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ADSR question
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crazeydazey



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PostPosted: Sun Jan 26, 2020 12:39 pm    Post subject: ADSR question Reply with quote  Mark this post and the followings unread

Hi,

I've just built this today and not really tested properly yet other than plugging it in and checking for smoke, I did find the LED seemed a bit weird and stayed dimmly lit and clicking the button made no difference but I have read various post saying it does do something like that so not too worried but also double checked everything and noticed it says to use 7555 not NE555 ... I don't think mine is a 7555, its just one I grabbed.. I'm guessing I should change that?? What is the difference?? I've never heard of 7555.

Will this not work? Could I have bust it putting the wrong chip in??

Cheers all...

This is what I used...


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JovianPyx



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PostPosted: Sun Jan 26, 2020 7:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

7555 is one of the more common numbers for a CMOS 555 timer. They are said in at least the datasheet I have to work in any circuit that calls for a 555 timer as a pin for pin drop in replacement.

The 7555 is better for two reasons, it uses less current and doesn't crowbar the power supply like the bipolar part will do. "Crowbar" means to short. The bipolar 555 has TTL output structure which is famous for turning both driver transistors on for an instant during state switching. I read somewhere this is done to speed the switching time, but it also causes a large current pulse from +V through the two transistors to ground. This current pulse affects other things in the circuit. The PAiA Fatman has two 555 timer VCOs in it and the crowbar causes the VCOs to lock together (soft sync) when the oscillators are close in frequency. One of the methods of fixing this is to replace the 555 timers with 7555.

If you're going to find timers, best that you find 7555. Cool BTW, there are also other numbers for CMOS 555, most include the number 7555 within the part number. I've seen ICL7555.

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Grumble



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PostPosted: Sun Jan 26, 2020 11:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
doesn't crowbar the power supply like the bipolar part will do. "Crowbar" means to short



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crazeydazey



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PostPosted: Mon Jan 27, 2020 1:23 am    Post subject: Reply with quote  Mark this post and the followings unread

ok so if I've understood properly a 555 could work but may go bang so don't Very Happy

I'll get some 7555s ordered then I think before I try it again.

Just another quick question though..

The LED... I have read other posts that it stays on and is dimly lit, that's fine, but am I right in thinking the LED is showing you the output, so if I had had a lots of attack and lots of release, when I click the button it will fade in, then when I let go it will fade back out again?

At the minute mine doesn't do anything just stays dimly lit... hopefully this is the known bug or the 555??

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JovianPyx



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PostPosted: Mon Jan 27, 2020 6:09 am    Post subject: Reply with quote  Mark this post and the followings unread

I'd need to see the ADSR schematic to help.

The image that Grumble posted is a bit extreme, I've never seen a bipolar 555 timer do that and in fact, I've never had a bipolar 555 timer even fail. The crowbar is a characteristic of the normal operation of the bipolar 555. The reason I won't use them is that the current pulse drawn during the crowbar period causes a voltage dip in the power supply. That voltage dip will affect other things in the circuit which you do not want.

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crazeydazey



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PostPosted: Mon Jan 27, 2020 9:24 am    Post subject: Reply with quote  Mark this post and the followings unread

No probs mate its ... https://www.yusynth.net/Modular/Commun/ADSR/ADSR-V2-sch.gif this one..

I've read somewhere the D5 and LD1 are the wrong way round on the layout... https://www.yusynth.net/Modular/Commun/ADSR/ADSR-V2-LAYOUT.jpg

Which does look wrong and that changing them to match schematic makes light work properly?? But I'm not going to try till I get my 7555 chip Very Happy

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JovianPyx



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PostPosted: Mon Jan 27, 2020 10:11 am    Post subject: Reply with quote  Mark this post and the followings unread

I can't read French, but I translated the bit about the LED which says that the LED indicates the progress of the ADSR. It looks like the LED is driven by the buffered capacitor voltage. I should think that at rest, the ADSR should not light the LED at all.

Now, from the schematic, I can know how it is supposed to work. What I can't know is what is on your bench. If the schematic is known to work, then there's probably a build error, so in that case you need to check all connections and all part values to make sure they are correct. If there are questions about the schematic's accuracy, you need to research those items and perform whatever changes are necessary.

The diodes D2, D3 and D4 look like they are correctly orientated in the schematic.

D5 and LD1 also look correctly orientated.

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crazeydazey



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PostPosted: Mon Jan 27, 2020 11:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry mate not sure why yours is French Very Happy mine is english.. unless Google automatically translates mine? But in case there is something you need to read in english I'll try posting the link again... (definitely in English this time Very Happy )
https://www.yusynth.net/Modular/EN/ADSR/index_new.html


I don't know if I do have a fault yet I haven't tested properly until I get the 7555, I just powered it on to check for smoke.. no smoke good.. pressed button on front expecting LED to go bright and nothing.. so unplugged before I did get some smoke Wink

As for D5 and the LED I think I read that on here somewhere about them being the wrong way round.. correct on schematic but wrong on PCB layout

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crazeydazey



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PostPosted: Mon Jan 27, 2020 2:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Found it.. I knew I'd seen it somewhere, but to be honest I don't think this is the one I'm thinking of, I'm sure I read it somewhere else too that the diode and LED are both the wrong way round..

http://electro-music.com/forum/topic-64424.html

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JovianPyx



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PostPosted: Mon Jan 27, 2020 2:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

You can check that by ignoring the layout for now and looking only at the schematic and the actual parts and make sure what you have soldered together is the same circuit as the schematic specifies. If your diode and LED are reverse of what the schematic says, then you need to correct that.
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crazeydazey



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PostPosted: Tue Jan 28, 2020 3:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, I'll give that a try when I get the 7555.. Though I've read more and more now and don't actually think the NE555 will go bang or do anything silly and that it will work well enough to give it a quick bench test, it''s just not ideal when it's in with other modules.. so might get impatient and check it before the 7555 comes Very Happy Very Happy
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PostPosted: Tue Jan 28, 2020 7:10 am    Post subject: Reply with quote  Mark this post and the followings unread

That is correct, it will not go bang unless you do something outrageous like trying to power it from 50 volts. If you look at the image Grumble posted, it's not even a 555. In fact, ICs are mostly difficult to destroy (especially with a bang). OTAs are a special instance, if the Iabc current is higher than 2.0 mA, the chip will die, but there will be no bang.

If you have a bipolar 555 - try it! The pinouts are the same, so no rewire is needed.

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flagada



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PostPosted: Tue Jan 28, 2020 2:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do you have a voltmeter? If so, measure the voltage at ADSR out. See what happens if you push the button. It should go up. If the attack pot is at zero it should go up immediately. If it is at 10 it goes up very slowly. Just ignore the LED. You can try this now with your bipolar 555.
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crazeydazey



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PostPosted: Wed Jan 29, 2020 3:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've just given it a test and I reckon it works?? Maybe??

I did what you said with the meter and i get a voltage when you press the button, I get a higher voltage with decay or sustain turned up (as I expected) I get the voltage slowly rising up with attack on, the more attack the slower it goes up (again as expected) and with release the voltage drops slower the more you turn it up (and again as expected Smile )

So that all looks good, and the LED seems to fade in and out fine as I expect it to do BUT... there still seems to be a lot of weirdness with the LED.

Firstly as mentioned before it is always on, just dim. I have checked the schematic and how I laid them out following the layout diagram, and it does look to me like they are wrong on the layout. I have swapped them round and it's not made any difference Sad

And the other odd thing it seems to do is sometimes when I click the button it comes on and just stays bright (like it's stuck on), another few clicks seems to release it again, but its just weird...

Hopefully this is just the light, when I come to try it for real I don't think I care too much what the LED is showing as long as it doesn't seem to get stuck its fine Wink

I've added a picture of the layout and how I think the schematic would look if it matched and the original schematic is in the background showing that D5 and the LED are the wrong way round.


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JovianPyx



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PostPosted: Wed Jan 29, 2020 5:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Raising R22 a bit might dim it more, but it will be dimmer for all stages.

At rest, the 555 timer can't discharge the capacitor to zero volts, so the ADSR output won't go all the way to zero volts. So the LED would be a little on possibly. And as you say, if it's just the LED is on a little at rest, no big deal as long as the ADSR works as it should with other modules.

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khakifridge



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PostPosted: Thu Jan 30, 2020 2:16 am    Post subject: Reply with quote  Mark this post and the followings unread

crazeydazey wrote:
I'll get some 7555s ordered then I think before I try it again.

Your TS555 is a CMOS part, so it's good to go.
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crazeydazey



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PostPosted: Thu Jan 30, 2020 2:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Bugger if i knew that I didn't need to order any Very Happy
Ah well better to have too many than not enough.. you never know I might build another one Wink

Just tried it with my VCO and VCA and it seems to work fine woo hoo, even the LED didn't act strange.. it was still dimly lit but meh I can live with that.

The only bits I haven't checked yet are gate in (I can use my midi to CV to test that) and the inv out, guess this is just the reverse of the output, I'm sure that will just work ( can't really see why I would ever need it ??)

Otherwise I'm pretty chuffed with it Very Happy

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AlanP



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PostPosted: Fri Jan 31, 2020 4:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've built one of these, and the LED does stay dimly lit all the time on my one Smile
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JovianPyx



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PostPosted: Fri Jan 31, 2020 5:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

It might be possible to use a diode to eliminate or reduce this and the fact the the ADSR output signal won't actually go to zero - or am I wrong about that?

http://scott.joviansynth.com/fatman/ADSR.html

I've tested the top schematic. Look at the output system, there is a diode after the first op amp and that diode is there to subract one diode voltage from the output effectively eliminating a "leaky" VCA. Perhaps this could be applied.[/url]

You're also welcome to try the 4069 ADSR.

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crazeydazey



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PostPosted: Sat Feb 01, 2020 2:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think the actual output signal is ok, I'm sure when I measured it it did go to zero, I think its just the LED ??

That 4069 of yours I would love to give it go (you can't have too many ADSRs Very Happy )

Looking at it though I'm a bit unsure about the power.. Am I right in saying it needs +8v 0v -12v??

My PSU gives out +15v 0v -15v ... so I guess I would need something to sort the voltages out.. I know i can get regs easy enough for the 12v but never seen one for 8v.

Sorry for being dumb, still a total beginner at this Very Happy

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PostPosted: Sat Feb 01, 2020 2:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

When I designed that, it was going into a PAiA Fatman which has +8v & -12v. However, there's no reason for it not to work at +15v & -15v just by changing the voltage and nothing else.

Some of the diodes form logical OR gates.

There is also a flip-flop formed by 2 inverters and some of the diodes.

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crazeydazey



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PostPosted: Fri Feb 07, 2020 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have finally got round to testing this properly and I'm not sure it is actually working properly Sad , the button is spot on works exactly how I expected it to work, however when I put a gate in from my midi 2 cv converter all the controls work fine except release, this just does nothing at all??
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PostPosted: Fri Feb 07, 2020 4:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

Release works with the button and not gate?

Both activate the same transistor. Does gate drop to zero or is it riding higher than zero?

Q2 is what drains the cap during release, so there might be a problem there.

The gate signal should be rather large when active. I would guess 15 volts judging from the 1 meg resistor between gate input and the base of Q1. And when not active, the gate should be very close to zero volts.

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gabbagabi



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PostPosted: Sat Feb 08, 2020 4:17 am    Post subject: Reply with quote  Mark this post and the followings unread

did you connect the grounds thogether at one point? this is nessesary.
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crazeydazey



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PostPosted: Sun Feb 09, 2020 3:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Not had chance to test the voltages this weekend, it is very weird as you say the gate and button both go through the same circuitry so it seems very odd for them to act differently???

gabbagabi wrote:
did you connect the grounds thogether at one point? this is nessesary.


No I just wired as shown on yusynth website I assumed all the grounds connected together on the PCB ??

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