Author Topic: “Frequency dependent negative feedback”  (Read 1689 times)

Bolty_Guitars

“Frequency dependent negative feedback”
« on: January 31, 2018, 06:12:15 PM »
Hi folks,

I have recently purchased a KAT treble booster which is the booster which Brian May Now uses. It is alleged by the maker that the circuit is “a radical new design incorporating frequency dependent negative feedback to enhance the band-pass characteristics of the unit”

As a novice this might as well be written in Latin.

I have built a number of treble boosters based around the Geo Fx circuit and have some of them lying around doing nothing. As I’m now using a wirelsss system (which the maker of the KAT booster says Is one of the reasons the negative feedback circuitry was added - to make the booster work better with Brian’s own wireless system) how would I go about creating additional circuitry to create a negative feedback loop which is “frequency dependent”?? It’s something I would like to try so that I can compare and see if it makes any difference!

I have trawled google for examples and explanations but most of what comes up is theoretical and no actual examples of circuits and components!

( KAT circuit is very well gooped so I can’t take a sneak peak)

Thanks
« Last Edit: January 31, 2018, 06:16:35 PM by Bolty_Guitars »

Phoenix

Re: “Frequency dependent negative feedback”
« Reply #1 on: January 31, 2018, 06:35:55 PM »
The vast majority of tube guitar amplifiers have "frequency dependent negative feedback" - the presence control reduces the amount of negative feedback in the high frequencies as it is turned up, therefore giving a perceived "boost" to the treble when turned up (actually a cut in other frequencies). Some amps also feature "resonance" controls (might be called something else like "deep" or "ultra", etc), which reduce negative feedback in bass frequencies when turned up.

The "radical new design" is just marketing-speak.

GibsonGM

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Re: “Frequency dependent negative feedback”
« Reply #2 on: January 31, 2018, 06:44:17 PM »
The "radical new design" is just marketing-speak.

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Phoenix

Re: “Frequency dependent negative feedback”
« Reply #3 on: January 31, 2018, 06:49:17 PM »
Oh! You know what, forehead slap moment! But I completely forgot active tone controls like the Baxandall and others, which are of course, frequency dependent negative feedback! That's VERY common to find in pedals, and just about every classic HiFi...  :icon_wink:


EDIT:
Then there's also things like partial bypassing of emitter/source/cathode resistors (which is really degenerative feedback, but is usually lumped in with "negative feedback" even though it doesn't reduce output impedance or increase input impedance like true negative feedback), or partial collector/drain/anode to base/gate/grid feedback, which is again, frequency dependent negative feedback. There's just countless examples that are common to see in effects pedals.
« Last Edit: January 31, 2018, 06:59:10 PM by Phoenix »

Bolty_Guitars

Re: “Frequency dependent negative feedback”
« Reply #4 on: January 31, 2018, 06:55:22 PM »
I figured it may be marketing speech!

The unit has no tone controls on it, just a gain pot like most other treble boosters so I’m guessing whatever negative feedback circuitry there is, is set/ fixed with resistors and caps.

Probably not doing much then!

Rob Strand

Re: “Frequency dependent negative feedback”
« Reply #5 on: January 31, 2018, 09:42:02 PM »
Quote
I have recently purchased a KAT treble booster which is the booster which Brian May Now uses. It is alleged by the maker that the circuit is “a radical new design incorporating frequency dependent negative feedback to enhance the band-pass characteristics of the unit”

Despite the possible marketing spin:   Frequency dependent feedback does change the sound.   It isn't the same as EQ because when a stage clips the feedback is removed so the effect the feedback network will either do nothing or something different.
The internet:  answers without the need for understanding.

Transmogrifox

Re: “Frequency dependent negative feedback”
« Reply #6 on: January 31, 2018, 09:52:24 PM »
This also begs the question about whether this is something like a compressor or expander with a filter in the side-chain...

I just don't know what this thing is, but either way I agree it doesn't sound revolutionary in any case.
trans·mog·ri·fy
tr.v. trans·mog·ri·fied, trans·mog·ri·fy·ing, trans·mog·ri·fies To change into a different shape or form, especially one that is fantastic or bizarre.

antonis

Re: “Frequency dependent negative feedback”
« Reply #7 on: February 01, 2018, 06:09:51 AM »
Excuse me for my ignorance (bliss..) but isn't ANY capacitance including negative feedbcak loop "frequency dependent"..??  :icon_redface:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

EBK

Re: “Frequency dependent negative feedback”
« Reply #8 on: February 01, 2018, 06:36:50 AM »
Excuse me for my ignorance (bliss..) but isn't ANY capacitance including negative feedbcak loop "frequency dependent"..??  :icon_redface:
Well, yes.  That was probably just an engineer messing with the marketing folks.  There are also custom-designed isolation-removing metallic signal paths in there, I'm sure.  :icon_wink:
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antonis

Re: “Frequency dependent negative feedback”
« Reply #9 on: February 01, 2018, 07:25:26 AM »
You -sometimes- are tragic, Eric..  :icon_redface: :icon_lol:

edit: Just wrote it to make our post No equal.. :icon_wink:
« Last Edit: February 01, 2018, 07:32:09 AM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Ben N

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Re: “Frequency dependent negative feedback”
« Reply #10 on: February 01, 2018, 07:29:31 AM »
Yeah, there are traces.

EBK

Re: “Frequency dependent negative feedback”
« Reply #11 on: February 01, 2018, 04:34:28 PM »
You -sometimes- are tragic, Eric..  :icon_redface: :icon_lol:
Are you saying that you felt like I was being mean?
« Last Edit: February 02, 2018, 05:38:33 AM by EBK »
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antonis

Re: “Frequency dependent negative feedback”
« Reply #12 on: February 02, 2018, 06:42:26 AM »
You -sometimes- are tragic, Eric..  :icon_redface: :icon_lol:
Are you saying that you felt like I was being mean?
I'm saying that in the Ancient Greek Tragedy nowdays ambigous mean..
(both drama & comedy are equally able to make you shed tears..)  :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

EBK

Re: “Frequency dependent negative feedback”
« Reply #13 on: February 02, 2018, 08:46:07 AM »
You -sometimes- are tragic, Eric..  :icon_redface: :icon_lol:
Are you saying that you felt like I was being mean?
I'm saying that in the Ancient Greek Tragedy nowdays ambigous mean..
(both drama & comedy are equally able to make you shed tears..)  :icon_wink:
Ok.  I understand now.  Thanks for clarifying.   :icon_smile:
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"I want to go back to being weird. I like being weird. Weird's all I've got. That, and my sweet style." --Maurice Moss