ROG tri-vibe - can it be altered for bass?

[ChrisKelly]

Hi first post!

Building a diy synth and I used the ROG tri-vibe which i found through this site (thanks  )

Works great for mid/upper frequency notes but i tried sending a bass through it and lost alot of the bottom end.

Does anyone know which part of the circuit I could change to allow lower frequencies through?

Cheers
Chris

[marcelomd]

Hi. Welcome!

The usual way to adapt a circuit for bass is increasing the value of the input/output capacitors. Try 100n-220n for the input capacitor. Maybe 10u for the output, but I think it won't make a difference.

The other way is blending the original signal with the effect. See ROG's splitter-blender.

[ChrisKelly]

Awesome - I'll give that a try

Thanks for the response! 

[Kipper4]

Welcome Chris.
That may or may not work. Some circuits neglect certain frequencies  at the outset. Because sometimes those freqauncies do not respond well with the effect.

It's customary to link to the schematic also.
So we're all reading from the same page.

http://www.runoffgroove.com/tri-vibe.html

For the cost it's worth the experiment with the caps though.
Let us know how it goes.

[ChrisKelly]

Sorry yep thats the schematic i used. Thanks for the help.

Weirdly the whole thing stopped working last night 

The lfo stopped on the whirl and swirl settings, and the vibe worked but very low volume and only very slight modulation. Frustrating. Ive trawled through loads of posts trying to see if anyone else has struggled with this build.

So far i've tried replacing the IC's. I'm using TL072's for UC2 and UC3, a NE5532 for U1 and an LM13700.
Before now the whole build worked fine! Good modulation on all settings etc.
- it's all on breadboard which i read can have inherent problems
- are the lm13700's sensitive to anything? could they have been damaged at all by something i have done?
- ive used an 386 amp driving 32ohm headphones which may have caused some issues. Its very sensitive to stray noise and gets hot the 10ohm resistor from pin 5 of the 386 gets hot so either a 386 cant cope with the 32ohm load or maybe i have a faulty breadboard.

Sorry for the dirge of info. If anyone has had similar issues i'd appreciate any tips. I'm new to all this so its possible ive made some rookie errors

Cheers
Chris

[anotherjim]

It relies on phase shifting I think. Bass frequencies probably don't shift enough. Looks to me that ROG have chosen coupling capacitors big enough for full range audio (although in synth work, many parts are pressed to also function in LFO ranges, I don't think this is one of them).
I'd guess the component values of interest are the 22n and 1.5n in each OTA section. Maybe only the 1.5n needs increasing - or both of them. I suppose changing both x2 to 47n and 3.3n might do to  lower the effect an octave, but that's only a guess.

Is the 10R that gets hot at the 386 in the zobel network across the speaker output? That getting hot is a sign of high frequency instability. Make sure you have power supply decoupling capacitors close to the 386 power pins, 100uF ought to do it. It should cope fine with 30ish ohm loads.

If you use multiple power strips on the breadboard, fit a decoupling cap on each one. ROG show a single 470uF for a pcb build, you can replace that with 100uF or 220uF on each power strip for the breadboard circuit.

[DrAlx]

I'd guess the component values of interest are the 22n and 1.5n in each OTA section.

+1.    I'd scale them both up by the same factor to increase the phase shifts at the lower frequencies.

Oh, and I've blown up a few OTAs while breadboarding.  Easily done by putting too much current into pins 1 or 16.

[ChrisKelly]

Thanks for all the help guys. I'll try swapping out the caps and check all my power supply bypass caps are on point too