281 clone project- taking orders now for last run of these..

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

For more details check the blog, link below...

EDIT - also on blog is power wiring... I'll not bother to upload here too...

LektroiD · Posted: Tue Nov 30, 2010 2:15 pm Post subject:

I have them both working now (sort of)..

The B Level pot I have wired (similar to my diagram - or the bottom most pot of your diagram) does nothing?

On your diagram there are now 3 pots. This has made it even more confusing - none of them are labelled as to their function.. I'm not sure which of the 3 pots is the "B Level" pot? (I have no space on my panel to place the additional two pots anyway)...

I noticed you are using revision 2 boards, mine are revision 3...

I'll try to get a pic of the front panel, but the whole thing is a mess until I can get it all bolted back together, once it's working.

LektroiD · Posted: Tue Nov 30, 2010 3:23 pm Post subject:

Ok, there's something odd going on, they both seem to generate waveforms correctly, but in quad mode they don't seem to do anything except occasionally I can get it to switch A on and off from B, it stays at +10V constantly then pulses A on and off leaving the DC offset at +10V.. It is literally an ON-OFF pulse, even though it should have an attack/decay slope, not a square modulating it

For example, it is absolutely impossible to create a waveform like this:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Also if I switch modes away from cycle, it will not start again in cycle mode unless I kick start it with an external trigger

This is the best I can get it to do:

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The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

The three pots (from top to bottom) are amount of external signal in to the PEAKcircuit (not on your panel, so ignore the pot and just go PEAK IN thru a 1N4148, amount of A to PEAK circuit, Amount of B. If you don't have pots ignore them, as it says on the blog.

V2 vs V3 - they look the same to me in this area apart from R47 being on the V3 board, if you compare them you would see that.

So do both boards cycle if left in cycle mode? or do you mean they just stop after a while? Mine stops unless triggered once, which I thought was a feature?

LektroiD · Posted: Tue Nov 30, 2010 5:06 pm Post subject:

The Bad Producer · Joined: Mar 08, 2009 Posts: 282 Location: The Manhole

Good news! To be honest I wasn't sure mine were working at first!

toppobrillo · Posted: Wed Dec 01, 2010 3:46 pm Post subject:

hey thats great u got it working Smile

russma · Joined: Oct 22, 2007 Posts: 14 Location: PNW

Based on the information in this thread, I made a builder's FAQ document so people wouldn't have to parse through all the PCB-ordering posts. Maybe someone will find it useful. Here's a link:

http://dl.dropbox.com/u/168766/281_notes.docx

russma · Joined: Oct 22, 2007 Posts: 14 Location: PNW

Is one 10v voltage regulator and one cap C4 enough for four boards? I'm using an LM7810C for the regulator.

rosch · Joined: Oct 03, 2009 Posts: 164 Location: germany

thank you, russma!
this helps a lot!

ultrashock · Joined: Dec 10, 2009 Posts: 40 Location: Vienna.AT

Dear ALL!
Just a simple question nothing really in depth just:
in sustained mode /------------\
if you release the key (the gate) in the middle of the attack phase - will the envelope:
1) decrease to zero at once without reaching the maximum (decay phase) or:
2) it will anyway reach maximum (10 volts or so) and then will fall down to zero?

The first case seems more convenient for me reminding an ordinary "ad\ar\asr" generators, but I have a suspicion that it's second stated above case (i'm just experimented with my own designs using discrete integrator and ota on the 281 cmos).

Thank you for your answers in advance!

Terrafractyl · Joined: Sep 21, 2010 Posts: 13 Location: Melbourne

Ok I am at the end of my nerve people, Its been an awful week of DIY and I just finished building my 2nd 281. Unfortunately it has exactly the same problem that my first one did (and still does) so now I have two dual 281's that don't work. Sad

Basically I have the same problem that 2 other people in this thread had (very short envelopes, attack and decay knobs do nothing, in cycle mode it produces a high 1khz approx tone)

But both of these other problems were fixed by either replacing the 5240 diode or switching the pins on the mpf102.

I have replaced these parts several times now, and still have the same problem. I have checked all the Cmos chips are getting 10v and the other IC's are getting the appropriate power.
I also have tried a bunch of different IC's and have swapped the cd4016 with a cd4066. Same deal, the outputs of the cd4066 DO seem to be passing the voltage changes from the attack and decay knobs, maybe the lm13700 is not functioning properly? I have tried swapping them out also.

Please, any advice on getting these 281's to work would make my day!

arnoid · Joined: Aug 23, 2009 Posts: 57 Location: Belgium

Hi

I build a quad 281 15V version. R7 & R8 1K

But the module doesn't cycle on 15V in cycling mode if I give it a trigger signal
The weird thing is if I put 12,80V to the module its cycling and working correct.

What shoud I do raising R7 & R8 ?
Sombody had the same issues Question

thx in advance
Smile

PS: it's not my power supply is strong enough (3,3A) and I tested it with just the 281 connected.

beautyofdecay_ · Joined: Aug 14, 2009 Posts: 38 Location: Netherlands

The trigger pulse should be 10V.
I had trouble triggering cycle mode at first but found out my trigger pulse peak voltage was too low.

arnoid · Joined: Aug 23, 2009 Posts: 57 Location: Belgium

arnoid · Joined: Aug 23, 2009 Posts: 57 Location: Belgium

toppobrillo · Posted: Thu Dec 22, 2011 3:10 am Post subject:

arnoid · Joined: Aug 23, 2009 Posts: 57 Location: Belgium

henrikgo · Joined: Jul 05, 2008 Posts: 40 Location: sweden

I have built four V3 PCBs and have some problems.

I can't get none of them to cycle, when in cycle mode, they will cycle twice then stop.

Also this one is really strange. After about 5 minutes one of the A-boards will hang in quadrature mode and just give a continuous gate, it happens every time. It release the gate when I flip the quadrature switch, but will hang again if I turn on the quadrature.
The other tho 281s that are linked will both hang in quadrature mode.
If I power off and then on again directly the modules will do the same thing. If I leave the power off for a while it's all good again for another 5 minutes.

Also the end pulses just work sometimes on some of the modules.

I really can't figure these problems out!?

henrikgo · Joined: Jul 05, 2008 Posts: 40 Location: sweden

Anybody?

djg · Joined: Nov 10, 2010 Posts: 12 Location: New York

To those with having cycle problems, my dual has been working great until I switched to a different power supply recently.

'A' would cycle fine, but 'B' would not. I always noticed that my 'B' was sort of "softer" and needed a stronger gate to get going in in the first place, but nothing would get it to cycle with the new PSU.

I checked it out on my bench supply and my 'B' would indeed cycle. I had noticed my new PSU was running going a little hot, measuring 15.65V +/ when I installed it, but figured it would be fine. So I cracked it open just now and trimmed it down to the appropriate levels, and lo and behold, 'B' is back to cycling.

Perhaps with too hot a power supply it is expecting a proportionally larger gate than 10V and with the circuit even the smallest deviation in the supply makes a difference? Just a heads up for those having troubles that it might be worth checking your supply voltages thoroughly.

henrikgo · Joined: Jul 05, 2008 Posts: 40 Location: sweden

My PSU is exactly +/-15V, but still these strange problems on all four of my 281 V3. End pulse will just work sometimes on some of the 281s, but then only when ASR is selected, AR doesn't give any end pulse. Quadrature works sometimes but usually just gives a continuous gate to both 281s. Cycle mode doesn't work properly either, most of the time it cycles twice then stop.

arnoid · Joined: Aug 23, 2009 Posts: 57 Location: Belgium

Bump
I still having cycling issues when driving the module on 15V

I took the module apart and checked with just one 281pcb because I tought It had something to do with using one voltage regulator for 4 pcb's but I have the same problem with just one pcb ?? It stops cycling when I go above 14V on the positve rail ? I have the same problem with the 4 pcb's ?

Sombody can help me out plz ?
I tryed to read the schematics I guess it has something to do with the CA3080 IC ?