An new twist on a LDR based envelope filter

[deadastronaut]

is the OPA1652 only available in SMD?...

[rring]

probably...its meant for super Hi Fi audio. I had a bunch leftover from another project and I just soldered on little legs so I could put in a breadboard when I did initial testing. The TS922 is in DIP also the TL972 and the OP213

I found a TLC2274 to try ....this evening  I'll see if I can get that to work?

[jatalahd]

the clamper circuit, combined with the half wave rectifier, forming a half wave voltage double with diode voltage drops. It has a slow rise time and it
bleeds away static charge relatively quickly with no signal.

Ok, I think I need to re-analyse the behaviour of D2. I see that there is a possibility that it does not function as a proper clamper in this context.

All in all its not very exciting but it works

Actually it is very exciting

StephenGilles:

how would you make the voltage at the junction of D3 and R4 only go high on the leading edge of the note played - or does it do this already? Would a sample and hold circuit be needed perhaps?

The time constant for charging C5 is C5*Rattack and for discharging C5*(Rattack+R4). As long as the discharge time is longer, the voltage over C5 will grow along with the current coming through D3. The voltage at the junction of D3 and R4 fluctuates until voltage at C5 has grown enough to stop D3 from conducting.

[rring]

FYI the TLC22 series of op amp does not work ... I see the same problems as before with TL072. Someday I'll figure out why.

[Seljer]

FYI the TLC22 series of op amp does not work ... I see the same problems as before with TL072. Someday I'll figure out why.

I've had bad issues with stability with TLC2272 on multiple occasions, even in very simple circuits where you think there never would be a problem 

[maartendh]

Used a BA15218 for U2, which works fine. Had to change c6 to 100n though, to get a noticeable sweep. Also replaced Led 3 (the one on the intensity) to a blue led - the green one did not seem to have enough effect in this spot (I used transparant green leds which give a kind of yellowish green light. Nice and easy build, thanks rring!

maarten

[Kipper4]

Now that Chip BA15218 is available in dip8 and is much cheaper than i could find all the others suggested especially in the uk.
Unless anyone knows differant.
Can you post an audio sample fo your working circuit please Maarten
Thanks

[rring]

 Yes looked at the data sheet -  this op amp is much like the others that I have gotten to work. I think this is a great choice and  others will work well also. Not sure what the issue is  with needing to use a different LED for the resonance adjustment? The choice of .01 uf was based on the sweep range of the photcell I used- if you have a phototcell with a range that is shifted lower - you would need a larger value -so could make sense. You get much more bandpass peeking when the photcell R (for LDR3) is  higher than the other two so you should be able to achieve this without critical or special choice of the LDR setup for LDR3. This seems a  little odd?

Maybe the values for R5 and R6 need to be adjusted higher? Also if with no signal you see volatge across R5- there is offset error- which would also expalain some of what you describe. Are you able to get a nice bandpass sound with the intensity turned all the way up? It sounds like you got it working.... but I am concerned that you had to fuss with it. I built three of them with very repeatable results. Perhaps it has to do with your LDR's vs mine?

[Kipper4]

Chips on back order.
Another one for the list.
I just love filters.

[Kipper4]

I'm about to redraw the schemo in Eagle and would like to know what the B+ is for?
thanks

[maartendh]

B+ connects to the battery, the 9 volts connect through the diode to the 9 v indicated in the circuit.
Haven had a chance to record a sample (audacity is giving me some problems on my new PC) yet, but as you are going to build this yourself probably you won need this.

Later in the weekend I will have a look at my LDR's to see whether I can find out what is different in my built.

Maarten

[Kipper4]

Thanks Maarten

I've been scouting out the data sheets and it looks like a LM6132 might do for IC2 and is half the price of the OPA1652 in the uk
and its available in DIP8
Data sheet here
http://www.ti.com/lit/ds/symlink/lm6132.pdf

[rring]

Here is a schematic with a much clearer function of B+ which is simply the battery connection that would go to the jack switch. Sorry about that - I seemed to be a little sloppy with this schematic - which understandably would annoying to other builders.




The LM6132 looks like a good choice.. again the cheapest one I found that looked good(in a DIP) was the TL972 which I found on mouser and digikey for about $.97 generand in stock. In fact the specs and price were so good I plan on getting some of these to use for general tinkering.

[Kipper4]

Thanks
My chips arrived today.
I'm doing a perf layout ready before i heat up the iron.

[rring]

I am very interested  to find out how it works for you - especially with a different op amp and I assume different LDR's?

[Kipper4]

I'm thinking of using GL5549 ldrs and I got some green 5mm diffused leds approx 100mcd on ebay, I'm nearly ready to go on this.
If anyone sees a problem with these please let me know.
GL5549=
@10lux 100-200k
10 dark
Link to the GL55 series photoresistors
http://akizukidenshi.com/download/ds/senba/GL55%20Series%20Photoresistor.pdf

Thanks
Rich

[rring]

I think ten lux is pretty close to dark? if so you should be good. Regardless, The led has to be able to get you down to 1K at high brightness to work with my cap values(.01) if you can get that low just make the caps smaller.

[Kipper4]

Thanks mate I'll do some testing maybe before I make a final decision on the ldrs.

[Kipper4]

Can someone please post some voltages. I'm losing signal after d3.

[samhay]

You won't be able to hear any signal after D3 as the signal is rectified at this point.
The audio path is Q1 -> IC2A -> out