Bitcrusher circuit problems

[oldrocker]

I can't believe this is giving me such problems.  I breadboarded two bitcrusher circuits to see which was better.  For some reason I can't get either one to work.  The input and output buffer sections are working but the S & H oscillator clock section is doing nothing.  This is such a simple circuit that I'm mystified that it's stumping me.  I know some said they have successfully built these but I'm not getting anything out of them.  I tried different dual op-amps like 4558, 1458, TL072'82 and 5532 but no change.  I even took it apart and rewired it but I still get the same result.  I'm surprised that this would be this difficult to make work.  It looks cut and dry to me but I can't make the clock section do it's thing.  I was hoping those who have built this could give me any advice on what to look for.
http://www.logmonster.com/images/full/?pic=24911275843_1174794150-422-14886.jpg
http://www.logmonster.com/images/full/?pic=AnalogBitCrusher_1174772303-422-14887.jpg

[nordine]

thats a common problem i've had with oscillators, these little details components introduce in circuits

i'd say lower that feedback resistor R7, to 47k... sometimes that all you need to get a bi-opamp osc running

also, low R4 (to 470k, or 560k), if the osc is already running but can't switch the jfet properly

[nordine]

oh, and i also suggest getting the Vb for the oscillator from a second Vref point, so you lower the inherent feedthorugh

[oldrocker]

Thanks I'll give that a try.  I did get it to start to oscillate some but the high pitch whine is loud.  The ring modulation sounds decent though when the guitar is playing.

[oldrocker]

Thanks nordine, 
That did the trick.  The 47k also took care of the high pitch whine also. I'm still experimenting with the circuit and I hope to come up with something and perfboard it.
Thanks again.

[dxm1]

Interesting - the first schematic you linked to has R8 at 1M, while the second has it at 100R. Which did you use?

[oldrocker]

It only worked for me with the 100R. 

[nordine]

Thanks nordine, 
That did the trick.  The 47k also took care of the high pitch whine also. I'm still experimenting with the circuit and I hope to come up with something and perfboard it.
Thanks again.

you're welcome 

now, about the different bit crushers out there... i like the best the original one, the nyquist aliaser

tried the one by bioroids and colin's one... and i think there's something.. too aseptic in the tone (?) they provide... the nyquist is the dirtier -and most versatile- of the three so it get my votes

[slacker]

I tried the second one, and I had to change R7 to 220K to get it to oscillate. I also lowered R4 to 500k to get the Jfet to switch.
There's a useful thread here http://www.diystompboxes.com/smfforum/index.php?topic=48809.0

[oldrocker]

Yes I have built the JC Maillets Nyquist Aliaser and I really like it.  I added the envelope follower to it to get that crazy sweep effect.  I was able to eliminate all bleed through using the voltage setup and separating the grounds.  I also added the separate cv input jack but I haven't figured out how to utilize it yet.
So I'm trying some other ones just to check them out.  I haven't got around to ordering the CMOS chips yet for the bioriods one Basicaudio did recently.  His sound samples sounded pretty cool. 
I'm basically using the bottom Colins schem too.  Although instead of the .0033uF cap I used a .1uF cap with better results.  I tried some lower values for R4 but it seems that the gate is switching okay already.  I'm still working things out .
http://www.logmonster.com/images/full/?pic=Nyquist1_1170007735-422-14677.jpg
http://www.logmonster.com/images/full/?pic=aliaser4_1169985910-422-14673.jpg

[oldrocker]

Well I pretty much tried all different components and ended up using two TL082's for the dual op amps and two GE 1N34A's for the diodes.  I used the Colins version except for changing R7 to a 47K and the .0033uF cap to a .1uF.  This seemed to be the best setup to my ears.  A little fuzzier and a touch louder than the original setup.  It sounds similar to the JC Maillets transistor one but not as in your face as that one.  I'll be boxing this up in the afternoon tomorrow and hopefully get going on the CMOS bioroids version soon.  These crazy ring modulation Analog Bit Crusher effects are pretty cool.  I'm really interested in the Slacktave using the CD4024 I saw posted today.  That one sounds really synthy which is one thing I really like.

[oldrocker]

[

[oldrocker]

Perfboarded and boxed up the Bit Crusher.  There is some high frequecy bleeding through.  I was going to try and do the same supply voltage and ground separation as I did on the first Nyquist Aliaser I built.
http://www.logmonster.com/images/full/?pic=defef1_1175063443-422-14890.jpg
http://www.logmonster.com/images/full/?pic=dtrwg2_1175010627-422-14891.jpg