tone thickening mods

[phsyconoodler]

I recently came across a couple of mods that are touted to 'thicken' or fatten the tone of an amp.
One mods was to add a 330pf cap across the input grid resistor and the other was to add a .0033uf cap in series with the negative feedback wire to the speaker or impedance selector.
  Anyone use these mods?I'm going to try them of course,but I was wondering if they are viable mods and don't muddy up stuff too much?

[TIMBO]

Is this one of the mods you are describing, I have no idea if it does make any difference as this amp was designed by a guy called Chris Cornell from the UK and i built it as per his schem, can't say i seen it added to other amps.Great little amp. Also the Marshall jubilee has a cap in series with the input resistor, i'm thinking that this would colour the input signal  Thanks

[Tone Junkie]

Phsyconoodler I do know that the .0033 with the -feedback is a built in resonance mod adds alot if you have shelved bass in the preamp so as not to be muddy they will usually run it in perallel with a 1meg resister. you can search and there is a formula to use to dial in what you want, i just use my cap switching box to find what sounds best, because I seem to be mathmatically challenged  . they have some good discussions at sloclone forum.
Bill

[phsyconoodler]

Timbo,
  I don't see either mods on your stinger amp and the Jubilee has the cap in series and not bypassing the 68k grid resistor.

I'm going to try the resonance this weekend and the bypassed input grid thing and I'll report the results.

[jjasilli]

A cap bypassing the input grid resistor:  for DC operation this seems to resemble series grid biasing, though this omits a cathode resistor:  http://www.tpub.com/content/neets/14178/css/14178_48.htm  This would seem to alter the bias point of the stage, if already cathode biased.  For AC signal operation I'm thinking it's a notch filter, though I'm not sure that's the exact terminology.  Here's some dizzying math:  http://www.allaboutcircuits.com/vol_2/chpt_4/4.html

Cap in series with a global NFB loop -- sounds pretty much like a simplified, fixed Presence control.

[phsyconoodler]

Hmmm....presence control? The cap goes to ground in a presence circuit but this one gets put in series with no ground reference.

[jjasilli]

Probably depends on the values in the circuit, and where the series cap is placed in relation to the series/shunt resistors in the NFB loop.

[plexi50]

Hmmm....presence control? The cap goes to ground in a presence circuit but this one gets put in series with no ground reference.

I have built a few amps using a resonance pot. And man it does work nice. Tightens the bass up nice to
Earth is resonance / Sky is presence. I dont think you can get the whole effect just using a cap alone
It really come alive and is very noticeable using a pot. Gets the full sweep range of more frequency change

[Jack_Hester]

I have built a few amps using a resonance pot. And man it does work nice. Tightens the bass up nice to
Earth is resonance / Sky is presence. I dont think you can get the whole effect just using a cap alone
It really come alive and is very noticeable using a pot. Gets the full sweep range of more frequency change

Do you have a pdf of the schematic for this amp, that I can look at?  I can follow your layout, if I hand-draw a schematic while I'm doing it.  I'm interested in what you've done and it's effects.  Thanks for posting the layout.

Jack

[Boots Deville]

The AX84 "October" schematic shows an example of a Resonance control.

At AX84.com it can be found under "Associate Projects".

Here's a direct link to the PDF.  The resonance option is on page 3.
http://ax84.com/october/October_Club_101010.pdf

-John

[Tone Junkie]

Here is another one showing the resonance control this is SDM,s site it has some great info like Sluckeys site does just differant stuff.
Thanks Bill
http://home.comcast.net/~jbjdav26/Resonance1.jpg

[darkbluemurder]

I recently came across a couple of mods that are touted to 'thicken' or fatten the tone of an amp.
One mods was to add a 330pf cap across the input grid resistor

I read about that as well but I think the guy that posted it made a reading error. The cap value should probably be 330nf. With a 330pf over a 68k you get a corner frequency for the boost which is so high that not even bears, cats or dogs can hear a discernible difference. Well, bats maybe :)

and the other was to add a .0033uf cap in series with the negative feedback wire to the speaker or impedance selector.
  Anyone use these mods?I'm going to try them of course,but I was wondering if they are viable mods and don't muddy up stuff too much?

I used a .01 cap in two 100W Marshalls. Really pumps up the bass.

Cheers Stephan

[phsyconoodler]

Does it do it in a good way without muddying up the tone?

[jjasilli]

I read about that as well but I think the guy that posted it made a reading error. The cap value should probably be 330nf. With a 330pf over a 68k you get a corner frequency for the boost which is so high that not even bears, cats or dogs can hear a discernible difference. Well, bats maybe :)

Seems right, also a cap in that position will defeat the grid stop function of the input resistor, and pass RF noise into the first stage.  So if a cap is used, it might be good to follow it with a grid stopper.

[plexi50]

I have built a few amps using a resonance pot. And man it does work nice. Tightens the bass up nice to
Earth is resonance / Sky is presence. I dont think you can get the whole effect just using a cap alone
It really come alive and is very noticeable using a pot. Gets the full sweep range of more frequency change

Do you have a pdf of the schematic for this amp, that I can look at?  I can follow your layout, if I hand-draw a schematic while I'm doing it.  I'm interested in what you've done and it's effects.  Thanks for posting the layout.

Jack

Here you go Jack. Sorry for the delay in answering your question.

[Jack_Hester]

Here you go Jack. Sorry for the delay in answering your question.

Thanks a lot!  I'll give it a good study now.  Have a good one.

Jack

[Jack_Hester]

Plexi50 -

By the way.  What software did you use to make your schematic?  Very clean look.  Thanks.

Jack

[plexi50]

I did not make the schem or layout. I got it off the web 5 or so years ago when there was a lot of new stuff poppin up online

[xm52]

A cap parallel to the input grid resistor in this configuration is, effectively, a high pass filter. Some call it a bright cap.  The lows are removed so the input sounds brighter.

[HotBluePlates]

Don't look at it as removing lows.

There is a voltage divider on that input circuit, made of the 100k resistor and 5.6M resistor. The cap across the 100k allows highs to bypass the 100k resistor, unattenuated. The rest of the signal is attenuated by the divider. By this action, the highs appear "boosted" when they are simply not reduced along with the rest of the signal.

So the cap by itself doesn't remove lows, so much as it allows highs to not be reduced.

[tonewood]

I'm going to try them of course,but I was wondering if they are viable mods and don't muddy up stuff too much?

Phsyconoodler- did either of the mods pan out?

Thanks

[moonbird]

So the cap by itself doesn't remove lows, so much as it allows highs to not be reduced.

So then it is like a "treble bleed" installed on the vol pot on a guitar - is that right? thx.

[jojokeo]

So the cap by itself doesn't remove lows, so much as it allows highs to not be reduced.

So then it is like a "treble bleed" installed on the vol pot on a guitar - is that right? thx.

yep, that's all it is.