Presence contol placement within NFB loop

[12AX7]

I was reading robrobinette's site and noticed he mentions that the presence works differently (seems to suggest "better")  when on the OT side of the NFB resistor. Anyone know what sort of difference it makes?

[acheld]

Just to be clear, we're talking about this page, right?  https://robrobinette.com/Voicing_an_Amp.htm#Presence_Control

His explanation doesn't make sense to me -- if you look at the schematic he is referencing, the presence control pot does not take input directly from the OT.   However, the resonance pot does, and maybe that is what he is really talking about -- putting the resonance circuit before the NFB resister. 

I'm not sure how much difference it makes putting the resonance control before the NFB resistor, but this is usually where it is placed in several modern circuits that I've reviewed recently.

[12AX7]

Yeah, he says "Generic Presence Control circuit. The Presence cap sends high frequencies to ground. The Presence pot varies how much high frequency signal is sent to ground. Removing high frequencies from the negative feedback circuit boost highs at the speaker. Placing the cap on the output transformer side of the NFB resistor will give best control authority."
I tried it and the amp lost about 90% of it's volume. I checked over and over to make sure i did it right. So i must be doing something wrong but for the life of me i can't figure it out.

[sluckey]

Yeah, he says "Generic Presence Control circuit. The Presence cap sends high frequencies to ground. The Presence pot varies how much high frequency signal is sent to ground. Removing high frequencies from the negative feedback circuit boost highs at the speaker. Placing the cap on the output transformer side of the NFB resistor will give best control authority."
I tried it and the amp lost about 90% of it's volume. I checked over and over to make sure i did it right. So i must be doing something wrong but for the life of me i can't figure it out.

What the heck is "control authority"?

I see those beers have worn off already.   

[12AX7]

They have indeed, and as to control authority who knows. I just thought this is something new i never tried so i'm always up for potential improvements. Either i made a mistake for HIS beers hadn't worn off when he wrote that.

[sluckey]

That was a Generic Presence Control circuit. You probably didn't have a proper generic amp to do the test. 

[pdf64]

It’s disappointing that Rob resorts to this type of nonsensical hyperbolics, doesn’t even bother explaining how to arrange a presence control with its cap like that 
If you can’t baffle them with science, blind them with BS.
It’s

[shooter]

 
I've always used it "If you can't charm them with wisdom, baffle them with B.S."

[bmccowan]

And if you can't baffle them with B.S. - well, you just ain't tryin' hard enough.

It’s disappointing that Rob resorts to this type of nonsensical hyperbolics

Especially since that is Gerald Weber's job.

[PRR]

It’s disappointing that Rob resorts to this type of nonsensical hyperbolics,... ....blind them with BS.

It also says "harrier", which is a jump-jet.

Instead of deserving vitriol and personal slander, maybe it just needs another editing pass? It's a MASSIVE page with tons of info.

[pdf64]

..
Instead of deserving vitriol and personal slander, maybe it just needs another editing pass? It's a MASSIVE page with tons of info.

Apologies, I didn’t intend such a strong effect.

[dwinstonwood]

...maybe it just needs another editing pass?

Or, two. I'm sure that an "NFB loop witch" is not some sort of electrical gremlin, but a typo.

[tubeswell]

an "NFB loop witch" ... .

which ole witch

[pdf64]

… I tried it and the amp lost about 90% of it's volume. I checked over and over to make sure i did it right. So i must be doing something wrong but for the life of me i can't figure it out.

I can’t think how to implement a presence control with its cap on the output transformer side of the NFB resistor 
How did you do it?

[12AX7]

… I tried it and the amp lost about 90% of it's volume. I checked over and over to make sure i did it right. So i must be doing something wrong but for the life of me i can't figure it out.

I can’t think how to implement a presence control with its cap on the output transformer side of the NFB resistor 
How did you do it?

just by swapping it to the other side of the nfb resistor

[pdf64]

Ah, there's a helpful diagram by that text 

I can't see how that's going to even function as an active control?
Seems to be a passive tone control across the amp's output, with minimum treble at lowest control resistance, contrary to the 'turn up for more presence' note?

[acheld]

What the heck is "control authority"?

Well, Robbie is a pilot, after all, and in that world it simply means that when you give a command via the control stick, the airplane responds accordingly -- you would think that is a given, but there are situations when it is not so.

Taking the analogy to its logical conclusion, I'd assume that he means that when you turn the knob, you can hear the difference. 

All that aside, there are plenty of good suggestions on his website.  I regard them as a smorgasbord . . . to be sampled, but not necessarily copied.    This is one that needs some work IMO.

[sluckey]

I get the military image of a Sergeant shouting "GIVE ME MORE PRESENCE!" and the pot responding "SERGEANT, SIR YES SIR". 

[dwinstonwood]

All that aside, there are plenty of good suggestions on his website.  I regard them as a smorgasbord . . .

Rob's site seems to be one of the first places new builders like me come across. I agree there's lots of good info there that's explained in a no-math format with plenty of layout illustrations. Smorgasbord is a good description... take what you want, and leave the rest. But, I was trained to be a hyper-critical text editor. 

[shooter]

SIR YES SIR

they did a great job in bootcamp of drilling that permanently into the brain...then I encountered my 1st Female officer
after 100 pushups on the spot, I was sent to PT (physical training) where you ran until you puked, I refused to puke but after 4hrs I did manage to pass out 

[sluckey]

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