anyone know of a simple transparent boost that I can add on to Tubescreamer?

[Hav]

Hey all,

I am putting 2 effects into one box, basically want a simple transparent boost before a tubescreamer, but slightly unsure as to how I could link two circuits together (want to etch just the one PCB).

Can anyone help me out with this? I have used the tubescreamer from General Guitar Gadgets, but cant find any SIMPLE boosters that don't require extra-ordinary components like Reserve Pots etc... it just gets too expensive. Would like to keep using the GGG layouts if possible...

Can I just link the Negative rails together on the PCBs?

I would want them to be on two separate DPDT switches (using Millenium Bypass), and most importantly the boost has to be completely transparent..

GGG TS: http://www.generalguitargadgets.com/effects-projects/distortion/tube-screamer/

Thanks in advance
ps/ still a bit of a newbie
:-)

[Mark Hammer]

R17 (1k), in that diagram, is jointly responsible for the gain of that op-amp stage.  If you increase it, the gain will also be increased.  Consider placing a 5k variable resistance (pot) in series with R17.  You can use the pot to set it for whatever amount of additional gain you want, and use a footswitch to simply bridge the pot to drop back down to the default gain dictated by R17.  Since the added gain occurs after the clipping stage, there should be negligible impact on tone.  Of course, because having a hotter output will impact on subsequent pedals and your amp, I hesitate to call it either clean or transparent.  But there is no deliberate change in tone anticipated.

[midwayfair]

R17 (1k), in that diagram, is jointly responsible for the gain of that op-amp stage.  If you increase it, the gain will also be increased.  Consider placing a 5k variable resistance (pot) in series with R17.  You can use the pot to set it for whatever amount of additional gain you want, and use a footswitch to simply bridge the pot to drop back down to the default gain dictated by R17.  Since the added gain occurs after the clipping stage, there should be negligible impact on tone.  Of course, because having a hotter output will impact on subsequent pedals and your amp, I hesitate to call it either clean or transparent.  But there is no deliberate change in tone anticipated.

Except that the gain is frequency-dependent on the setting of the tone knob, and will also vary with the tone knob's setting. Increasing it even to 22K when the tone knob is at minimum, for instance, would still be unity gain. And it wouldn't be transparent.

To actually do what you're suggesting, the op would need to disconnect the op amp side of the tone pot (removing the treble boost side of the control), connect C9 to R17, and C9 would need to be increased several fold to become a full-range gain stage.

[karbomusic]

If you are building someone else's layout/design then this is more than you want but I did similar by ripping out the transistor buffers (both of them) and replaced with opamps as buffers which I then turned into a transparent boost. Boost the input side if you want to drive the TS circuit, boost the output side if you just want to take the TS result and make it louder to push the input of the amp. The latter is what I used because I like pushing the input of tube amps.  

I actually went further than that, I used two dual opamps (2134s) and used the extra sides of both for a clean channel that passes through and also becomes a clean boost. Both of which are adjusted by a blend pot at the end of the chain before the volume pot. Result... I love it.

[alparent]

Would a LPB-1 in front work?

[induction]

Hi Hav,
It would be helpful if you could tell us what sonic result you are trying to achieve. There are plenty of fairly simple transparent boosts around (AMZ mosfet booster, MXR Micro Amp, etc.), but if you put them in front of your tubescreamer, the result won't really be transparent. Even if you put the boost after the tubescreamer, you will probably end up changing the tone coming from your amp. Are you looking for more distortion from the tubescreamer, more distortion from the amp, or just more volume from the amp? What kind of amp are you using?

[Mark Hammer]

Would a LPB-1 in front work?

Not really.  It would get more overdrive, but the clipping diodes set the maximum possible level.  If his intention is to simply have a louder output, any boost needs to come after the clipping.

Except that the gain is frequency-dependent on the setting of the tone knob, and will also vary with the tone knob's setting. Increasing it even to 22K when the tone knob is at minimum, for instance, would still be unity gain. And it wouldn't be transparent.

Well, you're right that the added gain would depend on the tone-control setting, since that control sets the gain of the op-amp stage as well.  But if a person has the tone set to where they want it, a little bit more series resistance will just make it louder/hotter.  I've replaced the 1k with 2k2 for a hotter output, and it still sounds like a TS.

[alparent]

Ok ... Would a LPB-1 after, work?

[Hav]

Thank you so much for your replies!

R17 (1k), in that diagram, is jointly responsible for the gain of that op-amp stage.  If you increase it, the gain will also be increased.  Consider placing a 5k variable resistance (pot) in series with R17.  You can use the pot to set it for whatever amount of additional gain you want, and use a footswitch to simply bridge the pot to drop back down to the default gain dictated by R17.  Since the added gain occurs after the clipping stage, there should be negligible impact on tone.  Of course, because having a hotter output will impact on subsequent pedals and your amp, I hesitate to call it either clean or transparent.  But there is no deliberate change in tone anticipated.

This sounds good, and I can't exactly engage in this conversation because I just don't know enough to do so, but if what Mark Hammer is saying, it will alter the sound of the Tube screamer too much?  BUT this is EXACTLY the kind of thing im looking for. A nice mod that will just let me boost the Screamer.

Hi Hav,
It would be helpful if you could tell us what sonic result you are trying to achieve. There are plenty of fairly simple transparent boosts around (AMZ mosfet booster, MXR Micro Amp, etc.), but if you put them in front of your tubescreamer, the result won't really be transparent. Even if you put the boost after the tubescreamer, you will probably end up changing the tone coming from your amp. Are you looking for more distortion from the tubescreamer, more distortion from the amp, or just more volume from the amp? What kind of amp are you using?

Hi! I am quite literally looking to have the tube screamer boosted. Why? I'm playing some rhythm with the TS, and want to roll into a solo, need the boost, but want the SAME (or as close to) sound as the TS. I don't mind if its slightly different to be honest, but If I have it in the order of BOOST > TS, and the boost is as transparent as it can be, it will do the job just fine right?

Those booster you mentioned, and please correct me if im wrong but they require some odd components. I can't check right now. Maybe its the case that i'll just have to buy a bunch of them anyway. Again, I would like to have just the one PCB to etch... so how would these link? 

End of day, I want a footswitch that will just BOOST my TS as cleanly as possible.

Thank you guys, hopefully someone can come up with a successful idea on how to do this.

[karbomusic]

End of day, I want a footswitch that will just BOOST my TS as cleanly as possible.

The best solution for that requirement would to simply place a clean boost pedal after the TS or last thing before the amp. That will take what you have and bring it up a notch. The only thing you need to worry about is slightly overdriving the input of the amp but tube screamers were designed and intended (IMHO) to do just that with a tube amp anyway and I think it will sound even better if it does push the amp input. Try it. YMMV.

[mth5044]

Ok ... Would a LPB-1 after, work?

Still, not really. The LPB-1 isn't really considered a transparent boost.

A SHO or a AMZ boost would do fine, but OP doesn't want a reverse log taper pot, although they are readily available.

Wait, does the AMZ need a C taper pot?

[karbomusic]

Still, not really. The LPB-1 isn't really considered a transparent boost.

A SHO or a AMZ boost would do fine, but OP doesn't want a reverse log taper pot, although they are readily available.

Wait, does the AMZ need a C taper pot?

Based on his last reply, I don't think that would really matter if all they want is what they already have a little louder. Maybe we are all are overthinking something simple. I might recommend the "variable gain" booster at the bottom of this article:

http://www.muzique.com/lab/boost.htm

[J0K3RX]

I am curious, have you actually tried this combination "boost > tube screamer" and, what is this running into? Everybody likes different things but in my experience a boost in front of a tube screamer does not sound too good... Especially if you are going to try to play a lead! If you are playing rythym and want a bump when you go into a lead but you don't want to drive the gain or level more then this called "volume" in which case you can just boost the volume or pay the sound guy $10 to push the slider up when you play a lead. You might try to put a second "level" pot on a foot switch and when you play lead you can toggle to different level setting.

[induction]

want the SAME (or as close to) sound as the TS. I don't mind if its slightly different to be honest, but If I have it in the order of BOOST > TS, and the boost is as transparent as it can be, it will do the job just fine right?

Just to reiterate what others have said, if all you want is to sound the same but louder, then boost > TS is the wrong way to go. The general principle is this: boost the input of a gain stage for more distortion, boost the output for more volume. If you put the boost before the TS it will get more distorted, but may not get any louder at all, depending on your settings. If you boost the output of the TS (assuming the TS goes straight to the amp), then it might get louder or it might just get more distorted, depending on what kind of amp you have and how close to breakup it already is. If I boost the input of my Vox AC-4 with the amp volume above 9:00, it doesn't get any louder at all.

For a definitive answer, we need to know what kind of amp you are using, and how you tend to have it set.

Does it have an effects loop? Sometimes a booster in the effects loop will do exactly what you want (just make it louder), even when the same booster at the amp input just makes it dirtier.

There are no odd components in a AMZ mosfet booster or a MXR Micro Amp, at least not by my definition of 'odd'. If the reverse log taper Level pot in the Micro Amp is a problem, just use a linear taper. It sounds like you want to set and forget it anyway, so the taper isn't a big deal. Or, as karbomusic says, build the variable gain booster in the link, which is pretty much the same thing as the Micro Amp after you add the hidden components except that the gain control is implemented slightly differently.

Edit: JOK3RX's idea of a stomp switch for a second volume pot could is a good idea, too. It might end up sounding the same as a booster after the TS. Whether that gives you more volume or more distortion still depends on your amp.

[Mark Hammer]

General question to those with more transistor insight that I have:   Can the transistor output buffer be tweaked to provide gain, instead of just being unity gain?

[PBE6]

Some simple ideas:

1. Insert a voltage divider using a normal 10k log pot after the common drain buffer (between C2 and R5 on the GGG schematic http://www.generalguitargadgets.com/pdf/ggg_its8_sc.pdf), and just add another 1-10uF cap after it (before R5) to block the bias voltage to the opamp. Then wire a SPDT switch (a 3PDT switch will work fine as well) that shorts lug 3 to lug 2 to bypass the top of the voltage divider and provide full volume.

2. Alternately, wire a DPDT switch (again a 3PDT switch will be fine) that bypasses the feedback resistors R7 and R19 and replaces it with a lower value resistor, or better yet a pot wired as a variable resistor.

Both of the above will provide additional volume and overdrive to the signal with minimal parts, but will always be filtered by the rest of the circuitry. If by "transparent" you mean the quiet and loud signals have a similar fundamental frequency response, these will work fine. If you're looking for your clean guitar signal only louder, any if the above suggested boost circuits should work fine (I find a simple TL071/TL072 opamp gain stage to be the easiest to work with, and no strange pots are required). Again, placing it before the Tubescreamer will give you more overdrive, placing it after gives you more volume (provided the signal isn't so hot that the booster - or your amp! - starts breaking up).

[YouAre]

Would a LPB-1 in front work?

Not really.  It would get more overdrive, but the clipping diodes set the maximum possible level.  If his intention is to simply have a louder output, any boost needs to come after the clipping.

Correct me if I'm wrong (which is often the case with you and I ), but clipping diodes only clamp the output level provided the input signal doesn't exceed the diode threshold, right?

Let's say we have a 200mV input signal. We apply that to our gain stage, let's say at 3x gain, and we get an output of 600mV. This will be below our theoretical 700mV diode voltage drop, so there's no clipping. Bump up that gain to 4x or 5x, and we get clipping and an output of around 700mV (probably a hair higher).

When the diodes conduct, we're essentially bypassing and shorting the gain pot. This effectively turns the stage into a unity gain buffer of sorts I guess? The gap in my understanding is how bypassing the gain put gives us the 700mV output, and not an output that matches the theoretical input 200mV.

Let's throw another monkey wench in here. What if we slam this with a boosted signal, let's say 2V. The 2V hits the diodes, they immediately conduct...then what? Does the output stay at 700mV, or is it closer to the 2V input?

[PBE6]

YouAre, this used to bother the bejesus out of me because if you put a Tubescreamer on a scope you see something quite different than what you expect.

In an ideal world, if you place diodes in the feedback loop of a non-inverting gain stage (just like the Tubescreamer), then once the boosted signal reaches their forward voltage threshold the diodes start conducting like crazy. However, this does NOT turn the gain stage into a unity gain buffer (this is the counter intuitive part - you would think the diodes turn into essentially straight wires at this point, but they don't). The reason is that the forward voltage drop across the diode affects the opamp performance, as becomes clear if you look at the governing equations:

Vout = Av(v+ - v-)

In a normal gain stage, v- will be some proportion of Vout based on the voltage divider formed by Rf and Rg. The trick here is to see that when the diode is conducting, v- is not simply equal to Vout as in a buffer, but:

V- = Vout - Vdiode

Subbing this back into the first equation we get:

Vout = Av(v+ - v-) = Av(v+ - (Vout - Vdiode))

Dividing by Av (a huge number), we get approximately:

0 = v+ - (Vout - Vdiode)

Solving for Vout:

Vout = v+ + Vdiode

This means that the output is a combination of the original signal (v+) and the clipped signal (Vdiode). This is responsible for the relative transparency of a Tubescreamer-style overdrive (if you listen closely, the original signal can be heard alongside the hash), as opposed to a MXR Dist+ style distortion where any signal above Vdiode is simply chopped off. This also explains the shape of the waveform of a Tubescreamer being fed a sine wave, which looks like a normal sine wave but pinched on the sides and stretched upwards in the middle.

In answer to your other question, the output from a 2 V input would be close to 2.7 V and not 0.7 V as you might otherwise expect.

[David]

What about an Adjusticator?  Pretty simple, runs on 9V, huge gain AND even cut if you need it.  You could crank the crap out of the Screamer's output but still keep the overall level manageable by cutting the level on the Adjusticator.

[ashcat_lt]

...
In a normal gain stage, v- will be some proportion of Vout based on the voltage divider formed by Rf and Rg. The trick here is to see that when the diode is conducting, v- is not simply equal to Vout as in a buffer, but:

V- = Vout - Vdiode
...

It's actually more correct to realize that the diodes are not switches, but basically variable resistors which get smaller as the voltage across them gets bigger, but that gets weird fast...

In practice it is about like you said - very much like a mix between the clipped signal and the clean.  In fact, you can get an interesting approximation by putting a clean blend pot into a diode-to-ground style distortion box, though a Rat will give you a lot more gain than a TS ever would.

The hard limit on the TS output is actually the opamp rails (or maybe the transistor buffer's limit).  Theoretically, with big enough power supply, it'll just keep getting louder and (at least after a certain point) sound cleaner* as the input or the gain of the opamp stage gets bigger.

I'm kinda wondering like Mark about modifying the output buffer.  I'm not real great with transistors, but it seems to me like making R14 bigger should increase the gain at that stage.



*That is, if it doesn't hit the rails, the output of the TS will have less distortion.  Whatever's downstream of the thing, OTOH...