A means of closing a JFET switch with a postive voltage?

[CDRIVE]

You're correct. I didn't understand. So I re - read this thread 3 times to see if I missed a clue. As far as I could see I didn't miss anything that would hint that it's a DC level that's being sampled. One would need to go back to your Will A Basic Buffer Be Sufficient topic in which you posted this Keyboard Schematic and then move on to your Biasing This OpAmp topic to realize that your keyboard will be outputting DC levels (0-9V) which are set by individual Pots assigned to each key.

Before we move on to this FET topic we need to talk about this Keyboard Schematic. I didn't catch it then and I'm surprised that no one else did either but I doubt it's wired like that. It's far more likely that one pole of each keyboard switch is connected to the wiper of each Pot. The other pole of each switch are common to each other (jumped) which then output to R1 in the Noise Toaster.

Do you see why I believe this to be true?

Now, hopefully, we can move on to this S&H issue. First off.. No, you can't eliminate the Buffer (Your Voltage Follower) as you did Here. The Voltage Follower is needed to eliminate the RC time constant that will be inherent in that circuit. When you hit a key you will want the sample voltage to rise as fast as possible and not be lagged by the RC Time Constant created there.

So, to recap please tell us if this is what you want:

(1) When a key is pressed a voltage level of 0-9V will be Sampled and Held when the key is released.

(2) When another key is pressed the Sample voltage in (1) updates to the voltage setting (Pot Voltage Divider) of the key just pressed.

(3) I think that's about it.

Do I get it yet??

Chris

 

[AFex54]

What will cause that voltage to fall back to zero?

What are you actually trying to do?

If you can explain it, the solution may not be what you're looking at.

nothing will cause it to fall to zero, it would maintain the last voltage until the next input from the keyboard takes its place.
all the keys are tuned to different voltages, but even pressing the same key twice would 'renew' the voltage on the cap that may have began to droop.

to clarify for someone who may not be familiar with synths the CV signal does NOT control the volume of the synth,
there is an entirely seperate system for volume, a Gate (brief summary) that is triggered simultaneously to the CV when you press a key press .
my point being that even though CV lingers right up until you press the next key it doesnt matter because you wont hear it in effect,

 

[AFex54]

You're correct. I didn't understand. So I re - read this thread 3 times to see if I missed a clue. As far as I could see I didn't miss anything that would hint that it's a DC level that's being sampled. One would need to go back to your Will A Basic Buffer Be Sufficient topic in which you posted this Keyboard Schematic and then move on to your Biasing This OpAmp topic to realize that your keyboard will be outputting DC levels (0-9V) which are set by individual Pots assigned to each key.

Before we move on to this FET topic we need to talk about this Keyboard Schematic. I didn't catch it then and I'm surprised that no one else did either but I doubt it's wired like that. It's far more likely that one pole of each keyboard switch is connected to the wiper of each Pot. The other pole of each switch are common to each other (jumped) which then output to R1 in the Noise Toaster.

Do you see why I believe this to be true?

So, to recap please tell us if this is what you want:

(1) When a key is pressed a voltage level of 0-9V will be Sampled and Held when the key is released.

(2) When another key is pressed the Sample voltage in (1) updates to the voltage setting (Pot Voltage Divider) of the key just pressed.

(3) I think that's about it.

Do I get it yet??


Chris

Yup thats it,

and unfortunately the keyboard is wired like this,
however this wiring reflects the physical layout of the pots and key switches in the enclosure, wiring any differently would conflict with the synths compact design.
physically the keys are at the bottom, the pots are mounted above the keys and the noisetoaster circuit boards are squeezed in just above the pots.

just an additional thought: a relay could be a simple solution to the switch problem, latency is in the single digit millisecond range ... for a LoFi synth this would be acceptable, and I really doubt you would notice it anyway

edit: Im noticing there are solid state relays?! is this my solution?

 

[CDRIVE]

I can't move on to discussing solid state switches until I get this nailed down. The way it's wired each pot will effect all the other pots. Are you absolutely positive it's wired like this? In other words if you set any one pot and switch to produce a given voltage and then move on to adjust another pot, doing so will change the voltage output on the first pot you adjusted.
http://postimg.org/image/n3w1j5f0d/

Chris

 

[CDRIVE]

This is how I think the keyboard should be wired. In this arrangement the pots are independent of each other unless more than one key is pressed at the same time.

Chris

 

[AFex54]

This is how I think the keyboard should be wired. In this arrangement the pots are independent of each other unless more than one key is pressed at the same time.

ChrisView attachment 21455

yes they are wired in parallel, which is so obvious now
im surprised I didnt notice this either,

however I notice this statement: ''physically the keys are at the bottom, the pots are mounted above the keys and the noisetoaster circuit boards are squeezed in just above the pots.''
this is a stupid statement and it actually highlights the solution,
there is the also the 9V input socket which is mounted above the noise toaster circuit board, the current wiring is almost an exact mirror image of you wiring diagram posted above, after a few adjustment all i have to do is switch the 9V input and keyboard output (they are right beside each other) to run it in reverse.

 

[CDRIVE]

yes they are wired in parallel, which is so obvious now
im surprised I didnt notice this either,

We have quite a few very knowledgeable and experienced members but like me they have their "Duh" moments. My guess is that this discrepancy wasn't caught do to the "It's 5 O' Clock Somewhere" factor.

Regarding your question about using a SSR for the sampling switch:
Maybe but I have a few ideas that would employ more common components. Let me spice a few ideas and get back to you.

Question: What will the lowest keyboard output voltage be? I need to know this because unlike a conventional S&H circuit your scheme will key the sampling switch with the same voltage that's being sampled. This will necessitate another voltage amplifier to drive the sampling switch control input. Capice?

Chris

 

[AFex54]

We have quite a few very knowledgeable and experienced members but like me they have their "Duh" moments. My guess is that this discrepancy wasn't caught do to the "It's 5 O' Clock Somewhere" factor.

Regarding your question about using a SSR for the sampling switch:
Maybe but I have a few ideas that would employ more common components. Let me spice a few ideas and get back to you.

Question: What will the lowest keyboard output voltage be? I need to know this because unlike a conventional S&H circuit your scheme will key the sampling switch with the same voltage that's being sampled. This will necessitate another voltage amplifier to drive the sampling switch control input. Capice?

Chris

there is also a diode on every keyboard switch before the potentiometer to give a separate 'gate' signal when you press the key(which is just 9V, its a special trigger for the synth)
I updated the diagram with the 'gate' signal for extra clarity :


this would be perfect for controlling the sampling switch instead of using the CV.

AND now i realise all these diodes will be backwards when I reverse the wiring!!! ive have a lot of soldering to do... damn it.

 

[CDRIVE]

I need to find my roll of extra heavy duty duct tape. I'm going to wrap my head with it to keep it from exploding!

In your last post I thought we had agreed that the pots and keys could not be wired like that. I read your reply as confirmation that the way I drew them is the way they're wired. Yet, your latest post STILL has the wipers common to each other!

I'm heading out to my watering hole where I can watch young hotties in skimpy outfits.

Chris

 

[AFex54]

I need to find my roll of extra heavy duty duct tape. I'm going to wrap my head with it to keep it from exploding!

In your last post I thought we had agreed that the pots and keys could not be wired like that. I read your reply as confirmation that the way I drew them is the way they're wired. Yet, your latest post STILL has the wipers common to each other!

I'm heading out to my watering hole where I can watch young hotties in skimpy outfits.

Chris

haha the pots will not be wired like that, If you can ignore pots and focus on red in relation to switches you will extract all the info you need from that diagram, In hindsight I should have edited your correctly wired keyboard diagram, sorry about the confusion!

''I updated the diagram with the 'gate' signal for extra clarity '' -me

this is the last time I post a misleading diagram, unless they are 100% applicable to the post I wont include it.

edit: just after realising the only way a seperate 9V 'gate' could be taken from a key switch is if the switch is before the potentiometer, so neither wiring can provide both a gate and a CV ...
so many problems starting to surface now, i thought I was ready to start the final wiring 2 months ago and now Im back to square one.

 

[AFex54]

so the simple answer is even more diodes:


I really hope we can bury the hatchet on this keyboard now

 

[CDRIVE]

Actually I'd rather not see any more schematics of what you're going to add or modify in the existing keyboard. What I'd like to see is the manufacturer's schematic. If that's not possible then a webpage with a sales description of it. Maybe some good photos might help.

For the last time... There is no way in hell that the keyboard was manufactured with the wipers of 20+ pots tied together like that.

Chris

 

[AFex54]

Actually I'd rather not see any more schematics of what you're going to add or modify in the existing keyboard. What I'd like to see is the manufacturer's schematic. If that's not possible then a webpage with a sales description of it. Maybe some good photos might help.

For the last time... There is no way in hell that the keyboard was manufactured with the wipers of 20+ pots tied together like that.

Chris

I built the keyboard myself , the keys were taken from an old keyboard but they are just pieces of plastic that go over the switches (which are leaf switches made out of very thin sheet of metal) to vastly vastly improve the look and feel of the switches,
the original diagram with all the pot wipers tied is exactly how it is wired right now,
I have not begun wiring the Noise Toaster PCB and its panel mounted components because I still have to get the keyboard working and add the sample and hold

 

[CDRIVE]

I built the keyboard myself

Once again you failed to divulge vital information. Do you remember My Rant way back in your original topic? Speaking of which,.. your decision to create multiple topics (3) that are actually the same topic isn't helping matters either. I just wasted a considerable amount of time tunneling through those topics to see if you ever stated, hinted or implied that your keyboard is a home brewed design of your own. NADA!

Now that I vented that out of my system I think we can move on. Please, no more surprises.

Yes, your last schematic (as shown) will work. Though your comments about reversing the existing diodes escapes me. They should be polarized exactly as you drew them here. Since you've been battling with your 9V battery limitation you may want to consider Schottky Diodes for the CV output bus to keep the voltage drop as low as possible. The Gate Diodes can be common switching diodes (1N4148) or 1N4002 Rectifier Diodes. What PN are using in there now?

there is also a diode on every keyboard switch before the potentiometer to give a separate 'gate' signal when you press the key(which is just 9V, its a special trigger for the synth)
I updated the diagram with the 'gate' signal for extra clarity :
View attachment 21464

this would be perfect for controlling the sampling switch instead of using the CV.

AND now i realise all these diodes will be backwards when I reverse the wiring!!! ive have a lot of soldering to do... damn it.

 

[AFex54]

Once again you failed to divulge vital information. Do you remember My Rant way back in your original topic? Speaking of which,.. your decision to create multiple topics (3) that are actually the same topic isn't helping matters either. I just wasted a considerable amount of time tunneling through those topics to see if you ever stated, hinted or implied that your keyboard is a home brewed design of your own. NADA!

Now that I vented that out of my system I think we can move on. Please, no more surprises.

Yes, your last schematic (as shown) will work. Though your comments about reversing the existing diodes escapes me. They should be polarized exactly as you drew them here. Since you've been battling with your 9V battery limitation you may want to consider Schottky Diodes for the CV output bus to keep the voltage drop as low as possible. The Gate Diodes can be common switching diodes (1N4148) or 1N4002 Rectifier Diodes. What PN are using in there now?

the 'reversing the diodes' thing became moot when I added the edit at the end of post #30
PN on the gate now are 1N4148s, I will get Schottkys for the CV

 

[CDRIVE]

I'd prefer to save myself the effort of sifting out an applicable Schottky. Perhaps another member has some suggestions?

Chris

 

[CDRIVE]

OK, I've spent a few hours simulating S&H circuits using BJTs, JFETs, MOSFETs, and chips for the Sampling Switch elements, using 9V as my supply restraint. Each circuit produced varying results from Switch OFF State leakage to not being able to charge the cap to the full 9V.

May I ask why you need S&H? I would think that you would want the Noise Toaster to follow your keys exactly as pressed an released. Would you be so kind as to elaborate?

Chris

 

[AFex54]

OK, I've spent a few hours simulating S&H circuits using BJTs, JFETs, MOSFETs, and chips for the Sampling Switch elements, using 9V as my supply restraint. Each circuit produced varying results from Switch OFF State leakage to not being able to charge the cap to the full 9V.

May I ask why you need S&H? I would think that you would want the Noise Toaster to follow your keys exactly as pressed an released. Would you be so kind as to elaborate?

Chris

sure,
its function is to accomodate the 'release' of a note,
a staple of musical synthesizers is the ability to fade out the volume of a note once you let go of a key.... a.k.a release.
its produces a much more fluid and organic sound, which is very important.
so I am seperately controlling 2 things with a keypress, the volume and the pitch
once you press a key the volume will be triggered (turned up) by the gate signal and the pitch will be set by the CV.
once you let go of the key the gate will turn off, which triggers the release, but without S&H the CV would cutoff once you let go of the key.
could be hard to understand, Im not the best at explaining things.


maybe Im overcomplicating it now but here in blue you have a visual of the volume according to the gate.
attack = the opposite of release, a fade in, another feature of any basic synth including the noise toaster
sustain = the volume is sustained until you let go of the key

 

[(*steve*)]

the proper way I'd for the key to trigger the asdr and for that to trigger (or gate) the signal source.

your approach could lead (if it worked) to some oddness at the beginning of a note having rapid attack.

that being said, my approach would be to use a diode or-Ing of the switches to generate a" sample" signal which I'd then converted to a pulse for the S&H and the asdr. A logic signal from each key could then be used to control a series of analog switches 4066 or similar to switch a control voltage to the input of the S&H.

Yuur keyboard won't be polyphonic though. For that you'd need an asdr for each key, but no S&H. If this is for a modular synth then you're probably only interested in the voltage and asdr output though.

 

[CDRIVE]

Damn! ASDR Envelope.. I had to Google it. Interesting!

Chris