HAS MY ’99 THUMB BO 5 BEEN MODIFIED?

[Heimrich]

Hi everyone, I'm new and I apologize if this is in the wrong section....I’d like to ask if someone could please help me to find out if my bass has been modified in some way.

I bought my ’99 Thumb BO 5 second hand in a shop and unfortunately, they couldn’t give me any info about the former owner of the instrument. As far as I know, the J/J MEC pickups in a Thumb BO bass are active, with an active preamp…That was confirmed by H.P. Wilfer who kindly answered an email giving me all the specs about the instrument via the serial number.

On the due premise that I have very little knowledge about electronics, wiring etc., I’m trying to use some time during this forced quarantine to fill such a gap and clarify some doubts. A couple of days ago I came across some discussions on the web about the “real” meaning of active vs. passive (how the term “active” is sometimes misunderstood, how a bass with passive pickups but active preamp has to be considered active…you surely know the debate much better than me), as far as I know in an active/active configuration such as the Thumb bass both the preamp AND the pickups are powered by the 9v battery, so if I disengage the preamp pulling the volume knob the preamp doesn’t work anymore but the pickups do, right? If I’d remove the battery, being the whole system active, the instrument should cease to function and no sound should be heard…

That’s where the problem lies.

I actually removed the 9v battery, I plugged the bass into the amp, I pulled the knob and with my surprise, it plays! Isn’t this what happens with the passive pickups? Always based on my very basic knowledge, in a passive pickups/active preamp instrument if I remove the battery the preamp deactivates but the pickups, not needing an external current, keep working…

I know it probably sounds like a dumb question but...is it possible that my bass has been modified/rewired to make the pickups work like passive? Or maybe does the instrument gets somehow current from the amp through the cable (amp is a Little Mark II that so far never gave me any problem, no hisses, noises, power drops...)? 

I attach some pictures of the electronics cavity, can you tell me if you see something wrong? As far as I’m concerned, it seems to me like the two battery wires have been cut and reconnected (there’s a sort of plastic/rubber wrapping on part of them). If any modification actually happened, is it possible to reverse it and put the instrument back to its original active/active configuration? How?

Thanks

[BassBunny]

The wires to the battery connector do appear to have been joined but it could just be to replace a faulty connector. It would be much easier to do it this way than trace back to one of the PCB to change it.

It does look like they are the original "active' MEC pickups as there is an additional red wire with each pick up wire. Maybe another email to Mr W asking it this is the way they should behave. It might be that these pickups also work in a passive mode and without a battery.

[Lfalex v1.1]

A little knowledge is dangerous, but I'll share what I have in the hope that it helps.

The pickups are original, and should be active. The passive MECs have a silver script on them.

I thought all Thumbs had an 18v eq system that took two 9v batteries (for extra headroom). It was certainly the case in the 1997 NT Thumb I tried. Yours has only one battery holder, though. Could this be the reason for the potential modification as supposed in the previous post.

Hope this helps a bit.

[atsampson]

In the interests of Science, I've just tried removing the battery from my '93 Thumb, which has the same active pickups (although it's been fitted with the later preamp board). In passive mode, the pickups do still produce a usable signal with no voltage on the red wire, they've just got much less gain than usual.

[OliverBlackman]

2 hours ago, Lfalex v1.1 said:

A little knowledge is dangerous, but I'll share what I have in the hope that it helps.

The pickups are original, and should be active. The passive MECs have a silver script on them.

I thought all Thumbs had an 18v eq system that took two 9v batteries (for extra headroom). It was certainly the case in the 1997 NT Thumb I tried. Yours has only one battery holder, though. Could this be the reason for the potential modification as supposed in the previous post.

Hope this helps a bit.

My old thumb 5 was 9v

[Heimrich]

15 hours ago, atsampson said:

In the interests of Science, I've just tried removing the battery from my '93 Thumb, which has the same active pickups (although it's been fitted with the later preamp board). In passive mode, the pickups do still produce a usable signal with no voltage on the red wire, they've just got much less gain than usual.

Thank you so much! So I'm not the only one, that's exactly what happens whit mine...I have to increase the gain and master on the amp but yes, it's still usable. As vfar as I know that shouldn't be possible in an active pu/active preamp design...My concern (in my ignorance) is that it could depend on some sort of...bad shielding (for lack of better word) somewhere in between the instrument and the amp

I will definitely send an email to H.P. Wilfer as BassBunny suggests. After all, no one is more qualified about Warwicks than him :-)

[Doctor J]

It's fine. Your pickup functions as a magnetic pickup in the normal way all the time, they just usually have a lot less coils than passive pickups and are far less prone to picking up background noise as a result. It contains an active pre-amp which boosts the output level to roughly what we accept as a standard. When the battery is flat or disconnected, it's only the pre-amp which stops working. A vibrating string over magnet and coils will still generate a quiet signal and that's what you're experiencing.

Edit -> Think of them as really, really low output pickups with an active circuit used to bring them up to an acceptable output level.

Edited April 26, 2020 by Doctor J

[Heimrich]

10 hours ago, Doctor J said:

It's fine. Your pickup functions as a magnetic pickup in the normal way all the time, they just usually have a lot less coils than passive pickups and are far less prone to picking up background noise as a result. It contains an active pre-amp which boosts the output level to roughly what we accept as a standard. When the battery is flat or disconnected, it's only the pre-amp which stops working. A vibrating string over magnet and coils will still generate a quiet signal and that's what you're experiencing.

Edit -> Think of them as really, really low output pickups with an active circuit used to bring them up to an acceptable output level.

Thanks a lot, that's very interesting...So when we say "active pickups are dead silent without a battery" it's not completely true, at the end of the day the passive pickup principle of  the string mechanical vibration producing magnetic energy that is then transformed in electric energy still applies...Just to be sure I get it right, the preamp is the treble/bass knob? Or there's a preamp inside the pickup (like EMGs) AND the active treble/bass EQ?

Edited April 26, 2020 by Heimrich

[Monkey Steve]

On 26/04/2020 at 11:51, Doctor J said:

It's fine. Your pickup functions as a magnetic pickup in the normal way all the time, they just usually have a lot less coils than passive pickups and are far less prone to picking up background noise as a result. It contains an active pre-amp which boosts the output level to roughly what we accept as a standard. When the battery is flat or disconnected, it's only the pre-amp which stops working. A vibrating string over magnet and coils will still generate a quiet signal and that's what you're experiencing.

Edit -> Think of them as really, really low output pickups with an active circuit used to bring them up to an acceptable output level.

yes this

I also only discovered this quite recently - one of my guitars has EMGs and because I don't play it plugged in very often I'd removed the battery a while ago.  I plugged it in to a tuner a week or so ago, tuned up...and then thought to myself "hang on, that shouldn't work".  Google then explained it to me

[Heimrich]

5 hours ago, Monkey Steve said:

yes this

I also only discovered this quite recently - one of my guitars has EMGs and because I don't play it plugged in very often I'd removed the battery a while ago.  I plugged it in to a tuner a week or so ago, tuned up...and then thought to myself "hang on, that shouldn't work".  Google then explained it to me

I see....Can I ask you what did you google? Is there some specific discussion you found (something like "active pickups working without battery")? I'm asking because I've searched a lot on the web before getting here on basschat but I haven't been able to find anything definitive about that...

[Monkey Steve]

Nothing much different to this really - a couple of forums where people agree that EMGs run with out batteries, but with low output and none of the usual EMG sound, and a couple of YouTube videos proving the point and showing what they sound like

the difference seems to be whether you can bypass the active eq section.  It’s very rare to have this on a guitar, so the pickups still have some output and that gets to the jack.  Where there is an active eq, as is more typical on basses, then the signal will not get through that without a battery.

Warwicks let you bypass the active eq, so I assume that’s why you can still play without a battery. Do you only get a signal with the active eq bypassed?

[Heimrich]

5 hours ago, Monkey Steve said:

Nothing much different to this really - a couple of forums where people agree that EMGs run with out batteries, but with low output and none of the usual EMG sound, and a couple of YouTube videos proving the point and showing what they sound like

the difference seems to be whether you can bypass the active eq section.  It’s very rare to have this on a guitar, so the pickups still have some output and that gets to the jack.  Where there is an active eq, as is more typical on basses, then the signal will not get through that without a battery.

Warwicks let you bypass the active eq, so I assume that’s why you can still play without a battery. Do you only get a signal with the active eq bypassed?

Yes, if I remove the battery the only way to get a signal is to bypass the active eq, I think what Doctor J wrote a couple of posts above is the best explanation of why this happens.

Now that you're telling me I think I've seen the YouTube videos you're talking about...

A couple of days ago I took part to a discussion on another forum about the "real" nature of active pickups, specifically the MEC J type active ones in  Warwick Thumb bass...It seems like there's a bit of confusion (or at least I AM a bit confused) about how the passive pickups/active preamp and the active pu/active preamp system works, the differences betwen them...Someone said that "if you disengage the active pre of a Thumb, what you're left with are the pickups, which are passive". That to me contradicts the Thumb specs as declared by Warwick itlself ("active MEC J pickups, active electronics").

Using as examples two Warwick models:

Corvette $$: passive pickups, active preamp. If I pull the knob, I disengage the preamp (thus the treble/bass eq), what's left is the passive pickups, the volume and the pu balance.

Thumb: active pickups, active preamp. Disengaging the preamp (this time I mean keeping the 9v battery), if I got it right, the pickups remain active, so they are still powered by the battery, the only thing to be bypassed is the preamp (same treble/bass eq as the Corvette)...Am I right on this? If not, how does it actually works? And, most important, why Warwick would call those pickups "active"? If it was true that "if you disengage the active pre of a Thumb, what you're left with are the pickups, which are passive", why bother to call them "active"?

Sorry, I didn't want to be long-winded ;-)

[atsampson]

The pickups are active - they contain a magnetic pickup feeding into a preamp powered by the red wire. The output from the pickups is fed through an active EQ circuit on the PCB in the cavity, which is what the pull-up knob turns on and off.

However, if you don't provide power to the pickups, you still get some signal out of them because of how the preamp circuit's designed. I don't know if there's a schematic for the MEC pickups around anywhere, but here's a schematic for an EMG active pickup that shows how this might happen - if you don't provide power to the pickup shown there, it won't have any gain (the output signal can't be any bigger than the original magnetic pickup can provide) but the signal will still leak through the op amp's feedback resistor R2 and make it to the output. This is one of the standard kinds of simple amplifier circuit that's used all over the place in audio equipment where you need a bit of gain, and the MEC pickups probably use a similar arrangement.

[Lfalex v1.1]

1 hour ago, Heimrich said:

Yes, if I remove the battery the only way to get a signal is to bypass the active eq, I think what Doctor J wrote a couple of posts above is the best explanation of why this happens.

Now that you're telling me I think I've seen the YouTube videos you're talking about...

A couple of days ago I took part to a discussion on another forum about the "real" nature of active pickups, specifically the MEC J type active ones in  Warwick Thumb bass...It seems like there's a bit of confusion (or at least I AM a bit confused) about how the passive pickups/active preamp and the active pu/active preamp system works, the differences betwen them...Someone said that "if you disengage the active pre of a Thumb, what you're left with are the pickups, which are passive". That to me contradicts the Thumb specs as declared by Warwick itlself ("active MEC J pickups, active electronics").

Using as examples two Warwick models:

Corvette $$: passive pickups, active preamp. If I pull the knob, I disengage the preamp (thus the treble/bass eq), what's left is the passive pickups, the volume and the pu balance.

Thumb: active pickups, active preamp. Disengaging the preamp (this time I mean keeping the 9v battery), if I got it right, the pickups remain active, so they are still powered by the battery, the only thing to be bypassed is the preamp (same treble/bass eq as the Corvette)...Am I right on this? If not, how does it actually works? And, most important, why Warwick would call those pickups "active"? If it was true that "if you disengage the active pre of a Thumb, what you're left with are the pickups, which are passive", why bother to call them "active"?

Sorry, I didn't want to be long-winded 😉

Yep. What you've said seems correct.

Skipping to last question, Active pickups are so called because they have an active component (a small amp, often in the pickup housing) which raises the output of the pickup. Such a pickup frequently has fewer windings (coils) and possibly a weaker magnet assembly. The pickup will still work without the active part, but the output is lower.

The benefit of less coils is (potentially) less noise. Weaker magnets mean less string drag for a given distance from the string, which can help improve sustain, especially if there's lots of magnet assemblies (HH stingray, for example).Finally, the pickup amp may well buffer or load the EQ stage in a way that improves its performance.

[Heimrich]

2 hours ago, atsampson said:

The pickups are active - they contain a magnetic pickup feeding into a preamp powered by the red wire. The output from the pickups is fed through an active EQ circuit on the PCB in the cavity, which is what the pull-up knob turns on and off.

However, if you don't provide power to the pickups, you still get some signal out of them because of how the preamp circuit's designed. I don't know if there's a schematic for the MEC pickups around anywhere, but here's a schematic for an EMG active pickup that shows how this might happen - if you don't provide power to the pickup shown there, it won't have any gain (the output signal can't be any bigger than the original magnetic pickup can provide) but the signal will still leak through the op amp's feedback resistor R2 and make it to the output. This is one of the standard kinds of simple amplifier circuit that's used all over the place in audio equipment where you need a bit of gain, and the MEC pickups probably use a similar arrangement.

Thank you so much, that basically supports what I thought, by pulling the knob I disengage the EQ  but the pickup preamp is still powered* thhrough the red wire hence the definition of "active anyway"(for lack of better word)

*of course keeping the battery in :-)

Edited April 30, 2020 by Heimrich

[Heimrich]

1 hour ago, Lfalex v1.1 said:

Yep. What you've said seems correct.

Skipping to last question, Active pickups are so called because they have an active component (a small amp, often in the pickup housing) which raises the output of the pickup. Such a pickup frequently has fewer windings (coils) and possibly a weaker magnet assembly. The pickup will still work without the active part, but the output is lower.

The benefit of less coils is (potentially) less noise. Weaker magnets mean less string drag for a given distance from the string, which can help improve sustain, especially if there's lots of magnet assemblies (HH stingray, for example).Finally, the pickup amp may well buffer or load the EQ stage in a way that improves its performance.

Thanks, so you too confirm that the EQ is the part that is bypassed when I pull the switch

[Lfalex v1.1]

23 minutes ago, Heimrich said:

Thanks, so you too confirm that the EQ is the part that is bypassed when I pull the switch

Theoretically, yes.

If your bass is unmodified, then that is what should happen. Pull up the knob, and the EQ section is bypassed. Unless your bass has been modified..

The level shouldn't drop too much as you switch from "EQ on" to "EQ bypass".

My Hohner B2AV has a trim pot to lower the output of the EQ stage to match its passive mode better, so no big volume jumps are evident when you switch. The tone just changes.

[Heimrich]

On 30/04/2020 at 19:17, Lfalex v1.1 said:

Theoretically, yes.

If your bass is unmodified, then that is what should happen. Pull up the knob, and the EQ section is bypassed. Unless your bass has been modified..

The level shouldn't drop too much as you switch from "EQ on" to "EQ bypass".

My Hohner B2AV has a trim pot to lower the output of the EQ stage to match its passive mode better, so no big volume jumps are evident when you switch. The tone just changes.

I've sent an email to H.P.Wilfer of Warwick, he kindly and patiently send me a long and exaustive explanation. Not only he  confirms the bass has not been modified in any way, he confirms as well what Doctor J wrote some posts above adding, in his own words:

   "Yes, Corvette $$ has Passive MM PU´s + active 2-Band El.

   Passive PUs are not connected to electricity. If he goes into passive mode with

   a pull-push pot (bypass), passive pu's continue to work as usual. The PU signal

   does not go through EQ but directly from the PU's to the socket. EQ is still

   connected to the battery but not active because the signal does not go through

   the EQ. EQ Treble / Bass function is off. Vol and Balance Poti continue to

   work as usual.

 

   With Thumb Bass, the function is the same as with Corvette $$. The only

   difference is that Thumb Bass has active PUs. A preamplifier is built into

   active PUs, which always requires power to function. That is why active PUs

   are always permanently connected to electricity."