I'm confused about boost pedals

Lebarque

I love setting my clean boost (Keeley Katana Mini) so that it pushes my clean amp to on-the-edge break up.

When I crank the volume on my Klon-style pedal (with gain right down) to achieve the similar level of on-the-edge break-up, the volume coming out of the amp is significantly higher. Why's that?

Also, what does 'high headroom' boost mean, such as the Thorpy Heavy Water?

TIA

slacker

Electronics baffle me but I think the klon runs internally at 18 volts giving more volume. 

fastonebaz

I think its a sign.... that you need more gain.... more is more. 

monquixote

Purely a guess but the Klon is a bit more mid forward so it might sound louder.

Danny1969

Most boost / dirt pedals are running from 4V really internally. You have 9V going in but you need a dual supply for audio so the only way to get that is to cut the 9V in half. Then 9V is +4.5V, 4.5V is 0V and actual 0V is now -4.5V .... now a dual supply but only around 3.8 to 4V of headroom really unless it's a rail to rail opamp or similar circuit. 

The last opamp in the Klon circuit does run at 17V or so from memory as the circuit has a 7660 chip which can raise the voltage and create a negative rail so that last opamp does have a lot of headroom. 

Headroom is simply the room between the lowest signal and the highest you can go before the signal needs to be a higher voltage than the supply voltage. Imagine a man jumping up and down in a house. The signal strength is the height of the man. The height of the ceiling is the supply voltage. The gain is how high you tell him to jump. If he is 5 foot and the ceiling is 15 foot then he can only have a gain of  x 3 before he hits his head

ecc83

 Not quite Danny. The 9V supply for op amp pedals is not "cut in half" but a 1/2 volt supply rail is derived. The usual way is with two equal value resistors in series. Better is to use a spare op amp section. Thus the chips still run at 9V and the peak to peak output should be close to 8 volts. That resolves to 4V peak or 2.8V rms. Can we say 3 V for R&R? Thus, max V out is 3V or about +10dBV and so, rather nicely I think, we get an 'operating' level' 300mV or -10dBV. Our well known "neg ten'.

The 1/2vss rail becomes the common 'zero volts' for the whole pedal.

And yes, better to boost just the mid band or you tend to get 'much'.

Dave.

Sporky

Lebarque said:

When I crank the volume on my Klon-style pedal (with gain right down) to achieve the similar level of on-the-edge break-up, the volume coming out of the amp is significantly higher. Why's that?

I think the two pedals have differently EQ'd outputs, and the Klon puts out less of the frequencies that push the amp into breakup, so the overall volume is higher when that happens.

If I remember correctly the Klon cuts bass and pushes upper mids a bit. Perhaps your amp breaks up first in response to lower frequencies, so by the time it's breaking up with the Klon on it's actually quite a bit louder than with a clean boost. Also mids tend to sound loud.

Danny1969

ecc83 said:

 Not quite Danny. The 9V supply for op amp pedals is not "cut in half" but a 1/2 volt supply rail is derived. The usual way is with two equal value resistors in series. Better is to use a spare op amp section. Thus the chips still run at 9V and the peak to peak output should be close to 8 volts. That resolves to 4V peak or 2.8V rms. Can we say 3 V for R&R? Thus, max V out is 3V or about +10dBV and so, rather nicely I think, we get an 'operating' level' 300mV or -10dBV. Our well known "neg ten'.

The 1/2vss rail becomes the common 'zero volts' for the whole pedal.

And yes, better to boost just the mid band or you tend to get 'much'.

Dave.

Well that's a bit nit picking don't you think ?

My point was an analog audio circuit isn't like a DC lamp circuit. It needs a dual supply and the only way to get 2 swings from a single supply is to cut it in half and use the  mid point as 0V  ... 2 equal resistors operating as a voltage divider is the most used, and in my opinion should be drawn as part of the main circuit, not drawn separately and called a power supply like so many pedal schematics do as this voltage divider affects the input impedance. 

ecc83

SO don't want to upset you Dan but to say the supply is cut in half is just wrong. The op amp output needs to sit at 4.5V to give the full Vss swing. The same applies even to discrete transistors where the collector voltage will also sit close to 1/2Vss IF the designer has done his job right!

In practice, "rail to ral" special op amps will give more headroom than discretes.

Dave.

Wazmeister

So, some boosts do have more headroom.

King here, as Ive tried many many, is the Cornish NB3. Seems to increade your volume, without od the sound.

Now, I own the Echoline SIGNAL DRIVER, which is an EXACT klone of the NB3; ive compared em side by side.

And no, Im not on commission but for £99 this is a no brainer. See the discount link here;

https://www.thefretboard.co.uk/discussion/comment/3843108#Comment_3843108

Sporky

I'm a bit confused by Danny and ECC's stuff.

I've always seen it as (in most pedals) the op-amp runs on single supply of 9v, and the signal is biased to 4.5v, so with a typical op-amp you end up with a signal up to 8v peak to peak.

If you run a voltage doubler in the pedal then you can either have the op-amp supply rails at about 9v and about -8.3v (because you typically lose 0.7v to the diode in the doubler circuit), or you have a single supply rail at about 17.3v and bias to half that. Then your maximum output signal is typically around 16v peak to peak.

No?

Danny1969

ecc83 said:

SO don't want to upset you Dan but to say the supply is cut in half is just wrong. The op amp output needs to sit at 4.5V to give the full Vss swing. The same applies even to discrete transistors where the collector voltage will also sit close to 1/2Vss IF the designer has done his job right!

In practice, "rail to ral" special op amps will give more headroom than discretes.

Dave.

Maybe I didn't use the right words to explain what I was getting at but I think anyone reading it will get the gist. By creating a halfway voltage point (cutting it in half in terms of voltage potential difference ) and calling that 0V the signal can then swing either side of it like an AC signal needs to. 

ecc83

I honestly can't see what the confusion is about? This is 'electronics 101' No matter the device, if you want the maximum, undistorted voltage swing from a stage you bias it so that the collector, anode* drain or op am pin 6 is at half the supply voltage (if you need a "sync separator' for your telly or 'scope. you don't!)

The 1/2 rail point is just a bias reference.

*Valves are slightly different from Silicon devices in that they cannot swing very close to zero volts. However, bottles have SUCH a massive voltage headroom in this context that a volt or ten matters little.

Dave.

Sporky

ecc83 said:

I honestly can't see what the confusion is about? This is 'electronics 101'

Indeed, and I went rather past that level at uni. I think it was when you went from 8V pk-pk to it being 3V. Or Danny's bit about it being a 4V supply internally - surely it's +/- 4.5V.

And none of it has anything to do with the original question!

Danny1969

Sporky said:

ecc83 said:

I honestly can't see what the confusion is about? This is 'electronics 101'

Indeed, and I went rather past that level at uni. I think it was when you went from 8V pk-pk to it being 3V. Or Danny's bit about it being a 4V supply internally - surely it's +/- 4.5V.

And none of it has anything to do with the original question!

I said dual 4.5V is the power supply but headroom more like 4V either way as most opamps can't swing to full rail unless it's a rail to rail opamp 

Dave, no confusion on my part. I know exactly how to bias an opamp or tranny stage from a single supply. It's just you didn't like my use of the words "cut the supply in half" ... rather than create a voltage divider of half the supply rail 

mgaw

Schemantics !

Lebarque

My thread seems to have been de'railed'! Thanks for speaking in English, @Sporky . Your suggestion about the differing frequencies pushing the amp into breakup sooner/later could well be right.

Thanks also, @Wazmeister . That's useful to know. Funnily enough, I probably lean to the opposite: boost pedals that push an amp into breakup sooner.

I'm still confused about what a high headroom boost is though. @ThorpyFX Heavy Water is marketed as such, but what are the benefits? Waz's assertion seems to be that means it will provide more of a volume boost and not push the amp into breakup so soon. But is that right?

And what effect do the quoted DB figures on pedals have? What's the advantage of having a 35DB boost over a 20DB one? I understand it will be louder, but does that mean more headroom etc. etc.

In my simple head, if you're running a clean amp and slam it with a boost, the clean sound will get louder to the point where the amp is receiving so much signal that it runs out of headroom and starts breaking up.

I'm still confused how DBs and boost headroom fits into this. And how different volumes and levels of breakup are achieved by different boosts.

ThorpyFX

Lebarque said:

My thread seems to have been de'railed'! Thanks for speaking in English, @Sporky . Your suggestion about the differing frequencies pushing the amp into breakup sooner/later could well be right.

Thanks also, @Wazmeister . That's useful to know. Funnily enough, I probably lean to the opposite: boost pedals that push an amp into breakup sooner.

I'm still confused about what a high headroom boost is though. @ThorpyFX Heavy Water is marketed as such, but what are the benefits? Waz's assertion seems to be that means it will provide more of a volume boost and not push the amp into breakup so soon. But is that right?

And what effect do the quoted DB figures on pedals have? What's the advantage of having a 35DB boost over a 20DB one. I understand it will be louder, but does that mean more headroom etc. etc.

In my simple head, if you're running a clean amp and slam it with a boost, the clean sound will get louder to the point where the amp is receiving so much signal that it runs out of headroom and starts breaking up.

I'm still confused how DBs and boost headroom fits into this. And how different volumes and levels of breakup are achieved by different boosts.

Ok, there is always variations as to how people use terminology with regards to pedals and amps. 

What I MEAN by high headroom boost is as follows,

firstly I describe headroom as the amount signal space you have before the pedal begins to distort itself. What this means with regards the heavy water is that it doesn’t distort itself until the very upper reaches of the boost knob. Until that point it just keeps on boosting the signal you put into it and making it louder in order to “hit” the front end of your valve amp harder. This essentially causes your amp to distort but without adding too much extra distortion to the mix. 

Now if you boost heavily into heavy water then eventually you’ll breach the headroom of the boost… everything has limits 

Hope that makes sense? 

Neilybob

Lebarque said:

I love setting my clean boost (Keeley Katana Mini) so that it pushes my clean amp to on-the-edge break up.

I share your love of this superb little pedal. When I use it to push my tweed 5E3 over the edge into distortion it is just epic. 

How do you have the internal dip switches set? 

Lebarque

ThorpyFX said:

Lebarque said:

My thread seems to have been de'railed'! Thanks for speaking in English, @Sporky . Your suggestion about the differing frequencies pushing the amp into breakup sooner/later could well be right.

Thanks also, @Wazmeister . That's useful to know. Funnily enough, I probably lean to the opposite: boost pedals that push an amp into breakup sooner.

I'm still confused about what a high headroom boost is though. @ThorpyFX Heavy Water is marketed as such, but what are the benefits? Waz's assertion seems to be that means it will provide more of a volume boost and not push the amp into breakup so soon. But is that right?

And what effect do the quoted DB figures on pedals have? What's the advantage of having a 35DB boost over a 20DB one. I understand it will be louder, but does that mean more headroom etc. etc.

In my simple head, if you're running a clean amp and slam it with a boost, the clean sound will get louder to the point where the amp is receiving so much signal that it runs out of headroom and starts breaking up.

I'm still confused how DBs and boost headroom fits into this. And how different volumes and levels of breakup are achieved by different boosts.

Ok, there is always variations as to how people use terminology with regards to pedals and amps. 

What I MEAN by high headroom boost is as follows,

firstly I describe headroom as the amount signal space you have before the pedal begins to distort itself. What this means with regards the heavy water is that it doesn’t distort itself until the very upper reaches of the boost knob. Until that point it just keeps on boosting the signal you put into it and making it louder in order to “hit” the front end of your valve amp harder. This essentially causes your amp to distort but without adding too much extra distortion to the mix. 

Now if you boost heavily into heavy water then eventually you’ll breach the headroom of the boost… everything has limits 

Hope that makes sense? 

Many thanks, @ThorpyFX ;

I'm finding that using PAFs into my Keeley Katana Mini results in light breakup at a volume level that's not much higher than when the pedal's off. This is a good thing for home playing, but does it mean that the pedal is a low headroom boost and is distorting itself rather than pushing the amp into breakup?

And if I used the high headroom Heavy Water, would it be much louder when a) the amp started breaking up or the pedal started distorting itself at the end of the dial?

And where do dB's fit into it?

ThorpyFX

Lebarque said:

ThorpyFX said:

Lebarque said:

My thread seems to have been de'railed'! Thanks for speaking in English, @Sporky . Your suggestion about the differing frequencies pushing the amp into breakup sooner/later could well be right.

Thanks also, @Wazmeister . That's useful to know. Funnily enough, I probably lean to the opposite: boost pedals that push an amp into breakup sooner.

I'm still confused about what a high headroom boost is though. @ThorpyFX Heavy Water is marketed as such, but what are the benefits? Waz's assertion seems to be that means it will provide more of a volume boost and not push the amp into breakup so soon. But is that right?

And what effect do the quoted DB figures on pedals have? What's the advantage of having a 35DB boost over a 20DB one. I understand it will be louder, but does that mean more headroom etc. etc.

In my simple head, if you're running a clean amp and slam it with a boost, the clean sound will get louder to the point where the amp is receiving so much signal that it runs out of headroom and starts breaking up.

I'm still confused how DBs and boost headroom fits into this. And how different volumes and levels of breakup are achieved by different boosts.

Ok, there is always variations as to how people use terminology with regards to pedals and amps. 

What I MEAN by high headroom boost is as follows,

firstly I describe headroom as the amount signal space you have before the pedal begins to distort itself. What this means with regards the heavy water is that it doesn’t distort itself until the very upper reaches of the boost knob. Until that point it just keeps on boosting the signal you put into it and making it louder in order to “hit” the front end of your valve amp harder. This essentially causes your amp to distort but without adding too much extra distortion to the mix. 

Now if you boost heavily into heavy water then eventually you’ll breach the headroom of the boost… everything has limits 

Hope that makes sense? 

Many thanks, @ThorpyFX ;

I'm finding that using PAFs into my Keeley Katana Mini results in light breakup at a volume level that's not much higher than when the pedal's off. This is a good thing for home playing, but does it mean that the pedal is a low headroom boost and is distorting itself rather than pushing the amp into breakup?

And if I used the high headroom Heavy Water, would it be much louder when a) the amp started breaking up or the pedal started distorting itself at the end of the dial?

And where do dB's fit into it?

 Correct the keeley katana is breaking up itself earlier. This isn’t a bad thing as the character of the katana is great. 

The heavy water will distort the preamp of your amp at the same point the katana does because the common denominator is the headroom limit of your amp. The katana will sound dirtier earlier because it will be adding its own distortion to the mix. 

The heavy water will remain cleaner for longer and when your amp starts to distort it’ll be the preamp doing its thing only. Push past that point and the heavy water will start to clip mildly and that’ll mix in with the amps distortion.

as for dBs… this is a logarithmic scale to describe sound pressure levels in this case. 

More dBs equals more boost available…