Baja Music Man guitar and bass onboard preamps

oldschoolbassplayer · Post by **oldschoolbassplayer** » 27 Sep 2021, 15:12

Jarno wrote: ↑27 Sep 2021, 14:14 Start with the resistors, then capacitors, semiconductors (IC's, transistors) last.
But in general, lower/smaller components before bigger ones.

I almost want to build my own tube amp now!

I'm looking forward to this it should be fun.

oldschoolbassplayer · Post by **oldschoolbassplayer** » 28 Sep 2021, 22:57

Jarno,

Did you know that solder has a shelf life? I have a 1-lb Kester .8mm (.031") 60/40 rosin core paper-weight manufactured Jul 07 17.

I guess I will not be buying any more 1-lb spools of solder, but before I go ahead and order less, I wondered if you had any solder thoughts or advice?

Jarno · Post by **Jarno** » 29 Sep 2021, 08:25

Does it still work properly? If it does, don't worry about it.

As to my preference, I use Stannol solderwire, with lead, not sure if that's easy to get where you are. There are several variants I think I've used HS and HF, both have no-clean flux, and I do not clean my boards.

deltafred · Post by **deltafred** » 29 Sep 2021, 09:33

oldschoolbassplayer wrote: ↑28 Sep 2021, 22:57 Did you know that solder has a shelf life?

That's odd because I have a roll that I started sometime in the 80's and it hasn't gone off yet.

oldschoolbassplayer · Post by **oldschoolbassplayer** » 29 Sep 2021, 09:39

I'm wondering how lead and tin go bad sitting is a closet? Probably the rosin core is what deteriorates but geez when I was a kid seems like a spool of solder lasted 10-years or you lost it...

What do you clean your boards with? Do you prep your boards in any particular way?

Are you an electronics guy that plays the bass or a bass player that knows electronics?

Jarno · Post by **Jarno** » 29 Sep 2021, 09:54

As mentioned in my post I do not clean, also no special preparation unless I etched boards myself, and they have been in a drawer for a while (very fine steel wool).

I myself am a mechanical engineer, with affiliation with electronics. The hobby has helped my career as well, I now lead a group of development engineers who do both mechanics and electronics (and software, really need to know more about that area) development.
Apart from that, a bassplayer, and I have built a rather big modular synth.

deltafred · Post by **deltafred** » 29 Sep 2021, 10:18

I've seen acid cored solder corrode over time but never rosin.

If needed (if they don't tin properly) I clean the solder pads with with a typist's eraser (a pencil shaped eraser where the "rubber" is loaded with fine sand). As we don't have typists anymore I guess that typist's erasures are no longer produced.

"Are you an electronics guy that plays the bass or a bass player that knows electronics?"

Good question, make your own mind up.

Back in the 60's I started messing with electronics when I was about 12 y.o. and started playing bass at 16. I worked in an electronics design lab in the early 70's then moved from design to commissioning and fault finding where I stayed until they moved the electronics design and production to another site. Software was in it's infancy and I retrained as a software engineer, finally ending up in software quality control where I was when I retired.

As far as bass playing goes I have been a weekend warrior since 1967 with occasional short breaks when life got in the way. I turned down a few opportunities to go pro because I had a family and a good career (with a pension at the end of it). I currently play in 3 bands and sub for a 4th.

oldschoolbassplayer · Post by **oldschoolbassplayer** » 29 Sep 2021, 11:07

Thanks guys - its good to know I am not getting advice from a couple of "internet experts"

I am grateful for all your help.

oldschoolbassplayer · Post by **oldschoolbassplayer** » 01 Oct 2021, 13:11

Any suggestions for a reasonably priced digital multi-meter that isn't junk?

Jarno · Post by **Jarno** » 01 Oct 2021, 20:23

Even the cheap ones are OK, still have one I bought from the dutch version of Home Depot a decade ago. Also have one from china which is OK (has capacitance and inductance measurements), I have a bench multimeter from Fluke which has seen better days (but it is more than 50 years old, and a dumpster find), and a analogue Hioki from the 80's which has no features, but always works (reading the dial is a bit of a puzzle).

flavio-san · Post by **flavio-san** » 11 Oct 2021, 13:28

Hi stompboxers, I've built the 2 band EQ preamp suggested by the great Bajaman (thank you Sir)

please find below my results

https://postimg.cc/ppqG3hq8

with pots:

https://postimg.cc/HrnZmYhN

FFT with EQ closed

https://postimg.cc/zHNKG7XB

FFT with Bass full open

https://postimg.cc/5QmvYz6m

FFT with bass and treble full open

https://postimg.cc/7brWzy5C

FFT with flat response (bass closed and treble somewhere near 3/4 open)

https://postimg.cc/dDRSmSC5

I will try this one on a P-J bass that I'm not using since the tone is not of my taste anymore (getting old maybe)

F

JudgeMingus · Post by **JudgeMingus** » 12 Oct 2021, 01:56

To revive discussion of the 'typist' erasers mentioned above - they are still available:
I found some on http://www.erasersticks.com/block-erasers.html
and one at https://www.aroundtheoffice.com/Richard ... ER-4421-BN

I haven't tried the ones I linked, but I suspect any old fashioned ink eraser would be abrasive enough to polish off superficial oxidation from copper traces.

jeepe · Post by **jeepe** » 07 Jul 2022, 11:50

hi,

(sure, I'm aware that this thread is spanning over, from 2007 to this day, 15 years, but Coca Cola never excuses themselves for continuing, so why should we?

)

So, I've just bumped into this 1K protection resistor soldered to the output jack, preventing sudden death of the IC when the signal input gets shorted...

http://www.musicmanbass.global/sr4-pups ... eb-part-1/
The IC chip can be damaged if the guitar lead becomes short-circuited (even momentarily). In 1982 the addition of an out-board 1K ohm protection resistor was recommended, and subsequently used, to protect the IC chip.

NOTE: The protection resistor is used in all new preamps, after its introduction, whether using either Tantalum or Electrolytic capacitors.

Do you guys usually add this resistor? I know, it is post '77, but this is just for safety, so why/not...?

..

bajaman · Post by **bajaman** » 07 Jul 2022, 13:42

can't hurt to fit it

deltafred · Post by **deltafred** » 08 Jul 2022, 09:54

There was a problem with the very early preamps where the opamp was sometimes damaged when a guitar lead was plugged in. Adding the 1k resistor cured the problem.

Leave it out at your own risk.

jeepe · Post by **jeepe** » 09 Jul 2022, 10:27

thank you very much!
course I won't leave it out

not because I'm cautious or anything, but I wouldn't be able to explain myself, should that accident happen, why I haven't applied it

Jarno · Post by **Jarno** » 11 Jul 2022, 09:15

As mentioned, can't hurt to fit it, but:
The datasheet for LM4250 explicitly mentions short circuit protection, so is this really needed?
Is this perhaps caused by the output cap?

jeepe · Post by **jeepe** » 30 Jul 2022, 04:04

hi, just one more bit of advice, I seek,

how about the 1.8nF capacitor?
what does it do, in the first lace? playing part in a filter? doing what exactly? (feels like I vaguely remember reading about this)

should we -- who still have a few lm4250-s -- use a ceramic cap, or chose a film cap, 1.5n or 2.2n?

(I have built it, using a ceramic cap, but I've broken my wrist and can't solder, nor can I play... for 4 weeks still)

Jarno · Post by **Jarno** » 16 Nov 2022, 08:47

I've used all sorts of caps, ceramic, film, styroflex, it's only rock and roll

Usually use 1n5, but recently I found 1n8, this influences the frequency where the tone controls work.

Baja Music Man guitar and bass onboard preamps [documentation]