Attempt at Nyquist Aliaser build... Failure so far.

[chris_d]

Hmm. Howdy. Loved the clips of this one, thought i might give it a shot, so far not so good.

I am using this vero layout: http://aronnelson.com/gallery/slackers-stuff/nyquistaliaserboard_final

I have subbed several things, possibly something critical, i was just hoping to get it going quick and dirty with what was lying around...

The subs are as follows:

1. 2N3904s instead of 2N5210
2. 2M instead of the 2.7M (also tried 3M, no change)
3. .0015uf instead of .001uf
4. 100k trimpot instead of one of the 10k trimpots.
5. 250k-L for both control pots instead of 100K and 47k.

I have bypass, but once engaged the sound goes away. If i CRANK the amplifier, very faint, clean guitar/input can be heard, and also a VERY faint buzz/oscillation noise such as produced by the Atari Punk Console, the pitch of which is changeable by manipulation of the "frequency" knob. This noise is entirely unaffected by the guitar signal.

I attempted swapping out the 2N5457s one by one with other 2N5457s, and with J201s. The trimpots do not have any major effect on the sound produced. The volume seems to work correctly in that it increases or decreases the buzz when manipulated, again, only noticeable with the amp cranked.

These are the voltages i get:

Q1 - D= 0.64v
       S=0.45
       G= 0

Q2 - E=4.97
       B=0.62
       C=8.49

Q3   D=8.49
       S=4.97
       G=0

Q4 - D=8.49
       S=7.74
       G=8.49

Q5 - E=3.23
       B=1.41
       C=5.36

Q6 - D=5.36
       S=3.23
       G=0


IC

1=2.38
2=1.76
3=1.75
4=2.38
5=5.36
6=4.06
7=1.8
8=2.38

I have been over the thing a few times looking for mistakes, and caught a couple, but even once rectified, i am not getting any change in output. Surely i have done something stupid, but what?

Any input would be appreciated. Thanks.

-chris

[MartyMart]

http://www.lynx.bc.ca/~jc/nyquistAliaser.html

Here's JC's article about it, worth a read to get it set up properly.
Your trimmer/pot values are way off and this may mean that "tuning" it in is proving difficult !
I can't get to mine for voltage checks today, but perhaps sometime tomorrow.

MM

[caress]

make sure to double check your opamp and make sure it's working properly.  i had two TL082's crap out on me in two different aliasers...   easy enough fix though, i just stacked another on top and soldered a few pins together!  also, make sure you are using a 10k trim attached to Q1.  if you go bigger than that, it's hard to get the resistance right.

[chris_d]

also, make sure you are using a 10k trim attached to Q1.  if you go bigger than that, it's hard to get the resistance right.

Haha. Of course that is the one that i have a 100K in! Looks like i will at least need to get a 10k trimmer to make this easier to sort.

Here's JC's article about it, worth a read to get it set up properly.

I have read that. Unfortunately, i don't think i understand it well enough to know what to do with the trimmers! If you could post some "good" voltages, it would be very helpful. I would love to have even an approximate target to aim for.

Thanks guys.

-chris

[oldrocker]

Except for the 100k trim pot all other part subs should be OK.

[caress]

i think the voltage between Q1 and A+ should be between 6.2 and 6.7.  somewhere in there should null the oscillator completely and you'll get zero (or close to zero...) bleedthrough.  i found that if it is lowered 1.6 or so volts, you get a kind of crunchiness and fizzle without the full-on aliasing sound...very nice.  i think if you're using a battery, it's a good idea to mount that trim as an external pot to quickly null out the oscillation.  maybe a 1k or so pot in series with the trim to have a little give-and-take...?

[slacker]

From your voltages it looks like you've got problems with Q1's drain, even with a 100k trim you should be able to get its voltage up to 5 or 6 volts. There's also something wrong with Q3, the drain should have about the same voltage as the source, it looks like yours is shorted to 9 volts. Check around the drain for solder bridges especially round the row above it as that has 9 volts on it.
Your IC voltages are all way off, you haven't accidentally used 220K resistors for R12 and R13 instead of 220ohm have you? Pin 8 should have about 8 volts on it and pin 4 should be about 1 volt.

[chris_d]

From your voltages it looks like you've got problems with Q1's drain, even with a 100k trim you should be able to get its voltage up to 5 or 6 volts. There's also something wrong with Q3, the drain should have about the same voltage as the source, it looks like yours is shorted to 9 volts. Check around the drain for solder bridges especially round the row above it as that has 9 volts on it.
Your IC voltages are all way off, you haven't accidentally used 220K resistors for R12 and R13 instead of 220ohm have you? Pin 8 should have about 8 volts on it and pin 4 should be about 1 volt.

O.k. I think i am making some progress...

Good call on the solder bridge, there was a tiny hair of solder making a jumper there, and bringing in 9v. Gone now.

I stuck a 10k pot in the trimpot's place, and just adjusting it by ear, i was able to get the thing to make some noise. Still not right by a long shot, but it feels like progress.

I am getting a nasty crunky fuzz crackle breakup with the frequency knob all the way down right now, but not the oscillating 8bit-like "synthy-ness" that i should be getting. More of a starved fuzz sort of sound really.

Clearly the TL072 is not happy, its voltages are roughly the same as before.

The 220 ohm resistors are in fact correct red/red/brown and measure to just over 210 ohms each.

These are the new voltages, minus the IC, which is pretty much as before:

Q1 - D= 3.89v
       S=0.52
       G= 0

*I can get Q1s drain to read 6v, but this is what it ended up at based on adjustment by ear.

Q2 - E=6.73
       B=3.89
       C=8.36

Q3   D=5.06
       S=6.73
       G=0

Q4 - D=8.36
       S=5.86
       G=5.06

Q5 - E=3.33
       B=1.43
       C=5.29

Q6 - D=5.28
       S=3.33
       G=0

Thanks for all of the input so far. Please keep the fix-it ideas coming! At least it makes a type of sound now!

-chris

[oldrocker]

I added the envelope follower mod to mine to get that auto up sweep.  It is a wierd sounding effect.  You might want to try it once you get it working.
You might want to try different fets even of the same type.  For example I used a J201 for the first fet and 5952's for the others but I had to swap some 5952's with others for better operation.  Also I like the LM1458's best for the dual opamps.

http://moosapotamus.net/IDEAS/nyquist/NyquistENV2.gif
http://www.logmonster.com/images/full/?pic=Nyquist1_1170007735-422-14677.jpg
http://www.logmonster.com/images/full/?pic=aliaser5_1169957698-422-14674.jpg
http://www.logmonster.com/images/full/?pic=aliaser4_1169985910-422-14673.jpg