Help with volume pedal electronics

Alec_t

Joined Sep 17, 2013
13,318
Here's a modification using a SPDT reed relay to ground the amp input, rather than use the 10k resistor:
SamplePlayerGateMod.PNG

Edit: A 10k resistor between the Input and ground would be useful, to shunt away any DC voltage that might arise from leakage of the output capacitor in the sample-player.
Two SPDT relays can be driven by the one comparator to handle stereo. If the Supply voltage is a regulated 9V or more you may get away with connecting their coils in series to minimise current consumption.
 
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Thread Starter

match999

Joined Mar 15, 2016
12
Here's a modification using a SPDT reed relay to ground the amp input, rather than use the 10k resistor:
View attachment 102857

Edit: A 10k resistor between the Input and ground would be useful, to shunt away any DC voltage that might arise from leakage of the output capacitor in the sample-player.
Two SPDT relays can be driven by the one comparator to handle stereo. If the Supply voltage is a regulated 9V or more you may get away with connecting their coils in series to minimise current consumption.
According to your Edit: So that means a 10K between the NO and ground, right?
 

Thread Starter

match999

Joined Mar 15, 2016
12
Hi Alec,

forgive my simple thinking but can the relay be replaced by a CNY17?
I was looking on the internet for components and came on SS relays and saw this one many times.
This would make it a SS switcher?

Edit:
I reread your post with the circuit again where you say that this gives more audible noise/clicks. So lets forget it.
Gonna focus me on the building of your circuit.
Can take sometime, since I'm busy with other projects also, but will post my progression here.
Thanks so much for your superb help!!
 
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Alec_t

Joined Sep 17, 2013
13,318
Here's a couple of simulated circuits (mono, but extendable for stereo), each using a pair of CNY17 for the gating. C1/R3 soften the cut-in and cut-out transitions of the gating.
The first circuit, with the optotransistors in series with the signal path, has a THD of ~2.2% with minimal audio breakthrough in the gated-off state whereas the second circuit, with the optotransistors shunting the signal path to ground, has a THD of ~1.3% but slightly more audio breakthrough.
SamplePlayerGate2.PNG
SamplePlayerGate3.PNG
I've attached respective .wav audio files for the circuit outputs if you want to compare them. Rename them to remove the ".txt" extension.
 

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Thread Starter

match999

Joined Mar 15, 2016
12
Well Alec, you amaze me!
Great suggestion!

I would prefer the 1st one, since the audio breakthrough could be irritating.

How would I expand this to stereo?
I mean just copy the dotted circuit and use that parallel besides the other is maybe too simple....
I'm sure you have a better solution.

Thanks!!!
 

Alec_t

Joined Sep 17, 2013
13,318
just copy the dotted circuit and use that parallel besides the other
Yup. That's why I added the dots ;). The Q3 transistor should be able to drive both dotted circuits as is, but if marginal you could reduce R2 to, say, 4k7. You'd no doubt want to add a switch for the 9V supply.
I've assumed a 9V supply, or did you plan to use something else? Easily modded if so.
Is the distortion acceptable? It might be slightly higher if the CNY17-3s are badly mismatched (the sim assumes perfect matching).
 

Alec_t

Joined Sep 17, 2013
13,318
Checking through the specs of the CNY17 again, considering that the optotransistors will be passing only a small current you could well increase R4 from 270Ω to 1k to reduce the LED current. That would save on battery power and also avoid having to reduce R2 for the stereo version.
Another thought: for a stereo version, further current economy should be possible with a well-regulated 9V supply by connecting all four LEDs of the dotted circuits in series.
 

Thread Starter

match999

Joined Mar 15, 2016
12
Yeah, now I'm in doubt. Actually the 2nd sample sounds more distorted to me....
And in general it would be dissapointing if after building the sound is not acceptable.

Could you also simulate a tone with the reed relay? Just for comparing with the above samples?
Then I know what the reference sound is.
As there is no THD and no audiobreakthrough, maybe that solution is still the best.
 
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