Ok guys, this is a topic Howie and I briefly touched on at the Hole but am wanting to fully flesh out.
We had a topic about booster pedals and I mentioned that, with my Boogie Roadster, that I use a PedalWorx Tejas (true-bypass TS808 pedal with a little extra feature) to tighten the lead channel up by cranking the volume on the pedal and killing the drive.
What I want to know is how this works. What is it about using that type of pedal as a clean-booster tightens things up? I thought it pushed the mids, but Howie briefly (without going into detail) mentioned that wasn't the case.
On a side note, it's good to see ya here Dar. I still have the Book of Dar bookmarked (mainly on how to use a compressor). Good sturff.
I may be wrong about this, or, I may have mis-understood what your asking Chris but, I think using a TS/other OD to "clean boost the signal" basically pushes more signal into the preamp valves. More signal in = more signal out + some extra compression giving more frequencies and gain for the poweramp valves to get thier teeth into and work with.
I actually do it a slightly different way with my set up in that I set the amp up clean and use the drive of the TS to get my crunch. With the volume balanced to unity gain (the point where the pedal gives the same volume on or off), I'll then boost the signal with a pedal or using the guiatrs volume, to further push the signal into the front of the amp thus getting the valves cooking. The reason I do it this way is that I can crank the poweramp to really perform and control the amount of front end push.
Hope this makes sense but no doubt both Dar and Howie will tell I'm wrong ;).
Good qeustion BTW and one I really hope we get some answers to. It would help me to REALLY know.
HOWIEEEEEE...........
it's too late to answer this fully tonight. I'll get some info together for you tomorrow and hopefully Dar will join in as well. I can already see that I didn't answer Chris thoroughly enough the first time ( :-[) In short, the output of the the amp is a complex series of parts starting at the guitar. Many guys are detuning, using big strings, turning the bass up on Mesa (LOOSE) amps and then "tightening" them back up with a screamer type pedal. The tightening IS NOT an actual tightening as changing the actual damping of the amp would be. It is simply a bass rolloff of bass frequencies. Most people say screamers have a mid hump. While some have a hump, what most people hear is the rolloff of the top and bottom.
more tomorrow...
Chris,
I'm sorry. I was on vacation last week and am busier at work than I thought I'd be since I was off all week. Had yard work Monday night and a double header last night so I was late getting home.
The info I have that I want to show is at several sources and I have to go looking for some of it. I didn't forget you and will get to this shortly
Hey Mr. Moderator... I can take this one, quick...
Basically, there are several things to keep in mind as distortion is generated - this is partly why it "goes wrong" in some instances. So hang with me, ask questions if you have them, I'll be more than happy to answer them.
The basic premise of distortion generation was started in the Fender Bassman and Marshall really picked up on it and "made it right..." In order to get a "clean" and a "tight" distortion that really "crunches" and "sounds good" (the latter item being HIGHLY subjective) the low frequencies need to be removed from the signal. In most amplifier topologies, and distortion pedal topologies, this is done using a high-pass filter (passes high frequencies and "blocks", or reduces, low frequencies).
In order to get this, various high-pass filters are used. As you're aware, the lowest string on a standard 6-string, in standard tuning, is roughly 84Hz (give or take a few). That's Low-E. Distorting this frequency, without any filtering generates some "ugly" distortion. This distortion is called "intermodulation" distortion and occurs as a result of sum/difference frequencies all coming together.
When a string vibrates, it has multiple tones that are generated. The first tone, the largest single frequency in amplitude, is called the "fundamental" and is the lowest note generated. Harmonics are also generated which are multiples of the fundamental. So, let's do easy math. Let's say the fundamental of the E string is 80Hz. The second harmonic of 80Hz is 160Hz. The third harmonic is 240Hz. The 4th harmonic is 320Hz. The fifth is 400Hz, etc. Each subsequent harmonic generated is 80Hz greater than the first one. Each doubling of frequency (fundamental x 2, fundamental x 2 x 2, fundamental x 2 x 2 x 2). A single guitar string will produce harmonics that you can hear up to the 15th harmonic in the series.
When distortion is generated, the tube/transistor/op-amp doesn't just reproduce the individual frequencies and then distort them. It actually becomes a "mixer" when it's operating non-linearly and not only harmonic distortion (generation of pure tones as per above) but intermodulation distortion is produced. Intermodulation distortion produces products that are the sum and differences of the various frequencies generated. So, a string vibrating will produce harmonics of 80Hz, 160Hz, 240Hz, 320Hz, etc... 80 + 160 = 240Hz (intermodulation) and 160Hz - 80Hz = 80Hz (intermodulation distortion). These sums/differences occur between the fundamental and all the harmonics. If you do the math, and add everything up, what you'll end up finding is that there is a "build-up" in the low frequency region which turns out to be very "muddy".
So, to "tighten" and/or "clean up" the distortion, it was learned that the signal must actually be "filtered" or "EQ'd" prior to distorting it. Common EQ points include 300Hz, 400Hz, 600Hz, 700Hz and 1kHz. When Fender uses distortion they commonly distort with a high-pass filter set to about 400Hz, or so. Marshall uses rather steep filters set at about 720Hz and our friends at MESA like to do their work with a 1kHz shelf. These various "shelves" also strongly define the "voice" of the amplifier and are largely the reason why you can tell a Marshall apart from a MESA apart from a Fender apart from a VOX (incidently, VOX's shelf starts at nearly 7kHz).
The folks at Dallas Arbiter figured this out with their "Treble Booster" which is a "two-in-one" circuit. The first function of this circuit is to significantly boost the guitar signal so that it overdrives the preamp tubes. The second function of this pedal was to shelve out the low frequencies so that distortion could be clearly generated and not sound flubby, or muddy, on amplifiers that were not originally voiced for distortion.
The TS9/808 type pedals have a roughly 720Hz high-pass filter built right into the first stage of the thing. Remember the 720Hz gig is where Marshall shelves their amps - the original "tube overdrive" sound which is why folks love the TS9/808 series so much. So, using this stage as a boost by "removing" the diode clipper would "tighten up" the distortion on the amp and provide a nice boost, too.
You can get a similar effect using a BOSS GE7 EQ and cutting everything below the 800Hz slider, at about 6dB cut per slider. So the 400Hz slider would be 6dB below the 800Hz. The 200Hz slider 12dB below the 800Hz slider and the 100Hz slider maxed out. Then, boost the "Level" control for some "heat" and you've got it going on. If you want a bit more "mids" in it, you can boost the 800Hz and the 400Hz just a touch. That'll bring up the "center" of each at about 600Hz.
OK... that got a little long... let me know if you still have questions.
Dar
well I could have said that! HAHAHA (of course, not as eloquently! :-)
Seriously, I have SOMEWHERE an actual frequency response plot of a stock TS9 and TS 808, and that's what I was looking for. To show in terms anyone can understand exactly what it does to the freq. response. Obviously it is rolled on top and bottom, but as mentioned the harmonics generated will add some top.
Also, note that the 720hz shelf is standard issue for STOCK screamers but MOST modded pedals use a lower shelf frequency for "fatter" tone. My Blues Pro is notably fatter than some of the screamer type pedals I've compared it too, for example. When I have my SRB 808+ it has a selectable "fat" switch which changed the shelf frequency so you could have the "standard" 720hz or so, or something more in the 400hz area (I think, didn't see exacly what values he used but it's a common mod in the BYOC forum. SPST switch with two caps, one standard, one "fat").
For a primer on Tube Screamers, go here
http://www.geofex.com/ and read "the technology of a tube screamer." Great info. I recently heard a clone of the famous Clay Jones OD which is basically a screamer with buffer sections removed, LEDs for clipping and a few other minor parts mods. VERY nice OD for the SMOOOOOTH thing. I have layouts for doing them on perf boards so that will be a future project.
Great info Guys 8-).
Dar/Howie, would a Rat clone employ a similar high pass filter in the curcuit? I initially found my Rat clone a little too dark. this was solved by reversing the 2 wires to the tone pot. It now works (as you would expect) in reverse (clockwise for less treble) but means the tone control has a greater effect overall. Apparently, this was done on the original Rat pedals.
Dar can probably answer this before I can even find a rat schematic. I think he stores schematics for just about anything you've ever heard of in his photographic memory! :-)
In general though, like Dar said in the amp voicing threads, MOST devices that intend to add distortion cut bass before the distortion part of the circuit so I'm sure a rat does. Don't know off hand at what frequency though.
re: this, if you've seen the pedals that have a pre-gain bass control though (MI Blue Boy Deluxe and Tube Zone come to mind since I've had both) you can hear easily what adding back the bass before the distortion does. It's actually kinda cool adds a loose wooly, what I call "old fender" type distortion to the tone. It immediately reminded me of a friends OLD fender amp that I played 30 years ago. Had this big loose fuzzy bass. It's a "thing" and it can be cool, but you certainly wouldn't want it for MOST tones. But pedals with this feature allow you to hear how a distortion pedal would sound if you didn't filter bass before OD (Same applies to preamp sections!) Some pedal makers add bass back after the OD part of the circuit so that the bass is still there, just not distorted.
The Rat does, indeed, include the high pass filter in the product. In fact, in the distortion stage it has two of them, one at 70-something hertz and one around 1kHz. One can be removed, the other modified, or both modded to meet your needs... heck you can remove components, jumper tham, or whatever, to get what you need out of this thing...
The RATT was, originally, designed to mainly work with Fender amps to help them sound more like Marshalls - mainly cuz Fender's didn't distort so it's voiced/geared more toward that application. Because of the "slope" in the Fender tone stack (I have another topic on this posted) they had to reduce the highs considerably in the RATT to get it closer to the Marshall slope which is why it'd be dull on a lot of Marshall-esque amplifiers out there.
Anyway... yeah, you can do it and you should come up with some pretty good results.
Dar
spud — Aug 13, 2008Great info Guys 8-).
Dar/Howie, would a Rat clone employ a similar high pass filter in the curcuit? I initially found my Rat clone a little too dark. this was solved by reversing the 2 wires to the tone pot. It now works (as you would expect) in reverse (clockwise for less treble) but means the tone control has a greater effect overall. Apparently, this was done on the original Rat pedals.
That's right, my Rat (a big old box Rat) has a tone pot that works backwards if I remember correctly. Man, that is the one of my hippest pedals.
and of the 4 rats I've tried, Chargers is the best sounding.
There are so many versions the Rat that the BEST suggestions (IMHO or course ;) ) are to get one and let keeley mod it OR get a BYOC and then you can KNOW you have one of the best because they are based off the best version and tweakable from there.