A better bass screamer

[marcelomd]

Please help me understand the differences in Bass and Guitar signals.

Suppose we assume that the Guitar pickup output is 1Vp for few cycles, what is the equivalent data for bass ?

Suppose we assume 720Hz is good place for mid hump for Guitar, what is the equivalent for Bass ?

Suppose we assume high pass filter of 60 Hz is good for Guitar, what is the equivalent for Bass

Suppose we assume 5000 Hz is upper limit of Guitar Speaker, what is the equivalent for Bass ?

Thanks

The answer is always: it depends =)

1- Signal levels: Depends on the bass. Active or passive? My G&L L2500, in passive mode, puts out +-3V on the attack according to G&L itself. It's a beast.

2- Depends what do you want to do. Distorted or clean? I like a clean boost at 250Hz, because punch. When playing alone, a TS on bass sounds pretty good, even with the bass cut. You get lost in the mix when playing in a band, tough.

3- The low B is +-30Hz and the low E is +-41Hz. If you are playing fast metal, cutting below 60Hz is not a big deal. If you are playing reggae, you'll like to boost below 60Hz.

4- Bass speakers are fuller-range, compared to guitar speakers. Gallien-Krueger CX cabinets (2x10, 4x10, 1x15) go from +-50Hz to 18kHz. But Ampeg says the SVT810AV goes from 50Hz to 5kHz.

[Fancy Lime]

Yeah, basically what Marcello said.

Signal levels are all over the place for guitars as well as basses. Designing for peak voltages somewhere around the 100mV-10V range will probably cover most cases but still not all. And that's two orders of magnitude! But that's why we have a gain pot and input protection diodes, isn't it?

Mid shaping is highly subjective. I like to emphasize the 700-1000Hz region on guitar, others don't. For me this is where the "personality" of the guitar lives. The 200-300Hz region tends to muddy the sound up on low power chords with lots of distortion. So best TU cut those on distorted guitars. For clean or less distorted single notes on bass, 200-300Hz is indeed where the punch is, so this is a good place for boosting bass guitar. I also like to cut 800Hz on bass, to give the guitars more room there. But most of these adjustments really depends on taste, the genre, the band composition, and of course the playing style of the players.

You can buy F# standard string sets. F# is at~23Hz. I usually aim at a -3db corner of 20Hz to be save. Putting additional high pass filters in the signal path later is always easy.

Some bass players use guitar cabs others have massive PA systems on stage to get that 20Hz to 20kHz response. Way more heterogeneous than the guitar speaker market.

Andy

[anotherjim]

Bass cabs can be as low as 3Khz when only 15" or 18" drivers were used. Standard Ampeg 6x10 will be similar to guitar 5Khz cabs except for the extended bottom end. There's also one with a horn and that extends to 18Khz on paper.

Pretty sure a lot of bass growl tone is from the speakers. The rest of the chain can be very clean. Lots of headroom in the amps and they can be set flat.

[Jubz]

Yeah input signals for basses are all over the place. Versus designing for a guitar you have to consider a few things:

- on board preamps are fare more frequent on bass than on guitar. Which impacts signal levels and input impedances
- even in very agressive styles you will see a lot of bassists playing fingerstyle, which outputs a very different sound than pick.

On a lot of classic designs (rats, muffs...) i feel like playing fingerstyle cant get me a really agressive sound, it's just plain mud and post clipping eq cant really fix it. I guess the success of pedals like the darkglass b3k for example comes in a large part from the consistent grind you can have out of it with passive or active basses and playing pick or fingerstyle. If you look at the schematic it really emphasizes the high mids and cut a lot of bass pre clipping. The "energy lives in the basement" statement really takes another dimension with bass distortions.

[niektb]

As per request, here is the TS-9 with a Bridged-T Low-mid control 


Here is a simulation of the low-mid control:


It dóes drop a bit of volume as it's a fully passive control, but I must say that it's quite transparent. It only cuts so start with that knob on max and then turn down till you find the sweet spot 

You can get the TINA-TI simulation file here in case you want to play around with values and stuff 
https://drive.google.com/file/d/1Yh1PMI3i3R_RlmXZO8fltIgL4XSmGxFf/view?usp=sharing

[sergiomr706]

Thanks niektb!

[Vivek]

Can Tina TI export schematics in LTSPICE format ?

[marcelomd]

As per request, here is the TS-9 with a Bridged-T Low-mid control 


Here is a simulation of the low-mid control:

Very nice.
When you mentioned the bridged T I thought it would be earlier in the chain, like the Sansamp and Darkglass. They also have a smaller notch later.

Darkglass B3K:


Actually, I went back to the schematics to comment here. Sansamp and Darkglass are pretty similar.

[Vivek]

Do you mean the notch on some Bass SansAmp ?

I see this 720Hz notch on the GT2 in the Tweed setting :

[marcelomd]

Do you mean the notch on some Bass SansAmp ?

That one. The older Sansamps (Bass Driver, GT2, TriAC) have one big notch after the first buffer and one smaller after the distortion. In the newer character series there's an active mid control in place of the first notch.

[Vivek]

I did not find smaller second notch on GT2


Yes, you are right about the Character knob on the Character series. It is merely a modified Mid control before the distortion, with low Q, and it is asymmetrical.

[marcelomd]

I did not find smaller second notch on GT2

Yes, you are right about the Character knob on the Character series. It is merely a modified Mid control before the distortion, with low Q, and it is asymmetrical.

I may very well be wrong. I was looking at that mess of switches that control the mic placing.

[niektb]

As per request, here is the TS-9 with a Bridged-T Low-mid control 


Here is a simulation of the low-mid control:

Very nice.
When you mentioned the bridged T I thought it would be earlier in the chain, like the Sansamp and Darkglass. They also have a smaller notch later.

Darkglass B3K:


Actually, I went back to the schematics to comment here. Sansamp and Darkglass are pretty similar.

Funny thing is that I didn't really mean to design it as a Tube Screamer for bass! It was my first ever guitar pedal circuit I made so I was mainly looking for a unique feature to add. I was inspired by the Framus Cobra Mid Control (which is said to have some very nice scooped sounds). But when I built it, i didn't raelly love it on guitar. But later I discovered that it was wonderfull on bass

I'm not totally sure why that is but here is my theory why it works (also áfter distortion). It's tight because there is so much low-end roll off and it doesn't need anymore of that (in fact, I think lowering the mids would require more gain to achieve the same amount of compression and drive). And the mid frequencies are the main contributors to generate the harmonics that go in the lower treble area which adds to the bite. Also, I come from a audio engineering background and scooping out a bit of low-mids is something I do often because thats where the muddiness recides with bass 
that said, I may just be talking bogus. I'm no expert when it comes to bass 

[Fancy Lime]

Hi there,

I finally tested the variable adaptive clipping thingamajig that I was waffling on about in Reply #18 in the odb1. It is as interesting as I remember from experiments long ago. Here is the schematic:



The Blend knob is called thus because it sounds pretty much like a clean blend. What actually happens is, that you get clipping as soon as the diode threshold is surpassed on one half-cycle. If the Blend pot is at minimum resistance, the caps are in parallel and the whole thing acts just like the clipping diodes in a Big Muff. If the Blend pot is at >0Ω resistance, the caps C7 and C8 get charged a little bit with each half-cycle and a voltage develops across the Blend pot. The signal now must be higher than the diode drop plus half of this voltage across the Blend pot in order to clip.

Yeah great, but how does it sound? If you play softly, it's just like normal back to back diodes in a TS. If you have the Blend turned up to a setting similar to the Gain setting, and pick harder, the clipping remains more or less the same as when you picked softly, but there is an additional clean portion to the sound that retains the original dynamics. So the overall effect is that the distortion intensity becomes almost independent of the playing dynamics and the output retains almost all of it's original dynamics. By adjusting the Blend, you can find the sweetspot between this extreme and the "normal" behavior, where the clipping changes and output remains constant as the input gets louder.

I don't find this overly useful for the purpose of this particular device, at least to my ears. However, as the first stage in a multi-stage-clipping type of overdrive (so, AIAB mostly), this could be really neat. Of for people who like their bass sound to have that clean blend sound. Which seems to be most of them so maybe this bass screamer is a good place for this clipping arrangement after all. Just not for my personal taste. I might think differently about it if I heard it in a band context, though. If you lower the values of C7 and C8, possibly make their values switchable, you get a "less clipping on bass" thing going on, aka a bass boost. This may be an interesting road to explore for bass overdrives.

I really wonder why I have never seen this kind of arrangement anywhere else. It's a bit too obvious. Does anyone else know who else used that?

Cheers,
Andy

[Elektrojänis]

How about having a separate cap for each polarity of the diodes and not connecting them at the center? You would need to separate the D1 and D2... And duh... A dual gang pot to separate the bass control for them.

No, that does not work because the caps just keep loading an loading on every cycle if only one diode direction is connected to them. That shifts the threshold up and up (or down and down). So this is not suitable for getting asymmetry.

Earlier I quicly read this but didn't really have time for thinking it through or answering. My head however started to crunch through this part and I think I understood it.

However, if you add a (variable) resistor between the two C-D junctions, the excess charge can discharge through the resistor. This makes a very nice "adaptive clipping threshold" circuit, great for a very natural dynamic overdrive.

And this par I totally missed first time around, but after understanding the first part I was going to come back with the idea that maybe the loading of the caps could be abused for some special signal dependent clipping behaviour... Oh well... You had it written there already... And then when I really got around reading this thread again, you have a full example circuit here already.

The Blend knob is called thus because it sounds pretty much like a clean blend.

Interesting, even though I kind of whished it would produce something more unusual.

Anyway... I think I learned something here, so thank you very much!

[Fancy Lime]

Moi Petri,

well, it is not super unusual but I think it can be useful. If you want more unusual, you can stick the same arrangement in series after an amplification stage to get adaptive crossover clipping. But in the negative feedback loop, it is mostly good for either the clean blend effect without the phase problems or for dynamic bluesy guitar playing. I experimented some more and found that it is useful to put a conventional clipping arrangement with a higher threshold in parallel, for example two antiparallel red LEDs. This sounds almost like two-stage clipping, very dynamic and expressive with a nice smooth transition from clean to clipped. I also like it better with a more full range clipping instead of the TS mid-treble boost in the gain stage. I should at some point try putting this thing in the clipping stage of a Blues Breaker type circuit. I am fairly certain that it could be useful there for a good amp-in-a-box kind of sound. For my personal taste, it may be a tad too "nice" and civil but one can always market that as "sounds exactly like tubes, man!". Anyway, there is lots more experimentation to be done on this circuit to find out where it fits into the grand scheme of things and how it is best used. Anyone wanna join me?

On an unrelated note, I redesigned the bass control a tiny little bit. Now the boost is a smidgen higher (just under 15db, up from 12db on the old version) and, more importantly, the pot response is a bit more even. On the old version, nothing much was happening above 3 o'clock, now it is pretty even all the way because that is where the extra 3db are sitting. Not perfect when you calculate the db-vs-pot-travel function but about as close as one can reasonably expect from a pot that is readily available without going overboard on the circuit complexity. Here is the new version:



I have also finally worked out some extra features for a deluxe version that allows to change the clipping character and treble via 3-way switches but I still have to put that into the schematic. Coming soon, promise.

Cheers,
Andy

[Fancy Lime]

Hi all,

like I promised, here is the Deluxe Version.



Chareacter switches the corner of the high pass of the gain stage between 1) 330Hz, 2) 660Hz, and 3) 1870Hz. You might call those Fat, Scream, and Rat Mode. You can alter the character of the drive quite drastically with this. Highly recommended. Change R5 and R6 to 2.0k for 723Hz in Scream Mode, or R7 to 1k for an OCD instead of Rat Mode.

Treble switches between 1) highest, 2) llowest, and 3) medium corner frequency of the low pass, which interacts with the setting of the Gain pot. Useful to adjust the bite but might not be necessary. If you can find a cap value here that works for you with your setup, you probably won't need this extra flexibility because the the interactivity with the Gain pot is such that you normally don't need to adjust the treble if you change the gain. But it's definitely a nice option to have.

Mids switches the upper corner of the Bass boost between 1) medium, 2) highest, and 3) lowest. Interactive with the Bass setting and effectively determining how much low mids are boosted along with the bass. Out of the three switches, I find this one the least useful and will probably leave it out of my first build.

Cheers,
Andy

[marcelomd]

Awesome!

[Fancy Lime]

Next iteration. Musing about how to make this as useful as possible for the wider DIY audience, I decided that many people simply expect a bass overdrive to have a blend pot for clean signal of some sort. I tried various different schemes but kept returning to the simplest one, the variable resistance in series with the clipping diodes, or the "just look at the gain formula, will you?", as I like to call it. I called the control "Dry". I have used this before and always liked it better than the "conventional" clean blend with a whole extra signal path and a mixer. Now I finally went to the trouble of trying to find out, who has used that before, and I could not find any commercial examples. Jack has an article on it, though, because of course he has: https://www.muzique.com/news/tube-screamer-mix-control/. The main advantage of this type of mix control is that it avoids the sometimes bothersome phase issues that can occur if you mix two separately treated signal paths back together. So there are no unexpected wholes in the mids that shift around when adjusting gain or tone controls or whatnot. The main disadvantage is, that you cannot do separate frequency shaping very easily (at least not without opening the door for other issues). For this reason, I had to also add a second ground leg on the first opamp (R6 and C4). This keeps the gain below about 150Hz constant. Without it, the string to string balance in the lowest register suffers when the Dry control is set high. The addition of the second ground leg has the added benefit that the bass and mids are pretty flat when the Bass knob is set to 12 o'clock, giving a nicely balanced sound with lots of room for cutting or boosting bass to taste.

I must say, I really like the Dry control more than I thought I would. Controls the punch very effectively. The interactivity with the Gain control is rather limited, so dialing in the right sound is not fiddly, as I feared it might be. Turing up the Dry adds volume, though, so that needs to be adjusted. I also figured out that I like a linear taper better for the gain knob in this thing. Seems to spread out the useful settings better. For good measure, I changed the volume pot to linear 100k as well, with a 10k resistor changing the taper to log-like. Always nice to get by on linear pots when possible. R9 and C12 form an additional low pass filter at 3300Hz, to remove the nails-on-blackboard frequencies.



This is shaping up to be my favorite bass overdrive by far. I really need to get my $#!+ together and make a PCB layout for this...

Cheers,
Andy

[iainpunk]

hey, cool that you kept going and came up with a new iteration. if i have space on my breadboard ill give this one a whirl.

Now I finally went to the trouble of trying to find out, who has used that before, and I could not find any commercial examples. Jack has an article on it, though, because of course he has: https://www.muzique.com/news/tube-screamer-mix-control/.

im kind of shocked that you coulndt find any commercial examples, seems such an obvious trick and it has been popular in the DIY  scene for quite a while

cheers