ADSR schematics do not match the PCB ??

[vcfool]

Hi,

I've been protoboarding the YuSynth ADSR this morning, following the schematics. When finished, I found it was not working: it didn't got any respone when gate in was applied. After checking all the connections twice and making sure it was all ok, I began checking the 3 transitor connections on the PCB tracks and I noticed it is different from the schematics:

On the schematics the Base of Q3 is connected to the Collector of Q1 through a 10N cap.
On the PCB the Base of Q3 is connected to the Collector of Q2 through a 15N cap.

So I changed that connection following the PCB and everything seems to work as expected now...

This is confusing me. Has anyone experienced this?
Am I doing something wrong? Maybe I am just misreading something...

By the way, I am using a normal NE555, by looking at the Datasheets I guess it will work the same as a CMOS 7555. Or shall I better look for a 7555?

Thanks everyone in advance!

[yusynth]

Hi

Yes you're right I made a mistake when I redrew the new version of the schematic. I am fixing this ASAP. The old version of the schematics was correct and I introduced the mistake when I wanted to improve the drawing... In French we have a saying : "betterness is the foe of rightness" ...

By the way you'd better use the CMOS version. The NE555 is known to have dramatic issues concerning the current it draws from the power line during the astable switching stage. The power draw goes up to 100mA during this transient. The CMOS version does not exhibit such issues.

[vcfool]

Hi,

Thanks for your answer.
After spending some time playing with the ADSR, I have another question reganding the way it acts:

Let's say you trigger the ADSR, let it reach the Sustain state and hold it there. Now the Sustain will work as a kind if Manual CV in all the envelopes I have tried so far. But in this one, you can only lower it, and it follows correctly, but it won't go up again.

So when in the Sustain state, (while holding the key and sound is on) you can only change the Sustain to lower voltages, not to higher ones. Once it reaches a Min. V it will not raise above this level again without re-triggering the ADSR again.
Is this normal operation on this design or shall I check connections again?

Not being native english speaking, I don't know if I am making myself clear.

BTW, I'll look for a CMOS 7555.
Thanks again.

[yusynth]

[vcfool]

Hi,

So I found a Motorola MC1455. By looking at the datasheet I can't make clear if this is a good replacement for the 7555...
Can somebody tell if it is a CMOS version or a normal 555?

Thanks!

[EdisonRex]

[vcfool]

Thanks!

[LetterBeacon]

Should I use a 10n or 15n polyester cap between Q3 and Q2?

The schematic and the BOM say 10n, but the PCB layout says 15n...

Thanks!

[yusynth]

10n or 15n doesn't make a significant difference in this case, use the value you have at hand.

[LetterBeacon]

Thanks for that.

Also, the schematic says C6 is 10nf but the BOM and PCB say it's 100nf. I've assumed it's supposed to be 100nf.

[yusynth]

correct I'll fix that

[yusynth]

Page fixed

[softfin]

I stripboarded one of these ADSRs from the schematic more than a year ago and couldn't get it to work.
After spotting this topic, I repaired it and managed to get it working straight away.Thanks for the correction !

[scriptstyle]

just noticed r18 on the schematic is listed as r10 on the bom. not sure if its already been mentioned?

[yusynth]

I'll check that and fix it, thanks for mentionning.