors in solid state amps. I'd use 47K max on the input of the 5532 and 10K instead of 470K at the output of the 5532. Higher values just encourage Johnson noise and who needs that? Current is cheap and even wimpy opamps deliver more than tube amps. The 5532 can deliver plenty of current to support a 10K load.

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Old 9th April 2012, 06:28 AM   #22
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It does seem from all you say that the problem could be down to the logic and you are hearing some kind of breakthrough.

Have you tried disconnecting the logic and manually driving the control pin between 0 and 5 volts with a switch ?

Is is possible that the logic circuitry is drawing a current pulse as it changes state and that this is contaminating the audio grounds ? Signal grounds and "digital" grounds should normally be separate.
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Old 9th April 2012, 09:24 AM   #23
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OK Aucosticraft, I'll connect up the capacitor as you suggest and let you know what happens. I have tried Conrad Hoffman's suggestion of 'softening' the control signal but it hasn't had much effect. I'll get back with the results soon. And yes, I do have a few CD4016 chips in my collection.

Mooly you have raised a good point. I have wired everything together using a common ground; perhaps this is the cause of the problem? There again, how do I create two independant grounds when both circuits are wired to the same battery pack? I haven't tried switching the analogue switch with an indepentant control signal but it's a good idea. I'll try it out and get back to you. I'll be busy this afternoon but I'll be back at the project this evening.

Hi Sratus46, thanks for your input. I can replace the resistors on the splitter circuit if you feel that they are too high; I don't want the circuit to drain too much power though because it uses on-board batteries and needs to be fairly efficient. I'm not building a stratocaster but the instrument in the avotar is an electric solid-body hurdy-gurdy complet with humbucker pick-ups. The output from the melody strings is pulsed by the speed of the crank and comes out stacatto. However, I still have that click in the circuit to get rid of!

Vielle568

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Last edited by vielle568; 9th April 2012 at 09:51 AM.
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Old 9th April 2012, 10:54 AM   #24
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The grounds are kept separate just by wiring them back individually to the battery. It's similar to wiring an audio amp and keeping the audio out of the PSU grounds where large circulating "hum" currents flow. You have to think in terms of each wire and conductor as being able to develop a volt drop in response to current flow and ask yourself whether that is going to affect or modulate the signal in any way.
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Old 9th April 2012, 11:27 AM   #25
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OK Aucosticraft, I'll connect up the capacitor as you suggest and let you know what happens. And yes, I do have a few CD4016 chips in my collection.



Vielle568
I wish the cap resi arrangement should solve the problem. but in case it dosent work and you need to work on CD4016, then here is the suggested connection.
the drawing is made quick using paint brush. it looks dirty. but this moment here had no alternative.
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Old 9th April 2012, 06:42 PM   #26
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I've been thinking over what you told me Mooly about having separate grounds for the analogue and digital circuits. As I mentioned before, I'd mixed up the audio circuits and the digital circuits using the same power source and ground.

To trigger the analogue switch there's a microprocessor that outputs a series of pulses. These are cleaned up through Schmitt inverting buffers (74HC14s) and fed to the analogue switch. These buffers output either zero or five volts. I tried switching the analogue switch using a seperate power source as you described Mooly but I ran into a slight problem; the switch needed a control voltage that was either ground or something above 2.4V; the pin unconnected allowed the switch to connect.

Being unsure if the zero volt output of the Schmitt inverting buffers were the same as ground I replaced the buffer chip with a 4016 configured as a SPDT switching between ground and 3 volts, and I connected this as the control signal to the analogue switch for the audio signal. The click has now diminished considerably, and it's only audible at low signal levels; it did not increase when the audio signal level was increased an so I can only assume that the noise was associated with the control signal and not the audio signal.

I'll try your idea Aucosticraft, it could remove the click completely. It won't take long to add a resistor and see what happens.

Vielle568

Last edited by vielle568; 9th April 2012 at 06:47 PM.
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Old 9th April 2012, 06:49 PM   #27
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Originally Posted by vielle568 View Post
I tried switching the analogue switch using a seperate power source as you described Mooly but I ran into a slight problem; the switch needed a control voltage that was either ground or something above 2.4V; an unconnected terminal allowed the switch to connect. Vielle568
Assuming the switch has CMOS type input you could tie the control input pin to zero volts via a resistor of say 100K. That's normal practice and would define logic zero for the pin. Then just apply 5 volts via the switch to turn on.
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Old 9th April 2012, 07:24 PM   #28
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Thanks for your idea Aucosticraft but it didn't work on my system. The signal being switched by the 4016 is only around 3V and the 10K resistor had the effect of shorting it to ground. With the resistor added to the circuit the second analogue switch being used to pulse the audio signals didn't have a control signal powerful enough to trigger.

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Old 9th April 2012, 07:32 PM   #29
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The analogue switch is a SSM2412 from Analog Devices. Yes, it's a CMOS device; I'll try what you're describing. I'm certainly picking up a lot of information in the course of this discussion. Thank you very much for your patience.
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Old 9th April 2012, 07:45 PM   #30
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Originally Posted by vielle568 View Post
Thanks for your idea Aucosticraft but it didn't work on my system. The signal being switched by the 4016 is only around 3V and the 10K resistor had the effect of shorting it to ground. With the resistor added to the circuit the second analogue switch being used to pulse the audio signals didn't have a control signal powerful enough to trigger.

Vielle568
I am just confirming if you have done what i suggested ( if i was able to tell you correctly )

option 1.

Keep your old arrangement with 74HCT14 & SSM2412 untouched. Then connect resistor as suggested( resi can be between 1E to 10E), in parallel to the capacitor at the output of NE5532 and input of SSM2412. and check if the click persists.

option 2.

keep your 74HCT14 in place. and replace the SSM2412 with the CD4016 ckt shown in above diagram. and check for click noise.


New option 3.

What is the DC voltage at output of NE5532. If you find DC voltage there, Add 47K in parallel to 1M resistor at the input of Ne5532. and check if the DC voltage at the output pin becomes zero. If yes, then replace input capacitor of 47nf to 47mfd. and see if the noise has disappeared.
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Last edited by Aucosticraft; 9th April 2012 at 07:56 PM.
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