Can anyone help me determine what I have here?

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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Tue Mar 13, 2012 5:34 pm

Can't believe I didn't do this sooner. http://www.seymourduncan.com/support/wi ... ic=3bandtc

Electronics folks, does anyone see anything about this that wouldn't work with two pickups? The only thing I see that doesn't match the diagram is that the white/green wire and brown wire on the red tower are switched (sorry for my electronics ignorance). The green/white and brown wires go to the correct spots on the push/pull pot, but are switched at the other end. I haven't gone through every wire yet, but so far that is the only thing I see off.
Last edited by Kurt Veltman on Tue Mar 13, 2012 5:44 pm, edited 1 time in total.
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Re: Can anyone help me determine what I have here?

Postby Halgeir Wold » Tue Mar 13, 2012 5:36 pm

Jolly good show!!! ;-) It's a Seymor Duncan STC-3A

Here's what you need..
http://www.seymourduncan.com/images/pro ... 60-105.pdf
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Tue Mar 13, 2012 5:54 pm

Next question - does the push/pull act as a single/dual coil? Then, there are mid and bass/treble pots...is the only one left a pan/blend between pickups?
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Tue Mar 13, 2012 9:26 pm

Ok, great work on identifying it!

Going by the order you listed the pots in your first post, the functions are:
1: Bass and treble
2: Mid
3: Master volume
4: Blend

I think the push/pull on the volume activates some sort of mid-scoop or "slap-contour" or whatever they want to call it, although it's not explicit in the document.

The two trim pots are apparently set at the factory for this "slap-contour". I'm surprised there is no master gain.

This unit is meant for low impedance active pickups, so it probably won't work very well with passives.

Hope you can make use of it Kurt, and thanks for helping out Halgeir!
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Tue Mar 13, 2012 11:42 pm

Greg, that is disappointing. I believe I got this when I bought Seymour Duncan Jazz and MusicMan style pickups. I was hoping to use it with the Bartolini's I am using on this build. When you say active, what details would I look for with the Bart's I have? I did a previous build with an EMG active pickup, where I believe the preamp was actually built into the pickup. Is this what you think this rig is best suited for? If so, isn't it redundant if there is already a preamp in the pickup?

Thanks again for you input.
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Wed Mar 14, 2012 12:08 am

EMG make active pickups a bit differently from most other manufacturers. They build the preamp directly into the pickup itself. This allows easy "cascading" of pickups, you don't have to worry how many pickups a seperate preamp was designed for, you can use whatever switching you want with their modular system. However, more and more manufacturers are adopting this approach, Seymour Duncan is among them.

The older system that some manufacturers still use is to make low impedance pickups to be used with a seperate preamp like this. The important factor in making sure a pickup will work with a seperate preamp like this is that the pickups are low impedance. Pickups are usually given a DC impedance value, passives are usually between about 4k and 16k. Actives for use with an external preamp are usually at most 4k, usually closer to 1k.
The problem now is finding somewhere to get low impedance bass pickups, unless you want to wind your own.
Having a quick look around, the Seymour Duncan Music Man pickup at 2.6k might be low enough impedance to work with this preamp.

I'm sure if you dig around some, you could find a few different pickups that would work.
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Wed Mar 14, 2012 8:26 am

Greg, after a look online I was not able to find a listed impedance for the pickups I have. After some playing around and quick searches, I came up with 5.14 for the bridge p.u. and 3.65 for the neck. Both were tested with the meter set on 20k Ohms. If I understand your previous comment correctly, these aren't a good match for the preamp, correct?
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Re: Can anyone help me determine what I have here?

Postby Mark Swanson » Wed Mar 14, 2012 8:28 am

I'd go ahead and give them a try Kurt. I think that they would be ok, let's see what Greg says.
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Wed Mar 14, 2012 8:39 am

The next question is if I can wire this so the push/pull makes it active/passive. Greg, I'm not a player, so I don't know what you mean when you refer to "slap-contour" as it applies to a pot or control. The only thing I know about "slap" is the style if playing.
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Wed Mar 14, 2012 9:16 am

Yeah, go ahead and give those pickups a try, they might not be optimal, but they should work. If you find that you're not getting enough treble response, you could try adding some "bright" capacitors accross the blend control. Try them out as-is first, if you need it I can give you more instructions.

Unfortunately you cannot easily change the push-pull from its current function to an active/passive switch. If you tried, it would deactivate the tone controls, as well as the master volume. The values of those controls are not appropriate for passive operation, and they're distributed through the preamp, so it would require very complex switching with this design.

The current function of the push-pull pot is to change from a relatively "flat" frequency response, to a "mid-scooped" response, which is appropriate for slap-style playing. I think you would find it more useful than an active/passive switch anyway.

We're making progress! It's looking more and more likely that this will work for you.

Good luck!
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Wed Mar 14, 2012 1:07 pm

Okay - update: I talked to the place I got the pickups I am using. They also sell this rig, so there was some familiarity with it. He said that I will need to switch the 100k push/pull and blend pots for 250k pots, and that should take care of it. A local guitar store said I should be able to use a 500k and be fine, if I can't find a 250. Getting closer!
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Wed Mar 14, 2012 1:58 pm

Yeah, switching out the blend pot for a higher value should help, problem is that proper blend pots aren't always easy to find, as they have a special taper, and are usually custom order territory. Most electronics supply places don't have them.

Stew Mac has some, but last time I ordered one, I found it didn't work quite how I expected, and tested kinda weird. Still, this is the type of thing you want. Go for the 500k rather than 250k.
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Fri Mar 16, 2012 7:37 am

Thanks for all your help and input Greg. I had already ordered the 250's based on the salesman's recommendation at Best Bass Gear (who have been a huge help with this and previous issues and purchases). I should be able to wire this thing up by next weekend, so I will let you know how it goes.

Thanks again for everyone's help.
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Fri Mar 16, 2012 10:26 am

Great Kurt, good luck!
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Tue Mar 20, 2012 7:50 pm

Alright, I heard from the salesperson that I bought the new pots from. After studying the diagram from the Seymour Duncan website, he realized that the volume pot is post-preamp. Apparently this means that the original 10k was the right choice after all. Naturally I already have the 250 in. What will this do if I try it like this? Will it wreck anything?
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Wed Mar 21, 2012 2:45 am

Well, the blend pot that you ordered (250k, correct?) is where the pickup signal enters the preamp, and it sets the input impedance. The original blend pot (100k) was probably a bit too low for passive pickups, so the 250k would be an improvement. The preamp then buffers the signal before sending it to the tone controls and then the volume pot. The output impedance of the preamp is probably around 1k, so the 10k master volume will work fine.
Just go ahead and swap out the blend pot, you won't damage anything.
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Wed Mar 21, 2012 2:52 am

On re-reading your post, it sounds like you changed the master volume pot rather than the blend pot.
So the new pot you got, is that a standard single gang pot? That won't work to replace the blend pot. You'll need to get something like I linked to above.

If you have replaced the 10k master volume with a 250k pot, it won't damage anything, but it will raise the output impedance of the preamp, which negates some of the benefits of having a preamp in the first place.
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Re: Can anyone help me determine what I have here?

Postby Kurt Veltman » Wed Mar 21, 2012 9:01 am

I switched both the blend and the master volume push/pull pot. After contacting the salesperson, he told me that the biggest issue I might have is that volume (going from 10k to 250k) might (if I understand correctly) drop off a little too abruptly. "It won't hurt anything. The sound will still be clear, but the rolloff on the taper of the 10k pot would be better. In other words, the volume drop-off when using the volume control may be too dramatic or sensitive, or perhaps less than ideal".

At this point I am going to try it and see if I need to change it when I have more time. I should know by the end of the day where it stands.
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Re: Can anyone help me determine what I have here?

Postby Greg Robinson » Wed Mar 21, 2012 10:50 am

The only difference in the taper would be if the 250k replacement were linear rather than audio (logarithmic). If they're both audio taper there shouldn't be a difference.
It will introduce some extra resistor noise because of the larger value (negligible, you probably won't be able to hear it), and will shift the low pass a bit higher which might make it pick up high frequency noise more easily, but again, nothing you should be able to hear.
Use it how you've got it now, only worry about changing back if you have some problems.
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Re: Can anyone help me determine what I have here?

Postby David King » Wed Mar 21, 2012 1:29 pm

Isn't the 10K master volume pot post preamp? If that's the case it needs to stay 10K. I have 4 of these preamps sitting in the drawer here and they all came with 10K vol pots and all came out of passive basses.
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