Am I crazy or is this a reasonable idea?

[WaveshapeIllusions]

In my efforts to put together an internal bass preamp, I have run into some issues. I have realized that 9V is not enough headroom for what I want. I have also decided that a rechargeable battery pack would be nice. Now, I've seen some 12V batteries, but they don't have much of a capacity. I would also rather not have to drill or route anything out, which means I have space for just one 9V. I was considering using some of those lithium phone or camcorder batteries, but those are usually 3V7.

So, my solution is to step up the voltage. At first a switchmode supply seemed like a good idea. But, seeing as how I like the idea of imitating a full size amplifier, a small linear supply sounds fun. If I drive an oscillator with the low voltage battery, I could treat it like a small version of the mains. If I set the oscillator to a high frequency (100kHz?) the transformer wouldn't need to be too big, especially since my circuit doesn't use much power. The high frequency would also mean smaller filter caps.

Now, I know this is a roundabout difficult way of doing this. I could just as easily use a voltage multiplier IC or even phantom power. However, I think putting something like this together would be a fun experiment. It could also be good practice for putting together a full size supply, while being reasonably safe.

So, to put it simply, could I use an oscillator and a battery to drive a linear supply?

[Quackzed]

i'm not sure about the 9v power supply, just wanted to suggest a few easier options... couldnt you divide down the output of the bass 'before' the 9v circuit? say with a 10M/5M voltage divider. then into a 9v preamp (eq , diodes, cleanblend, etc.) then just re-amp the signal up to normal-ish output levels? with an rail to rail op-amp you should be able to deal with a passive bass signal i'd think... or you could even add an extra 2 AAA batteries into the fray for 12v (more like 14v when fresh) after all 9v's are just a bunch of aaa cells in series... might be easier and even smaller spacewise. just a few options to consider  btw i hear good things about the fet twin for bass (phil lesh wristbands not included) but you probably have a pre you want to use.

[Netbat]

Hi, may I put my 1 cent, as power convertion is more my thing ...

Given that you REALLY can't use a 9V battery, in order to step up voltage, a boost converter seems a better solution ... I mean, theoretically you COULD make an oscilator to drive a transformer (BTW, the higher the frequency, the smaller the transformer  ), but I don't see why... And, I can't even imagine how to create such low impedance circuit ...

Also, there is the space restriction ... see that most Li ion batteries will be larger than a 9V battery, in some of its dimentions...

Anyway, I think you'll be better using a boost converter with a higher switching frequency and good filtering caps ...

Hope it helps ...  

[PRR]

> could I use an oscillator and a battery to drive a linear supply?

Yes, but:

Square waves are easier and more effective,

For un-isolated supply of low step-up, a coil is simpler than a transformer,

Transformer/coil size does go down with frequency BUT transistor and rectifier effciency falls at high frequency,

When you done all this optimization, you have a Switch Mode Power Supply, as used in EVERYTHING these days.

9V to say 24V is an unusual specification; you may have a hard time finding either pre-made supply or pre-wound magnetics.

The computations for these things always baffle my old linear analog mind.

And the essence of audio is in adjusting your signal to fit your equipment, not in building heroic gear because you can't manage your signal. (IMHO)

[Digital Larry]

I have realized that 9V is not enough headroom for what I want.

Ah... why not? 

And on a separate note, you didn't happen to buy an Akai Deep Bass synth pedal from me on eBay about 5 years ago did you?   

[WaveshapeIllusions]

Thanks for the replies. So it's doable, which is nice to know.

This is pretty much a "just for the hell of it" thing. I guess I don't really need the headroom, but I kind of want it. Something about putting out a 9V peak signal sounds cool. I also might put a buffer after the volume control. I tried that in a previous iteration, but the supply limit messed up the sweep. The buffer might be a bit excessive though.

Honestly, my main goal is to use a rechargeable phone battery. I figure that if I'm stepping it up anyways, it might as well be higher than 9V. I could use a rechargeable 9V battery, but the idea of using my phone charger for my bass is kind of attractive for some reason. Most of them have separate charge pins so I wouldn't even have to remove it. That would be nice. Currently the battery is in the bridge pickup cavity of my EB3 (those mini-buckers are useless) but a flat phone battery could fit in the control cavity.

Square waves are easier to rectify to DC, I agree. Aren't they harder to filter though? I would assume the extra harmonic content adds noise. And doesn't the sudden switching usually add noise too? For example the 555 timer IC thumps every time it switches states, right? Thanks for pointing out that efficiency falls at higher frequencies, I didn't think about that.

I realize a regulator would help with that noise too, but then the supply would be stiff. In most cases that's a good thing, but I kind of would like a bit of supply droop. I'm basically going for a small-signal version of a bigger amp. Similar to Runoffgroove's projects, but a bit more.

I'd figure 4 stages sounds about right. Input gain, make-up gain after tone stack, unity phase splitter, totem pole output. Drawing from the ideas given in my earlier thread on distortion without clipping, there would be interstage attenuation to keep the levels right. A bit of clipping doesn't hurt, but too much sounds bad on bass in my opinion. Actually a higher supply might be good in that case. But I figure that if I'm imitating an amp I might as well use a linear supply like one too.

Realistically, I might not even need a transformer though. There are some diode-based voltage multipliers, no? If I just ran the output of an oscillator into one of those I'd still get OK results. It would also be safer practice for building a linear supply, right? At least safe in that it does not connect to the mains.

So yeah, that's my goal. Pretty weird, huh? I guess that answers my question: I am crazy!   Well, thanks for the advice and suggestions.



Digital Larry: I did not buy an Akai pedal from you five years ago. I probably would have liked to though, those things are sweet.