cool reverb apart from switch spdt 'pop' issue

[samhay]

That doesn't half sound ok, and it sounds like I missed some fun - hope the cat is still talking to you Rob.
Am I correct is now assuming now that: everything works; it will oscillate with feedback at max; but the tails still don't sound great?

[deadastronaut]

^ yep,  full oscillation , but tails still too short...

the cat is fine now that we have oscillation , but she's stil quite concerned about the economy and the U.S shutdown at the mo.

[mmlee]

Hey,
Liking the look of this tails mod, will keep an eye out for it.

In the meantime I've attempted a vero layout, there are standing resistors which I'm sure some of you will dislike and to be honest I'm not sure if some of the caps will fit in the spaces.  I'm pretty certain there'll be a few mistakes, especially getting lugs 1 & 3 muddled on the pots .  If someone could give it a look over for me I'd really appreciate it.

I used RG's Rev1.6 schematic and I've included the DIYLC file if anyone wants to tinker with it.

https://www.dropbox.com/sh/80zyw6uyxoi9xh8/-6SQw_IlCN

Cheers,
Marcus

[samhay]

^ yep,  full oscillation , but tails still too short...

the cat is fine now that we have oscillation , but she's stil quite concerned about the economy and the U.S shutdown at the mo.

Nothing like a bit of financial uncertainty in the global markets to unsettle the local feline population.

I have had a bit of a think about the IC2c - the op-amp mixer into the brick. I think the gain of the feedback signal will get a bit uncertain when the FET closes as it will become maximally 22k / (22k ||FET on resitance) and the frequency response will get really strange. However, this should still alow the wet signal to pass though, so I am like always, a little confused.

Does the oscillation when feedback is at max stop if you switch to tails mode?

[deadastronaut]

^ yep,  full oscillation , but tails still too short...

the cat is fine now that we have oscillation , but she's stil quite concerned about the economy and the U.S shutdown at the mo.

Does the oscillation when feedback is at max stop if you switch to tails mode?

yep it sure does...

[slacker]

That last clip dounds great, we're close now I can feel it. As an experiment to test Sam's thoughts if you just stop playing, leaving the effect engaged, do you get good tails? If you do then I think Sam's right and we need to dick about with the mixer a bit.

[samhay]

I was going to suggest the same.

As an aside, I find that with the design I have on the breadboard, it gets louder as it oscillates until the brick starts clipping. This sounds about as nasty as clipping can get, and very different to op-amp clipping. Does this design do this too?

[deadastronaut]

hi ian,

yes massive trails when on as normal ....but bypassed (fet) not so ...gets cut short.


@sam: it can get nasty/distortion...but if careful (220k as FB resistor) its very controllable now..

[samhay]

OK cool.

So you have a 220k feedback resistor, and 100k feedback pot and R6s are both 22k?

Edit - I have an idea. We could place the FET in the feedback path of the op-amp and remove the 22k to Vb (but leave a 10k or 22k in the feedback loop parallel to the FET). When the FET closes, the gain of the dry signal -> 0, while the wet should be ~ 1. You will probably have to reduce the 220k feedback resistor to ~100k.

Take a look at Merlin's Glassblower for an example of the FET switch used as suggested: http://www.valvewizard.co.uk/glassblower.html

[deadastronaut]

OK cool.

So you have a 220k feedback resistor, and 100k feedback pot and R6s are both 22k?

Edit - I have an idea. We could place the FET in the feedback path of the op-amp and remove the 22k to Vb (but leave a 10k or 22k in the feedback loop parallel to the FET). When the FET closes, the gain of the dry signal -> 0, while the wet should be ~ 1. You will probably have to reduce the 220k feedback resistor to ~100k.

Take a look at Merlin's Glassblower for an example of the FET switch used as suggested: http://www.valvewizard.co.uk/glassblower.html

morning, yep 220k/100k fb pot, both R6's 22k.

edit : like this?.


so the fet switch would be between pins8/9 ( with the 100pf/22k) with a 10/22k between 8/9 also....fb resistor to 100k.?...sound right?


@marcus: mmlee: hold fire for now..

[samhay]

something like this:

[deadastronaut]

ahhh right gotcha!..i'll give it a go.

so this then..

[samhay]

Not quite - you still want to take the feedback from the brick's output, like in the previous schem, but you want the feedback to go to the (+) input of the op-amp.

[deadastronaut]

HOLD ON...ithink i have it..

schemo above corrected?..

[samhay]

bingo.

First things first, but you may need to play with the feedback resistor to get oscillations again.

[deadastronaut]

righto... back in a bit..

[deadastronaut]

ok, tried that.

now when fet switch (led is on) i get clean signal , no reverb.   ( not even a hint, which is good)

when switch led is off i get full reverb...(oscillations still good)

but tails still cut short...when switched

[samhay]

So it stops oscillating at max feedback when the tails is engaged? I will have to go back to scratching my head for a bit.

I guess on the bright side, we are learning rather a lot about FET switching.

[deadastronaut]

yep, it dies off pretty quick, even at oscillation.

[samhay]

OK, this shouldn't be that hard.
With the switch open, we have a gain of 2.2 for for the dry signal (R6/R9) and a max of < 1/2 for the wet ( 100k/220k + whatever voltage divider effect we have between the feedback and reverb pots).
With the switch closed, we have a gain of nearly 0 for the dry signal and the wet should be unaffected if there is no resistance from (-) input to ground.

What are we missing? Do we need to get both of these to a gain of ~1?