vtl5c1 Subs

[ruffrecords]

There are photocells that don't use CdS and CdSe, but they don't work well for audio as a drop-in thing. The H11F1 won't do it without careful negative feedback, for instance (that's a guitar pedal, but it gives an idea), but it's incredibly fast, cheap, and compact, so maaaaaybe it's worth figuring out a way to make those work.

I cannot find any reference in the links to it needing careful negative feedback. V=Can you point me in the right direction?

Cheers

Ian

 

[midwayfair]

There are photocells that don't use CdS and CdSe, but they don't work well for audio as a drop-in thing. The H11F1 won't do it without careful negative feedback, for instance (that's a guitar pedal, but it gives an idea), but it's incredibly fast, cheap, and compact, so maaaaaybe it's worth figuring out a way to make those work.

I cannot find any reference in the links to it needing careful negative feedback. V=Can you point me in the right direction?

Cheers

Ian

Hmm maybe write to Ray. I linked to it as an example circuit but I can't remember where he talked about the hoops he to jump through to get it distortion free.

A bunch of us pedal geeks have also tried getting it to work in tremolos but it was a bust.

 

[benb]

There are photocells that don't use CdS and CdSe, but they don't work well for audio as a drop-in thing. The H11F1 won't do it without careful negative feedback, for instance (that's a guitar pedal, but it gives an idea), but it's incredibly fast, cheap, and compact, so maaaaaybe it's worth figuring out a way to make those work.

Wait a minute ... if you want "incredibly fast" why not just use a regular electronic VCA chip?

 

[PRR]

> any reference in the links to it needing careful negative feedback.

https://circuitsalad.com/2013/03/02/the-opto-compressor-revisited-simple-and-works-well/

"This design has the folowing features:
.....
"a darlington transistor as a shunt/shunt feedback amplifier. The biasing and feedback (from the collector to base) is critical to the design. The reason is that it keeps the voltage across the OPTO FET very low so as to keep its behavior linear. With out this feedback – there can be distortion."

He's got the opto-FET on a "summing node". If an ideal sum-node, that would do nothing, because signal voltage is always virtually zero, nothing to divert. The NFB amp is not infinite gain, there's possibly 20mV signal at the sum-node. FET over 100K will do little; FET under 100K reduces signal gain (and increases noise gain).

There is not feedback to control the FET's instant resistance.

Of course slow-decay feedback is used to control the FET's resistance over time versus signal for a limit/compress action.

 

[ruffrecords]

Thanks PRR, I missed that. It is actually quite an odd design. One problem with an opto FER is there is no opportunity to do the normal FET distortion reducing feedback (which is what I was expecting). Thinking about it, what is the advantage of using an opto FET? Why not just use a FET?

Cheers

Ian

 

[PRR]

> Why not just use a FET?

Indeed.

Loose 3-leg JFETs do come in a broad spread of Vto. Confusing to new designers, and hard to make two builds work "the same". But the Opto-FET will be using low-Vto devices for easier drive, and we probably want high-Vto for low distortion.

> opto FET is there is no opportunity to do the normal FET distortion reducing feedback

If stuck on a desert island, I *suspect* you "could" add a bit of signal to the LED drive and get the same effect. Might take days to trim. Kinda makes "opto isolation" more moot.

 

[gyraf]

..and let's face it, we're not into opto compression for the isolation it provides - but because of the linearity, near-voltage-independence, and the inherent timing characteristics. This makes the optofet path more or less no-go.

(Still haven't heard back from the EU-commision)

Jakob E.

 

[pucho812]

The more I think about this, since the vtl5c1 is just an LDR and led in one package. I don't think there is anything preventing me from using a LDR and led combo  that is covered.  hmmmmm now to find a  comparable LDR and LED combo....

 

[benb]

The more I think about this, since the vtl5c1 is just an LDR and led in one package. I don't think there is anything preventing me from using a LDR and led combo  that is covered.  hmmmmm now to find a  comparable LDR and LED combo....

The LED part is easy enough. You might want to quickly decide what LDRs you want and make a "Lifetime Buy" (including more than what you need, so you can find good matches) because those are the part of the Vactrols (TM brand of LED/LDR combo) that keep them out of the EU market. If the rest of the world isn't a big enough market and/or these are banned elsewhere, all manufacturers might stop making them.

A lot of the mojo in these light-and-LDR isolators (before LEDs were common they used small light bulbs, and the filament on/off time added even more to the response time) is the previously mentioned "inherent timing characteristics," including (perhaps especially) the LDR memory effects. As far as I can tell, the main thing that makes the Vactrol brand special is they meet tighter specs, and didn't vary from unit to unit as much as other makers' LDR-based products. The light-to-resistance response generally varies a lot from unit to unit, thus they have to be selected and matched for applications such as stereo bus compressors.

Here's some good info from the Horse's Mouth on Vactrols and such:
http://users.ece.gatech.edu/~lanterma/sdiy/datasheets/vactrol/perkinelmer_vactrol.pdf

 

[joaquins]

..and let's face it, we're not into opto compression for the isolation it provides - but because of the linearity, near-voltage-independence, and the inherent timing characteristics. This makes the optofet path more or less no-go.

(Still haven't heard back from the EU-commision)

Jakob E.

I knew a local guitar pedal brand who used to control their pedals digitally with LDRs. I don't know if they are still in the same path, I guess so, a friend used to work there. Quite easy implementation avoiding interaction between analog and digital being completely isolated (other than PS) so not much care on the PCB needs to be taken, they worked as complete different departments for the digital control and the analog path. In fully analog gear I'm with you, no advantage from the isolation.

About the H11F1, I guess they couldn't bother in dopping a gate to that get, why calling it get? looks more like an opto-slightly-dopped-Si-bar. As opposed to the opto BJTs where they need to build the full transistor and sometimes they take the effort to put the base available to the outside world.

Now if looking for performance the VCA is the way to go, but the simplicity of the LDR is nice. I don't know how something like this scheme would do with a fixed CV and optodiodes. Maybe that's something new to try, maybe already out there, I haven't seen it.

JS

 

[pucho812]

just informed by our parts supplier that  the VTL5C1 is obsoleted/discontinued and unavailable. 

Up until recently we were just eating the higher cost.  But now no more.

 

[midwayfair]

just informed by our parts supplier that  the VTL5C1 is obsoleted/discontinued and unavailable. 

Up until recently we were just eating the higher cost.  But now no more.

People have had good luck with the Xvive clones in some very picky circuits. They're also relatively inexpensive. I'm not sure where to get their 5c1  (if you find out let me know, because I need a 5C1 alternative for my Cardinal trem, which is extremely picky, and I'm running low on 5C1s) but Smallbear has their 5c3.

EDIT: Smallbear still has some 5C1s in stock.

 

[pucho812]

well we use them in our optical compressors. I thought about making some with a photo resistor and a LED but I can't find a photo resistor with a dark Ω of 50M like the 5c1

 

[PRR]

> can't find a photo resistor with a dark Ω of 50M

1) you probably do not need 50Meg

2) nearly all LDRs will go to 50Meg if you leave them in the dark long enough

More likely you want >1Meg some time soon. The non-audio markets for LDRs don't really care. So the makers do not bother testing and specing the far end of the dark tail.

 

[midwayfair]

> can't find a photo resistor with a dark Ω of 50M

1) you probably do not need 50Meg

2) nearly all LDRs will go to 50Meg if you leave them in the dark long enough

More likely you want >1Meg some time soon. The non-audio markets for LDRs don't really care. So the makers do not bother testing and specing the far end of the dark tail.

Speed can also be important ... though a compressor probably doesn't care about lightning fast speed if it's optical.

puncho, Smallbear has at least two discrete LDRs that do a good job on high resistance: They have one called "Hi-Dark" that is usually for phasers and vibes, which goes to HUNDREDS of MOhms ... and its on resistance is comparable to most uses of the 5C1. They also have a $1 LDR, the 9203, which can easily hit >5M in a relatively short span. I'd try both of these.

I should also mention that they have a "clone" of the 5C1/5C1 made for them by Macron, but I will tell you that the on resistance is much lower than the 5C1 under normal use, and it's definitely slower. I wouldn't solder it to a board if I could help it without accepting that some changes would have to be made to both the LED driver and whatever voltage divider it's one leg of. It wreaked havoc on a bunch of peoples' guitar pedal builds. (E.g. makes a Mutron III sound like trash.) They're inexpensive and they MAY work. I've used a couple in guitar pedal compressors just fine.

 

[pucho812]

thanks I'll look into it. 

 

[pucho812]

update... as it currently stands any vtl5c1 available is fetching upwards of 25.00(USD) found a box of 4000 ready to use. I think I am going to retire.  ;D

 

[Whoops]

update... as it currently stands any vtl5c1 available is fetching upwards of 25.00(USD) found a box of 4000 ready to use. I think I am going to retire.  ;D

Nice one.

How about the other VTL5Cxx units? does your supplier also has boxes of those?

attached the different models

 

[Whoops]

The more I think about this, since the vtl5c1 is just an LDR and led in one package. I don't think there is anything preventing me from using a LDR and led combo  that is covered.  hmmmmm now to find a  comparable LDR and LED combo....

" hmmmmm now to find a  comparable LDR and LED combo...."

yes thats the most difficult part, because a lot of circuits were already done and thought of with specific VTL5C units in mind and their characteristics.

Providing you can still get a good supply of different and suitable LDR's, and those will disappear also eventually because in fact those are the components with cadminum, doing a DIY optoisolator is easy enough, what is difficult or might be not possible is having the same characteristics as the the Vactrol units.

 

[pucho812]

" hmmmmm now to find a  comparable LDR and LED combo...."

yes thats the most difficult part, because a lot of circuits were already done and thought of with specific VTL5C units in mind and their characteristics.

Providing you can still get a good supply of different and suitable LDR's, and those will disappear also eventually because in fact those are the components with cadminum, doing a DIY optoisolator is easy enough, what is difficult or might be not possible is having the same characteristics as the the Vactrol units.

Yes, exactly. Just need to find the right photo resistor and work it from there.