Some questions on ROG Omega

[Ucho]

I've got a couple of questions about Runoffgroove Omega

1) Is the Mosfet stage a unity gain buffer or it also amplify the signal coming from the first stage ?

2) Is the whole circuit inverting?
If I understand correctly, since the Jfet stage inverts and the mosfet does not (because the signal is taken from source), it is. Am I right?
If yes, how to make the circuit non-inverting (besides adding something like RG Keen's polarity reverser)? Maybe taking the output from mosfet drain, but how to do it without altering the behaviour of the stock circuit (if possible)?
Or we could just add another inverting stage which has to be 'clean' and unity gain. Where to put it?
Also, if there's no simple solution, if I'd want to add the said polarity reverser, I shouldn't add it at omega output since it will be pretty high, since it's a booster... so maybe putting it in front of the omega?

The reason behind all these questions (now I realize they're more than a couple, sorry ) is that I'm going to put it in a box with a fuzzface clone (which should be non-inverting, but even if it's inverting it's not a problem, see below) in parallel with a clean signal (or slightly overdriven with a Peppermill), maybe using ROG Splitter-Blend.
If you are wandering why i just don't use the Splitter-Blend integrated polarity reverser, that's because the omega will be footswitchable. So, if i set it up to be in phase with the clean signal when only the fuzz is on, it will be out of phase when the omega is added, while if i set it to be in phase when both the fuzz and the omega are ON, it will be out of phase when the omega will be bypassed....

So, back to THE question: IF the omega is inverting, how to make it non-inverting?

[Ucho]

Bumping...

IF the omega is inverting, how to make it non-inverting?

Any hints?

[oskar]

The Omega inverts

try this inverter in between the level pot and output cap...



oskar

[Ucho]

Thank you oskar.

It looks vaguely similar (altough different) to Geofex Polarity Reverser (also used in ROG Splitter-Blend).

Wouldn't placing it at the output of Omega saturate the IC due to omega high otput level?
Maybe placing it in front of the circuit would avoid this problem?

[Ucho]

What about taking the output from the mosfet drain, placing a 10k fixed resistor in place of the master pot, and then using pot (10k-100k) wired as a 'classic volume pot'?

[soggybag]

Couldn't the circuit be modified so the MosFET was non-inverting? FET's and BJT transistors can work in a non-inverting mode. Or would this break the special quality of this circuit. Maybe the FET input buffer could be changed to a non-inverting arrangement?

[Ucho]

Couldn't the circuit be modified so the MosFET was non-inverting?

The problem is that the mosfet stage IS non-inverting, making the whole circuit inverting because of the first stage (which is inverting). If the mosfet stage was inverting, than the whole circuit would have been non invertig (-1 x -1)

Actually, if I understand correctly, in a mosfet the otuput from the drain is out of phase to the input (at its gate), while the output from the source is in phase.

Anyway, that (modifng that stage to make it inverting) would be my preferred solution.
But I think that taking the output from drain vs source has also other differences (impedance, and maybe 'volume').
For example, IIRC, in AMZ Mosfet Booster article, Jack suggests a mod where you could take the output from the mosfet source (instead of its drain as the stock circuit) to have a very low output impedance, but also (again, IIRC) a lower output volume, to use it as a buffer (and actually that is the role of the mosfet stage, as stated in the Omega article).

would this break the special quality of this circuit.

That's was I was thinking about... i really don't know

Maybe the FET input buffer could be changed to a non-inverting arrangement?

Actually, the FET stage, I if am not wrong, isn't a buffer (which the following mosfet stage is, reading the article).
I also think that a non inverting stage has less gain than an inverting one, but, again, I don't know very well the argument (and maybe my the last sentences contain a lot of wrong things... in that case please correct me).

I think that I could just place a polarity reverser (as the RG keen's or oskar's ones) in front of the circuit. I think it should work.
But I'd like to know if there's some other solution, maybe working on the circuit it's just a matter of some small changes....

[petemoore]

  transformer ?
  I've never seen one used as an inverter but it seems like it would invert.
  Makes the circuit look cool too.

[Ucho]

Thank you peter, I really appreciate how you're trying to help us noobs.

  transformer ?
  I've never seen one used as an inverter but it seems like it would invert.
  Makes the circuit look cool too.

I have no idea on how to apply this, but I agree it would make the circuit look good.

Actually, if I have to add some circuit to invert the signal then maybe I would go with RG's polarity reverser, if there isn't any simpler alternative.
As I said before, I'd really like to understand if it would be possible to simply work on the circuit itself, maybe on the mosfet stage, without adding any other circuit...

BTW, again, thanks for the input.

[Celadine]

Transformer as inverter - see the lower section of the wob*l*tor - 'phase switch':
http://www.aronnelson.com/DIYFiles/up/Wobulator_v3.pdf

[Ucho]

Thank you Celadine.

So it's just a matter of which lug of the secondary goes to output and wich one goes to ground?
From the schem, having the input signal on "upper" lug of primary, and ground on lower one: if output is taken from the upper lug of secondary (lower to ground) the obtained signal is in phase, if the output is taken from lower lug (upper to ground) the signal is inverted.
Did I understood right?

Is only the trasnformer needed for the job?
What kind of transformer is needed (OEP1200?! never heard of... any common substitute?) )

Which solution (transformer vs IC polarity reverser) would perform better (if there's any difference) for what I'm trying to achieve?

[Celadine]

No prob

So it's just a matter of which lug of the secondary goes to output and wich one goes to ground?...if the output is taken from lower lug (upper to ground) the signal is inverted.
Did I understood right?

I hate to qualify this, but I haven't built the Wob yet.  Looks like you've got it right, though.

Is only the trasnformer needed for the job?
What kind of transformer is needed (OEP1200?! never heard of... any common substitute?) )

Its a 600:600 audio transformer, others have recommended the mouser 42TM016.

Which solution (transformer vs IC polarity reverser) would perform better (if there's any difference) for what I'm trying to achieve?

Ah, the transformer definitely gets more mojo points.     Basically, no difference.

[Ucho]

Thank you Celadine.

So it's just a matter of which lug of the secondary goes to output and wich one goes to ground?...if the output is taken from lower lug (upper to ground) the signal is inverted.
Did I understood right?

I hate to qualify this, but I haven't built the Wob yet.  Looks like you've got it right, though.

I guess the words I've used aren't 100% technically correct, but you got the idea 

Its a 600:600 audio transformer, others have recommended the mouser 42TM016.

Thanks, I'll look for it.

Which solution (transformer vs IC polarity reverser) would perform better (if there's any difference) for what I'm trying to achieve?

Ah, the transformer definitely gets more mojo points.     Basically, no difference.

I agree about the transformer mojo factor 
So I can go with it, it also looks very simple to implement.

Do you think would there be any problems placing it after the booster (eg distortion caused by high otuput level from booster or higher impedance after the transformer)?
Or I should place it at omega input?

Again, I thank you Celadine, and sorry for my noobs questions and my noob way of 'explaining' things (not to talk about my noob english writing  ).

By the way, I'm learning a couple of interesting things because of this thread (that's one of the reason why this forum is great), thanks guys

[petemoore]

Do you think would there be any problems placing it after the booster (eg distortion caused by high otuput level from booster or higher impedance after the transformer)?
Or I should place it at omega input?
  A good transformer might cause some signal loss..how much depends on what it depends on...
  600:600 might be a good thing to have around or in there anyway...I really don't know, never tried it.
  I guess just splice one in there and seeing what it does, can't say for sure you'll like it, maybe so though.
Again, I thank you Celadine, and sorry for my noobs questions and my noob way of 'explaining' things (not to talk about my noob english writing   ).

By the way, I'm learning a couple of interesting things because of this thread (that's one of the reason why this forum is great), thanks guys

[Ucho]

  A good transformer might cause some signal loss..how much depends on what it depends on...

Do you mean loss of volume and/or 'tone' loss (losing some frequencies)?

Maybe I could just simply put a one-transistor inverting  buffer/booster-set-for-unity-gain in front of the ciruit... OR i can go with the transofrmer OR with RG's polarity reverser.
I've got a lot of choices

Anyway I still didn't found out to modify (if possible) the circuit itself (the mosfet stage).