Transformer Coupled Splitter - power switching

[zpyder]

Hey ya'll.  As I understand it, in R.G.'s Transformer Coupled Splitter at http://www.geofex.com/FX_images/splitter.gif, the entire top section (2N3904, 2N3906, 4.7k resistors,...) is only to switch two batteries on an off based on whether or not the input is connected.  Having said that, I think I'll leave it out of my build since I will be running it by adapter only.

However, do the 27uF/.1uF cap pairs in that section perform any filtering function?  I see that I will set GND to 0 volts by grounding both +9v and -9v, but should I ground them again through the capacitor pairs?

And also, when a plug is inserted into the input jack, a connection to ground is made available which goes through that first 4.7k res and then to the base of a 2N3904.  I'm wondering if I need to recreate that ground connection in another context way when not using the swithcing circuit... It would seem that I would need to, but I can't figure out how/where...

any help appreciated !

thanks,
zpyder

[Pushtone]

Looks like filtering alright. You could know instantly if it makes a difference by breadboarding this and replacing the 47uF/0.1uF with jumpers.
It was said that you can never have enough filtering. You also might have filtering passives in your wall wart, maybe.

How are you doing the +/-9V bi-polar supply with a wall wart? Charge pump?
Did ya get the transformer spec-ed in the gif? Mouser 42TM081? How is that, size wise?

Are you using a TL071 preamp, or another. Not important just would like to know.

Is this related to the vocal effects-loop project? I ask too many questions.

[R.G.]

the entire top section (2N3904, 2N3906, 4.7k resistors,...) is only to switch two batteries on an off based on whether or not the input is connected.

It is, yes.

Having said that, I think I'll leave it out of my build since I will be running it by adapter only.

Does your adapter make both +9V and -9V at the same time (that is, is it truly bipolar, or is it alternately halfwave rectified)? This is important because some opamps latch up if one power supply gets to be more than a few volts when the other is not yet started, as it does in the alternat halfwave version. I've actually built an adaptation of that same circuit that turns both sides on only when both sides are over 5V in magnitude, and it keeps latchup from happening.

But then some opamps don't latch on power up, so you may be OK anyway.

However, do the 27uF/.1uF cap pairs in that section perform any filtering function?

Yes, they do. they keep the power supply impedance from both sides low to ground. This is important in bipolar applications. Leave that in.

I see that I will set GND to 0 volts by grounding both +9v and -9v, but should I ground them again through the capacitor pairs?

More to the point, place the capacitor pairs across both the +9V->gnd and -9V->gnd supplies. The caps don't create a ground, they filter the power supplies to ground.

And also, when a plug is inserted into the input jack, a connection to ground is made available which goes through that first 4.7k res and then to the base of a 2N3904.  I'm wondering if I need to recreate that ground connection in another context way when not using the swithcing circuit... It would seem that I would need to, but I can't figure out how/where...

It's not necessary. That path only turns on the power switching. If you remove the power switching, you don't need the path through that 4.7K resistor.

[zpyder]

Thanks for the replies guys,

For my power supply, I have tried using two 9v batteries and I tried using two 9vdc warts.  Maybe I'm wrong there, I'm not sure.  I just wired up the two batteries/the two dc supplies as I saw them in the schematic.  Have I missed something here?

I did figure that those caps are filtering, and I realized after reading the schematic more that the connection to ground made by the input jack was only in fact activating the transistor network which was in turn closing the two dc supplies' connections to the circuit.  So I decided to omit that.

However, latching.  I'd never heard of that before and I wonder if that is what's happening here.  I'm using an LM833.  I plugged the two batteries in at as close to the same time as I could, which was several second apart.  My splitter's not giving an appropriate output.  With the 2 9v batteries, I was able to get a completely distorted, very underdriven signal, with sustain that was so small that it was negative.  Thinking maybe the batteries weren't supplying enough juice, I alligator clipped on two 9vdc adapter outputs, which both measured 12-13vdc on my voltmeter.  Now I get a harsh buzzing at all times, but no signal whatsoever.

Can latching cause an IC to fry?  Specifically my LM833.  If so I guess I'll have to throw this one away and include the entire power switching circuit...

Did ya get the transformer spec-ed in the gif? Mouser 42TM081? How is that, size wise?

Yup I did.  42TM018 actually (not 81).  It's about the size of a quarter, cubed.  and I seem to have seen it spec'd in several schematics...

Are you using a TL071 preamp, or another. Not important just would like to know.

I'm using an LM833 as spec'd.  Does this answer your question?

Is this related to the vocal effects-loop project? I ask too many questions.

No, it's not, though the ideas could very well be used in conjunction.  This is related to my new amp    The 42TM018 is a 1:1 ratio by the way.


suggestions on my bipolar power supply?  Am I doing it entirely wrong...?

thanks,
zpyder

[Pushtone]

Charge pump.

I haven't gotten to it yet myself but the charge pump could do it from one 9v batt or 9v wall wart.

I'm set up to power a FS&H-A1 build this way.

http://www.geofex.com/circuits/+9_to_-9.htm

[zpyder]

Charge pump.

Hmmm... Two independent 9vdc sources will not suffice?  I've seen this charge pump before, but assumed it was a method to get bipolar if you didn't have the convenience of two independent supplies.

zpyder

[R.G.]

However, latching.  I'd never heard of that before and I wonder if that is what's happening here.  I'm using an LM833.  I plugged the two batteries in at as close to the same time as I could, which was several second apart.  My splitter's not giving an appropriate output.  With the 2 9v batteries, I was able to get a completely distorted, very underdriven signal, with sustain that was so small that it was negative.  Thinking maybe the batteries weren't supplying enough juice, I alligator clipped on two 9vdc adapter outputs, which both measured 12-13vdc on my voltmeter.  Now I get a harsh buzzing at all times, but no signal whatsoever.

Can latching cause an IC to fry?  Specifically my LM833.  If so I guess I'll have to throw this one away and include the entire power switching circuit...

Latchup because of power supply sequencing is a subtle one that can bite you. It bit *ME* and I knew about it, at least theoretically. Many opamps have fairly fragile input transistors, and this in combination with the fact that the substrate silicon is isolated by a reverse-biased junction from every single one of the active devices can cause an SCR-like latchup where the whole chip conducts current from the + to the - supply if the "SCR" gets triggered. Some opamps are guaranteed latchup-free on their datasheets, some are not.

I first ran into power sequencing in powering memory chips. Early memory chips used +12, +5V and a -5V substrate bias. You had to bring up the -5 first, then the +5 and +12, with the +12 rising no faster than the +5. If you didn't, you could fry the chip. At that time the hot memory chip was the 1103, which was one K (all of 1024 bits!!!!!!!) and cost about $10 each. They were very fast (about one microsecond access time) and were the cat's meow for mainframe computer memory, which IBM was selling for $1M per megabyte (that being composed of 8196 chips on boards plus parity chips, support logic and testing). Customers took a dim view of their new million dollar memory being fried by your power supply taking a false step.

We've come a long way from there, but you can still hit problems. Opamps still like it if the power supplies ramp up at the same rate, like mirror images of each other. A step to full voltage is OK, but mirror image is nice. Do you have a  double pole switch you can concoct to turn both batteries or power supplies on at the same time? Failing that, turn the negative supply on first. Or try leaving the connection in the middle of the two 9V supplies unconnected and make a resistor/resistor/capacitor "ground" for the circuit. That setup guarantees that you get mirror-image power supplies by forcing the "ground" to always be in the middle.

I don't know that this is your problem, but it's where I'd look next.

But while we're chasing zebras, do yo know that your ground wiring is correct?

[d95err]

Hmmm... Two independent 9vdc sources will not suffice?  I've seen this charge pump before, but assumed it was a method to get bipolar if you didn't have the convenience of two independent supplies.

Two independent 9V adapters would work (wouldn't it?). If you want to daisy-chain one of them to something else, you need to remember if it's using positive or negative ground though.

[zpyder]

Okay, now I'm completely confused.   

I've rigged it up so that the +9v and -9v power sources are switched, as to avoid any latching.  I've replaced the LM833 in case it was damaged earlier.  I can't seem to get anything out of this circuit other than a buzz/hum and a cyclically occasional "flickering" sound.  I checked with my DMM and I'm actually getting around 25vdc across pins 4 & 7.  That should be fine as far as I can tell (datasheet says supply voltage is 36V)...  I'm using this layout, which I created myself: http://aronnelson.com/gallery/transformerABY/Transformer_Isolated_ABY_Perf?full=1.  I noticed that C6 & R10 need to swap places, and also that the connection between R8 and GND needs to be switched - this is to be switched by the stereo input jack.  Both of these I've accounted for here...

Scratching my head  ... I don't see any errors... and I've checked and checked

My only thought is that I'm using my transformers wrong.......?

As far as I can tell from the datasheet, I have them set up right with pins 1 attached to the res,cap/res series,pair after the LM833 output.  pins 3 to ground.  pins 4 to output tips, and pins 6 to output shields.  That is assuming this:
                              ___
                          __|   |__
                        /    |   |   \
833 output ---1  |    |   |    | 6 _______________________  Tip
                        |    |   |    |                |
           N.C.-- 2  | P |   |    | 5 --N.C.     \/\/\/\----| |--
                        |    |   |    |   ___________________|____  Shield
         GND ---3  |    |   |    | 4
                        \  _|   |__/
                             |__|

Can anyone confirm/deny this??


I also did some searching and came upon this: http://geofex.com/FX_images/humfree2.gif.  But I do believe that this version http://www.geofex.com/FX_images/spltr2.gif should work just fine.

!?

zpyder

[zpyder]

Code Select Expand


                       ____
                   ___|   |___
                  /   |   |   \
833 output ---1  |    |   |    | 6 ___________________________  Tip
                 |    |   |    |           |
       N.C.-- 2  | P  |   |    | 5 --N.C.   \/\/\/\---| |--
                 |    |   |    |   _______________________|____  Shield
       GND ---3  |    |   |    | 4
                  \ __|   |___/
                      |___|



[zpyder]

bump - can someone confirm the following 42TM018 pinout when used in this fashion: http://www.geofex.com/FX_images/spltr2.gif?

Code Select Expand


                       ____
                   ___|   |___
                  /   |   |   \
833 output ---1  |    |   |    | 6 ___________________________  Tip
                 |    |   |    |           |
       N.C.-- 2  | P  |   |    | 5 --N.C.   \/\/\/\---||---
                 |    |   |    |   _______________________|____  Shield
       GND ---3  |    |   |    | 4
                  \ __|   |___/
                      |___|



thanks,
zpyder

[Ardric]

The layout in the gallery looks to be for a single opamp.  The LM833 is a dual.

I think you've got the transformer pinout right.

[zpyder]

The layout in the gallery looks to be for a single opamp.  The LM833 is a dual.

Holy crap!!  haha.  I checked the datasheet for the chips that I have and I you're right.  thanks for catching that.  Crap!

zpyder

[zpyder]

Well, I swapped out the LM833 for an NE553, but I'm still not getting satisfactory results....  I'm getting what turns out to be kindof a cool distortion, but certainly NOT the clean signal I want.  Plus this weird "flickering" noise that makes me think of a capacitor that's charging and discharging every second or so...... hmm

zpyder