Mark Hammer Idea

[Kipper4]

Oops copy and paste error. My drawing.
C5 c7 need to be 10uf NOT 1uf.

[ElectricDruid]

There's a lot on that schematic that I don't understand. That leads me to believe that it's too complicated!

Firstly, I don't understand how the first op-amp is supposed to produce full-wave rectification. I'll have to simulate it and have a look.

Secondly, I can't believe you need two more op-amps and so many diodes and electrolytic caps just to do variable attack and decay. Although I suppose you've got to compensate both the diodes, so maybe you do. Just seems over-complicated to me, and makes me think "there must be a simpler way...".

Aside from throwing a lot of "stuff" at the problem, it seems to work fine, so that's all good.

I don't understand it that well, but I'd have thought you've done the right thing going to Vb. That's the equivalent of the centre "Ground" in the original circuit.

Tom

[Kipper4]

Fair enough I get where your coming from Tom.
So based on your reccomendation
http://www.play-hookey.com/analog/feedback_circuits/full-wave_rectifier.html
I drew this.
since the diagram was a block diagram with brief explanation, I'm not sure it's a good reperesentation
so I'm looking for clarification
Thanks
Rich

[Kipper4]

Scratch that. I think I found it over at Rod Elliots.
Only difference is the diodes are reversed. fig4 here
Right?

http://sound.whsites.net/appnotes/an001.htm

[Kipper4]

I've breadboarded fig 4 and it works ok.
I did buffer the front end and put an inverting op amp led driver on the back end with a gain of ~100-200.

I tried the diodes oreintated both ways and concluded that it inverts the led action.

[Kipper4]

Quick update.
I've been testing full wave rectifiers. Heres some ghetto lab notes.



link
http://imgur.com/E5uuBih

edit images edited

[Kipper4]

Re Fig D
I might need to buffer the V/2 Vb as the rest of the circuit is unsettling the input buffers voltages.
I hooked up an amp to the buffer output (via a cap) and noticed its getting very splatty(tech term) on harder played noted.
fig D hardly responds to lightly played notes but hard strummed ones extinguish the led which might be a useful feature in a project where the second (phaser) effect is only supposed to come in when played hard.
I also will stick the cro probes on it and see if i can spot anything useful. DC wise at least.

I might have to play with the Merlins Engineers Thumb recifier next.

[ElectricDruid]

In all of those schematics, you're rectifying with reference to Vb, and then smoothing with reference to Ground.

That doesn't seem right. If your signal is all "positive" wrt to Vb, then you need to have your envelope referenced to Vb too, no? Otherwise you're suddenly adding on a Vb-sized offset at the bottom. I can believe that might get "splatty" (to use the technical term).

What do you think?

Aside from that, you've still got the "changing attack time changes envelope level"problem mentioned in the article you posted, which is why they'd used *quite* so many op-amps. But I still think there must be a better way... I just can't quite *actually find  it* yet...

Still, only a question of time, right? How old are we?!? Years to go yet!

Tom

[Kipper4]

Years to go yet Tom I'm only in mid 50's.

What do you think of using the engineers thumb rectifier in combination with your 13700 cross fader?

I'll look at referencing the charge cap etc to Vb.

[StephenGiles]

Is there anything useful in this?
https://www.dropbox.com/sh/2aedsoafmaa3bc7/AACiigi5aVYTjrPP1ybQMO_oa?dl=0

[Kipper4]

Thanks Stephen I'll have a good read.

[StephenGiles]

and this lot from Aphex which they removed from their website!!!
https://www.dropbox.com/sh/gwftwz5hfx1ijvn/AAC3pUtghFVp2qe2HeCu-flpa?dl=0

[anotherjim]

Thing with precision rectifiers is you can only get Vb to near +supply (if positive rectifier) or Vb to 0v (if negative rectifier). They make more sense with bi-polar supplies when a positive rectifier can do 0v to near +supply (if some DC gain added).

There are trick designs using CMOS op-amp, taking advantage of the fact that these don't mind the input going negative. So the input is AC coupled and 0v referenced. These think they have bi-polar supply, but as they can only produce positive output, anything negative is ignored (sounds like description of someone with an MBA!). The output can range 0v up to near +supply if some DC gain is built in.

I've messed with precision rectifiers quite a bit and not sure if they are worth it.

I go for diode charge pump half wave. They are rectifiers and voltage doublers. Ground referenced output and perfect for single supply amps that can work in and out to 0v like the 358. Ideally, I'd precede it with an amplifier that can swing closer to the +supply than a 358 can, because it can only use the swing above Vb (but must have swing below Vb to prime the pump capacitor).
If you want full wave, an inverted signal can be fed to a second positive charge pump and blended with the first.
Unlike a precision rectifier, they do blank input below the diode threshold - but do you want every little noise from the guitar to kick the envelope?

[EBK]

These think they have bi-polar supply, but as they can only produce positive output, anything negative is ignored (sounds like description of someone with an MBA!).

nice one.

[Kipper4]

Thanks Jim.
I'm thinking I need a rectifier that only really reacts to hard strumming.
Since the concept is that the phaser notches only kick into the mix when strummed harder.
I've done a fair bit of messing with rectifiers too. I'd like to get something in the parish of a 5v pp swing so I can experiment with Toms lm13700 single vca

Here

http://electricdruid.net/wp-content/uploads/2015/06/VCBigMuffTonecontrol.jpg

Form this article
http://electricdruid.net/single-vca-crossfader/

I'll go back over the charge pump rectifiers.
I'll find a link to my first concept idea so you can get a better idea.
Thanks
Something's are worth taking your time over. I'd rather not, in the future wish to redesign it.
Rich

[Kipper4]

The cmos idea you talk about Jim is it the way he mentioned here

http://www.diystompboxes.com/smfforum/index.php?topic=113273.40

[Kipper4]

Sorry I missed your post Stephen.
Looks like I have some more reading to do. Thanks.
Rich

[StephenGiles]

Sorry I missed your post Stephen.
Looks like I have some more reading to do. Thanks.
Rich

I couldn't remember if I'd passed that Aphex stuff your way.

[Kipper4]

I think the DOD440 has a charge pump rectifier.

http://www.generalguitargadgets.com/pdf/ggg_ef440_sc.pdf

[anotherjim]

Yes, the DOD is a perfect example. D1 and it's position right before D2 is vital. The Range pot ( the pump pre-amp gain) is a good addition as you can't really make the envelope detection with fixed performance suit everything.