Bass guitar FET preamp

[Schotky]

Originally Posted by bucks bunny

Could you pls elaborate on this?

X196 series are CMOS, it's the least favorable architecture for audio. Similar for Bipolar, maybe a bit better but both are not the best choice for high impedance, and then FET brings best performance in audio, or sounds most organic or least digitized so to speak. Along that, FET is especially beneficial in high impedance audio due its very high input impedance, in this case instrument amplification

[Schotky]

Originally Posted by Rick PA Stadel

Wow! That is spectacular! What a huge time investment .. with a really gorgeous result.

Seriously - Just Beautiful

Thanks Rick, glad you like it it does consume a lot time though....probably wouldn't do it again

Still digging for the 'bookmarks' concerning 9V battery life that I had all queued up when we were last working on this. Also botched my secondary plan to have some of my very own '5457s to fiddle with by now. Where-ever does the time go ..?

Do you mean you'll do more simulation?

IIRC JMFahey suggested 400uA as a good target Drain current. I'd venture that he has built many more such devices than I have, so let's run with it. We'll come up with a bias circuit that's reasonably stable over battery voltages from 18 to 14V or so, and that doesn't soak up 164uA just to provide the service. That just seems too wasteful to me since the JFETs aren't consuming any of it.

That sounds very reasonable, it looks like in total we could get around 1mA or so, that would be perfect!

Just please keep in mind that I have the PCB made already by that schematic so mods should be somewhat able to be applied "over" that

[bucks bunny]

Originally Posted by Schotky

X196 series are CMOS, it's the least favorable architecture for audio. Similar for Bipolar, maybe a bit better but both are not the best choice for high impedance, and then FET brings best performance in audio, or sounds most organic or least digitized so to speak. Along that, FET is especially beneficial in high impedance audio due its very high input impedance, in this case instrument amplification

There is hardly any valid argument given. Some JFETs are superior devices concerning noise - but if you do the math and consider impedance of your pickups - you will find the differences marginal.

[Schotky]

Originally Posted by bucks bunny

There is hardly any valid argument given. Some JFETs are superior devices concerning noise - but if you do the math and consider impedance of your pickups - you will find the differences marginal.

It's not about the arguments as such, it's about the tests done that create the argument. It's the tests that are done over so many years that bring FET as the primary choice for audio. I go with that, I didn't dive in it but there is a reason why it's like that.

Yeah the difference isn't going to be light years, they are all amplifiers and amplify a signal, just some are better for specific usage, like FET's are closest to a "tubey" sound. The difference is small but enough to be a preference for a specific circuit. Also the quality of the architecture plays a role.

[Schotky]

Hey Rick, I know you mentioned you're also on another thread, so I don't mean to disrupt that. Was curious if there is a possibility to finish this before NY? It's been sitting on my desk for some time, I've tried several things in meanwhile with not too different results.

You think this is doable?

[JMFahey]

Very short answer: just do it, you have enough good data to work on

The worst options have already been pruned out, those which remain are all reasonable.

Pick one

To help your decision, consider not only "sound" (although obviously this is the primary concern) but practicality, space, parts availability, etc.

Absolute worst case, flip a coin, no "bad" choices remain

[Schotky]

Originally Posted by JMFahey

Very short answer: just do it, you have enough good data to work on

The worst options have already been pruned out, those which remain are all reasonable.

Pick one

To help your decision, consider not only "sound" (although obviously this is the primary concern) but practicality, space, parts availability, etc.

Absolute worst case, flip a coin, no "bad" choices remain

Haha that's an interesting way of putting it. Yeah both choices that left sound good, not sure I can hear a difference between the two, but I don't understand the whole dynamics there. Rick is mentioning the dynamic range, that's what confuses me. If I go with the "wider dynamic range" I'm a little higher in battery consumption for a 2 transistor circuit.

If I go with the good battery life option, then dynamic range is in question... I don't know what I need to hear here I may be missing something, I don't know...

[Schotky]

Meanwhile, I have one question if I may. Cause I'm going to use two preamps in the bass and want to save battery of course, I'm switching the power on them along the output via one DPDT switch on the volume pot. This creates a pop audible enough, more or less as loud as the signal.

Has anyone dealt with this before? It's not that practical to lower the volume down on the main amp to switch between the preamps and then bring the volume back up again. I was thinking of adding a calculated value cap in SERIES on the positive power supply. Will this actually delay or smoothen the power-on state on the preamp? Will it work at all or maybe mess with the preamp or the sound? Don't really want to experiment before I get some thoughts on it.

I'm immensely thankful, people have been so helpful and nice and I've asked so many questions I'm about to feel ashamed.

[Kay Pirinha]

A capacitor in series with a DC voltage source will eventually (after it is charged) shut down the supply completely.

Why don't you use a TRS type phone socket in your guitar with the negative battery lead connected to the ring lug? This also avoids the possibility that your batteries are getting discharged it you forget to trip the on-off switch.

And it's always been good practice to first plug the cord into the guitar, then connect it to the amp. Otherwise you may get nasty noise even with a passive, unpowered instrument.

Best regards!

[bucks bunny]

Agreed. And the lazy guys like me use the Neutrik Silent switiching plugs.