Stingray aftermarket 2 band pre

[UncleFluffy]

so is running the LM4250 on 9 volts with the 220K resistor safe? the specs sheet claims the LM4250 can tolerate up to 18 volts. I'd rather solder a resistor only once instead swapping them

Yes. Basically those two resistors are there to hold pin 3 at 4.5 volts (half the supply voltage). In principle any two identical resistors will do that, however in reality the opamp input current adds an invisible "third resistor" to ground. For the LM4250, this invisible resistor is much bigger than 2M2 so you can ignore it. For something like a 741 it's lower so the other resistors have to be lower to compensate.

The price you'll pay for dropping the resistors down is decreased battery life - roughly about 2x the current drain, in fact.

 

[BassLife77]

Yes. Basically those two resistors are there to hold pin 3 at 4.5 volts (half the supply voltage). In principle any two identical resistors will do that, however in reality the opamp input current adds an invisible "third resistor" to ground. For the LM4250, this invisible resistor is much bigger than 2M2 so you can ignore it. For something like a 741 it's lower so the other resistors have to be lower to compensate.

The price you'll pay for dropping the resistors down is decreased battery life - roughly about 2x the current drain, in fact.

got it! thanks!

 

[xaxxat]

Just mailed out the boards - expect a present from the mailman sometime soonish.

In hindsight, I'm not super-happy with the quality of the results here. They should work but aren't as clean as I'd like. Homebrew photo-etch boards are fine for one-off prototypes but QC is too difficult when making multiples.

If there's demand for more boards please let me know and I'll look at having them made by a real PCB house. I'm guessing that we'd need to order 20 or so to make the numbers work.

I think you should start selling these in kits. Put the wife to work drilling the holes and packaging and mailing the kits.

 

[xaxxat]

I see that the LM4250 will handle +18 volts. I wonder if it would be worth trying?

 

[UncleFluffy]

I think you should start selling these in kits. Put the wife to work drilling the holes and packaging and mailing the kits.

That's actually not such a bad idea. The kits part, I mean, anyway.

(Drilling and packaging can be partly automated. Doing it that way would mean less headaches).

 

[UncleFluffy]

I see that the LM4250 will handle +18 volts. I wonder if it would be worth trying?

I don't like running things at 100% of rated spec, they tend to age too quickly. You can always try it - the chips are only $1 each or so.

My advice would be to put a couple of dropper diodes in series with the supply to give you a volt or two's headroom. Still a touch more than is ideal but better than running the opamp at redline.

 

[xaxxat]

That's actually not such a bad idea. The kits part, I mean, anyway.

(Drilling and packaging can be partly automated. Doing it that way would mean less headaches).

Something like this would be a cool project too:

http://cgi.ebay.com/ws/eBayISAPI.dl...42649&ssPageName=STRK:MEWAX:IT#ht_2327wt_1161

 

[xaxxat]

I don't like running things at 100% of rated spec, they tend to age too quickly. You can always try it - the chips are only $1 each or so.

My advice would be to put a couple of dropper diodes in series with the supply to give you a volt or two's headroom. Still a touch more than is ideal but better than running the opamp at redline.

Yeah, I don't know if I need the headroom. I might put one board in a box and play with it, using a 9 and 18 volt switch. Like you say, if it lets the smoke out, it's a cheap fix.

Which reminds me - I need to order some parts...

 

[Coelho]

Let me know when can I get one.

 

[UncleFluffy]

Let me know when can I get one.

If enough folks are interested (10 boards would run $6 each, 100 would be $1.50) I'll do a run at a pro board house. That would be a fully screen-printed + solder masked board.

Might do occasional one-off homebrew runs but no guarantees as to when I can fit them in. Definitely not until I've got myself a better printer as that's limiting the quality of what I can produce here.

 

[BassLife77]

the boards look great! but I keep breaking bits trying to drill the holes I have zero experience in this so I gotta find somebody with a drill press in order to get a unwavering 90 degree angle

 

[Jerry J]

the boards look great! but I keep breaking bits trying to drill the holes I have zero experince in this so I gotta find somebody with a drill press in order to get a unwavering 90 degree angle

I got mine too! YEAH! They do look great. Fortunately I do have a drill press. I just need to get busy and chase down the parts.

In my case I have a '95 3-band SR so this is so I can convert it to a 2-band. I want to keep the original plate, pots and harness intact so I need to hunt down everything.

Thank you so much UncleFluffy! I just need to figure out how to keep those beers cold while in transit to SF.

 

[UncleFluffy]

Please test everything before drilling holes in your bass! I have been known to make mistakes ...

 

[BassLife77]

I got mine too! YEAH! They do look great. Fortunately I do have a drill press. I just need to get busy and chase down the parts.

In my case I have a '95 3-band SR so this is so I can convert it to a 2-band. I want to keep the original plate, pots and harness intact so I need to hunt down everything.

Thank you so much UncleFluffy! I just need to figure out how to keep those beers cold while in transit to SF.

I got all the components from Digikey. The treble and bass pots I got from Mouser. I'm gonna try a linear 25K volume this time to see if there is a difference. I got it here and it was fast shipping [Invalid or Expired Link Removed] Its a 20mm bushing though, not 16mm. I gotta add washers to make it even with the other pots

 

[bongomania]

Got mine too, thanks a bunch man! I'll report on the results soon.

 

[mongo2]

Thanks, and a tip-o-the-hat to you sir.

 

[xaxxat]

Thanks! I got mine. They look great. Waiting on parts. This is going to be fun...

 

[luzceloffan]

lol, i wish i could have a photoech board too xD , but i'm so far far away xD , I'm about to built this pre for my squier CV 60s P , i have already built a portable headhpones amplifier using the iron technique for the board , ferric clorure and lots lots of minutes drilling and soldering xD , i hope u post some sound samples so i get more interested in building this

 

[BassLife77]

drill press worked like a snap. all the parts and wires fit nicely.
now the hard part..

 

[UncleFluffy]

I was staring at that for 10 minutes thinking "what angle's that from? I don't recognise that part" then realised it was from wikipedia not the preamp board ... doh!