Active electronics bypass?

[dunkelfalke]

Hello forum,

I bought new active electronics for my bass and would like to add a bypass switch for it so I can use the bass in a passive way. It would be great when the switch could also switch the battery off at the same time.

Is it possible? If yes, how?

This is the current chematics:

[sumgai]

dunk,

Take a look at this:



Note that you need a 3PDT for the bypass operation. That is, if you want "true bypass", which most folks do. This will completely remove the active circuit from the signal path, and also shut off the power to the IC when it's not 'active'.

Note that red 'X' in two places. Your diagram shows not one but two tone controls, a bit odd. If you elect to keep the left-most tone control, then you can place it at either A or B. Position A will have the control on at all times, active or passive - that may be handy. Position B will have the tone control on only when active, and off when passive.

Note also the placement of the tone control after the volume control on the op-amp's output. This is again non-standard, but if it works and sounds the way you want it, then you don't need to change it. Personally, I think I might eliminate this second tone control altogether, and use the first one at Position A.

While using the same volume control for active and passive sounds like good sense (save some DM/€), the values for each are not equal. Passive likes 250~500KΩ pots, and active likes it way down, about 1/10th of that. You could wire in each kind, selected by the switch.... sorry, I didn't think to do that before posting my drawing to Photobucket.

And last but certainly not least, active or passive, those tone capacitors are not gonna be pretty! 683µf will pretty much swamp all your signal - your output will approach ga' nicht, sehr schnell! You might roll them down to about 68nf, or even less, I think you'd enjoy that a little more.

HTH



sumgai

[dunkelfalke]

Thank you!

I was thinking... would it make sense to add the tone controls for each pickup before the blend pot? That way I would still have got two tone controls, but for each pickup a separate one.

Also, what would be better - to put a 500k volume pot before the preamp or a 50k after it?

How would the circuit look like after all those mods?
And - if it is not too time-consuming for you - how would it look like as a drawing? I am still not that good at reading circuits.

[sumgai]

dunk,

I'd personally put the 50KΩ volume pot after the op-amp. You already have a pair of large-value controls (the blender) ahead of the op-amp, and you're about to install some addtional tone controls, so the "front end" of the op-amp is not gonna be happy with you if you insert yet one more volume control there.

And yes, you can simply connect each tone control directly across each pickup, that will work. While both pickups have their negative leads going to ground (they're in parallel), in the future you may wish to put them in series. For this reason I recommend that you "think ahead", and not create a situation that you'll later have to "unsolder, move, resolder" a bunch of delicate component leads.

And finally, I have to say that sadly, I'm not all that good at "free hand" layout drawings. I tend to think as a circuit designer, so I keep from thinking in terms of "where does this go...." in the physical sense. But I'm pretty sure that John, wolf, or some other member will come along and do up a nice one for you. Forgive me?   (Fellow Nutz, can ya help a brother out? Please?

HTH





sumgai

[wolf]

Okay sumgai,
I think I'll give that a try.

[dunkelfalke]

Just a little additional wish ;D

Since 3PDT switches are far too expensive and I've got lots of DPDT switches lying around, maybe a better idea wouldn't be a true bypass which switches off the battery but just a tone bypass, for which a DPDT switch should be enough...

Many thanks in advance

[wolf]

Here it is - I hope it's correct.
Sorry Dunk, I just saw your comment now and so maybe someone else could rework this?

[dunkelfalke]

Not needed, wolf. Your picture made me understand how to do it. Thank you very much!

[sumgai]

wolf,

Thanks for the assist!

However, the same side of each half of the blender goes to ground.... there needs to be a "cross-over" such that one side goes to ground at the same time as the other side is going to the output. Reverse the leads to one side or the other, and all will be good.

Other than that, it looks good. +1 for coming to the aid, above and beyond the call of duty and all that.


~!~!~!~
dunk,

wolf doesn't show the tone controls across the pickups, but I think that's pretty straightforward, right? If you do that (put in two tone controls, one for each pup), then I suggest eliminating both of the other tone controls. (But it now dawns on me, this is a "store-bought" circuit, yes? Then if the tone control is part of the circuit board, you might as well leave it in there. There's not much point in tearing up a circuit that you just bought, unless there's a real problem of some kind.)

HTH




sumgai

[sumgai]

Ah, two more points to bring up....

One, the battery can be switched by the jack, via the good old TRS scheme. And...

Two, those 68nf caps are still a bit too much. Unless these pickups have more "ice pick" than Roy Buchanan's Telecaster, then I think you'll be better served with either 47nf or 33nf. (That would be 0.047µf or 0.033µf.) But them's my personal thoughts about what value to start out with - you may decide differently.

[wolf]

Okay, here's the newly revised circuit:


Yes, it seems I made a few mistakes on that last one. I misread the "blend pot" wiring thinking that it showed wiring from a "left-right" perspective. No, it actually was opposite winding. (Yet another case of the potentiometer schematic symbol causing additional confusion).

Also, I guess I took the easy way out for the output jack switch and I can't believe I put 68 nf caps in there. Well, I hope this is closer to what the circuit should be.

And thanks to everyone for the good words and the karma points.

[dunkelfalke]

Dec 15, 2009 22:52:41 GMT -5 sumgai said:

wolf doesn't show the tone controls across the pickups, but I think that's pretty straightforward, right? If you do that (put in two tone controls, one for each pup), then I suggest eliminating both of the other tone controls. (But it now dawns on me, this is a "store-bought" circuit, yes? Then if the tone control is part of the circuit board, you might as well leave it in there.

It is store-bought, but that's okay. Your suggestions make more sense for me than the original configuration. I do understand how to remove the original tone and volume controls and replace them with my desired configuration (and a DPDT on/on/on switches right after the pickups for the humbucker/humcanceller/single coil configuration)

Many thanks also to you for your explanations.

[dunkelfalke]

It just crossed my mind... when the circuit is in the passive mode I cannot use the volume pot.

If I wire the passive connection before the 25kOhm volume pot, it would kill the whole sound. But if I use a 500kOhm volume pot in active mode, then - if I understand correctly - the useful range of the pot would be nearly zero.

Is there some solution for it?

[sumgai]

Dec 16, 2009 3:19:52 GMT -5 dunkelfalke said:

It just crossed my mind... when the circuit is in the passive mode I cannot use the volume pot.

If I wire the passive connection before the 25kOhm volume pot, it would kill the whole sound. But if I use a 500kOhm volume pot in active mode, then - if I understand correctly - the useful range of the pot would be nearly zero.

Is there some solution for it?

Yes. You could use a separate volume control in each path. To keep from drilling extra holes, you could use a "ganged" dual pot. That's the same thing as a blend pot, but this time, the two sections are of different values. I think newey has recently discussed this, but I forget where.....

Your understanding of values is correct. A 500KΩ pot in the active section will make like all the "action" occurs from 2 to 2½ or thereabouts. A 25 or 50KΩ pot is best here. And of course the reverse holds true for the passive part of the circuit - too low a value will mean you get almost no output at all, even when set to '10'.

500K x 50KΩ might be a bit difficult to find, but I'm sure other values can be made to work. For instance, a 1M x 100KΩ pot is easy to find, and you could solder a resistor in parallel with each of the two sections. Simply use a 1MΩ resistor for the larger section, that will bring it down to 500KΩ, ditto for the 100KΩ section - a 100KΩ resistor soldered across the two outer terminals will reduce the value to 50KΩ. (Keep in mind that these are approximate values - the manufacturing tolerance in making these parts is up to 20%, so when you measure them with your meter, you may not see the exact value you were expecting.)

HTH


~!~!~!~
wolf,

Your latest looks great! ;D




sumgai

[dunkelfalke]

Thank you. By the way, now I understand why the original volume pot of this circuit is linear - it prolongs the useful range somewhat even while being of such a high value.

[dunkelfalke]

Hello guys
it looks like I do need help with the tone pots. I wired everything up today and nearly everything works perfectly except the tone pots. They both affect the neck pickup only

Other than that everything works as planned and sounds sweet. Thanks a lot for everyone who has helped me so far.

/edit: curiouser and curiouser. I thought I have realised my mistake, rewired the tone pots and now the bridge tone pot works just fine, as long as the neck tone pot is opened. The neck tone pot doesn't affect the sound at all as long as the bridge tone pot is opened. When one of the pots is closed, the other works like a volume pot

Maybe I should better go to bed now.

[wolf]

Hi dunkelfalke,

Looking over my diagram more closely, it seems to me that the tone pots control both pickups. It also seems that the "right hand" tone pot only works when the circuit is active.

Maybe I should attempt another redrawing.

******************************************************
Edited to Add: and here's the new drawing:

Okay, in this way, one tone pot works only during the passive mode and the other only works in the passive mode.

[dunkelfalke]

I decided to go a different way and to put the tone pots directly after the pickups, before anything else.

[dunkelfalke]

Never mind, and thanks to you, wolf. I've done it with the help of the wiring pictures of Les Paul from your website. Now everything works as it should, although the change in tone is pretty weak - maybe I should try different capacitor values for a bass.