Adding active/passive switch questions.

[Mirthoneist]

Firstly, I'd like to say I'm an amateur bassist and don't know very much about bass electronics, although I'm very good at soldering.

I have a 2008 Ibanez SR530 bass with the Bartolini MK1 pickups/preamp. I know they are not the best, but they are good enough in my current financial situation.

Anyways, I've been doing some research, and I've heard that they make push/pull knobs. So, I was wondering if anyone can give me some guidance on what kind of push/pull knob I'd need to buy so that I can switch from active/passive using the up position for passive, down for active? Any recommended site I would buy this from would greatly help too. And most of all, how would I go about wiring it? I found the diagram that I think is the same (From Ibanez's site for a 2006 SR500), so I posted that below.

I was reading another thread, and someone said that if you did make an active/passive switch via a 25k ohm push/pull knob (which I believe this is), then your balance(blend) wouldn't work? If someone can clarify if this is true or false, and if true what I can do to remedy that issue, it'd be greatly appreciated!!!



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[line6man]

It appears from the diagram that you have active pickups, because of the value of the blend pot. You should be able to add an active/passive switch without changing the value of the volume pot.

If you have passive pickups, you need to make sure that the volume pot is of the appropriate value to control a high impedance signal in passive mode.

 

[bassbenj]

Firstly, I'd like to say I'm an amateur bassist and don't know very much about bass electronics, although I'm very good at soldering.

I have a 2008 Ibanez SR530 bass with the Bartolini MK1 pickups/preamp. I know they are not the best, but they are good enough in my current financial situation.

Anyways, I've been doing some research, and I've heard that they make push/pull knobs. So, I was wondering if anyone can give me some guidance on what kind of push/pull knob I'd need to buy so that I can switch from active/passive using the up position for passive, down for active? Any recommended site I would buy this from would greatly help too. And most of all, how would I go about wiring it? I found the diagram that I think is the same (From Ibanez's site for a 2006 SR500), so I posted that below.

I was reading another thread, and someone said that if you did make an active/passive switch via a 25k ohm push/pull knob (which I believe this is), then your balance(blend) wouldn't work? If someone can clarify if this is true or false, and if true what I can do to remedy that issue, it'd be greatly appreciated!!!

Well, you've really bitten off more than you can chew here! Just a quick look around the net show that you are exceedingly lucky to have found ANY diagram of this. Most folks have not been able to find anything. Did the MK1 pickups/preamp come with the bass or was it added later?

According to talk on net the MK1 preamp already has a push-pull active/passive switch on the volume control! Also If you buy this preamp and pickups separately the wiring diagram is impossible to get. The pots come with it all pre-wired so you are assumed to only need to connect ground and the pickups.

Looking at YOUR diagram we note the volume and blend pots are 25k. This would be the value for active pickups. If your pickups are active (require a battery to work) then there is NO WAY you can install an active/passive switch that does anything meaningful. Passive pickups will usually have these pots with a value of 250k or 500k. (k means 1000 so 250k = 250,000 ohms).

So my advice would be to first yank your control cover and look at the back of the volume pot. Does it have a push/pull switch there? Next unsolder two wires off of the volume pot. and measure the resistance between the outer ears. If it's 25k then there isn't much you can do but put it back together. If it's like 250k or higher then go do the same thing to the blend pot. If it's 250k or higher come back to learn how to wire an active passive switch. If not, you can't put that kind of switch on the bass because the pickups are always active.

 

[Mirthoneist]

Thanks for the information, fellas.

bassbenj: The bass came with the MK1 pickups/pre from the factory. Also, I just opened up the cover to look inside. The volume is definitely not a push/pull unfortunately, but what I did notice is that the volume pot says "Alpha B500", and I can't see what's after the last 0, as there's solder on top. Not sure if that makes a difference.

So I guess the diagram is not the same, which is from a 2006 model, whereas mine is from a 2008.

Anyways, I've been giving thought to getting the Bart NTMB preamp for about $150, which comes with the pre and new pots, active/passive push/pull on the volume and mid-frequency push/pull on the mid, and just be done with it, keeping the pickups in there. Not sure how much of a difference it'll make, but I think the MK1 pre is pretty sloppy.

 

[FunkMetalBass]

It probably just says B500k, in fact, I can guarantee that it says that with 99.9999999999999999999999999% accuracy (nobody would a small potentiometer like 500-ohms). Interesting that they use a linear pot.

However, that now means that the diagram you have does not accurately depict what's in your bass, but I suspect the volume pot is placed BEFORE the preamp in the signal, which makes an active/passive switch very easy to wire:

 

[jesterbass]

The pickups are most certainly passive. I have the preamp the original poster attached in the schematic on a Cort from 2006. (Cort manufactures Ibanez products in their factories so they are pretty similar in philosophy and equipment) This year I bought an Ibanez that supposedly has the same pickups/eq, MK1 soapbars + MK1 three band pickup. The preamp is different (I bet it is the same as the original poster has currently on his bass). The pickups are same size, still passive, but definitely not the same tonally, I actually did some A/B recordings with them. They also have slightly different DC resistance. And listen to this: the pot values are 500K for blend (not surpsising), but 25K for volume! Even if his pickups were active, I believe what the original poster actually wants is a preamp bypass switch.

PS. on the original schematic, the blend is only 25K because you will notice that the pickup signal goes through some preamp stage of some sort, then goes out to blend at what I believe to be a lower impedance. Then it goes back to the pre for eq. Because of this design, you can not bypass the preamp, if that's what is desired. The Cort did have a "bypass" switch but all it did was set the eq flat.

 

[jesterbass]

...and FWIW, my SR705 electronics, which could very well be what the OP has on his bass, is pickups -> blend(500k) -> pre -> volume(25k) -> jack. So I believe a preamp bypass is perfectly doable with a switch or push pull pot. Come to think of it, it's not surprising the volume is 25k, since it is post preamp.

 

[line6man]

...and FWIW, my SR705 electronics, which could very well be what the OP has on his bass, is pickups -> blend -> pre -> volume -> jack. So I believe a preamp bypass is perfectly doable with a switch or push pull pot.

If the volume pot is after the preamp, that pretty much guarantees that it is controlling a low impedance signal.

If you have passive pickups, you will need with place a higher value volume pot before the preamp, otherwise the resistance of the volume pot is going to put some serious resistive loading across the pickups in passive mode, costing you output/treble.

 

[jesterbass]

Is there an easy way to measure the preamp's output resistance? Volume post pre indicates high z, but low pot value indicates low z (i think?).

 

[line6man]

Is there an easy way to measure the preamp's output resistance? Volume post pre indicates high z, but low pot value indicates low z (i think?).

No, it's not easy to measure the impedance, but you don't need to. I have never heard of a high impedance preamp, and can't think of any reason why such a thing would be desirable. Preamps give you a low impedance output, most pickups have high impedance outputs, so you need to move your volume pot before the preamp, where the impedance will be high in both active and passive modes, and make sure it's the right value for a passive pickup.

 

[jesterbass]

Well, I just tried pre output wire vs ground and it is 100KOhm.

 

[jesterbass]

No, it's not easy to measure the impedance, but you don't need to. I have never heard of a high impedance preamp, and can't think of any reason why such a thing would be desirable. Preamps give you a low impedance output, most pickups have high impedance outputs, so you need to move your volume pot before the preamp, where the impedance will be high in both active and passive modes, and make sure it's the right value for a passive pickup.

Very clear, thanks!

 

[bassbenj]

...and FWIW, my SR705 electronics, which could very well be what the OP has on his bass, is pickups -> blend(500k) -> pre -> volume(25k) -> jack. So I believe a preamp bypass is perfectly doable with a switch or push pull pot. Come to think of it, it's not surprising the volume is 25k, since it is post preamp.

IF what your bass has is a 500k blend pot and a 25k volume pot, and the volume is wired to the jack (slider to jack out, one side ground, other side it output from preamp. You are pretty much home free. The active-passive switch will be wired as shown in this thread. Input to the preamp will be the output of the blend control (all that stays the same) and the output of the preamp will be that wire going to the outer ear of the volume pot.

What you'll need to do, however is to change the volume pot from 25k to 500k. Did you actually measure the value of your volume pot? [outer ear to outer ear with slider and input wires removed] Note that making this change in the volume control value will only have the effect of making the bass less able to drive long cables. In other words it will have some high frequency loss in passive OR active modes like a passive bass if you use a long cable on it. With a normal length cable you shouldn't notice a thing. It seems to me that if your volume pot already says B500? on it, it is likely it may already be 500k.

 

[line6man]

IF what your bass has is a 500k blend pot and a 25k volume pot, and the volume is wired to the jack (slider to jack out, one side ground, other side it output from preamp. You are pretty much home free. The active-passive switch will be wired as shown in this thread. Input to the preamp will be the output of the blend control (all that stays the same) and the output of the preamp will be that wire going to the outer ear of the volume pot.

What you'll need to do, however is to change the volume pot from 25k to 500k.

You also have to move the volume pot to before the preamp. Having a 500K volume after a preamp is not going to do you much good.

 

[Graza]

Discovered this thread 9 years later, and thought I should clear something up: what bassbenj said about the effect of the 500k volume pot meaning not being able to drive long cables and getting some high frequency loss, won't affect active mode IF the volume is moved to before the preamp.

I'm about to install an active/passive switch in my bass, which has "passive"/hi-z pickups, hi-z blend pre-preamp, and a low-z volume pot post-preamp, and I was wondering what value to use when I changed it. Reading this thread made that obvious - high value before the preamp. Perfect, thanks guys!

PS: in theory there is potentially more noise doing it this way at lower volumes as any noise added by the preamp will be amplified fully without attenuation. But that's only at low volumes (rare for me), and only if you have a noisy preamp (I hope not, but will soon find out!)