Active preamp, no EQ

[Rob22315]

With that many controls, it sounds like you're replacing an existing active setup. You'll have to convert that to a passive setup, then add the buffer. IIRC, you want a volume control and a 'balance' switch. You said you didn't want tone so the bass/mid/treb can all come out.

All of that is simple enough to do.

 

[KingRazor]

With that many controls, it sounds like you're replacing an existing active setup. You'll have to convert that to a passive setup, then add the buffer. IIRC, you want a volume control and a 'balance' switch. You said you didn't want tone so the bass/mid/treb can all come out.

All of that is simple enough to do.

Yes, my current bass has an active setup that I would be replacing.

 

[Rob22315]

Based on rumblinbass' signature, he's a professional at this so you may want to PM with him about what you want. He can probably whip out an opamp-based circuit quickly. He/she also seemed really motivated to help.

I can adapt my buffer to what you need too but I don't have an existing opamp circuit to offer. You'll have to build the circuit yourself. It's not hard to do but basic soldering and electronics skills will be required to do what I did.

 

[KingRazor]

Based on rumblinbass' signature, he's a professional at this so you may want to PM with him about what you want. He can probably whip out an opamp-based circuit quickly. He/she also seemed really motivated to help.

I can adapt my buffer to what you need too but I don't have an existing opamp circuit to offer. You'll have to build the circuit yourself. It's not hard to do but basic soldering and electronics skills will be required to do what I did.

Already have a convo with them going, just trying to learn more.

I have no soldering or wiring knowledge, so I'm going to leave that part to someone else. I just want to know what to buy. After that I"ll either hand it over to my local shop (or, if for some reason they refuse to mess with a DIY setup, I'll hand it off to one of my friends and have them do the soldering work).

 

[Rob22315]

Do you know that your pups will work with a passive setup? I don't know all the details of every pup but as I understand it, some pups have electronics built in and won't work in a passive setup. Some 'active' pups are really just passive pups with a preamp but have a lower output than pups designed for passive setups so they'd require a preamp or a higher gain buffer. Some 'active' pups would work in a passive setup and not require much gain out of the buffer.

I added a buffer to passive pups so I wasn't worried about gain.

 

[KingRazor]

Do you know that your pups will work with a passive setup? I don't know all the details of every pup but as I understand it, some pups have electronics built in and won't work in a passive setup. Some 'active' pups are really just passive pups with a preamp but have a lower output than pups designed for passive setups so they'd require a preamp or a higher gain buffer. Some 'active' pups would work in a passive setup and not require much gain out of the buffer.

I added a buffer to passive pups so I wasn't worried about gain.

I understand this.

According to Ibanez' website, the pickups are passive humbuckers. So I'd be replacing an active preamp that is being used with passive pickups for a buffer to be used with said passive pickups.

If the information on the Ibanez site is inaccurate, and the pickups are in fact active, I should be able to simply remove the preamp that is already in it and just have a pair of active pickups with no EQ, right?

 

[rumblinbass]

oh, the passive/active pickup discussion...

Most of the time the term "active pickup" refers to a passive pickup connected to a separate preamp in the control cavity.
EMG makes a pickup that has a preamp inside the pickup assembly.

kingrazor,
you really don't have anything to worry about. if there is active electronics inside that pickup it will not affect anything.

Here is what I think is the simplest way to accomplish what you want - balance and volume:
Connect each pickup to either side of the a high value linear pot. One pickup to the top and the other pickup to the bottom of the pot. The high value will prevent too much loading on the pickups. However, the ideal solution would be to add a couple of op amps to drive the pot.
From the wiper of the pot to the input of a non-inverting voltage follower op amp circuit. If you want gain, that is easy enough to accomplish...you just need to figure out how much gain you want.

Here is a rough parts count (I haven't drawn a schematic yet):
- one single package op amp
- one high value (250k or 500k) Linear pot
- one 100k audio pot for volume control (some people like linear)
- 3 electrolytic caps, 4 if you want gain (I think?)
- 3 resistors, 4 if you want gain
- maybe a couple more poly-film and/or ceramic caps

that's really about it, unless a couple op amps are needed to drive the balance pot. I will try to get a block diagram together.

if anybody has any input it would be appreciated. I do design pro-audio gear but I may be missing something in this specific application.

I haven't really put too much thought into the rotary switching...

 

[Rob22315]

If the information on the Ibanez site is inaccurate, and the pickups are in fact active, I should be able to simply remove the preamp that is already in it and just have a pair of active pickups with no EQ, right?

Not necessarily. If there are electronics in the pups, the pups will need power to operate. If the pups are designed to operate with a preamp, then your buffer needs to be designed with more gain.

Based on what Ibanez says, you'll be good-to-go with a low gain buffer. I swapped the pups on my GSR200 with Dimarzio DP126 and didn't notice much difference between the level of passive output of the Dimarizios over the Ibanez. The sound did improve so I consider the Dimarzios to be an upgrade. That plus I bought the GSR200 used (it was about 8 or 9 years old when I got it) and noticed some of the magnet poles seemed weak.

 

[Rob22315]

that's really about it, unless a couple op amps are needed to drive the balance pot. I will try to get a block diagram together.

if anybody has any input it would be appreciated. I do design pro-audio gear but I may be missing something in this specific application.

I haven't really put too much thought into the rotary switching...

The OP only wants volume and the rotary switch - no balance pot/circuit needed. See a previous post for what he wants off the switch.

I'll post the JFET design and a picture to this thread later this evening just so you can see what it looks like. It's really small - about the size of a postage stamp. Unless you're willing to tune it to the JFET characteristics (which takes extra work and equipment), I'd stick with an opamp based design.

 

[Rob22315]

Here's a picture -

[Invalid or Expired Link Removed]

 

[KingRazor]

This is my current setup:

 

[Rob22315]

And the schematic:
[Invalid or Expired Link Removed]

 

[rumblinbass]

The OP only wants volume and the rotary switch - no balance pot/circuit needed. See a previous post for what he wants off the switch.

I have talked a little with kingrazor via pm about this. I was just merely offering the simplest solution.

I have seen that FET ckt you posted on several sites. it's a great little circuit. you are right though, an op amp solution would be simpler than most discrete circuits.

The rotary switch selection that kingrazor posted may not be that easy to do. I'll have to give it some more thought it just seems that the switching might be a bit complicated and may require a multiple gang rotary. What I do like about it is that it allows for a direct path to the op amp without going thru a pot.

 

[Rob22315]

If you can get a double pole rotary, you might be able to do it with one rotary. I originally wired up my precision pup with a dpdt switch to go from parallel to series. The only difference was that it was louder in series (it's supposed to sound different too). You can download the dpdt switch wiring from Dimarzio for free if you want to see how they did it.

I rewired the switch to go from active to passive and disconnect the battery.

 

[bowthing]

acitve preamp and no eq? Yes please!

DIY. ic (op amp) or discrete -it's easy, its cheap.
if this is the route you would like to go in - pm me, I'ld love to help.

Can you point to some good buffer circuits? I've tried building a JFET one, and had pretty dismal results w/ regard to noise. I just installed a Bart AGDB-918 last night, and it is spectacularly quiet, lots of gain, low distortion, I LOVE it. Have no idea whether it uses op amp or fets...

 

[SGD Lutherie]

JFETs should be ultra quiet. I've been making them for years, and was using them to boost the output of low impedance pickups I used to make. Even at 10X boost they were very quiet with no noise.

Try this one:

Change the output cap to 5µF.

 

[bowthing]

JFETs should be ultra quiet. I've been making them for years, and was using them to boost the output of low impedance pickups I used to make. Even at 10X boost they were very quiet with no noise.

Try this one:

Change the output cap to 5µF.

Thanks! I think that's very close to what I tried, so I wonder if I just got a bad J201....

 

[thebisch]

What is the 50K pot on the Stratoblaster you posted? It looks like a gain control if I am remembering my analog electronics correctly.

JFETs should be ultra quiet. I've been making them for years, and was using them to boost the output of low impedance pickups I used to make. Even at 10X boost they were very quiet with no noise.

Try this one:

Change the output cap to 5µF.

 

[SGD Lutherie]

What is the 50K pot on the Stratoblaster you posted? It looks like a gain control if I am remembering my analog electronics correctly.

It's a gain control. It goes from unity to really loud! I was able to drive a power amp with one of these.

It's a self biasing circuit, but if you don't think you are getting the right gain or if it's noisy, it could be an under spec JFET.

But I've used JFETs from Radio Shack in the past, and they sounded fine.

 

[darkstorm]

For converting passive basses to HiZ without tone controls, the EMG AB Afterburner pickup booster would work and also give you controllable boost when wanted. Useable for both bass and guitars.