Designing to make notes feedback? (REVISED TITLE)

[SILVERGUN]

I've been experimenting with an additional gain stage on an AB763 circuit and I've noticed that one note on the guitar seems to feedback and swell into a harmonic much easier than the rest...effortlessly really
In this case it's the C# on the 14th fret of the B string...I'm sitting in front of the speaker cabinet, and if I pick that note and hold it, it just wants to take off,,,and I like it, and would like to understand more about what is actually happening and how I can design to enhance it throughout more of the guitar's range......I've had a similar experience by adding a ton of gain into the T-wreck circuit, but I'm more interested in figuring out how to do it at moderate gain settings....
I'm sure it's got something to do with boosting the frequencies where the harmonics reside, but how can I make that more predictable?

What makes this happen?... and is there a way to make it happen more consisently?.... and across the entire fretboard?
It seems to be present in some Dumble amplifiers, and this video is a great example of where i'd like to go with it.......
In the video, Larry Carlton uses a volume pedal which was also modified by Mr. Dumble, for a high end boost,,,and it would seem as though that's got something to do with it......any input is greatly appreciated, as the main goal would just be to learn more about how to get closer to this effect in an amp design,,,,without just cloning a Dumble design and not really understanding what is happening.

Thanks to Tubenit for posting this in Video Clips, and giving me something to dream about  
Please see 1:06 and 1:50 in video for prime examples of the magic moments I'm talking about (although it is present through the entire video)

LarryCarlton Emotions Wound Us So

[Willabe]

I'm sure it's got something to do with boosting the frequencies where the harmonics reside, but how can I make that more predictable?

What makes this happen?... and is there a way to make it happen more consisently?.... and across the entire fretboard?

Yes I think that's true but there's more.

It could just be from standing waves in that room. Depending on a room's dimensions certain frequencies can double or even triple.

Or it could be that you have enough volume/energy that the volume continues to shake the string or some of both because their the same thing energy wise in the room. Chicken or the egg.

I have seen, sure you have too, Rory Gallagher and others walk up to their amp stacks when they wanted FB. They would get close enough while having the PUP's facing the speakers that the amps sound would continue to cause the string to ring by itself, FB.  

Many times when playing out at a bar the bass player can hit a certain note and all the glasses and beer bottles will start to dance off the tables.

There are math formulas for determining room dimensions for new construction music rooms, studios, concert halls, etc, so that won't happen.

I saw a picture of the floor of a stage 1 time years ago where Ted Nugent was going to play that night. A roadie had put duct tape down in a large semi-circle/crescent shape on the floor with tape hash marks along different points with a note next to them, A, C, B, etc. When Ted wanted a certain note to feed back he would stand at that spot and let her ring.

I've never seen that picture again or from anyone else's stage and have never read any information on how he figured out how to do it, measurement wise. I'm sure he stumbled on to it playing different gigs over the years and set out to refine it. If the room is large enough it should take any standing waves out of the equation and would then "only"        depend on the amps volume, the guitars PUP's and the guitar itself.    

I have read that if you can get a single note to feed back and then while still letting that note FB and turn your bodies position with respect to the amps speakers, the FB will change from the fundamental feeding back to harmonic FB.


                   Brad          

[SILVERGUN]

I saw a picture of the floor of a stage 1 time years ago where Ted Nugent was going to play that night. A roadie had put duct tape down in a large semi-circle/crescent shape on the floor with tape hash marks along different points with a note next to them, A, C, B, etc. When Ted wanted a certain note to feed back he would stand at that spot and let her ring.

Well that's pretty cool.....never heard that before........ now that's control 

I have read that if you can get a single note to feed back and then while still letting that note FB and turn your bodies position with respect to the amps speakers, the FB will change from the fundamental feeding back to harmonic FB.

I guess that's what we're seeing at 1:50

I wonder what/if any part the actual type of speaker plays?

[Willabe]

Well that's pretty cool.....never heard that before........ now that's control  

Me too, never heard about it before or since. Ted used to try and buy all the Gibson Byrdland's he could so no one could get his sound. Not many were made so at 1 point I seem to recall he had about 2/3rds to 3/4s of them.       Kinda silly they're not easy to play at that kind of volume.

I'd bet he wanted to keep a lid on the FB tape circle thing too.

I wonder what/if any part the actual type of speaker plays?

     But I guess it would act as a filter to some degree at certain frequencies? Mid range humps in the speakers frequencies output curve fall in different places and different dB peaks for different speakers .


                             Brad             

[Willabe]

You've probably have seen this (live from the Baked Potato) but if you notice Carlton's amp is loaded for bear when full up. So much so he probably couldn't control it with the volume pedal full up.

But that's not how he uses it to play. He needs all the volume in reserve for getting it to FB when he want's and to get the nice volume swell with it. He doesn't keep playing when he goes to the FB thing. Watch him, he hits the note and then brings up the volume pedal. He then has to bring the volume pedal back down to play more. It's part of sculpting the FB note, bring it up and bring it back down, with a bend it makes it cry. 

Larry Carlton uses a volume pedal which was also modified by Mr. Dumble, for a high end boost,,,and it would seem as though that's got something to do with it......

It's probably to keep the high end harmonic's in the notes overall tone mixed where he want's it while doing the volume swell. Cut some of the high end sparkle out and it might not have as much of the crying tonal effect he want's.

It's an art, a performing art. If I had a chance to play that same set up where he has the controls adjusted I would not get the same sound. It took him time to develop the technique to get that sound. It really is beautiful.   

http://www.el34world.com/Forum/index.php?topic=11325.msg114162#msg114162


                       Brad     

[Willabe]

I guess that's what we're seeing at 1:50

Yes it is harmonic FB there, how he's getting it? Maybe positioning or maybe with his fingers or maybe both sometimes.    

I just went and listened to both vids of the song and he's getting fundamental and harmonic FB at different times all the way through. Sometimes he starts with the fundamental and gets it to change to the harmonic on the same note.

As far as the modded volume pedal, it's probably just like moding the volume control on a guitar. As you turn down a volume control you introduce a large resistance to the signal and the 1st thing to go is the high end. That's why as you turn down the guitars volume it starts to get muddy.

BTW, Tone Quest Report mag. has printed a wiring diagram a couple of times in past issues, for a 2 HB PUP, 2 volume/2 tone guitar that stops that from happening and they swear by it. Won't work for a Strat.  

So instead of using the guitars VC he's using a foot pedal but it's still the same to the signal.

And he keeps his foot on the pedal the whole time while he's playing. He keeps adjusting the volume as he plays even if just slightly. It's like having a 3rd hand, but he's got it down to where the 2 (right hand/foot) work as 1. He coordinates his foot with his right hand picking at the same time for different tonal/dynamic nuances. Like I said before it took him some time to learn how to do this and to develop it.

Hammond organ players do the same type of thing, always leaving their foot on the volume pedal but just not for FB. Well as long as they're not playing the bass pedals. He could have picked up on this being around Hammond players and re-thought it for guitar?  


                      Brad            

[jjasilli]

Resonance:  http://en.wikipedia.org/wiki/Resonance

[SILVERGUN]

I wonder what/if any part the actual type of speaker plays?

   But I guess it would act as a filter to some degree at certain frequencies? Mid range humps in the speakers frequencies output curve fall in different places and different dB peaks for different speakers .

Maybe that's what makes the EVM 12L a speaker of choice for LC.......from what I've read it's got more of broad high end response than most typical commercial guitar speakers....

You've probably have seen this (live from the Baked Potato) but if you notice Carlton's amp is loaded for bear when full up. So much so he probably couldn't control it with the volume pedal full up.

But that's not how he uses it to play. He needs all the volume in reserve for getting it to FB when he want's and to get the nice volume swell with it. He doesn't keep playing when he goes to the FB thing. Watch him, he hits the note and then brings up the volume pedal. He then has to bring the volume pedal back down to play more. It's part of sculpting the FB note, bring it up and bring it back down, with a bend it makes it cry.

RIGHT....I like where you're going with this......have the amp set to "take off" but use the volume pedal as the limiting factor


And, I understand that this is a combination of elements that come together to make this happen.........the volume pedal needs to allow the highs to pass at lower volume settings,,,,simple right, and comparable to the application of bright cap on a volume control

[SILVERGUN]

Resonance:  http://en.wikipedia.org/wiki/Resonance

Thanks jj,,,great reading there.....of course, the internet is my friend

Is this something that you've given much thought to?

[SILVERGUN]

This has me thinking....and that's a good thing...
I'll just continue to throw stuff out there, because it will allow others to correct my thinking or expand on the theme....

Could I be inhibiting this harmonic feedback effect in my amps by using high value (470K) grid stoppers, between stages on the preamp tubes?,,,,,,,obviously yes,,,right?

[Willabe]

Maybe that's what makes the EVM 12L a speaker of choice for LC.......

   But is that the speaker he prefers for all his amps or just for the Mesa?

RIGHT....I like where you're going with this......have the amp set to "take off" but use the volume pedal as the limiting factor

I'm not going anywhere with this, it's just what he's doing. It's just how it works for his set up.    

And, I understand that this is a combination of elements that come together to make this happen.....

Yes there are a number of things coming together including who's driving the rig and how he's driving the rig. Put me in the best machine built for the Indy 500 and I'm not going to win, in fact I'd crash in the 1st lap or 2.

I'm not saying you can't learn it but you still have to learn how to make it happen playing wise. Meaning if you build an amp where in the right hands it will do what his amp(s) can do with a volume pedal and you can't get it to happen, then you keep tweaking trying to make it happen. You might miss it but then again you might not. I'm not trying to discourge you but it is something to consider and not rule out.  

How many players that can play like that, that FB sound and tone? I can't think of any. Santana and others get FB but it's just FB of a note or 2 at times. Not the same thing at all. Even a small amp set at PUP height on a chair, turn up the amp, hit a note, get the PUP's close enough to the speaker so the speakers volume keeps pushing/shaking the string and FB. I've done it with my BF PR on about any note I wanted to.

the volume pedal needs to allow the highs to pass at lower volume settings,,,,simple right, and comparable to the application of bright cap on a volume control

Sorry, I should have been more clear on that. As I remember it was you who posted back some time ago that his volume pedal was modded to increase high end as he turns it UP not as he turns it down. And I wrote both in different sentences, that it increased and decreased highs as you push the pedal down in volume. That was my mistake. You'll have to nail that down because it will make a huge difference which way the high end boost goes when moving the VP treadle up or down.  


                  Brad    


Edit; Jimi and Jeff Beck get FB while doing bends with their fingers and using the wang bar.

[Willabe]

Could I be inhibiting this harmonic feedback effect in my amps by using high value (470K) grid stoppers, between stages on the preamp tubes?,,,,,,,obviously yes,,,right?

I would say no not obviously.

1. If you have so much gain in the preamp that you need to have a large enough grid stop, so you have to use them. Or maybe decrease the gain to use smaller GS's? It might be a balancing act? I've only seen him use a Mesa amp, that I recall anyway. If you know which Mesa he's using look at it's schemo for ideas. If it's a dumble good luck.

2. I've seen Kevin O'Connor write a number of times that series resistance in high gain amps adds to the smoothness and sustain of the distortion.

3. Tubenit and Geezer have worked on many different designs to get a very smooth sustain sounding amp and they use some large grid stoppers and some large series R's in them.



                     Brad      

[jjasilli]

I've been toying around the edges of hi-fi including speaker building. Here resonance is a bad thing, because unwanted notes spontaneously arise which are not part of the actual signal of the music program.  All pieces of matter have a natural resonance.  If you apply energy to matter, knock on it for example, it will vibrate and produce a tone.  The tone its natural resonant frequency.  

The soundboard of an acoustic guitar is often designed to resonate at A-flat, if you tap on it.  Hence an amplified acoustic guitar tends to resonate & feedback at about 100Hz.

Sustain is a feature which may be desirable in the production of tone of an electric guitar.  This can happen by "accident".  The guitar string produces its fundamental note plus harmonics, which are higher pitched overtones.  The amp doesn't know they are harmonics and treats them all as fundamentals.   Every time each note goes through an amplification stage, new harmonics are generated by the tube which get amplified by the next stage.

Then there's IM -- intermodulation distortion.  If 2 (or more) notes go through a tube amplification stage (second order distortion), then a specific set of new harmonics will be created.  E.g., if the fundamental notes are 100Hz and 250Hz, the output tones will be 100, 150, 200, 250, 350 & 500Hz.  With all these overtones being generated, and given enough volume, at some point the guitar-amp-speaker-venue combination is bound to go into oscillation & resonate at its natural frequency.

It is also possible to purposefully design a circuit to oscillate and feedback at specific resonant frequencies.  

[Willabe]

I forgot, pedal steel players keep there foot on a volume pedal all the time too. They keep a lot of untapped volume on hand. Hitting harmonics and hang a note or slide a chord up or down, then turn up the volume for longer sustain. They do that all the time.

Carlton knew/saw that too.


             Brad    

 

[jjasilli]

Good point!

[SILVERGUN]

I forgot, pedal steel players keep there foot on a volume pedal all the time too. They keep a lot of untapped volume on hand. Hitting harmonics and hang a note or slide a chord up or down, then turn up the volume for longer sustain. They do that all the time.

Carlton knew/saw that too.

That explains where the Sho Bud volume control on his board came from........I'm glad I brought this up because it's starting to make more sense to me just by talking about it....

2. I've seen Kevin O'Connor write a number of times that series resistance in high gain amps adds to the smoothness and sustain of the distortion.

Well, that also explains some of what i'm seeing in the dumble schematic that I was looking at and questioning.........where he'll have a series 100K before the grid leak (usually pot) and then a moderate value grid stopper

[SILVERGUN]

Sorry, I should have been more clear on that. As I remember it was you who posted back some time ago that his volume pedal was modded to increase high end as he turns it UP not as he turns it down. And I wrote both in different sentences, that it increased and decreased highs as you push the pedal down in volume. That was my mistake. You'll have to nail that down because it will make a huge difference which way the high end boost goes when moving the VP treadle up or down.  

Yeah... I went back and found that,,,and I was actually quoting a quote from LC's tech:
Alexander brilliantly installed a small 9V circuit board, which boosts the highs proportionately to the output level; typically Sho-Buds tend to lose highs in that process.
 
and,,,I'm still not sure what it means, but i'm going to assume that it would be like any other volume control, and lose highs naturally as the resistance is increased.......so it was modded with a "bright board" to counteract that occurance,,,and increase highs with the pedal backed off at lower volume,,,,,allowing those harmonics to come through even with the pedal at a minimum setting

Is a typical ShoBud volume pedal active or passive?

[SILVERGUN]

Yes there are a number of things coming together including who's driving the rig and how he's driving the rig. Put me in the best machine built for the Indy 500 and I'm not going to win, in fact I'd crash in the 1st lap or 2.

I'm not saying you can't learn it but you still have to learn how to make it happen playing wise. Meaning if you build an amp where in the right hands it will do what his amp(s) can do with a volume pedal and you can't get it to happen, then you keep tweaking trying to make it happen. You might miss it but then again you might not. I'm not trying to discourge you but it is something to consider and not rule out.   

Don't worry too much about that....I got this 
We're all chasing something,,,,right?
For me to be inspired by sound after all of this time is amazing,,,,and i'm very happy that I have figured out how I want to sound when I grow up 

I've always been a heavy player, but more inspired by Gilmore than Satriani,,,,,,this fits right into my dream of how it should be....

I know your not much for the whole high gain scene,,but you must admit, this is a pretty cool use for it

[Willabe]

Alexander brilliantly installed a small 9V circuit board, which boosts the highs proportionately to the output level; typically Sho-Buds tend to lose highs in that process.

Yeah that's not worded very clearly is it? Hmmm.....  

That explains where the Sho Bud volume control on his board came from........

He's a studio guy and Sho Bud volume pedals were considered, still are I think, THE BEST ever for ease of foot movement control and for reliability/toughness. They go for big bucks if you can find one and that's been for a long time.

Is a typical ShoBud volume pedal active or passive?

Passive.


             Brad    

[Willabe]

Well, that also explains some of what i'm seeing in the dumble schematic that I was looking at and questioning.........where he'll have a series 100K before the grid leak (usually pot) and then a moderate value grid stopper

Too much signal you have to get rid of some of it or you'll get nasty sounding grid blocking distortion. All high gain amps do it.

Notice the small value pot also. 100k pot lets more signal bleed to ground than a 250K,500K or 1M.

Look at what JJ just posted in another thread today on this very topic;

http://www.el34world.com/Forum/index.php?topic=16012.msg155898#msg155898



             Brad      

[tubeswell]

If the gain of the circuit produces sufficient gain in the frequency bandwidth that corresponds to the resonant frequency of whatever string on your geetar does it for you, that ought to ring your bell and produce the mojo you are craving.

And it doesn't require as much gain as you might think. For example, with the vol and tone dimed, even a simple a supro t-bolt circuit can do this with several types of guitars, even single coil guitars. In fact in lots of ways, the simpler the circuit the better. Even a tweed deluxe or a tweed tremolux etc with a fuzz pedal in front of it can be made to behave like this.

[Willabe]

We're all chasing something,,,,right?

Yep.

For me to be inspired by sound after all of this time is amazing,,,,and i'm very happy that I have figured out how I want to sound when I grow up  

That's good.

I've always been a heavy player, but more inspired by Gilmore than Satriani,,,,,,this fits right into my dream of how it should be....

I like Gilmore but to me some of his best work is on the Another brick in the Wall album and the lyrics/story line on that are to upsetting to me, so I don't listen to it. Same thing for me with AC/DC, can't handle the lyrics, never could, even when they 1st came out and I was still wild.    

I don't get Satriani at all, but to each his own. I watched an Eric Johnson vid from Austin City Limits the other day, didn't get it either. I just don't hear it.    

If you like it that's good.

I know your not much for the whole high gain scene,,but you must admit, this is a pretty cool use for it

Yes it is very cool sounding. But it's also how Larry Carlton is using it for tonal color for what he want's to pant sound wise.

I like a guitar to sing at times but I don't like the extra noise/crunch is maybe the best way to say it. But that's me if you like it, well.... then you like it. I do like the 2 early big Thin Lizzy albums a lot, but there songs are very melodic not just rock crunch.

Layla and Rory Gallagher's "Irish Tour" album are 2 of my all time favorites, ZZ Top, Tres' Hombres and DiGalos sound great to me. Carlos's 2nd and 3rd albums are great sounding to me. I love The Very Best of Mountain, but again West is a very melodic guitar player. Of coarse the Allman Bro's. and Dickey get's a great tone after D.A. had past.      I love a lot of Joe Walsh songs, solo and with the Eagles. The other Eagles guitar player, I forget his name, has/had great tone to. Stuff like that I love.

I love the 2 guitar players on the intro for Sweet Jane on Lou Reeds live album, Dick Wagner and Steve Hunter. But I don't listen to it much any more, lyrics. Pretty said to sing about your love for smack.    

Wagner is the guy who really played Train Kept a Roll'n for Joe Perry because at the time he was to deep into the medicine jar to play. 


                Brad    

[SILVERGUN]

Yes it is very cool sounding. But it's also how Larry Carlton is using it for tonal color for what he want's to pant sound wise

And that's good enough for me....I can see myself going more "smooth jazz/blues" in the coming years,,,and this is the way I want to go with it......
Female singer,,,blue lights,,,1 x 12" mini stack 
I've come to the conclusion that I can't cover every base,,,,but this tone is a must for me......
I've never been much of a high speed guy,,,,and I've always used delay to "simulate" sustain.......if we can put these puzzle pieces together and I can get close to this kind of control, it will help light the fire again

Look at what JJ just posted in another thread today on this very topic;
http://www.el34world.com/Forum/index.php?topic=16012.msg155898#msg155898

I did read that and thought it was a great response....I was hoping that someone was going to address his question,,,,,because I was thinking the same question

[Willabe]

and this is the way I want to go with it......
Female singer,,,blue lights,,,1 x 12" mini stack  
and I can get close to this kind of control, it will help light the fire again

If I told my wife "here's what I want to do for my next band, female singer, blue light's...."  she'd do this as I was telling here;  

Your on your own there buddy, not my idea. You don't want to light the wrong fire.   

              Brad          

[Willabe]

I've always used delay to "simulate" sustain.......if we can put these puzzle pieces together

Yeah forgot that, Carlton's known to use a delay and a good compressor, after all he's a studio guy. Probably a little verb too, wouldn't hurt.


        Brad          

[birt]

if you use a stompbox graphic EQ or a rack mounted with the bypass on a footswitch it's quite easy to do a single note feedback. with a full size rack mount EQ you could combine certain frequencies to boost and cut others so you get the exact feedback you want.

[SILVERGUN]

If the gain of the circuit produces sufficient gain in the frequency bandwidth that corresponds to the resonant frequency of whatever string on your geetar does it for you, that ought to ring your bell and produce the mojo you are craving.

And it doesn't require as much gain as you might think. For example, with the vol and tone dimed, even a simple a supro t-bolt circuit can do this with several types of guitars, even single coil guitars. In fact in lots of ways, the simpler the circuit the better. Even a tweed deluxe or a tweed tremolux etc with a fuzz pedal in front of it can be made to behave like this.

I'd like all notes on all strings to want to do this
From an amp design standpoint,,,,how should I be trying to accomplish this?
1) Would it make sense to use smaller series resistance between stages, to allow more highs to pass
2) Should I be more concerned with allowing more highs to pass than a usual amp , because most of the harmonics that I want to amplify exist above the fundamental freq. range of the guitar
3) Are there any existing designs that lend themselves well to this concept (other than the Dumble ODS)
4) I'm also considering switching to a chambered or semi hollow guitar,,,,assuming than will contribute to the goal as well....good idea?
5) What techniques should I focus on to enhance the amps ability to do this?
6) Along the lines of what birt mentioned....would it make sense to use an onboard EQ similar to those on acoustic electrics?

I'm just not ready to let this thread die 

[jazbo8]

What tubeswell said is correct, it is all about generating enough gain in the signal chain (whichever way you get it) to get positive feedback going, then it's a matter of controlling how much and when you want to the feedback to happen (that takes skill and experience).

[SILVERGUN]

What tubeswell said is correct, it is all about generating enough gain in the signal chain (whichever way you get it) to get positive feedback going, then it's a matter of controlling how much and when you want to the feedback to happen (that takes skill and experience).

Thanks again jaz,
I guess ODS it is........why try to improve on perfection?
I am just hoping to learn more about how to make that happen,,,,I guess that's what the breadboard is for

There were times during the Twreck experiments where it would come and go,,,and I tried to harness it,,,and it is tough to not overdo gain while trying to exploit feedback 

[tubenit]

SilverGun,

The amp that I got the most feedback from was the original Tweed Overdrive Special with the 5E3 tone stack.  However, it had a tone like it was a wah pedal (notched in the mide position) also. Not a bad thing just a unique tone.

This was that amp:  http://www.soundclick.com/player/single_player.cfm?songid=9488477&q=hi&newref=1

On that recording, I used the TOS into the Carolina Overdrive Special's power amp with VVR.  Essentially the same power amp as the TOS but it had the VVR added.

I should've mentioned that even though the amp sounded "cranked", that using the VVR in the recording,  the volume was so low that you could've had a conversation over the volume. 

Actually, my recording system is pretty lousy for getting a cranked tone at any significant volume at all. The recording will come out like "mud" and somewhat distorted (not in a good way)

With respect, Tubenit

[jjasilli]

Theory:  http://www.intuitor.com/resonance/circuits.html    http://en.wikipedia.org/wiki/Electrical_resonance    http://rfic.eecs.berkeley.edu/142/pdf/book_chap7.pdf    http://ieeeb.okstate.edu/lecturenotes/EET-4654%20Microwaves/Lecture%2019%20Resonant%20Circuit%20Design.pdf

Guitar specific:  http://www.ehow.com/how_2215450_use-electric-guitar-feedback.html
Boss FB-2 Feedbacker Booster Guitar Pedal Review | Full Compass   
http://diy-fever.com/misc/diy-sustainer/
http://www.hobby-hour.com/electronics/s/cs2-compression-sustainer.php

[tubenit]

That's a pretty cool pedal, IMO.  Thanks for sharing the video.

Tubenit

[SILVERGUN]

The amp that I got the most feedback from was the original Tweed Overdrive Special with the 5E3 tone stack.  However, it had a tone like it was a wah pedal (notched in the mide position) also. Not a bad thing just a unique tone.

Thanks T,
 I'm gonna revisit that schematic and compare it to an ODS and see if I can see any consistencies.....and then take it to the breadboard and see if I can exploit anything that might turn it into a feedback machine  .......

[tubenit]

Something I would experiment with is trying an input resistor that is somewhere between 10k-22k (22K is what Dumblish amps seem to use alot).

Typically, I use 33k but have experimented with values down to 10k and it does give it a more "pushed" sound.

With respect, Tubenit

[SILVERGUN]

Thanks jj....
I always thought I wanted one of those pedals,,,and then after seeing LC do it without one I was more interested in what is actually making that happen....so I also really appreciate those theory links

I have also recently looked into the fernandes sustainer (similar to that DIY sustainer).....and again,,,just wondering if there is an approach that I can take while voicing a new amp that would make this more likely to happen....
I'm sure that a lot of guys spend a lot of time trying to reduce positive feedback  

What if any effect does LNFB have on a stages ability to "generate" feedback?

[tubenit]

What if any effect does LNFB have on a stages ability to "generate" feedback

In my experience, it totally kills the ability to generate feedback. I have removed the LNFB on every amp or D-ator that I tried it on. Actually on the D-lator I put it on a switch and never used it.

I should've mentioned that using the midboost and PAB together contributes ALOT to notes blooming ....... sustain...........& feedback.  Downside for me is the amp has alot of hiss with the PAB engaged. And I don't care for that.

With respect, Tubenit

[SILVERGUN]

Something I would experiment with is trying an input resistor that is somewhere between 10k-22k (22K is what Dumblish amps seem to use alot).
Typically, I use 33k but have experimented with values down to 10k and it does give it a more "pushed" sound.

That makes sense.....the lower the value there,,,the easier highs will pass

My welding machine mind wants me to believe that more current through that first stage would help too  ...
So maybe a 220K plate load resistor on that first stage makes sense....
I guess it makes more sense to try to generate the feedback in the early stages?...(similar to the outboard devices)

What if any effect does LNFB have on a stages ability to "generate" feedback

In my experience, it totally kills the ability to generate feedback. I have removed the LNFB on every amp or D-ator that I tried it on. Actually on the D-lator I put it on a switch and never used it.
I should've mentioned that using the midboost and PAB together contributes ALOT to notes blooming ....... sustain...........& feedback.  Downside for me is the amp has alot of hiss with the PAB engaged. And I don't care for that

Thanks again,,,,you probably have mentioned that somewhere before.......I'm not real big on switching,,,BUT, in this case it might be cool to just have the mid-boost and PAB on one switch ,,,labeled "feedback inducer"      "FI".......and include maybe one other critical component, so with that switch engaged,,,it's a feedback machine......switch off, and it's a rhythm machine
I like the idea of that approach a lot!

[tubenit]

I keep thinking of things I've tried that have helped induce feedback.

Dropping the resistor values prior to the OD trim pot.  And trying different cap values across OD trim, OD send and OD level. 

Ironically, each amp seems to be different regarding where a silver mica or ceramic cap across the OD pot wiper to side would work.  In other words, on one amp it may sound across the trim pot ......... then another across the level pot, then another across the send pot and so on.   

I also found the value and type of cap mattered.  Sometimes a ceramic cap sounded "better" than the silver mica and sometimes it didn't.  I'd try values from  120p to 390p on those pots.  This can easily be done with an assortment of caps and two wires with insulated alligator clips.

To recap ................. IF I were having feedback as a goal, I'd probably:

- build the TOS with 5E3 tone stack or use the typical Dumblish tone stack with
  PAB and midboost

- lower the resistor value into the OD trim pot (or even remove it)

- try caps across each of the OD pots to side

- lower the input resistor to 10k - 22k range

- maybe have a 10uf cathode cap on the first gain stage of the OD section.

With respect, Tubenit

[SILVERGUN]

I'm sure you've said all of this before,,,and I really appreciate you taking the time to consolidate all of these thoughts here...

I'll try to take my time and report actual results for each action taken...

It's gonna take me a week to get back to the bench, but at least I have a focus now.

[HotBluePlates]

Well that's pretty cool.....never heard that before........ now that's control  

Me too, never heard about it before or since.

Slash did something almost exactly the same... have a roadie mark the spots on the stage where his guitar would feed back.

... Ted used to try and buy all the Gibson Byrdland's he could so no one could get his sound. ...   Kinda silly they're not easy to play at that kind of volume.

I once played an ES-330TD through a Super Reverb on ~6-7. I had to fight to keep any note from feeding back. The ES-330TD is like a 335 but has no block running down the center of the body. So the acoustic resonance of the body just made every note want to howl. Controlling that could be a nightmare.

Which reminds me: is your guitar resonant acoustically? I have a very-light ash-body Tele with 3 brass barrels for the bridge. If I put my ear against the body, I hear all notes played *loud and bright*. Any given note can be felt ringing/vibrating in the neck and though the body. Certain notes will tend to have prominent harmonics, like the G on the B-string @ the 8th fret. Even acoustically, that one tends to ring as a fundamental then sustain into an octave-up harmonic. It's very noticeable amplified and with distortion.

For both of these, the guitar can influence feedback notes.

In the video, Larry Carlton ...

... sounds like he's got the amp loud, and with a sh!t-ton of distortion. The teble also seems to be turned down a bit, so the distortion may not be obvious at first.

I played one of Tubenit's amps once, recording a solo for a blues song. Listening back to the recording it sounds as if I'm playing fairly-clean unless I hit a double-stop. Two notes together make it obvious there's a lot of distortion going on. To me, Larry's sound is like it's so distorted it has started to become smooth-sounding and almost-clean again. Treble roll-off keeps the top from getting harsh in this case.

And I'm pretty sure you know if you add enough gain to any guitar/amp setup at any volume level, you'll eventually get feedback sustain.