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Running Pedals at 18V


bassist_lewis
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I got a Fulltone OCD last week, and its a great "transparent" overdrive, though also has a nice mid-push with the HP switch. It runs at 9V and 18V, so I got an adapter because every forum says that running at 18V is better than 9V (more headroom, more dynamics etc). I AB'd it at both voltages and honestly I can't hear or feel much difference. Maybe a tiny bit more top end/high-mids.

Are my ears dumb or is it just another of those pedal myths?

Edited by bassist_lewis
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I know its not the same as a pedal, but I could definitely hear a difference powering an 80s EMG precision pickup with 18v compared with 9v, in fact once I was used to hearing it with 18v it actually sounded quite unpleasant with 9v - almost like it was overcompressed. I couldn't however hear a difference doing the same comparison with a more modern EMG PJX set

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Like hifi it's the law of diminishing returns. Technically it'll be better at 18v but to your ears it'll be minimal. Then there's the other pedals your signal will go through, plus your amp, plus your speaker cab....

Edited by Boodang
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6 hours ago, bassist_lewis said:

I got a Fulltone OCD last week, and its a great "transparent" overdrive, though also has a nice mid-push with the HP switch. It runs at 9V and 18V, so I got an adapter because every forum says that running at 18V is better than 9V (more headroom, more dynamics etc). I AB'd it at both voltages and honestly I can't hear or feel much difference. Maybe a tiny bit more top end/high-mids.

Are my ears dumb or is it just another of those pedal myths?

 

I call cow poop on 18v, the vast majority of audio processing in the world is done at half a volt or less so not sure why bass preamps or effects would get some magic benefit from a massively higher voltage. I cant hear any fundamental difference between my 18v status and a 9v active (or even passive) instrument. 

Edited by bassman7755
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9 hours ago, bassman7755 said:

 

I call cow poop on 18v, the vast majority of audio processing in the world is done at half a volt or less so not sure why bass preamps or effects would get some magic benefit from a massively higher voltage. I cant hear any fundamental difference between my 18v status and a 9v active (or even passive) instrument. 

 

But some electronic devices eg OpAmps don't operate to the same spec' at lower voltages. A 9V supply means that an OpAmp is running at only +/-4.5V. Let's say it needs a 1V headroom so a 3.5V peak. This approximates to a 2.5Vrms signal. A transient from a medium to high output passive pickup can exceed this. Plus spec in terms of THD+N etc is likely worse than at higher voltage supply. Then if it's on a battery then that battery voltage will fall a bit over time and make the situation worse. (How it decreases depends on the battery chemistry type).

Increasing the voltage to 18V likely more than doubled the signal headroom (because the 1V gap needed to the voltage rail doesn't double) and the audio spec is probably better.

Of course, if you are running some high gain "Ultra Shred" pedal it probably doesn't matter and you may prefer the result with lower supply voltage. Hence the thing about "vintage" batteries that 'sag' analogous to voltage sag in some amp designs 

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Dave Hall used to say that some of his preamps would run at 9V but would give much better performance with 12 or 18. Sadly he's no longer around to ask. 

 

I have an elderly Ibanez chorus pedal from the 80's which requires 18V, but the first circuit drops the voltage down to 12V. Maybe this was Ibanez's way of coping with sagging analog batteries.

 

I also have a Triton overdrive which includes an internal 'pump' circuit to increase the 9V supply to 18V. I guess that Triton know what they are doing and aren't doing this just to be clever, so there must be some practical benefit. Empirically, it's an excellent sounding pedal so I'm a believer.

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Dave Hall pedals have an internal ‘charge pump’ that doubled the voltage internally, so a 9v dc supply would become 18 by the time it hit the components.

 

I tried my DHA deals at 12v, then experimented with them at 9v - there was a noticeable difference in the sound; the break up came in earlier and the tone control didn’t sound as good.

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I think the main difference with the higher voltage is greater headroom- essentially allowing greater amplitude before clipping. In terms of a preamp, it means that transients will be reproduced more accurately, or basically it will provide greater clean volume. This is also a good thing for keeping, say, modulation effects distortion free.

As for an overdrive it will push the clipping points further round the dial, making for less saturation, but greater range at the bottom of the dial.

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4 hours ago, rmorris said:

 

But some electronic devices eg OpAmps don't operate to the same spec' at lower voltages. A 9V supply means that an OpAmp is running at only +/-4.5V. Let's say it needs a 1V headroom so a 3.5V peak. This approximates to a 2.5Vrms signal. A transient from a medium to high output passive pickup can exceed this.

 

But you could presumably just passively voltage divided the input before the opamp input (which is what the volume control in the bass is doing essentially). Also why are all these 9v effects units and preamps not clipping all the time if this is such a problem ?. Also my B4-1 sounds exactly the same at 5v USB power as it does at 9v so presumably internally its running at just 5v.

 

Quote

Plus spec in terms of THD+N etc is likely worse than at higher voltage supply. Then if it's on a battery then that battery voltage will fall a bit over time and make the situation worse. (How it decreases depends on the battery chemistry type).

Increasing the voltage to 18V likely more than doubled the signal headroom (because the 1V gap needed to the voltage rail doesn't double) and the audio spec is probably better.

 

So why does hifi and studio equipment get by just fine with high SNRs when using  line level signals everywhere, the highest level being +4db / 3.5v peak to peak ?. 

 

Still not convinced this is anything other than voodoo folklore to part bassists with more money.

 

Edited by bassman7755
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14 minutes ago, Jus Lukin said:

I think the main difference with the higher voltage is greater headroom- essentially allowing greater amplitude before clipping. In terms of a preamp, it means that transients will be reproduced more accurately, or basically it will provide greater clean volume. This is also a good thing for keeping, say, modulation effects distortion free.

As for an overdrive it will push the clipping points further round the dial, making for less saturation, but greater range at the bottom of the dial.

I tried using it at higher gain about an hour ago and I think there was slightly less compression that at 9V, not something you would notice in a band situation. I also haven't noticed any difference in where it starts to break up or the variation at lower settings, between the two voltages.

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17 minutes ago, bassman7755 said:

 

But you could presumably just passively voltage divided the input before the opamp input (which is what the volume control in the bass is doing essentially). Also why are all these 9v effects units and preamps not clipping all the time if this is such a problem ?. Also my B4-1 sounds exactly the same at 5v USB power as it does at 9v so presumably internally its running at just 5v.

 

 

So why does hifi and studio equipment get by just fine with high SNRs when using  line level signals everywhere, the highest level being +4db / 3.5v peak to peak ?. 

 

Still not convinced this is anything other than voodoo folklore to part bassists with more money.

 

I'm leaning towards voodoo... still a great pedal though.

Edited by bassist_lewis
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2 hours ago, bassist_lewis said:

I tried using it at higher gain about an hour ago and I think there was slightly less compression that at 9V, not something you would notice in a band situation. I also haven't noticed any difference in where it starts to break up or the variation at lower settings, between the two voltages.

A circuit with a particular gain structure will have less overdrive when running at a higher voltage given the same input signal.

 

The question is - if you increase/decrease the gain inline with the rail voltage, does the circuit behave significantly differently. In the case of this pedal, does it sound any worse, or have a noticeably worse SNR at the lower voltage if you turn the gain down to compensate ?, I'm guessing not. "headroom" / "dynamics" are just SNR i.e. relative not absolute, if you have proportionately less noise at the lower voltage then there is no headroom reduction.

Edited by bassman7755
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8 hours ago, bassman7755 said:

 

So why does hifi and studio equipment get by just fine with high SNRs when using  line level signals everywhere, the highest level being +4db / 3.5v peak to peak ?. 

 

 

 

Hi. I see your whole post. But quickly on this - cos I'm on mobile and a tediously slow train from London to Brighton 🙄 - the pro line level is nominally +4dBu that does indeed equate to approx 3.5V pk-pk. But any system is expected to handle peak levels in the range of typically 21 to 24 dBu requiring Voltage rails in excess of +/- 9V or 12V.

Typical pro audio gear runs OpAmps at minimum +/-15V and typically +/-17V.

 

 

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8 hours ago, Stub Mandrel said:

18V can compensate for poor design, allowing you to be careless about gain levels during processing.

 

In theory, you don't need that headroom even if processing signals for line level inputs.

 

But what are you taking as "Line Level" ? 

+4dBu / -10dBu or ???

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1 hour ago, rmorris said:

Hi. I see your whole post. But quickly on this - cos I'm on mobile and a tediously slow train from London to Brighton 🙄 - the pro line level is nominally +4dBu that does indeed equate to approx 3.5V pk-pk. But any system is expected to handle peak levels in the range of typically 21 to 24 dBu requiring Voltage rails in excess of +/- 9V or 12V.

Typical pro audio gear runs OpAmps at minimum +/-15V and typically +/-17V.

 

But nevertheless high end hifi gear can exceed 100 db snr at much lower signal levels than this. 

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17 hours ago, bassman7755 said:

 

But nevertheless high end hifi gear can exceed 100 db snr at much lower signal levels than this. 

 

Audio specifications can be, let's say, a somewhat confusing area. I know. Been there Done that etc. But basically, depending on the definitions you are using, you don't really get better than 100dB SNR.

Yes - a good mic amp may give an Ein of, say -127dBu. But that is typically at a gain of 60db. So actual noise level at the output is -67 dBu. So if you are setting the gain at 60dB to give an output level of +4dBu then your nominal SNR is 71 dBu.

As gain decreases the Ein increases a bit. So while the signal may increase by, say, 20dB, thus requiring a gain of 40dB to give the same output level, the noise added at 40dB is a bit  more than that added at 60db so the actual SNR wrt the input signal is better than the figure at 60dB gain but not by the full 20dB decrease in gain and noise may have already been added by any preamplification.

Edited by rmorris
Technical clarity.
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On 30/10/2021 at 14:27, Jus Lukin said:

As for an overdrive it will push the clipping points further round the dial, making for less saturation, but greater range at the bottom of the dial.

 

It depends on how the circuit operates. If the effect is due to a signal getting 'near' a voltage rail (or something a bit more complex related to the voltage eg affecting the operating point of a transistor) then yes.

But if the process is basically independent of the voltage level as long as it doesn't go too low - eg clipping levels defined by diodes - then the controls won't really alter. Although the circuit will probably have a different audio spec performance due to differing voltage rails. Of course, some pedals etc will have internal voltage regulation in which case - to a first level - everything will be the same until the voltage is too low and it starts to go wrong !

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