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Some wiring assistance for Active Passive switch please...

L

Luke73

Oct 26, 2004
959
24
53
Melbourne, Australia
www.myspace.com
#1
Hi all,

I have a Cort Artisan A4 bass, which I love very much, but would like to modify it slightly.

It currently has Volume, Blend, Bass, Mid and Treble with an EQ on/off switch.

I would like to rewire it so that the EQ on/off switch becomes an active/passive switch.

After looking at the schematic, I see that the pups are wired directly to the pre amp, which sends a signal to the blend pot, whose output can be switched to either pass through the active EQ, or go directly to the volume pot (EQ on/off).

I think that if I want to have active/passive I'll need to wire the pups directly to the blend pot, and then switch between sending the signal to the pre amp and the volume pot for active passive operation.

I'm not sure if that will work effectlively though, as it looks as though the pre amp expects to see two inputs (one from each pup). If it only receives one input from the blend pot via the switch whilst in active mode, will it work?

I'd appreciate any ideas to help make this work.

Please see schematic via the following link:

Link Removed

Many thanks ;)

Luke.

:)
 
#2
FWIW:

Don't know about the diagram (diagrams make my head hurt), but if the pups are passive, you shut the eq off, and you've got output, then you've got a passive mode. If the pups are active, you can't have a passive mode.

Sounds to me like they're calling an A/P switch EQ on/off. So my guess is, you've got one already. If the b/m/t pots do nothing with eq off - that's passive.
 
#3
I think what Luke wants is to bypass the preamp, at the moment if the batery dies during a gig you have to replace it since you can't use the bass in pure pasive form.

Luke, check the wiring for the C series on corts web site, they can be run pasive but the electroncs a different.

[Invalid or Expired Link Removed]
 
#5
Guys, I already know it's not an active passive switch (and the pups are passive).

It's an EQ on/off switch. It just sets the EQ flat, and bypasses the EQ controls. The signal still goes through the pre amp.

I want an Active/passive switch.

In order to get that I'm pretty confident I'll have to re-route the pup outputs to the blend pot instead of the pre amp (and probably change the value of the blend pot to 500k). Then I'll switch between sending the blended signal to the volume pot (passive mode) and the pre amp (active mode).

I'm just not sure if the pre amp will be happy only seeing one (blended) input rather than two inputs (one from each pup).

Thanks for the link emils - I'll check out the schematic for the C series.

Anyone else have any ideas?
 
#6
I'm looking at doing this same thing (see the "Making my active bass PASSIVE" thread), or possibly just ripping out the pre-amp entirely. From what I gathered from the Cort forum, the blend pot is currently 25K, so would have to be changed to a 250 or 500 to work well with the bypass.

Link Removed
 
#7
Luke73 said:
Guys, I already know it's not an active passive switch (and the pups are passive).
Click to expand...

Sounds like a pretty goofy setup. For a passive switch the pup signal will have to go through blend/volume before going to the pre. You can look at the Aguilar and Bart diagrams on their sites to see how they throw in a passive switch and maybe get some ideas.

Mess of wires going into that pre and you'll have to figure out what to do with any free leads to make it work.

I'm not following the single pup thing either - only a single lead into the pre comes from the blend becuase the singal is .........blended.

You won't need a 500K pot but 25K will choke passives down to nothing. 250, maybe even 100 would get you by.

I would start by routing one of the pups (whichever you favor bridge or neck) straight to the jack to get some idea of the passive tone. It may not be anything you'd want to use anyway. If so, you're doing all this for nothing.
 
#8
Luke73 said:
I'm not sure if that will work effectlively though, as it looks as though the pre amp expects to see two inputs (one from each pup). If it only receives one input from the blend pot via the switch whilst in active mode, will it work?
Click to expand...
You might want to trace the input side of the preamp and see if the inputs go straight to the blend or if they are buffered first. I am guessing they are buffered since the blend pot is a low value.

My gut feel is that this is going to be hard to do since you need to switch two inputs. You might be able to do it with small relays that fail in the passive direction. Then the switch would just turn the power on/off.
 
#9
The leads from both pickups go into the pre-amp. They then go back out (still seperate) to the blend. The push-pull determines whether the line from the blend goes back into the pre-amp to be EQed, or straight to the volume. So I think having a single lione going into the pre for EQing should be OK.
 
#11
millahh said:
The leads from both pickups go into the pre-amp. They then go back out (still seperate) to the blend. The push-pull determines whether the line from the blend goes back into the pre-amp to be EQed, or straight to the volume. So I think having a single lione going into the pre for EQing should be OK.
Click to expand...
Yes, but the EQ is probably expecting a very low impedance and you will be feeding it a high impedance from the pickups. Will this be a problem? Hard to say without seeing the schematic. Do we know if the preamp is opamp based or transistor based?
 
#12
millahh said:
I'm looking at doing this same thing (see the "Making my active bass PASSIVE" thread), or possibly just ripping out the pre-amp entirely. From what I gathered from the Cort forum, the blend pot is currently 25K, so would have to be changed to a 250 or 500 to work well with the bypass.

Link Removed
Click to expand...

Yes, as you can see by the schematic in my original post, the blend pot is 25k ;)
 
#13
luknfur said:
Sounds like a pretty goofy setup. For a passive switch the pup signal will have to go through blend/volume before going to the pre. You can look at the Aguilar and Bart diagrams on their sites to see how they throw in a passive switch and maybe get some ideas.

Mess of wires going into that pre and you'll have to figure out what to do with any free leads to make it work.

I'm not following the single pup thing either - only a single lead into the pre comes from the blend becuase the singal is .........blended.

You won't need a 500K pot but 25K will choke passives down to nothing. 250, maybe even 100 would get you by.

I would start by routing one of the pups (whichever you favor bridge or neck) straight to the jack to get some idea of the passive tone. It may not be anything you'd want to use anyway. If so, you're doing all this for nothing.
Click to expand...

Yeah, it is a pretty goofy setup. That's why I'd like to change it.

AWESOME bass ;) But I don't see why they've configured the electronics in this manner. The EQ on/off switch is next to useless. An active/passive switch would be far more useful for me.

RE: the single line into the pre amp comment....at the moment the pre amp sees two inputs - one from each pickup. If I route the pickups to a blend pot first, the blend pot will only be sending one signal to the pre amp rather than the two it currently sees. That's what I meant. ;)
 
#16
seanm said:
Yes, but the EQ is probably expecting a very low impedance and you will be feeding it a high impedance from the pickups. Will this be a problem? Hard to say without seeing the schematic. Do we know if the preamp is opamp based or transistor based?
Click to expand...

I'm not sure if the schematic for the pre amp is available. Perhaps not. The wiring schematic is in my original post.

I don't know if the pre amp is op-amp or transistor based I'm afraid.

;)
 
#17
To be honest, I've been tempted just to remove the pre amp all together, and go completely passive.

...but then I'd have a battery cavity unused, and six holes (vol, blend, bass, mid, treble, and switch) to fill up. Even with vol, vol, tone, tone, and series/parallel I'd have one left over.

I know I could just have dummy pots but I don't like that.

Anyway.....any more pre amp wiring ideas?

:bassist:
 
#19
Luke73 said:
I know I could just have dummy pots but I don't like that.
Click to expand...
Could I ask why not? I removed the tone control on some of my P basses. I just leave the unused pot in place. Sometimes I mess with the knob during songs just to mess with peoples minds. I make a big deal about dialing in "just the right tone" and nobody else can hear a difference :p
 
#20
Luke73 said:
To be honest, I've been tempted just to remove the pre amp all together, and go completely passive.

...but then I'd have a battery cavity unused, and six holes (vol, blend, bass, mid, treble, and switch) to fill up. Even with vol, vol, tone, tone, and series/parallel I'd have one left over.

I know I could just have dummy pots but I don't like that.

Anyway.....any more pre amp wiring ideas?

:bassist:
Click to expand...

Coil taps? MK1s are humbucking. And given that, you might not need the series/parallel.
 

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