Stupid question - why do some basses have two batteries?

[tauzero]

On 02/08/2023 at 10:02, ahpook said:

You're missing the whole joy of soldering angle

 

Oh, did I mention that before ?

 

 

[Chienmortbb]

6 hours ago, tauzero said:

 

 

In my apprentice days, 50 odd years ago, the biggest threat said in an electronics workplace was “ I’ll stick that soldering iron up your derrière, handle first”. Looks like she would have no trouble getting it back out. 

[Chienmortbb]

On a serious note, Boring electronics warning (Bb?) one of the best reasons for using a higher voltage is that the circuit will operate for longer even when the batteries are close to discharge. Transistors and Integrated circuit designs will have a minimum working voltage beyond which the circuits become non-linear. In the case of fuzz, overdrive and drive circuits, more non-linear and unpredictable.

 

Most Operational Amplifiers work on twin rails with one positive and one negative rail. To use them on 9V  means some form of voltage divider, so each side has only 4.5 volts nominal. The voltage divider may itself reduce the available voltage.  Take the workhorse TL072, this has a minimum working voltage of 4.5V. If you use a rechargeable 9V NiMh battery the nominal voltage is 8.4V and as it discharges it will reach 4.5V before two batteries in series that would be  at 9V at the same point in the discharge cycle. 
 

Now the voltage swing of an Op Amp  is limited by the supply voltage so at 4.5V, in an ideal world, that would be 4.5V peak to peak, 2.25V peak or just just over 1.5V RMS.  Using 18volts (2 x 9V) that would double the minimum output to 3.0V RMS,  a more useable output.

 

Of course modern Op Amps will operate on much lower voltages but clearly, these are more expensive and often not used on many designs. 
 

 

[GoodShowSir]

8 hours ago, tauzero said:

 

 

At first I was like, well as least she isn't soldering the CPU fan like the kid... then I saw it. Good thing she has eye protection on!

[ahpook]

8 hours ago, tauzero said:

 

 

 

 

Now we're getting somewhere - slightly (but only slightly) nearer my age...hair's closer...

 

But....something's not quite right - she's feeling something, but I don't think it's joy...

 

 

I may have to do y'all a selfie showing the real joy of soldering when I get home.

[tauzero]

2 hours ago, Chienmortbb said:

Now the voltage swing of an Op Amp  is limited by the supply voltage so at 4.5V, in an ideal world, that would be 4.5V peak to peak, 2.25V peak or just just over 1.5V RMS.  Using 18volts (2 x 9V) that would double the minimum output to 3.0V RMS,  a more useable output.

 

I had a look at the NE5534 specs yesterday as it had happened to be mentioned. The typical output voltage p-p was supply voltage minus 4V, so +/- 15V (30V supply) gave typical 26V p-p. Presumably a 9V (4.5V +/-) supply would result in typically 5V p-p. But the actual output is typically around 150mV p-p so 5V is well more than plenty - more than 0dB line level in fact.

[Chienmortbb]

22 hours ago, tauzero said:

 

I had a look at the NE5534 specs yesterday as it had happened to be mentioned. The typical output voltage p-p was supply voltage minus 4V, so +/- 15V (30V supply) gave typical 26V p-p. Presumably a 9V (4.5V +/-) supply would result in typically 5V p-p. But the actual output is typically around 150mV p-p so 5V is well more than plenty - more than 0dB line level in fact.

You are not wrong but of course the output of some pickups when using a plectrum or slapping is much higher, from memory peaking at well over 1V and the techniques for rail splitting are not perfect. The NE5532 is one of my favourite chips but a 9V battery would drain fast with the NE5532.
. Using 18V and a low power OpAmp will give a much longer time between battery changes/charges.

 

In an ideal world basses would use 18V used to create +9, 0, -9V. That is what the chips need but it would require an on/off switch on the bass rather than rely on a stereo jack socket. 

[Hellzero]

33 minutes ago, Chienmortbb said:

In an ideal world basses would use 18V used to create +9, 0, -9V. That is what the chips need but it would require an on/off switch on the bass rather than rely on a stereo jack socket. 

This is exactly how the MTD-Bartolini preamp is working and, to me, the only one on the market, but you can't buy it as its only made for Mike Tobias.

[Woodinblack]

11 hours ago, Chienmortbb said:

In an ideal world basses would use 18V used to create +9, 0, -9V. That is what the chips need but it would require an on/off switch on the bass rather than rely on a stereo jack socket. 

 

Not necessarily - there are jack sockets with actual switches on them. They used to be more common than they are now, but they certainly must still be around.

[Hellzero]

3 hours ago, Woodinblack said:

 

Not necessarily - there are jack sockets with actual switches on them. They used to be more common than they are now, but they certainly must still be around.

 

https://pcjcustomguitars.co.uk/9-pin-jack-socket/ 

[Woodinblack]

More like this:

 

https://www.retroamplis.com/1/4-Stereo-Enclosed-Jack-DPDT-1

 

[Hellzero]

9 minutes ago, Woodinblack said:

More like this:

 

https://www.retroamplis.com/1/4-Stereo-Enclosed-Jack-DPDT-1

 

Urm, urm, this is exactly the same! 😉

[Woodinblack]

6 minutes ago, Hellzero said:

Urm, urm, this is exactly the same! 😉

oh sorry - I just saw the schematic and assumed it was a single pole one!

 

But yes, like that. Good for power control and doesn't interfere with the few wireless units that don't like stereo plugs (not sure what they are but they have been mentioned).

[sandy_r]

On 04/08/2023 at 01:03, tauzero said:

 

 

...i think that the safety glasses are only there to catch her eyeballs when they pop out 😨

[crazycloud]

On 05/08/2023 at 18:02, Chienmortbb said:

In an ideal world basses would use 18V used to create +9, 0, -9V.

Why? Pretty much every ADC/DAC in existence uses a single rail biased supply for the opamps and you're more than happy to use them everywhere.

 

On 05/08/2023 at 18:02, Chienmortbb said:

That is what the chips need

No, they don't.

[KingBollock]

On 04/08/2023 at 01:03, tauzero said:

 

 

A more believable photo than the time the local paper came to the college where I was learning electronics. They chose me as the poster boy, for some reason (probably my long, flowing, blond locks). When I was approached by the photographers, I was soldering something to a pcb. But when they asked me to pose for the camera, they didn’t like the soldering iron… So they got me to do the exact same pose, but holding a pair of pliers instead…

 

I ended up on the front page looking like that! Oh the shame!!