Author |
Topic: Fender slope resistor revisited |
Brad Sarno
From: St. Louis, MO USA
|
Posted 7 Oct 2004 6:06 am
|
|
Back about a year ago a bunch of us were discussing the changing of the value of the 100k slope resistor in a Fender Twin tone stack to 56k. The theory was that this would shift the center of the mid-dip up from 500Hz to about 800Hz. Recently I took a closer look at the actual EQ curve on my Twin (with a stock 100k? slope resistor). With the tone controls all at 6, that mid dip was indeed right at about 500Hz. But this type of tone circuit is "interactive". Then when I set the EQ for my steel tone at t-3.5, m-4, and b-5, that mid dip rolls on up to 800Hz anyway. By changing the slope resistor to 56k, that mid dip rolls up even higher up around 1kHz, perhaps too high.
So early attempts to get the mid dip shifted from 500Hz to 800Hz by altering the value of the slope resistor were unnecessary as this shift happens automatically if you have a typical steel EQ setting with the treble at around 3.5-4.
What's got me thinking lately is how the Webb has that dip firmly fixed at 550Hz, regardless of your tone settings. And there's the Evans HV EQ that has the mid dip also at around 500Hz, but if you add the "depth" control, it bumps that dip on up to around 800Hz. Pretty cool. Most Peavey guys seem to dip at 800Hz.
If you think of Lloyd's Twin tone, based on his settings, he's getting a dip at around 800Hz. By raising the treble from 3.5 to 5.5, that dip shifts downward. Any Webb user (set on #2) will have a HUGE dip at 550Hz. I guess that's the heart of the Webb voice. That may be useful for those with modern Peaveys with the sweepable mid control wanting to experiment with different voicings. I analyzed an older Evans LV amp and it had a dip down around 375Hz. I think that's also where the Standel's have their dip. It's also where the Webb puts it's #1 setting dip, however the Webb's dip is HUGE where the Evans and Standel are less extreme. The mid dip frequency and amount is the key to the general "voicing" of an amp it seems.
My vote (currently) for the Twin is to keep that slope resistor at 100k.
[This message was edited by Brad Sarno on 07 October 2004 at 07:22 AM.] |
|
|
|
Rick Collins
From: Claremont , CA USA
|
Posted 7 Oct 2004 7:45 am
|
|
Brad,
I also use my Webb 6-14E (4 ohm JBL) for Hawaiian music on my Fender Dual Professional (trapezodial pickups). With these thinly wound pickups, it seems that I must set the Tone Selector on #3; or I cannot dial in any acceptable tone. Does this make sense to you?
Also, the booklet that came with the amp. recommends starting with the Sensitivity control set wide open (on 10). Technically, what would be the occasion for backing this setting down? And, what would be the practical lower limit.
...just looking for the most technically logical starting settings for this Fender guitar.
Many thank, Rick
|
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 7 Oct 2004 8:42 am
|
|
Rick, that does make sense. The Webb's #2 midrange dip is HUGE, I mean HUGE. Older steel pickups are generally lower impedance which also means that they don't need so much mid cutting. Your choice of the Webb #3 setting makes sense. That's the "flat" setting with no mid dip. You can still get some mid dipping with the 3 tone controls and if you want to use it, the graphic EQ.
The sensitivity control is meant to be full on unless you happen to be sending the amp a very hot signal. Your Fender guitars surely won't be that hot. In my experience, the more you back down that Webb sensitivity knob, the more thin and bright the sound. The more you crank it, the fatter and warmer the sound. You want to drive those FET's in the Webb a bit so keep it cranked up.
I've read that Jimmy Day used #3 on his Webb as well.
Brad Sarno
|
|
|
|
Michael Brebes
From: Northridge CA
|
Posted 7 Oct 2004 11:01 am
|
|
The Fender style tone stacks are VERY interactive. The Mid pot also changes the frequency curve for the Bass pot as well. The Treble control is a balance pot between the high frequency part and the output of the Bass/Mid tone section. Very crazy but works.
On one of the Marshall amps, which uses a similar style tone circuit, the resistor you speak of was replaced with a pot so that you could dial in the slope frequency ranges for the Bass/Mid. If you feel adventurous, replace the 100K resistor with a 50K resistor in series with a 100K linear pot, which would give you 50-150K range. |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 7 Oct 2004 1:10 pm
|
|
Yea, but be very careful if you try to put a pot in place of the slope resistor. Not only is the voltage high, but also there's a problem when you have DC voltage on a pot wiper it can make lots of noise when you move it. There's a couple of hundred volts on that resistor because it comes right off the plate. You can decouple it with a cap right after the plate. Great idea to be able to tweak that slope value.
Brad |
|
|
|
Ken Fox
From: Nashville GA USA
|
Posted 7 Oct 2004 3:30 pm
|
|
For what it is worth I have done it to several amps and really liked the difference, even on guitar. I usually mod channel one with a 56K slope resistor and add reverb/tremolo. That way channel one gets the extra gain stage of valve 4, as well as now being in phase with chanel two. I find the tone more middy to the ear, a nice change for some rooms. The nice thing about the above mod is two useful channels, with two different voices.
Like Brad, I have played with the Duncan tool (Tonestack) and agree the tone controls do interact. However I feel you still get something very nice with the 56K slope mod. I would only do it on the first channel and also add reverb. That way you still have the stock channel 2, nothing lost at all in this equation!![This message was edited by Ken Fox on 07 October 2004 at 04:32 PM.] |
|
|
|
Jim Peters
From: St. Louis, Missouri, USA, R.I.P.
|
Posted 7 Oct 2004 3:51 pm
|
|
Ken, you've given away my secret! With my Tele(rock & blues), I have a SF Deluxe with the mod you just described. The BIG difference that I use is this: I compress one channel and run the other straight! There is absolutely no squashing of the note, and the compressed channel is only heard when the note starts to decay, the compressed channel keeps it going-EG- more sustain. It works great, and since the power tubes are driven by twice the input stage, you get more power tube action at a lower volume. I highly recomment it, and it's easily changed back. Sorry to drift, good luck at The Venice tonight, Brad!.JP |
|
|
|
Ken Fox
From: Nashville GA USA
|
Posted 7 Oct 2004 6:21 pm
|
|
Interesting, Jim. My main amp is a 1965 Deluxe, non-reverb with a JBL D-130F. I use an RV-5 for the reverb, DDL-10 (Ibanez delay), a Boss CS-3 compressor. I was thing this afternoon about running both channels, one straight in and the other from the effects board. I got to try this, you described just what I was hoping to achieve. |
|
|
|
Jim Peters
From: St. Louis, Missouri, USA, R.I.P.
|
Posted 7 Oct 2004 10:03 pm
|
|
It will depend on your compresor, a Dyna comp won't work( on the modded amp) because it flips the phase. I use a Nashville Tele with a brown modded Ts9 tubescreamer, and the compressor in an old Boss Me5 pedalboard, with Great results. Good Luck, JimP |
|
|
|
Rick Collins
From: Claremont , CA USA
|
Posted 8 Oct 2004 7:13 am
|
|
Many thanks for the information on the Webb amp. Brad. The response is exactly as you stated.
Rick |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 8 Oct 2004 10:55 am
|
|
I had to compare the Duncan tonestack calculator with real world. My Twin gave me curves pretty darn close to the calculator, but not exactly. I guess all those carbon comp resistors and their varying real values will throw any Fender off a bit.
I like the 56k slope R for guitar more than steel because I'll typically have the treble up higher, like 5 or 6. With the 56k and that setting, that puts that dip at around 800 or so which does sound nice. It's just that on steel with the treble back around 3.5, the mid dip can get a bit too high up for where I'd like the steel mid-dip.
I like the idea of having one channel of each. I think I'll try it. I was considering putting a 3-pos switch with 2 resistors across a 150k slope resistor. That way you could have a variety of mid dip positions. I think it makes sense to have one fixed slope resistor so that plate always has a good fixed load. Then let the switch just add in parallel either resistor one, resistor two, or none to drop the value. That seems to be a safer way to do it since there's pretty high voltage off that plate. I'd like to try a value that gives me my steel treble setting but keeps the dip down at 500 to see what the Twin sounds like voiced like a Webb. I'm guessing about 150k. Hmmm...
Brad |
|
|
|
Jay Ganz
From: Out Behind The Barn
|
Posted 8 Oct 2004 11:19 am
|
|
Hey Brad,
If you'd like, I can email you the preamp
schematic for the new Steel-King amps.
You need Adobe acrobat reader though. |
|
|
|
Donny Hinson
From: Glen Burnie, Md. U.S.A.
|
Posted 9 Oct 2004 4:52 pm
|
|
My favorite "tweak" is to raise the value of the slope resistor to 180 or even 250k, and then change the bass pot to a 1-meg.
Try it...and you might like it!
|
|
|
|
Michael Brebes
From: Northridge CA
|
Posted 11 Oct 2004 7:11 am
|
|
My preferred tweak is increasing the 10K Mid pot to 25K. Changes Mid and Bass response, alot more of both, while still giving you the option of dialing in the area covered by the 10K pot with numbers 1-4 on the knob. |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 11 Oct 2004 12:35 pm
|
|
I'd be curious to know what Tom Brumley has in his '59 Bassman for a tonestack. Stock would have been .022, .022, and 250p with a 56k slope right? That Fender of his is maybe the best sounding steel amp I've heard. Maybe someday he'll let one of us pull the panel off and take a peek.
Brad |
|
|
|
Bob Snelgrove
From: san jose, ca
|
Posted 11 Oct 2004 7:51 pm
|
|
Toms' tone was the undisputed champion in St. Louis this year. (IMO Since he was using his BM and a new SK, I couldn't tell what was what but overall it was pure Heaven
bob |
|
|
|
Jay Ganz
From: Out Behind The Barn
|
Posted 12 Oct 2004 5:52 am
|
|
I have an original '59 sitting right here. |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 12 Oct 2004 7:28 am
|
|
Jay, if you get a chance, let us know what those 3 caps are in the tonestack. And the slope resistor. They're all bundled together.
Yea Bob, at the steel shows Brumley is usually the tone champion in my opinion. That Steel King sounded pretty good, but that ol' Bassman is magic.
Brad |
|
|
|
Bill Hatcher
From: Atlanta Ga. USA
|
Posted 12 Oct 2004 8:12 am
|
|
I have worked on several old 4-10 tweed Bassman amps. I am always amazed at how wonderful they sound. I did a comparison with a new Fender Bassman reissue and an original. The old ragged Bassman sounded remarkably better. I wondered if the passing of so many years had anything to do internally with the original amp sounding so much better, but then I remembered being a kid in the middle of Alabama in the early 60s. All the good country players I knew raved about the old 4 10 tweed Bassman and told me to find one and that they sounded so much better than the new Fender amps that were out. Considering the new Fender amps that were out then were the white,black and Cream colored amps that are so popular and expensive today, those old pickers knew something about tone and getting a good sound. |
|
|
|
Ken Fox
From: Nashville GA USA
|
Posted 12 Oct 2004 12:22 pm
|
|
Brad, I sent you a schematic of the 59 Bassman. Note the amp had three gain stages before the inverter. Oddly, a 56K slope resistor as well and how about that, a 25K mid pot. All this is sounding like our favorite mods for a Blackface/Silverface amp! [This message was edited by Ken Fox on 12 October 2004 at 01:46 PM.] |
|
|
|
Bill Hatcher
From: Atlanta Ga. USA
|
Posted 12 Oct 2004 12:33 pm
|
|
Ken Fox.
Thanks for the Fender mod info!!! |
|
|
|
Jay Ganz
From: Out Behind The Barn
|
Posted 12 Oct 2004 1:38 pm
|
|
Brad,
This one is dated May' 59 & it's got a 250pf,
.02mfd, & .1mfd with a 100K slope resistor.
All the caps (& even the solder) are untouched
from the factory. I'd be curious whether Tom's amp has the old original Jensen P10-R speakers
since those affect the tone alot more than
the slope resistor. |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 12 Oct 2004 2:33 pm
|
|
Cool. Thanks Jay. I figured that there would be some variations around that period. Time to plug some numbers into the Duncan calculator.
Bill, I agree on that reissue Fender thing. The reissues only look like the originals. They surely don't sound as good. Inside they're (most of them) printed circuit boards and cheap grade metal film resistors and mylar caps. The circuits are pretty true to the original as far as the schematics go, but the layout is completely different. The lack of point to point wiring is also a key issue I think. The new transformers also are probably different sounding. Fender does make a few of these exotic hand made reissue amps that are quite true to the original, but they are well over $2000 and are in a special category. Most Fender reissue stuff just doesn't live up to the original, by a long shot. I love that rugged military grade build quality of the old stuff. I much prefer my '69 Twin, '68 Deluxe Reverb, and '68 Princeton Reverb over just about any amp available today.
Brad |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 12 Oct 2004 2:38 pm
|
|
Yea Ken, that old Bassman has 3 gain stages with volume control before it ever even hits the tonestack. I bet that has something to do with the sound. All that unvoiced gain up front. And the treble pot directly feeds the phase splitter. Very interesting. Hmmm.....
Brad |
|
|
|
Brad Sarno
From: St. Louis, MO USA
|
Posted 12 Oct 2004 2:43 pm
|
|
Jay, Brumley got that amp from Leo Fender in or around 1965. Leo had removed the tweed and covered it in Black Tolex. He also put in a JBL D130 and a reverb circuit for Tom. Tom's sound was from a single 15" JBL. Never, as far as I know, did he use the 10" speakers. I've also seen Tom use Blackface Twins with 2-12" D120's in recent years. That Bassman is only about 45 watts. Blah blah blah...
Brad |
|
|
|