Before I start ordering a bunch of parts, I ran a couple of Tone Stack Calculator models that I would like you experts to take a look at.

The first one shows the normal Fender tone stack (lowest trace) and then sequentially changing only the treble cap from the original 250p value to 300p, 390p, 500p, 680p, 820p and 1000p.



The next one shows the normal Fender curve (lowest trace) and then changing the mid cap from .047 to .022 and also the treble cap from 250p to the same values as above.



It looks like changing the treble cap adds more mid-range frequencies to the top end (and shifts the mid-dip to lower frequencies)and changing the mid cap adds more mid-range frequencies to the bottom end.

Would either of these have the effect I am trying to achieve, or should I look in other directions?

BTW, the guitar is a Mullen SD-10 with a TrueTone 17.5K pickup. Amp has a JBL K-130-4. It sounds pretty good now, but I'd just like to tame the top end a little.

[This message was edited by Mark Herrick on 22 June 2005 at 12:47 PM.]

The problem seems to be that the amp was designed for a regular guitar playing through the stock 12" speakers with the EQ set flat (everything on 5.5). When I play through a Twin with two 12s, my settings for pedal steel are completely different than what I suggested for you above. Then I have to set the bass around 8, the mid around 5.5, and the treble around 2. This compensates for the fact that a steel has way more highs than a regular guitar. A steel guitar is a one-plank solid body with no neck joint and only a bridge pickup.

My tone controls are set very much like you suggested; Bass 2, Mid 6, Treble 3. I'll play with them more and see how it sounds.

Having to crank the mids up so high was not something I expected, but without doing that it's like you say, in the "mud." I've also read that using linear pots rather than audio taper gives you more useable range. Not ready to do that kind of major surgery...

Jon:

quote:

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--I'm a candyass and refuse to fire up the amp until I have it back in the cabinet--

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Yeah, that's how I fried the hum balance pot in the first place...but then again, you haven't really lived until you've scared the sh*t out of yourself...I love the smell of ozone in the morning; smells like...victory...

I had a JBL E-130 in the amp previously and was actually surprised at how different the K-130 sounds. It seems to be much warmer, which I like. I have a line on another K-130 which I'll have to have re-coned. (You out there lurking, Joe?)

I have a '76 Twin, w/ a JBL and an Oxford 12".

The amp is so bright I set the treble on 3 and the mid on 5, no bright switch.

Good luck,
Drew

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Drew Howard - website - Fessenden D-10 8/8, Fessenden SD-12 5/5 (Ext E9), Magnatone S-8, N400's, BOSS RV-3

I recently tried that on my amp. Set the mids on ten and the bass and treble on zero. Didn't tweak even. Having an instrument that has onmly high I can get really irritated by too much treble. This works pretty well.

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If you can't hear the others you're too loud, if you can't hear yourself you've gone deaf

[This message was edited by Terje Larson on 23 June 2005 at 09:59 AM.]

Mark, I think that you are putting too much focus on messing with the midrange voicing of the tonestack circuit. Your tonestack calculator screenshots indicate that your value changes only really addressed the mid shape. Your comments were about taming the treble frequencies. I've found that much of those issues can be addressed with capacitors. If your amp is stock, it probably has a ceramic treble cap as well as a number of ceramic caps in the signal path. Most fender tweakers will yank the ceramic treble cap and drop in a silver mica 250pF cap instead, or perhaps a high voltage film cap. And then all the coupling caps that are ceramic can be replaced with film/foil types. This lets the Fender tone shape stay the same, buy harmonically warms up and sweetens the highs, removing the crispy, sandpapery edge. Lots of people like the 716p series of Orange Drops. They're kind of bright and snappy sounding, but much smoother and silkier than the stock ceramics. I've heard dozens of Fenders come to life with the removal of ceramics, especially when the amp is played clean and not too overdriven. If there's a bright cap strapped across the master volume pot, then I agree that you should snip it as well.

Generally I wouldn't mess with that brilliant Fender tonestack voicing if you're just trying to tame the highs. Definitely keep that bright switch off as well. Don't forget that when you move the treble control on a Fender, the midrange dip moves around too so that knob is actually serving multiple functions, unlike other tone circuits like in a Peavey, Webb or Evans.

I have already replaced the ceramic treble cap with a 250pF silver mica.

At one point I did remove the cap from the MV control, but I couldn't tell any difference so I put it back.

I don't use the bright switch at all, but my understanding of it is that it only has an effect at low volumes; anything above about 4 and there is no effect. (I have confirmed this myself by testing.)

As far as the Orange Drops, my amp has all Blue caps (like OD's, only blue) which I have been told are good caps and should be left in. Are you suggesting I replace all the smaller value ceramic caps (.001, .003, .01, etc.) with Orange Drops?

[This message was edited by Mark Herrick on 23 June 2005 at 01:34 PM.]

Try this...

C1=100p
C3=68n
R1=200k

Respectfully speaking, you should not really be having this kind of issue with a Twin. These things have been used forever by so many great players factory stock with no changes to the tonestack, the 250K caps , blue or orange caps, whatever. I have rebuilt so many of these amps.

If you have never taken an old Fender amp and "blueprinted" it then you really have never heard how spectacular these things really sound. When you blueprint a car engine, even a new one, you look at the specs on the mechanical drawing of the engine and you remachine or replace stuff in order to bring the engine as close to the EXACT tolerances the thing was designed at.
A Fender amp will run on parts that are 10 to 20% out of spec. If you will take the amp and replace the old caps in the tone circuit with new caps (orange drops are just fine) with the exact values as per Fenders' design and the resistors in the phase inverter and preamp section with precision resistors and the grid resistors with precision flame proof resistors and do the filter caps you will hear a remarkable difference in the amp. If you have old caps and old filter caps and old tubes and old load dropping resistors in the power supply, you can do all the tonestack modeling you want to and you will not get the desired results. Also the general condition of the output transformer will have a bearing on the sound of the amp. What kind of preamp tubes are you using? You can change the sound of the amp with them.

I don't know about all of this. The first thing I would do with a Silverface 70s Fender amp is to take a AB763 Fender Blackface twin schematic and start changing the silverface back to a blackface. That would improve the tone of the amp tremendously. Note that no one has reissued the silver face twin amps yet!!! These silver face twins were NOT the same amps that Leo designed. The tech geeks that took over after he left were just itching to change things to make the amps run more linear and be "better"--what a crock. Just put it back to the original design and see what a difference it makes.

If Lloyd or anyone else prefers to use the clean range of a warm black face in the studio (and mike it live to get the needed volume), I'm all down with that. And if they want to use the big dirty range for distortion in blues and rock, that's fine too. I wish I could afford a black face twin dedicated for that purpose.

All I'm saying is that in the rush to solid state amps in the '70s, it sort of got overlooked that the silver faces, especially the last few years of them with the 135 watt ultralinear transformer and the 180 watt Super Twin, had it all for pedal steel. A 135 watt sliver face Twin has as much clean volume as a Nashville 400 (I've made the side-by-side comparison), and a Super Twin has as much clean volume as a NV 1000. Yet they still have tube warmth, allbeit not quite as much as the black faces.

As some of us have grown weary of the sterile solid state sound, we have discovered that the silver face Fenders can give you back most of that warm all-tube sound, and still have the clean volume needed for steel. And since the black face fetish of 6-stringers has caused so much prejudice against the silver faces, they don't have high collectors' prices and cost half as much as the black faces, and also less than new solid state amps with comparable volume.

The silver faces sound way better than any solid state amp. If they are not quite as warm as black faces, they have the advantage that they play clean all the way to the top, so you are not carrying around the weight of a 100 watt tube amp with only 60 or so clean usable watts. You have 100, 135 or 180 clean usable watts of warm all-tube sound. And that usable volume is equivalent to 200 to 300 solid state watts. Today, in large venues where a tube amp does not have enough volume, you usually have a good PA, and you can mike it. Also, today if you need crunch and distortion, you can get it with any of hundreds of effects units and modelers. You don't have to carry around extra tube weight for that. I happen to play in a lot of small rock clubs where the expected volume level is very high, but they do not mike the guitar amps. A black face Twin would not have enough clean volume for steel, but my silver face Dual Showman reverb or Super Twin do.

Some additional thoughts...
I fired the front end up with a Seymore Duncan "Pickup Booster" (25db gain). For guitar it gives a nice tube breakup at very low volume.

Also, who has experimented with taking out two of the four tubes?
I'm more interested in low volume gigs, and cool tone (I like the broken up sound to be available at full V-ped for steel. Dan Tyack has this down with his THD rig!).
Any difference between removing the outer two and/or inner two?
Any other tonal change, etc?
Thx,
~pb

[This message was edited by Pete Burak on 24 June 2005 at 09:43 AM.]

I think the JBL K-130 sounds pretty warm, and I like the "crispness." (It is an original 4-Ohm cone.)

I have done a Blackface mod on the phase inverter circuit, but I couldn't sense much difference. The filter caps have also been changed (Sprague Atoms) as well as the grid resistors on the power tubes and plate load resistors on preamp tubes.

Pre-amp tubes are: V1 GT 12AX7M (don't use this channel), V2 JAN Phillips 12AX7WA, V3 Mullard CV-4024 (12AT7), V4 GT 7025, V5 GT 7025, V6 Mullard CV-4024. Power tubes: Phillips 7581A.

I usually keep the MV on about 7. If I go higher I start to get some noise. Preamp volume usually on about 7 as well.