Optical tube compressor

[bcarso]

Since R3 is one of the few labeled with a ref des I suppose that is so.

Note also that the circuit won't work as shown if the optoemitter is an LED---there needs to be some recharge path for the coupling cap to it.

I for one am getting a bit frustrated by this coyness, and I doubt that I am alone.

 

[bcarso]

I had two girlfriends: Ana Lag and Ana Lead. I was going through a phase I guess.

One of them thought I was advanced, and the other made me feel retarded.

 

[analag]

I see plenty of tubes and one photoemitter symbol (D1) but no photoconductor, hence no variable gain and no compression.

I guess AC1 is supposed to be the signal input, but there is no indication of the output.

I updated and sent the schematic to Kubi to repost. D1 is part of a Vactrol Opto-isolator. R3 is actually a 100k pot with the LDR strapped across it, much like the La2a. R1 and R2 is also a pot.

 

[analag]

Note also that the circuit won't work as shown if the optoemitter is an LED---there needs to be some recharge path for the coupling cap to it. I you knew anything about anything you would know you're wrong. I have two such units in my studio and they work,guy.

I for one am getting a bit frustrated by this coyness, and I doubt that I am alone.

If such a simple circuit frustrates you what will you do when I show off my more high resolution stuff

 

[analag]

[quote author="solder_city"]'real advances in tube technology'? well, i aint impressed so far. Yes son, REAL advance it begins with thinking outside the box. That's why the current state of music is so monotonous because you all do the same thing the same way.

cant you guys see that this person is just yanking your chain?[/quote] Am I ? I took a cheapo Marshall mic and put a 6N1P running at 250V and 16ma, nothing special just twice as much volts and 10 times as much current, result? Un$%&*believable.

 

[gyraf]

Now try to behave, good people..!

It might well be that analag has some real knowledge and ideas that he wants to share with this forum, and - even though his tone is a bit pretentious - sharing knowledge is always good.

It's probably just a question of time before our good newcomer has read through enough of our archives to realize what - and specially how - we do around here.

--

Analag,

Welcome to "The Lab"..!

If you look around and read the threads, you'll find that this place is one of the finest collections of people who are creative, competent, and willing to share information on a no-bullshit basis. Don't be scared off by the negative comments by some members already in this thread - it's just that we are used to deal with each other in a much more modest and respectfull way than your initial posts show. This needs not be a problem at all, I'm sure that when you've gotten used to this forum - with it's pretty hardcore designers and engineers - all things will fall into place...

All the best,

Jakob E.

 

[kvintus]

Good post, Jakob!

Welcome Analag!

/Anders

 

[daArry]

always the gentleman

 

[gyraf]

Thanks, Kubi..!

Analag - what kind of opto is used?

Some quite slow opto type would probably be needed here in order not to distort at low frequencies..?

I guess that the opto's LDR part goes in parallel with the output level pot (marked "gain") - forming a voltage divider with the 100K resistor that goes to the output pot?

Is there any particular reason why you don't use a simple transistor or opamp stage (maybe even running off heater voltage) for the LED-driving - to save a nice ECC82 tube - and to reduce heat and current?

Jakob E.

 

[SSLtech]

Think about this for a moment.

The 1µF capacitor has a diode in series with it. current can flow one way through it. It can charge up. Durrent can never flow out of it. That means that once it the bucket is full, no more current flows in, therefore the LED will not light any more.

It won't work as shown. Simple as that.

Furthermore, if and when the drive voltage on the other end of the cap falls back down, the diode is reverse-biased, possibly beyond its safe level, possibly not, but there's a real chance of breakdown without protection.

There's also no current limiting resistance in series with the LED...

Might I suggest a signal diode in the opposite direction, in parallel with the LED? -I suspect that there is at least the chance that this part of the circuit might function something like correctly then. As it is, its a non-starter.

Keith

 

[bcarso]

Keith: Thank You for the corroboration.

But we are assured by mr analag that this functions in his studio.

As Stockhausen said after Morton Feldman described an elaborate dream involving Morty's carrying Karlheinz through the snow,

"Etwas ist nicht in Ordnung."

I will try to be nice now.

 

[PRR]

> There's also no current limiting resistance in series with the LED...

Think before you pick nits.

I know a little about tubes too. That 12AU7 is a very effective resistor. Without looking at the curve, I'd guess you can't get 30mA out of it, and that only for peaks: well within sight of the ~20mA rating on most LEDs.

> Current can never flow out of it.

There are such things as "AC" optos, with two back-connected LEDs. That will work. No matter that it isn't shown that way on the schematic: these drawings also don't show which resistor is the opto-R, they are hastily drawn.

Also the single diode WILL reverse-breakdown. At around 7V. So all that changes is that the threshold is higher than a hasty glance suggests. Reverse-breakdown is not harmful (not at the current the 12AU7 will pass).

I think it has a lot more resistors than I would use (even allowing for the several resistors that seem to be merely simulation place-holders). I'm baffled by the use of both cathode feedback and plate-grid feedback. Sure it works, but there are other ways to do it. Is it more euphonic? I don't know. U5 seems to be working awful hard considering its load. The B+ bypass for U1 seems pointless. U6 will suck great spikes of current and should probably be further up the supply chain.

 

[bcarso]

Yeah, I though about the possibility of an undeclared second LED, and also about breakdown-based capacitor resetting. And yes, it could be a drafting error---easy to do.

Maybe LEDs have gotten a lot more consistent since I measured them for reverse breakdown, but I recall a huge range of voltages, nothing from which a rule-of-thumb like 7V emerged, like the breakdown of a silicon base-emitter junction.

More worrisome is the response I got when I pointed out the problem with the C to the LED. If this circuit has been designed by its promoter, one would expect an explanation.

Instead I get this:

"Note also that the circuit won't work as shown if the optoemitter is an LED---there needs to be some recharge path for the coupling cap to it. I you knew anything about anything you would know you're wrong. I have two such units in my studio and they work,guy.

I for one am getting a bit frustrated by this coyness, and I doubt that I am alone.[/quote] If such a simple circuit frustrates you what will you do when I show off my more high resolution stuff"

 

[analag]

[quote author="gyraf"]Thanks, Kubi..!

Analag - what kind of opto is used?

VTL5C4/2 are used

Some quite slow opto type would probably be needed here in order not to distort at low frequencies..?

I use the fastest ones I could find, it does not distort at low frequency. If you notice, the signal that drives the gain reduction amp comes from the output of the first voltage stage or U1 and at the same time the LDR is connected to U1's input. This seems to eliminated the frequency distortion you suggest might be taking place.

I guess that the opto's LDR part goes in parallel with the output level pot (marked "gain") - forming a voltage divider with the 100K resistor that goes to the output pot?

In parallel with the volume control

Is there any particular reason why you don't use a simple transistor or opamp stage (maybe even running off heater voltage) for the LED-driving - to save a nice ECC82 tube - and to reduce heat and current?

I use a tube connected exactly as you see in my schematic, you may use a resistor in series with the LED say 120-470 ohms, this will tune the slope of the unit. In this particular compressor the same tube tube has been functioning since 1998 with no problems, in my studio. One more thing, it's quite funny and a little aggravating when people sit at their computer (they know who they are) and theorize that an LED cannot be driven like it's shown and I know this to be otherwise. This is a rather simple but excellent device in terms of sound quality and compression give it a try.

Rowan (Analag)

Jakob E.[/quote]

 

[analag]

I love it when you hate me guys, but somebody will build this compressor and love it as much as I do. I might sound arrogant but their are a lot of ridiculers and egotists in here, kids I assume. Thanks to those who offer me a warm welcome. I am here, and with a new project real soon, maybe this weekend. What shall it be, something as simple as an adjustable input impedance DI or my high resolution transformerless input Microphone Pre. Well I'm off to firing up my soldering iron can't sit all day and theorize about what will and what won't work. Ha ha

Analag

 

[chrissugar]

The VTL5C4 is not the fastest vactrol, it has a very slow release, 1.5 seconds. That long release probably simulates in a way the memory effect of the T4B optocoupler from the LA2A and that is probably the reason why you don't have distortion at low freq because it responds slowly.
The VTL5C1 is the fastest vactrol available.

By the way I'm sure nobody hates you but I think your behaviour is the reason why many of us are not very happy with you.
Personally I think it is not the best way to introduce yourself.

chrissugar

 

[PRR]

> the same tube tube has been functioning since 1998 with no problems

The opto compressor/limiter I designed (from pure concept, not another LA-2 topology) in 1980 is still in use today, and has now recorded thousands of hours of precious live concerts. I grant that it is not tube. (1980 was a poor time for tubes; also the original use was portable recording)

> kids I assume

Not any more. I remember when kitchen radios and TVs had to warm-up. I fixed, upgraded, and designed (and made a living with) a lot of bottle-stuff before the decline, fall, and rebirth of tubes. That's why I know a 12AU7 is a darn fine resistor and current-limit, and could barely blow-out an LED if it tried.

But this crowd has a mix of people who don't know Ohm's Law, and people who can poke a pin in any ballon. Your sketches and comments could be clearer. A photoresistor should be clearly labeled and its light source indicated with a note or dotted line, otherwise someone is sure to misunderstand. And my non-kid eyes appreciate putting an explicit ZERO in front of decimal points: ".1" looks like "1" to my eyes, especially on a dotty background grid. "0.1" is harder to mis-read. (Yes, I have been known to mis-read "R1" and "R2", and give a long explanation about the wrong resistor.... some days I should just stick to PlayDoh.)

 

[analag]

Ok guys, the thing works and I thought I would share it. As for my dramatic entrance, why not, it's often the best way to feel out a room temper levels and philosophical stand points, I mean. I got some proverbal responses too. Excellent. I even have favorites at this point but this is subject to change in a positive way I'm sure. 29 years at it started well before I was a teenager. As to Mr PRR I will do a better job documenting my schematics in the future. By the way cathode follower and grid feedback aka plate follower equals lower output imedance and very low noise. I hate noise I guess. As the saying goes "it's all good". And now gentle folks it's time for a Heineken or few.

Analag

 

[JustinS]

... I don't think anyone here is uninterested in "original" thinking. NYDave, Fred Forsell PRR (& many more who contribute to The Lab) get a lot of respect for presenting new & original ideas! The fact is as my mum says "You've got to give respect to get respect". Waltzing in to a forum and being mysterious / arrogrant / whatever is never going to win you friends. And your comment about Recording.org being a place "where folks really know what they're talking about" - obviously implying that here people don't... Heck I don't know much about anything, but there are plenty of people here who do, and you know what... the great thing is that most of them are saintly in their willingness to help people of all knowledge levels along the way!

Justin.

 

[analag]

What happened to my thread.

EDIT- Sorry about the fuss. Much of the non-technical conversation has now been moved to the Brewery. -PRR

I've been working on an OTL amp all day and when I get to the forum, I find you people squabbling. Boys it's hard at times to be a man, but tighten your belts and let's get back to the technical stuff. Kubi did you say the schematic got bugs?

Analag