MIJ Fender Jaguar Bass preamp - schematic and PCB

Pickups, wiring schemes, switch techniques and onboard active electronics for guitars
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lolbou
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Post by lolbou »

Hi!

I've had this bass in for nasty buzz and hum that got even worse after someone else's attempt... Wires were very thin and brittle, shielding paint was somehow inefficient. So I went rewiring it all and properly shielding it. It is dead quiet now, and plays really well. I did change some of the stock caps (on the preamp and tone control) for better quality ones (these were like the plastic transparent ones found in many Boss pedals). I do like the active preamp, it's a nice feature on this good sounding passive bass. And the neck is really nice if you're into fast and thin ones.

I did trace the preamp and drawn another PCB for those willing to try it out or wanting to upgrade with other values/specs.

Here are the guts:
preamp.jpg
preamp component.jpg
Here's my hand-drawn schem:
jaguar preamp schem.gif
And PCB and layout (wire colors matches the one in the bass, diagram is available online):

(File amended and reposted below)

D1 and D2 are small signal diodes. I guess D3 is a protection diode.

Oh, and I did forget to write down the transistor type :slap: :slap: ... Some 2SCxxxx I can't remember. I can remember these to be high gain ones (hfe around 400 IIRC). If anyone has the info, just chime in! I'll ask my friend to remove the pickguard on his next restring...

Feel free to spot any mistake...
Last edited by lolbou on 09 Oct 2012, 21:45, edited 2 times in total.
Reason: Schem and layout updated as per bajaman's comments
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Post by bajaman »

I traced one of these a couple of years back - pretty sure that the emitter resistor on the first transistor is 6k8 not 680 ohms.
Also the last transistor gain stage should have the 47p capacitor attached between base and ground not the second transistor buffer stage.
cheers :thumbsup
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Post by bajaman »

Jaguar Bass Wiring diagram.pdf
(370.7 KiB) Downloaded 308 times
from the fender download site
:wink:
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Post by lolbou »

Thanks for your input Steve! :D
bajaman wrote:I traced one of these a couple of years back - pretty sure that the emitter resistor on the first transistor is 6k8 not 680 ohms.
Seems like R3 and R9 are identical indeed, please blame my colorblindness, although I REALLY did take my time to actually read these... :( :slap: I must admit that I'm not familiar enough with the transistors circuitry to actually expect values...
bajaman wrote:Also the last transistor gain stage should have the 47p capacitor attached between base and ground not the second transistor buffer stage.
But the PCB pics show no such capacitor for Q3? :scratch: Another revision?

Now, any recollection of the transistor type?

Add-on:
Fender_Jaguar_Bass_controls.jpg
Fender_Jaguar_Bass_controls.jpg (22.52 KiB) Viewed 1263 times
ps: the 47p cap can easily be added on the PCB at the base Q3, and removed from the second stage... Again, is this an error of some sort from Fender? Does this really matters on such stages? I deeply lack the theory... :(
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Post by bajaman »

The 47p cap rolls off some of the gain at radio frequencies (well above our hearing range :wink: ).
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Post by lolbou »

Good morning bajaman, thanks for your explanation. :) But was that 47p cap placed on Q3's base in your unit? It really looks like it isn't on this one...
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Post by bajaman »

hmmmm - yes it is connected to Q3 on your board layout :wink:
I think it must have been a mistake by whoever fabricated the board for Fender though.
the transistors were Japanese low noise types from memory - MPSA18 or BC550C or 2N5089 etc will all work fine.
cheers
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Post by lolbou »

bajaman wrote:hmmmm - yes it is connected to Q3 on your board layout :wink:
I'm afraid it's not or I REALLY don't get what you mean, lol :oops: :scratch: The trackside picture I did provide isn't inverted, so what appears on the right hand side is related to what's on the left hand side on the component-side picture I can't believe I'm typing this...
bajaman wrote:I think it must have been a mistake by whoever fabricated the board for Fender though.
I'll update the PCB to have the extra pads for this 47p on the output gain stage. Considering the first gain stage being somehow identical, I admit this makes sense... And potential builders may end up with the choice! :wink:

Thanks again for your comments on this,

Cheers

Laurent

edit ps : the "missing" cap don't show on the PCB drawing that appear on the wiring diagram from Fender too. evrything else matches, even the C and F pads that are left unconnected in the wiring scheme (and then omitted in my PCB)... Weird...
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Post by lolbou »

Here's the new PCB and layout file in pdf. Added the "missing" 47p cap fron Q3's base to ground.
Jaguar preamp.pdf
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Post by darmstat »

Did anyone find out what the exact transistors that were used for this circuit?

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Post by lolbou »

You can definitely trust bajaman's suggestions above for transistors. :wink: Just make sure the pinout is correct.

Unfortunately, I haven't had the opportunity to look inside the very bass since my friend took it back... :(
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Warning this person is Dyslexic, so subject and information can jump around the posts, just ask to explain set part that is, or could turn green and in the increadable sulk :(

Post by AngelLaHash »

Im guessing you are British with the Resister as BOXES, every thing seems to be going ZigZag Lines.

Im going to see if i can build one on vero board one time, but first off
you given suggests for the Transisters but what about the Diodes
i see you have two types im guessing, D1 & D2 and then there is D3

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Post by lolbou »

AngelLaHash wrote:Im guessing you are British with the Resister as BOXES, every thing seems to be going ZigZag Lines.
I'm not. :wink: But that's just the way I prefer for resistors. I can't get used to zigzags for resistors...
AngelLaHash wrote:you given suggests for the Transisters
Sorry again for forgetting to write down the correct reference while tracing... :slap:
AngelLaHash wrote:but what about the Diodes
Try 1N4148 for D1 and D2.

I don't really know what zener to choose. Is it intended here for some kind of regulation or is it a simple polarity protection? I should have looked it more precisely. :slap: again.

Anyway, for a first try on vero, D3 ain't that important as long as you use a clean power supply and correct polarity.
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Post by deltafred »

AngelLaHash wrote:Im guessing you are British with the Resister as BOXES, every thing seems to be going ZigZag Lines.
You guess wrong.
what about the Diodes
i see you have two types im guessing, D1 & D2 and then there is D3
D1 and D2 look like zeners to me, voltage unknown.
D3 I would go with IN4001 (/2/3/4/5/6/7)

Edit - lolbou beat me to it, I must learn to type faster.
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Post by Duckman »

bajaman wrote:Also the last transistor gain stage should have the 47p capacitor attached between base and ground not the second transistor buffer stage.
So, 47p cap C10 at Q2 base in the hand traced schem must be placed in Q3 base?

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Post by bajaman »

So, 47p cap C10 at Q2 base in the hand traced schem must be placed in Q3 base?
it certainly seems a more appropriate place to place it - it does absolutely nothing on Q2 :roll:
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Post by dmdago »

It's an old post but I've just bought the preamp so I want to help you. The transistors are 2SC3112, (http://alltransistors.com/transistor.ph ... stor=14135)

I will check the diodes that seemed to be just like you recommended.

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Post by dmdago »

Simple and dummy question... The resistors are 1/4W?

Thanks

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Post by dmdago »

I've just checked the diodes. The zener diodes are BZX85C-5V1, I presume that it can be replaced by 1N4733A. The other diode is difficult to read or I'm pretty dumb, it says something like N760, N670, N076 or something like that. I've checked on google but nothing comes out with that part number.

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Post by SussexTech »

AngelLaHash wrote:Im guessing you are British with the Resister as BOXES, every thing seems to be going ZigZag Lines.
It's all about boxes in 2017: IEC 60617

Read more http://www.resistorguide.com/resistor-symbols/

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