Need help with a power supply.

[navybass]

I'm about to get a 76 Series 1 bass (should be in my hands on Friday).  The problem is that it doesn't have the power supply with it.  I have all the components I would need to make one, but I would like to see a schematic of one to make 100% sure I wire it up correctly.  I have a 24v center tapped transformer that I will be using, which should be fine, as it will provide +&-12v.  Does anyone know where I may be able to get a schematic?


I'll post pics of the bass as soon as I get it.

[slawie]

I have this.

It has been posted before so I guess it would be OK.
Mods please delete if I have breached any rules.

Welcome to the fold.

[JimmyJ]

Hey Navy,

As you can see the Alembic PSU supplies +/- 15-20v, usually around 18v I think.  I've got a couple units which work well at +/- 15 and I think you should be fine with +/- 12V (because it's able to run on +/- 9V from the batteries).  Very flexible preamp!

Tell us more about the new/old bass.  Where'd you find it?  Serial#?  Pics when you can!

Enjoy!
Jimmy J

[navybass]

Thank you all, and thank you Mica for sending me the schematic in my email. 


I got the bass today and she is great.  I love her.  She is my first Series I, but not my first Alembic.  Pictures are coming soon.


Anyway, I was wondering the purpose of the 2 20K resistors on the output.  It seems to me that they would attenuate the output signal.


The one I got has a stereo 1/4" jack and the 5 pin connector.  What I was wondering is if I could just use a 1/4" stereo to mono adapter to get both pickups to work.  I am building the power supply and will be using that when it's done. 

[StephenR]

Not sure how to do it but the 1/4" jack can easily be rewired to supply a mono signal. I had a master volume put in my Series I recently and was offered the option of having the jack rewired but decided to keep it stock. Expect someone here will chime in with how to do it...

Enjoy your new bass, looking forward to the pics.

[JimmyJ]

The reason for the two 20k resistors is to sum the two pickup outputs to a mono signal.  You can't just short two op-amp outputs together because one output then tries to feed into the other and this causes some weird interaction.  So with 20k on each leg, the outputs are effectively 40k ohms apart and the signal where the 2 resistors meet is mono.  If you run the bass in stereo these resistors are not in the circuit.

Make sense?

I can't find a current link to the pdf of instructions but as mentioned you can alter the bass to send mono out of the 1/4" jack if you want.  Or you can build a stereo to mono cable.  But either option involves those "summing" resistors.

Jimmy J

[navybass]

Thanks, that makes sense. 

[rv_bass]

Here's a link to the 1/4" stereo to mono wiring on the FAQ page:

http://club.alembic.com/index.php?topic=270.0

I have a series 1 with stereo 1/4" jack that I use as both stereo or mono with these two cables, works fine either way:

http://www.sweetwater.com/store/detail/IPBQ2Q20


http://www.sweetwater.com/store/detail/YGQ2FQ1?adpos=1o13&creative=54989267161&device=t&matchtype=&network=g&gclid=COX426DRxc0CFRNahgodmicI2g

[navybass]

My home made power supply is done and works perfectly.  It actually puts out +- 20VDC.  Thank you all for your help.  I'll take some pics of the power supply and post them here.  I actually made a couple of mods like an on/off switch and LED's to monitor the voltages.