Baja low noise low current drain bass guitar preamp 121218  [documentation]

Original effects with schematics, layouts and instructions, freely contributed by members or found in publications. Cannot be used for commercial purposes without the consent of the owners of the copyright.
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bajaman
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Post by bajaman »

thetragichero wrote:hey it works! and it's LOUD!
bass control isn't doing anything but the bass is in a state where I'm okay with that. treble control has a lot of range, from slightly dull to almost shrill - I like it!

I don't have a 'clean' bass amp (not really my style), so I will have to wait to hear it through the DI at church

but this old has some new life!
good - did you use 2N5457 ?
check your pot wiring - the bass control range should be huge - are you using 250k pot ?
check that you are using 100n, 47n, 100k and 8k2 :wink:
keep going :wink:
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thetragichero
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Post by thetragichero »

2n5457, made the necessary resistor changes
250k log pot (I think I just realized from the schematic that key=b means linear...it's push/pull to give series/parallel for the neck humbucker so I'll have to live with a non-ideal taper... I imagine bass would mainly be set and forget anyway, unlike treble that I can tweak several times per song if required)

if i'm reading the schematic correctly, the bass control is setup like a variable resistor/rheostat (only wiper and one of the lugs used) as opposed to a potentiometer (wiper and both lugs used), yes?

it's bedtime anyway

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Post by marcao_cfh »

thetragichero wrote:if i'm reading the schematic correctly, the bass control is setup like a variable resistor/rheostat (only wiper and one of the lugs used) as opposed to a potentiometer (wiper and both lugs used), yes?
I don't think that will make any difference. You'll just chamge the resistance between wiper and one lug anyway.

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thetragichero
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Post by thetragichero »

Image

gonna give this another try with k117 (these look genuine). I think this will work better in my pbass with two dissimilar pickups than one of the original music man preamps...

(thinking of laminating some old solid cabinet doors together to make a (5 string) jbass body and I think that would work better... check back in like two years lol)

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Post by marcao_cfh »

So I finally built and tested this one. I made the mistake of wiring both tone pots in reverse, since I'm not good on understanding tone stacks I go for the luck, it's a 50/50 chance of getting it right :lol:.

The first thing I must say is this is loud. So loud it easily distorted my amp when I turned the bass volume to the max. I didn't tested it too much because I used a guitar amp and don't want to abuse the speaker.

I'm still doing some tests because I found out this preamp is noisy when the treble is full. This is probably due to the bass I'm using have no shielding, so I removed the whole thing and I'm shielding it before test it again. But I had to post here to say this preamp sounds amazing, and I'll surely be putting it on the bass of some friends.

Is there a guitar version on your plans? :twisted:

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Post by marcao_cfh »

Ok, so I shielded the bass and played with this preamp a little bit more. This is a little beast and what I can say to all the bass players is to just build it! I loved the distorted bass sound I can get at full volume.

With a shielded bass and 9V battery, it's dead quiet. No noise at all. Mine is still noisy, but it's because I'm powering it with a 18650 battery along with a charge module and a MT3608 based step up module to get 9v out of the 18650 battery. I tried a few things to get rid of the noise, but with no luck. I'll probably just use a 9V battery. If I use one rated for 400mAh, one battery should last 5000h, which is a lot of time.

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Post by thetragichero »

sourced some genuine 2sk117 Ys and built this for my pbass. this doesn't seem as loud as the other version, and I like that. I may have to revisit the bass with 2n5457 version to see where I went wrong, but I'm SUPER HAPPY with this in my #1 bass
tested the current draw. 46uA not too shabby!

thanks again!

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Post by Johnston_evo3 »

Okay I'm maybe being a complete noob here hedged with a touch of paranoia because I'm forever ordering the wrong bits.

I've ordered the parts up for the 2N5457 version (Because I could get all the bits from one place without hassles). But I've read the schematic as having non-polarised Capacitors. BUT when I look at Jarno's layout and thetragichero's made up board I see polarised caps.

Have I screwed up or just being an undereducated noob and missed something?

TIA

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Post by plush »

Johnston_evo3 wrote:Okay I'm maybe being a complete noob here hedged with a touch of paranoia because I'm forever ordering the wrong bits.

I've ordered the parts up for the 2N5457 version (Because I could get all the bits from one place without hassles). But I've read the schematic as having non-polarised Capacitors. BUT when I look at Jarno's layout and thetragichero's made up board I see polarised caps.

Have I screwed up or just being an undereducated noob and missed something?

TIA
You can either use polarized electrolytic/tantalum caps or non-polarised ceramic or non-polarised electrolytics. I'd prefer to use ceramics.
When using polarised caps, just rotate them with + pointing to the the higher voltage.
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Post by Johnston_evo3 »

Thanks for that. Thought I had cocked up.

I still have some Fender jack sockets kicking about when I ordered the ones for the FX loop rather than the input :oops: :oops:

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Post by perfector »

Instead of 2N5457 can J201 be used?

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Post by bajaman »

perfector wrote: 20 Sep 2019, 09:53 Instead of 2N5457 can J201 be used?
no - not without altering resistor values ;-)
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Post by asbestosaurus »

What is this particular transistor arrangement called? I've seen it only once before (with another bjt as the n-type controlling device). It seems really interesting I'd like to do more research on it

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Post by bajaman »

asbestosaurus wrote: 11 Oct 2021, 09:00 What is this particular transistor arrangement called? I've seen it only once before (with another bjt as the n-type controlling device). It seems really interesting I'd like to do more research on it
the anti-symmetric pair ;-)
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Post by melonmelon »

Hi Bajaman, is there an equivalent to the 2SK117(Y) witch is VERY difficukt to get here in Europe? Could also be an SMD-FET...
Thanx a lot
Harald from Austria

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Post by marsbel »

Hello, They are available, and in stock from: https://www.musikding.de/2SK117-GR

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Post by jeepe »

marsbel wrote: 17 Apr 2022, 11:42 Hello, They are available, and in stock from: https://www.musikding.de/2SK117-GR
NO!
watch what you say! :) seriously, it is the "GR" version, not good for this circuit...
as Bajaman said it multiple times, the "Y" version is needed for this application...

different "ending" (Y / GR / BL) mean different IDSS "range".... see in the datasheet...
pedal building, tracing and sharing is such a beautiful freedom movement... If only it could be viewed as a future heritage, but it really is ephemeral, as it seems

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Post by lars-musik »

Hi folks,

i just finished the preamp (first schematic in this thread) for a friend of mine after he decided that this was the best sounding from a collection I prepared for him, Now I proudly installed it into his bass but he feels that he looses a lot of treble when turning the volume down. The volume pot is a 250K-A at the input. My first instinct would be to just transplant the volume control to the output, but we have some switching going, so that the bass can also be used passively (utilising a stereo pot for “treble” and “tone”).
What could cause this and how could I counteract this?
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Post by Serge75 »

Maybe you could put volume control after tone control, and switch between only passive tone and volumen or active baja circuito plus passive tone and volumen? Maybe that way you can enhance active highs and then give It a passive cut? But this would requiere one more knob.

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Post by Lukasen »

I think that to preserve the treble in the sound, it is advisable to place the volume pot instead of R17 and remove C16 at the same time. But it will definitely lower the input impedance of Q2.
(Another possibility that came to my mind, the volume pot at the input together with the treble bleed circuit, but it's a bit of a strange solution.)

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