• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

DIY Stingray 3EQ Preamp

#201
I recall that the preamp does pass some sound when the battery is disconnected, but is silent when the battery is connected. There may be something keeping the battery from powering your board. I see you used film caps for the 1uF caps (the large grey boxes) instead of electrolytic (polar) caps. That could be the issue, though I'm not certain.

EDIT: When I get the chance, I'll put together a project list on Mouser so you guys can see exactly what I use.

EDIT2: Another idea just crossed my mind. The board may not be properly grounded. Can you post a picture of the entire preamp with the jack, pots, and battery clip?
 
#202
domdec314 said:
I recall that the preamp does pass some sound when the battery is disconnected...

I see you used film caps for the 1uF caps (the large grey boxes) instead of electrolytic (polar) caps. That could be the issue, though I'm not certain.
Click to expand...


First part is true, however faint. Second part, yeah. Don't be throwing non-polar caps into the power circuit. I just looked at an extra board I have of this design; they should be polar.

And hey, Nigel: I'm still running this design. Thanks for the inspiration last year. It's the blue one on the left:

A2PTXur.jpg
 
#203
Oh and uhh, don't reverse the polarity of the DC inputs. I've inadvertently burnt out some ICs doing that.

Now that I mention it, don't be afraid to replace the IC -- I might even suggest it as a troubleshooting method once you've assessed the capacitor thing. I have a whole stack of ICs sitting around just for that reason.
 
#205
It looks like the board isn't grounded. First of all, if that's a stereo jack, the black wire from the battery clip should be wired to the ring lug of the jack. This way the battery will disconnect when the cable is unplugged. The lug on the volume pot that the black wire is connected to needs an additional wire going from the lug to the back of the pot. It looks that wire is missing.

I'll make a new, more detailed wiring diagram when I get the chance.

EDIT: This diagram from Seymour Duncan shows how the jack, battery clip, and volume pot should be wired.

Link Removed
 
#207
Passinwind said:
Did you ever post a prettified schematic? I finally got around to doing a model in LTspice, but I'd like to be sure I'm modeling the right thing. ;)
Click to expand...

I thought the hand-drawn one was pretty clean. I just threw this together:

3eqschem.jpg


If anybody wants to try something cool, check out the new program called LiveSPICE:

http://www.livespice.org/

It lets you simulate schematics with real audio in real time. Here's the file for the preamp:

[Invalid or Expired Link Removed]
 
  • Like
Reactions: -Boscoe-
#209
I made the changes that were suggested (other than changing the caps) and the volume, treble, and bass work but, no mid control, could be the caps. Also, out put is very week. I'll order the new parts and have another go at it. I do have another question though. I have a 250K blend pot for the pick ups, will it work or do I need a different value?

Thanks for the help
Tedward
 
#210
It looks like your 3.6k resistors are wrong. The color bands on the 3.6k resistors should be Orange-Blue-Red-Gold. It looks like you have 3.6M. These are part of the Mid control and are most likely the source of the problem. I also noticed you're using 6.2k instead of 6.4k but that's probably close enough to not make a noticeable difference.

As far as the blend knob, I've never done it before, but here's a diagram from Seymour Duncan:

Link Removed

Wire the pickups to the blend pot just like that. The black wire going from the blend pot to the master volume pot would instead go from the blend pot to the input of the preamp board.
 
#211
Thank you so much for all this information! I actually did this circuit on a breadboard with some slight variations:

a) I'm using a TL072 instead of TL062.

b) 10nf instead of 8,2 nf capacitors.

c) Some resistances are not exactly the ones suggested but combinations of other resistances that overall are very close to those required. For example, R11 = 6,4K in my circuit has been replaced by two resistors, 10K and 18K connected in parallel, which roughly gives me an equivalent resistance of 6.42 K, etc.

d) I'm not using the preamp volume pot. I'm just going directly to the output jack in the bass. Why? Because i thought i could use the two volume controls that were already in the bass, cause i'm thinking this preamp as if it was in an external box. But i believe it was a mistake, cause when i move those volume pots the noise is just awful. So, i WILL install the volume pot from the preamp maybe tomorrow and see how it goes.

Anyway, after a lot of ridiculous mistakes and connections, i plugged it on an old and cheap Ibanez Gsr200, and it sounded like a beast! Low frequencies are really fat, mids are absolutely dominant, and highs are classy and cristaline. There are a few things i must solve yet. In fact, i have a question:

Is it normal to have a small delay before the circuit kicks in, once the cable has been plugged in?

Finally, just for your amusement, here is a picture of what i did: :D

PIC_13-12-22_03-18-06_zpsb7fe2b1e.jpg



Cheers and thank you again! :bassist:
 
#212
domdec314, you are right about the 3.6k resistor. I checked the order and the wrong one was sent and it slipped by me. And the 6.2K was used because they didn't have 6.4K. I ordered the parts from Small Bear.

I figured that blend would be wired in the normal way.

Thanks
Tedward
 
#215
Tedward said:
Putting the order together and I'm having trouble finding the electrolytic caps. Small Bear and Digi-Key are out of stock. Will these work?
Invalid Link Removed

Tedward
Click to expand...

The 10uF cap on your board (the orange one) should be fine as long as it's 10uF. It's the two 1uF caps you need to replace. Here's one at DigiKey:

Invalid Link Removed
 
#217
domdec314 said:
It's been brought to my attention that the 1uF caps don't have to be polar electrolytics. I don't know why they would be marked as polar in the schematic if it didn't need to be, but I'm not comfortable enough with electronics to have a definitive answer.
Click to expand...

Dom,

Electrolytic caps are smaller and cheaper than film ones in the usual values used for filtering DC power supplies, but either kind generally work fine as long as they meet the needed voltage ratings. Size is at a premium in most effects and onboard preamps, but you will sometimes see big nonpolar film caps used exclusively in audiophile tube power supplies, and even more often as small value bypass caps across much bigger electrolytics in all sorts of stuff.

The schematic markings are there so you orient the polarized ones correctly, if that's what you use. You're right to spec what the schematic shows, but 1uF is right on the limit of "pretty easy to swap in a nonpolar one" in a lot of cases.
 
#218
Passinwind said:
Dom,

Electrolytic caps are smaller and cheaper than film ones in the usual values used for filtering DC power supplies, but either kind generally work fine as long as they meet the needed voltage ratings. Size is at a premium in most effects and onboard preamps, but you will sometimes see big nonpolar film caps used exclusively in audiophile tube power supplies, and even more often as small value bypass caps across much bigger electrolytics in all sorts of stuff.

The schematic markings are there so you orient the polarized ones correctly, if that's what you use. You're right to spec what the schematic shows, but 1uF is right on the limit of "pretty easy to swap in a nonpolar one" in a lot of cases.
Click to expand...

Thanks for the info. I had a feeling that might be the case, and I now I know. :bassist:
 

Latest posts

Top Bottom
Back