Musicman Wiring Genius Needed

[fu22ba55]

I need to send my '79 Sabre body (pre EB) to someone reputable to repair / restore the preamp to its original glory. I have a feeling that mine has been taken out before, and maybe rewired somehow... In talking to shrigg about his new Sabre, and how the swtiches function, it's clear that something is screwy with my center (series/parallel or phase or w.tee.eff) switch.

I wanna yank the neck off, ship the body to someone to go over solder join by solder join, and send me back a happy '79 Sabre. I have the original pre... someone just wired one of the switches funny.

I do NOT have a wiring schematic, so I'm looking for a 80-year-old guitar wiring master who already has this schematic in his drawer, or in his head.

Who should I send my baby to? Should I ship this thing overseas to John East? I'm hoping there's someone stateside in the US of A. Midwest would be even better, since that's where I am.

Thanks.

 

[line6man]

Well, I can draw you a diagram for the setup if you describe it.
I just can't give you any preamp and pickup color codes.

 

[SGD Lutherie]

Here's a Sabre II preamp schematic.

I have a '78 Sabre preamp here. It was loaned to me to examine.

I'd also be happy to do that work for you if you like.

 

[fu22ba55]

Well, I can draw you a diagram for the setup if you describe it.
I just can't give you any preamp and pickup color codes.

That's just the problem... I'm not 100% sure what that center switch was originally intended to do... series / parallel, or in/out of phase.

I'd also be happy to do that work for you if you like.

That is awesome and amazing news. I will be in touch!

Every time someone posts a schematic on Talkbass, an angel gets its wings.

 

[SGD Lutherie]

That's just the problem... I'm not 100% sure what that center switch was originally intended to do... series / parallel, or in/out of phase.

Here it shows it as a phase switch:

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That is awesome and amazing news. I will be in touch!

Every time someone posts a schematic on Talkbass, an angel gets its wings.

It used to be hard to track down this stuff... now with the internet it's pretty easy.

 

[mikeswals]

It's a phase switch. And was a terrible idea. Out of phase completely drops the volume and thickness to almost nothing.

 

[line6man]

It's a phase switch. And was a terrible idea. Out of phase completely drops the volume and thickness to almost nothing.

Although I've never played one, I completely agree.
Phase switches are almost always useless unless you like weird nonsense sound effects.

 

[SGD Lutherie]

Yeah, dumb idea. I had them on a couple of basses back in the day because it was something you could do to get new tones, but it's pretty useless.

One way to get some bottom in is to run one pickup through a cap when it's out of phase. That will limit the low end from that pickup, so the out of phase tone would have more bottom. Something like a .022µF to .0047µF should work fine.

 

[recnsci]

Here's a Sabre II preamp schematic.

That's one weird preamp.


David, I've noticed in another thread that you have fiddled with Sabre p'ups and measured DCR (which turned out to be quite low). Do you have any idea whats inductance and capacitance of that p'up?

 

[SGD Lutherie]

That's one weird preamp.

The Stingray preamp is pretty weird as well. The choice of op amp is very weird. Originally they didn't even switch off the battery when you pulled the plug out!

Great sounding preamp though. I'm going to be making those soon (the Stingray version).

David, I've noticed in another thread that you have fiddled with Sabre p'ups and measured DCR (which turned out to be quite low). Do you have any idea whats inductance and capacitance of that p'up?

No, sorry. I don't own an LCR meter (or have a bridge setup), so I can't tell you the inductance. Trying to get a capacitance reading on a pickup will only yield a nonsense reading from the meter.

I can tell you that the alnico 5 rod magnets are between 307 and 404 Gauss.

 

[line6man]

That's one weird preamp.


David, I've noticed in another thread that you have fiddled with Sabre p'ups and measured DCR (which turned out to be quite low). Do you have any idea whats inductance and capacitance of that p'up?

Why do you need to know the inductance and capacitance?
You really won't get any usable information out of the numbers, pickups are complex impedance devices and it's difficult to make any accurate calculations that could be used to related to their tonality.

 

[SGD Lutherie]

Why do you need to know the inductance and capacitance?
You really won't get any usable information out of the numbers, pickups are complex impedance devices and it's difficult to make any accurate calculations that could be used to related to their tonality.

That's why I don't own an LCR meter yet. It's useful to see what the inductance is when designing pickups, or for checking for shorts. That's about it.

There is no way to read capacitance of a pickup, and that isn't information that's ever needed. It's very small, and the capacitance of the patch cord is far greater.

 

[timbledum]

Normally you ask for help and everyone says pay someone to do it better than you can. Here OP asked to pay someone and he got a whole lot of unsolicited help!!! Awesome!

 

[line6man]

That's why I don't own an LCR meter yet. It's useful to see what the inductance is when designing pickups, or for checking for shorts. That's about it.

There is no way to read capacitance of a pickup, and that isn't information that's ever needed. It's very small, and the capacitance of the patch cord is far greater.

Yep. The capacitance is more-or-less meaningless.

Every component has an inductance, a capacitance and a resistance, however, this is not to say that they are all significant. The capacitance of a pickup is parasitic, forming due to the fact that the pickup wire is insulated. The insulation acts as a dielectric between the conductive wires, which creates a very tiny (100-200pF?) capacitance.

Pickups are MUCH more inductive than capacitive.
The inductance is usually several Henries. (Right?)

 

[SGD Lutherie]

Pickups are MUCH more inductive than capacitive.
The inductance is usually several Henries. (Right?)

Yes, pickups are inductive. They are basically inductors. The coil has inductance based on how much wire and the shape, and the cores and magnets can have inductance.

The typical inductance is between 6 and 12H, but it can be all over the place. It tells you about as much as the DC resistance does, as far as the tone of the pickup.

But it's good to know when making copies of pickups, or for quality control (checking for shorts).

The Extech 380193 is the most widely used meter, since most LCR meters wont give meaningful numbers when used with pickups.

 

[recnsci]

Why do you need to know the inductance and capacitance?

On first glimpse on schematic, my initial reaction was "this is all wrong". At least from engineer point of view. It's inverting configuration, p'up impedance will interact with imput impedance with a dip at resonant frequency. Further more, it's basically baxenadll eq with unbuffered p'up on it's butt. P'up impedance could interact strongly with HF eq. During max hf boost there is only 'bout 2nF of capacitance between p'up and virtual ground, it's like having active eq boost at max and passive tonecontroll cut at min, at the same time.

While this could be all technically wrong, it's actually great. That HF sahping is not available by any other means, 'cus you can't have interaction of your mixer EQ with p'up impedance.


If MM p'up impedance is very low, all these effects are much less pronounced. If its comparable to usual p'up impedances, you could have sorta' "MM tone" in a box. Or controll cavity on bass.


David, there is crude vay to measure impedance, with out flimsy LCR meters. More later


edit:

...yeah, and it will work (more or less) with out battery. Whoever designed this knew waht he/she was doing.

 

[SGD Lutherie]

David, there is crude vay to measure impedance, with out flimsy LCR meters. More later

Yes I know how, but we were talking about inductance. And when then, as I said I don't have a bridge.

If MM p'up impedance is very low, all these effects are much less pronounced.

2K. 1.5K on the older ones.

...yeah, and it will work (more or less) with out battery. Whoever designed this knew waht he/she was doing.

How do you figure that? The tone controls are in the op amp's feedback loop.

 

[recnsci]

Yes I know how, but we were talking about inductance.

I shouldnt have mentioned inductance, I know that RLC params' are very crude approximation. I should have said "whats modulus of impedance at 1KHz? 5K? 20K? 50K". That's what relevant anyway. BTW by measurment I meant homegrown variety of Link Removed, just with out fancy Tektronix or whatever lab gear.

2K. 1.5K on the older ones.

Yeah, I saw that thread. But thats with both sides of 'bucker in parallel? Since there is Sabre varitey that singlePU-siglecoil mode, I guess that pre works ok with 4K p'up, which is well enough in vicinity of typical J and P stuff.

How do you figure that? The tone controls are in the op amp's feedback loop.

Yeah, that's why I said more or less. All controlls would get screwd up, level would drop, it will sound weird, but there will be something at the output. With typical noninverting high impedance buffer, without battery output is dead silent. Nada.

That 4250 programable OA is nice touch as well. If you have Sabre at bench, maybe you could try to underbias it severly, like 10M or more for Rset. Maybe it could be even wierd fuzz thing on stroke of switch.

 

[shrigg]

Here's what's under the hood of my new-to-me 79 Sabre. Pics of the rest of the bass here.

I agree that the center switch loses all gusto when out of phase. Then again, it DOES bring the funk in a stinky sorta way...

Hope the pics prove useful!

Best,
Darren

 

[fu22ba55]

Mmmm... that bass is so clean. Nice job on the pics shrigg. Thanks.