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bluetweed
12-07-2006, 05:33 AM
What happens when I go lower than the 100K value slope resistor in a blackface circuit?

ChickenLover
12-07-2006, 06:39 AM
Try this (http://www.duncanamps.com/tsc/index.html) and see for yourself. :AOK

Blue Strat
12-07-2006, 07:33 AM
Better yet, install a 33K resistor with a 100K pot in series and HEAR for yourself.

brad347
12-07-2006, 08:25 AM
Will someone be a dear and tell me finally what a slope resistor actually does? Educate me!

donnyjaguar
12-07-2006, 08:28 AM
Tell me more about this 33k & 100k pot, BlueStrat. Are you swapping the Bass or Treble control? What's the net result? Will it get rid of some of the "mid-scoop" (which is what I'd like to get rid of in my one amp) ?

DJ

Blue Strat
12-07-2006, 08:30 AM
Will someone be a dear and tell me finally what a slope resistor actually does? Educate me!

Check out the link above to be sure. It sorta sets the center frequency that the tone controls operate over. Changing the value slides the frequencies at which the tone controls operate, higher or lower in the spectrum.

bob-i
12-07-2006, 08:35 AM
Lowering the slope resistor will add bottom, take away highs and reduce the effectivness of the tone controls. Raising it will have the opposite effect.

brad347
12-07-2006, 08:36 AM
Thanks!!

brad347
12-07-2006, 08:37 AM
Bummer. I'm on a mac and mac isn't supported with the tone stack calculator.

Blue Strat
12-07-2006, 09:42 AM
Bummer. I'm on a mac and mac isn't supported with the tone stack calculator.

Damn! Seen any of the recent Mac TV ads? ;)

brad347
12-07-2006, 11:17 AM
nope. I don't have a TV. :)

What are they like?

Blue Strat
12-07-2006, 11:33 AM
nope. I don't have a TV. :)

What are they like?

The Mac guy tells the PC guy about all the fun things he can do on his Mac while the PC guy berates him for not being able to do any "serious" work.
:p

mbratch
12-08-2006, 07:10 AM
The Mac guy tells the PC guy about all the fun things he can do on his Mac while the PC guy berates him for not being able to do any "serious" work.
:pYeah, by "serious" work he actually means spending loads of time installing and running programs to try and rid your PC from ad-ware and viruses. ;)

I'm running Linux and, happily, the TSC is supported, and I get the benefit of not having those pesky email viruses distributed by the Microsoft Virus Propagation Tool... er... I mean... Outlook. ;)

vibroverbus
12-08-2006, 07:14 AM
nope. I don't have a TV. :)

What are they like?

TV's? well, they're kinda like computers, except you just turn it on and wait for stuff to go by. and you can't talk back to it. well you can, but only during sporting events and political debates.

ChickenLover
12-08-2006, 07:40 AM
Computers are just fancy TVs...in fact, at my job we call the computers 'TVs'. "Turn off your TV Joe...it's time to go home".:D

donnyjaguar
12-08-2006, 09:31 AM
Watching TV cuts into my practice time too much. :)

Blue Strat
12-08-2006, 09:36 AM
Watching TV cuts into my practice time too much. :)

Not if you're practicing while you're watching:)

tjs
07-16-2007, 11:46 PM
Lowering the slope resistor will add bottom, take away highs and reduce the effectivness of the tone controls.

In what way does it reduce the effectiveness of the tone controls?:confused:

Blue Strat
07-17-2007, 06:21 AM
In what way does it reduce the effectiveness of the tone controls?:confused:

A 7, for instance, is "the new 4". :)

You'll have to turn them to a higher setting to get the same effect you did with the old slope resistor.

Wakarusa
07-17-2007, 06:51 AM
BF Fender tone stack, controls centered, screenshot from Duncan's software. Red = 100K, yellow = 56K, purple = 33K.

http://www.wakarusaamp.com/tmp_pix/tgp/tonestackslopes.jpg


So it becomes pretty obvious that it's called a slope resistor because it changes the slope of the curve as it descends into and rises out of the "mids scoop". There are also some other side-effects --
- the range of adjustment for any of the tone controls (the effectiveness referred to above) changes with the slope resistor.
- the insertion losses (how much the tone stack attenuates the signal overall) change with the slope resistor.
- the center frequency of the mids control changes with the slope resistor.
- the width of the "mids scoop" changes with the slope resistor.

In more literal terms, the insertion loss change is due to the change in the load seen by the driving stage because the slope resistor is in parallel with the previous stage's plate resistor. Also, because the tone stack is effectively a collection of RC filters you're changing the "R" in RC which changes the center frequency of the filters and the filter's Q (the narrowing or widening of the mids scoop).

One other tidbit to keep in mind if you try Mike's idea re: a potentiometer in place of or in addition to the slope resistor is that the slope resistor in this tone stack sees full plate voltage from the previous stage -- so if you make it a front panel control it's likely to be scratchy from the large DC voltage it sees.

Blue Strat
07-17-2007, 06:59 AM
One other tidbit to keep in mind if you try Mike's idea re: a potentiometer in place of or in addition to the slope resistor is that the slope resistor in this tone stack sees full plate voltage from the previous stage -- so if you make it a front panel control it's likely to be scratchy from the large DC voltage it sees.


True. I must've put a cap before my slope pot in a hotrodded Princeton/Deluxe Reverb I did 'cause I'm not getting the scratchiness.:AOK

VaughnC
07-17-2007, 07:12 AM
True. I must've put a cap before my slope pot in a hotrodded Princeton/Deluxe Reverb I did 'cause I'm not getting the scratchiness.:AOK

Yup, I used a .1/600v uf cap in front of the slope control I've been experimenting with to keep the + voltage from the previous stage off of it. I also use a detented pot so I can find a previous setting easier. After much experimentation though, I settled on 68K as my favorite value with my Strat and eventually put in a fixed resistor. Interesting experiment on a homebrew amp I've been tinkering with.

Blue Strat
07-17-2007, 07:17 AM
Yup, I used a .1/600v uf cap in front of the slope control I've been experimenting with to keep the + voltage from the previous stage off of it. I also use a detented pot so I can find a previous setting easier. After much experimentation though, I settled on 68K as my favorite value with my Strat and eventually put in a fixed resistor. Interesting experiment on a homebrew amp I've been tinkering with.

Cool idea on the detented pot. What part did you use? I find that I like using the range of the slope pot for Strats vs Humbucker guitars as you'd expect. It can also be useful for dialing in a little extra "sumfin" on either type of guitar.

VaughnC
07-17-2007, 07:34 AM
Cool idea on the detented pot. What part did you use? I find that I like using the range of the slope pot for Strats vs Humbucker guitars as you'd expect. It can also be useful for dialing in a little extra "sumfin" on either type of guitar.

Mouser Alpha 313-3000F-100K.....has 11 detented positions, 18mm so it's small enough to add to an existing amp if there's limited space.

Blue Strat
07-17-2007, 07:35 AM
Mouser Alpha 313-3000F-100K.....has 11 detented positions, 18mm so it's small enough to add to an existing amp if there's limited space.

Nice! Thanks, I'll put that on my Mouser "wish list".:AOK

Wakarusa
07-17-2007, 07:38 AM
Yup, I used a .1/600v uf cap in front of the slope control I've been experimenting with to keep the + voltage from the previous stage off of it.

Adding the 0.1uF coupling cap also affects the frequency response and phase shift of the circuit. The significant effect is a rolloff in the bass response. With a 100K slope the addition of the .1uF has bass response down 3dB at 15Hz, 1.5dB at 30Hz and 0.5dB at around 75Hz. Given your average Fender's tendency to be a bit farty in the low end, this is probably a desirable (even if unanticipated) result. You might even want to try a smaller value for the coupling cap.


http://www.wakarusaamp.com/tmp_pix/tgp/tonestackcaps.jpg

Blue Strat
07-17-2007, 07:44 AM
Since low E is at 80hz, would this really matter much?

VaughnC
07-17-2007, 07:49 AM
Yeah, the .1 uf shows up on response curves but I hear very little difference by ear.

Wakarusa
07-17-2007, 08:16 AM
Since low E is at 80hz, would this really matter much?


Surely you're not suggesting that a Deluxe Reverb isn't the perfect amplifier for drop D speed metal? http://www.wakarusaamp.com/tmp_pix/tgp/icons/407.png.gif


All kidding aside, you're absolutely right. Freq response curves can be misleading because the guitar's useful range is pretty limited (say 80Hz-4KHz for a standard tuning with useful overtones/harmonics up to maybe 6KHz). Too often, folks using Duncan's tone stack tool slide the bass response control back and forth and see a whopping change in response without realizing that most of the effect is below guitar frequencies (which is, natch, why the some bass controls seem to have so little effect in the real world). What's hard to show in a static picture is the impact of the input coupling capacitor on the range of the bass control. As the input cap decreases in value you narrow the bandwidth of the bass control so it's dynamic behavior (and how it influences the mids) changes quite a bit.

Rosewood
07-18-2007, 12:57 PM
Todd, is your last name really shock? If it is your middle name better not be electrical.

Wakarusa
07-18-2007, 02:12 PM
Todd, is your last name really shock? If it is your middle name better not be electrical.

Oh yeah. Imagine the endless entertainment from this during the 12 years I spent as an electrician :AOK.

Other good candidates have been the medically inspired "toxic" and the more literate "future". On the up side, I get to name amplifiers things like "Therapy", "Syndrome", and "Treatment".

Rosewood
07-18-2007, 10:49 PM
Man you were destined for this work, you didn't have a choice.