So where do I solder the capacitor thing ?

[ambient]

Following on from my other recent thread about wanting to add a passive tone control.

I've bought a capacitor, so where do I get it soldered ?

This is the inside of my control cavity.
[attachment=218045:unnamed.jpg]


It's a Bartolini preamp, I just want to add a capacitor to give the effect of a passive tone control permanently turned down, cutting the treble, I'll add that using the active preamp.

Looking at the photo, the silver knob thing at the top is the volume control, the thing that the 2 black wires from pickups go to is the balance control, that's it hidden under the bundle of wires next to the blue thing. The blue thing controls the gain.

Many thanks in anticipation of your replies .

Edited April 27, 2016 by ambient

[HowieBass]

I'm no expert but I'm not convinced you can add a capacitor to an active preamp circuit and modify the tone shaping in the way that you hope. Someone else on here is sure to know better than me regarding a modification but I just wonder why you can't cut enough treble using the circuit as it is?

[gelfin]

Best place to ask this is in Repairs and technical.

[Grangur]

[quote name='HowieBass' timestamp='1461788610' post='3037722']
I'm no expert but I'm not convinced you can add a capacitor to an active preamp circuit and modify the tone shaping in the way that you hope. Someone else on here is sure to know better than me regarding a modification but I just wonder why you can't cut enough treble using the circuit as it is?
[/quote]
This.

Even if you were to add a passive style tone pot on the output of the pre-anp, you can't ignore the electronic reaction between the tone pot and the circuit of the preamp.
I wouldn't do it. But I too am no expert.

[ambient]

I used to have a John East pre in my old Modulus, that had a passive control, I'm hoping to replicate that.

[icastle]

Just soldering a capacitor in there isn't going to make it into a passive bass.

Even if the pickups are capable of working purely passive, for starters you'll need to come up with a way of cutting the power.

Then you're going to have to find a way of disconnecting the pots from the active circuit and switching in your capacitor.

Got to say, I'd be more inclined to just leave all the tone controls in their centre detent position (i.e. neither cutting or boosting anything) and have done with it.

EDIT: Just spotted the Bartolini reference - I may be unremembering this, but I seem to recall Barts were only usable as active pups?

[MoonBassAlpha]

Initially just wrap the legs around the signal and ground wire at the output socket and see if that gives you the effect you want.

[MoonBassAlpha]

[quote name='icastle' timestamp='1461789897' post='3037740']
Just soldering a capacitor in there isn't going to make it into a passive bass.

Even if the pickups are capable of working purely passive, for starters you'll need to come up with a way of cutting the power.

Then you're going to have to find a way of disconnecting the pots from the active circuit and switching in your capacitor.

Got to say, I'd be more inclined to just leave all the tone controls in their centre detent position (i.e. neither cutting or boosting anything) and have done with it.
[/quote]
OP is only wanting to add a passive tone control after the active bit, but without a pot, just the effect of it being fully turned off.

[3below]

[quote name='MoonBassAlpha' timestamp='1461789961' post='3037743']
Initially just wrap the legs around the signal and ground wire at the output socket and see if that gives you the effect you want.
[/quote]

Sound non invasive advice (pun unintended) and this follows on from what was established in the previous thread.

[ambient]

[quote name='3below' timestamp='1461790697' post='3037752']
Sound non invasive advice (pun unintended) and this follows on from what was established in the previous thread.
[/quote]

That simple ?

Brilliant, thanks .

I took the back plate off, and thought aarggggh .

[ambient]

The pickups go first to the balance control, then to the volume control. There are 2 wires attached to the volume control, one goes straight to the output jack, the other goes to the preamp.

If I wanted to add the passive tone before the preamp. Could I get the capacitor soldered between these two ?

[Grangur]

If you're really wanting a passive tone control, the best option would be to take out the pre-amp and fit a new pot it one of the pre-amp control holes.

You then solder the hot output from the blend to the left leg of the tone pot and from that same leg on to the jack.
Then connect the capacitor between the centre leg of the tone pot and earth.

I you Google "bass tone pot wiring diagram" you'll find a diagram.

If you're still unsure about it, John KioGon does a good harness so I believe.

If it were me, I think I'd take out the entire original harness and fit a new one. That way you can always refit the bass to original configuration to sell it. A passive harness is cheaper enough.

[pfretrock]

[quote name='HowieBass' timestamp='1461788610' post='3037722'] I'm no expert but I'm not convinced you can add a capacitor to an active preamp circuit and modify the tone shaping in the way that you hope. Someone else on here is sure to know better than me regarding a modification but I just wonder why you can't cut enough treble using the circuit as it is? [/quote]

A passive tone pot/cap works by forming a (adjustable) low pass filter (low pass = treble cut) in conjunction with the inductance of the pickup. It works because the pickup has inductance.
A pre amp would have a low impedance drive, so that the eq you just dialled in is not affected by the following circuit (capacitance of guitar cable, etc)
Adding a cap to the output may be detrimental, as suggested above, since the pre amp may not be able to cope with normal tone cap values (47n - 100n). But you could try it! I suspect it might need a big cap to cut treble at this point and get muddy.
Has the preamp not got suitable eq built in already?

[Dad3353]

Let's try a bit of electronics 101 for dummies... We'll assume that you know about frequencies from your musical education. Electricity goes from DC (Direct Current, no oscillations...) to AC (Alternating Current...), which corresponds, roughly to musical frequencies. Capacitors are a barrier for DC, but will allow more and more AC to pass as the frequency is raised. Low frequencies don't go through much (bass...); higher frequencies go through more (treble...). Now, let's suppose a wire connects the o/p of your pre-amp (the jack socket...) directly to earth. No signal will come out of the jack, as it will all go through the wire to earth. We'll replace the wire (a short-circuit...) with your capacitor. This will not allow (much...) bass to 'leak away' to earth, but will allow more and more treble to 'disappear'. The exact amount of leakage, and at what frequency, will depend on the value of the capacitor. The simple test, as mentioned above, is to just do it; connect the capacitor between the o/p jack 'live' connection, where the pre-amp signal is connected, the other end to earth. This will not explode the pre-amp, and will cut some signal, depending on the frequencies being played. If you like it, solder it in place. If it doesn't please, try other values until you find one that does what you want. Report back here in case of problems, success, black smoke or howling feedback.
The simplest way is to take it to someone competent and explain what is wanted and they'll do it. Experiments can be fun, though, as long as one keeps in mind that the proper of an experiment is the possibility of failure.
Hope this helps in some odd way.

Edited April 28, 2016 by Dad3353

[3below]

[quote name='Dad3353' timestamp='1461837806' post='3038004']
The simple test, as mentioned above, is to just do it; connect the capacitor between the o/p jack 'live' connection, where the pre-amp signal is connected, the other end to earth. This will not explode the pre-amp, and will cut some signal, depending on the frequencies being played. If you like it, solder it in place. If it doesn't please, try other values until you find one that does what you want. Report back here in case of problems, success, black smoke or howling feedback.
[/quote]

+1 Dad3353. As a variation, you could make up two wires with croc clips on the ends (better still, borrow these - e.g. find a local school science teacher). Affix these to the jack socket ring and tip connections. The other ends can be used to investigate which capacitor you want. There are many other 'test rig ' possibilities (as mentioned in the earlier thread).

Edited April 28, 2016 by 3below

[pfretrock]

[quote name='3below' timestamp='1461840256' post='3038031']
+1 Dad3353. As a variation, you could make up two wires with croc clips on the ends (better still, borrow these - e.g. find a local school science teacher). Affix these to the jack socket ring and tip connections. The other ends can be used to investigate which capacitor you want. There are many other 'test rig ' possibilities (as mentioned in the earlier thread).
[/quote]

Wire a jack plug to a jack socket with 2 short lengths of hook up wire. Connect in line between bass and lead. Connect capacitors to taste. Saves messing around inside the cavity. Keep soldering iron well away from body (yours and the bass). Yes report back, unless you get the black smoke.

[ambient]

Thanks for all of your replies.

I don't want to remove the Bartolini preamp, I use it a lot. It's just that with the East preamp that I had in my Modulus, it had a passive control too. I used to have the passive rolled off totally, and just used to adjust the highs using the active control.

The passive control affects a different frequency range than the actives, it sounds so much nicer. Less 'clanky' if you like. That's maybe why I've never gotten on with Musician basses, they sound too 'clanky' to me.

Ideally I'd change the Bart to an East, but I can't afford that.

Here's a schematic for the wiring for the Bart pre.

[url="http://www.bartolini.net/wp-content/uploads/2013/12/NTMB-Archive.pdf"]http://www.bartolini.net/wp-content/uploads/2013/12/NTMB-Archive.pdf [/url]

[pfretrock]

[quote name='ambient' timestamp='1461843036' post='3038068']
Here's a schematic for the wiring for the Bart pre.

[url="http://www.bartolini.net/wp-content/uploads/2013/12/NTMB-Archive.pdf"]http://www.bartolini.net/wp-content/uploads/2013/12/NTMB-Archive.pdf [/url]
[/quote]

That helps.
Attach capacitor between 'Yellow 2" and ground. The cap will then be in the normal passive configuration. Commonly tone caps are 47n, so one of these should be equivalent to a passive tone wound fully anticlockwise. To get it equivalent to fully clockwise, put a 250k resistor in series. Try different values using the crop clip tip given previously and a resistor may not be needed. Cap value will depends on how much you want rolled off and what the pickup inductance is.

[Dad3353]

Yes, this ^^ is rolling off the treble before it even gets to the pre-amp. It should work just as well, but may give a different result to the ears. No harm in trying both (before pre-amp or at the jack...) except for the fiddling around involved. Pre-pre-amp may be more susceptible to picking up stray interference (buzzing, Radio 4, Police or coastguard messages...).

[Twincam]

[quote name='ambient' timestamp='1461843036' post='3038068']
Thanks for all of your replies.

I don't want to remove the Bartolini preamp, I use it a lot. It's just that with the East preamp that I had in my Modulus, it had a passive control too. I used to have the passive rolled off totally, and just used to adjust the highs using the active control.

The passive control affects a different frequency range than the actives, it sounds so much nicer. Less 'clanky' if you like. That's maybe why I've never gotten on with Musician basses, they sound too 'clanky' to me.

Ideally I'd change the Bart to an East, but I can't afford that.

Here's a schematic for the wiring for the Bart pre.

[url="http://www.bartolini.net/wp-content/uploads/2013/12/NTMB-Archive.pdf"]http://www.bartolini.net/wp-content/uploads/2013/12/NTMB-Archive.pdf [/url]
[/quote]

Are you sure you can't afford it? Pm sent

[3below]

[quote name='pfretrock' timestamp='1461842932' post='3038066']
Wire a jack plug to a jack socket with 2 short lengths of hook up wire. Connect in line between bass and lead. Connect capacitors to taste. Saves messing around inside the cavity. Keep soldering iron well away from body (yours and the bass). Yes report back, unless you get the black smoke.
[/quote]

Even better solution Even stranger I am teaching A level Electronics today.

[pfretrock]

[quote name='Dad3353' timestamp='1461846722' post='3038135']
Yes, this ^^ is rolling off the treble before it even gets to the pre-amp. It should work just as well, but may give a different result to the ears. No harm in trying both (before pre-amp or at the jack...) except for the fiddling around involved. Pre-pre-amp may be more susceptible to picking up stray interference (buzzing, Radio 4, Police or coastguard messages...).
[/quote]

I don't agree. Or should I say Spice (q.v.) does not agree. Modelling with the cheap ubiquitous TL071 amp, it is quite happy driving a capacitance load with virtually no roll off of frequency. But I only went up to 1uF.
Of course it will depend on what is in the active electronics, whether they have used a good audio amp, or a cheap transistor - which would have a higher output impedance and tend to roll off more than an audio amp with a low impedance output.

But no harm in trying.

If I was doing this I'd put a 250k trimmer pot (like the one in the photo) and tone cap between the yellow 2 lead to ground and tweak the pot.

[pfretrock]

[quote name='3below' timestamp='1461847796' post='3038151']
Even better solution Even stranger I am teaching A level Electronics today.
[/quote]
Non-invasive surgery is always the best, I used to be a brain surgeon.

[Guest bassman7755]

Just be aware that by connecting a cap across the preamp output you are loading it so it will probably reduce battery life. Connecting it across the pickup output before the preamp would not have any effect on power usage (and is more likely to give you the tone you want).

[Dad3353]

The answer's a lemon; suck it and see.