Low volume output on SD STC-3A install

[super mario]

Just getting back to forum - have been away for quite a while. I really need some input from the SD experts here.

Recently "upgraded" the electronics on my late 80's Yamaha BB5000A from the stock active circuit to Seymour Duncan's STC-3A (figuring with 4 holes already there, with a stacked bass/treble would pickup a mid cut/boost control). Everything gets installed as per the instructions - 9V power to the SD board and to the pickups (Yamaha's 80's P/J active pickups); white leads from the pickups to the blend pot; red and bare leads from the pickups to ground.

The result: Extremely low output volume wise, at full volume I have 1/3 the output I have with my stock non-active Ibanez bass through the same amp, same settings. Also the blend pot is extremely scratchy....even traded it out for another pot that was working fine, same scratchiness. Also the P pickup has low/zero output.

Thoughts?????? I really like the Yamaha, but am thinking that I have something going bad wrong to have such a low output. Oh, the battery is relatively new - so decent voltage there (no, I did not multimeter - probably should have).

 

[jeremy]

Re: Low volume output on SD STC-3A install

something is obviously wrong. was this purchased new?

if the pups are active, the red wire should probably be going to the battery. at least thats the wire that other active pups use for power

 

[super mario]

Re: Low volume output on SD STC-3A install

something is obviously wrong. was this purchased new?

if the pups are active, the red wire should probably be going to the battery. at least thats the wire that other active pups use for power

Yes - the wiring system was purchased new off Amazon from an online dealer. Regarding the red wires, there are two coming from each pickup. There is a single red wire separate from the red wire in each wiring harness (i.e. bare lead, white lead and red lead). I have tried to research the wiring on these pickups to see if I am missing something....but due to the age of the bass the wiring diagram does not seem to be readily available.

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

If the stock Yamaha pickups are active, they require a +9v supply from the same "star" distribution feed as the EQ PCB.

If the Yamaha pickups are, in fact, passive, the DC resistance value of the STC-3A's dual-ganged Balance control will be unsuitably low.

 

[super mario]

Re: Low volume output on SD STC-3A install

If the stock Yamaha pickups are active, they require a +9v supply from the same "star" distribution feed as the EQ PCB.

If the Yamaha pickups are, in fact, passive, the DC resistance value of the STC-3A's dual-ganged Balance control will be unsuitably low.

Funkfingers - the stock pickups had the "single" red wire soldered to the +9V feed from the battery, i.e. hot wire from battery feeding both pickups and the Yamaha pcb board. That is how I have it soldered up at the moment with the SD board. In terms of tone control, with the blend set to the "J" pickup I get plenty of bass and treble shaping, even the mid can be dialed up and down. It is just the overall output is too low. Of course the "P" pickup is another story as I have had numerous output issues in the past (another post, another time).

 

[jeremy]

Re: Low volume output on SD STC-3A install

how low is the j in the bass compared to the strings? usually you can crank active pups pretty close

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

the blend pot is extremely scratchy.

Define scratchy. Do you refer to the sound quality or the physical sensation as the control knob is rotated?

....even traded it out for another pot that was working fine, same scratchiness. Also the P pickup has low/zero output.

This statement suggests either extreme bad luck in having two dud dual-ganged pots or that something must be connected up incorrectly.

What DC resistance value is your non-SD/Basslines substitute Balance pot?

*

This attempt at remote diagnosis is rapidly approaching the point at which photographs of your wiring will be required.

 

[super mario]

Re: Low volume output on SD STC-3A install

how low is the j in the bass compared to the strings? usually you can crank active pups pretty close

Good thought, but the "J" is sitting pretty high already. It is the noticeable difference in the output with the SD system as opposed to the stock Yamaha system. The SD is nice and clear just no wall of sound when wide open.....The "P" has been iffy from day one, thinking a frayed output wire there that comes and goes. Also as I installed this only a few days ago, the fact that the blend pot has been scratchy when dialing towards the "P" pickup has me wondering if there are other issues as well. Going to check the DC resistance of these pickups, but have a question - as they are "active" do they need to be seeing +9V when you test?

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

I have tried to research the wiring on these pickups to see if I am missing something....but due to the age of the bass the wiring diagram does not seem to be readily available.

Did you not make a sketch of the stock wiring before disconnecting the pickups from the original Balance pot?

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

Regarding the red wires, there are two coming from each pickup. There is a single red wire separate from the red wire in each wiring harness (i.e. bare lead, white lead and red lead). I have tried to research the wiring on these pickups to see if I am missing something....but due to the age of the bass the wiring diagram does not seem to be readily available.

Please clarify. Is that one white, one bare, one red OR one white, one bare, two red? (Only the first option makes electrical sense.)

Per pickup, the separate, flying thin red wire is the power feed. Everything else, I would expect to be bundled together under plastic insulation for most of its length. Where the conductors emerge, the white insulated one ought to be the hot signal carrier and the bare ought to be ground.

Next question - where have you chosen to ground your two pickups? (The official printed SD/Bassline schematic diagram omits to mention the pickup ground cables.)

 

[jeremy]

Re: Low volume output on SD STC-3A install

the pot scratchiness isnt a good thing and might indicate something amiss. you dont need 9v power to get a resistance rating from the pup but i have no idea what reading youll get. most active pups are really low winds that use a battery powered preamp to boost and shape the weak signal from the coil.

like funk asked, what value is the substitute balance pot? good clear pics would be nice

 

[super mario]

Re: Low volume output on SD STC-3A install

I did not as I had worked with balance pots in the past and had gone terminal to terminal in making the solder reconnects. The way the balance is set up - pickup hot leads (white wires from pickups) are on the center lugs....."J" upper, "P" lower; jumper across the outer lugs output lugs to the grey/brown lead to the PCB board, black (to grd) across remaining outer lugs and pot chassis. I will work on pics....will have to dismantle the setup as that is one super crowded hole.....

 

[super mario]

Re: Low volume output on SD STC-3A install

Oh - the replacement pot is a 250k (spare on hand from Stew Mac).

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

Oh - the replacement pot is a 250k (spare on hand from Stew Mac).

This alone explains some of your difficulties. By making this change form 100k to 250k, you have converted your STC-3A into an STC-3P. (P for passive!)

 

[super mario]

Re: Low volume output on SD STC-3A install

This alone explains some of your difficulties. By making this change form 100k to 250k, you have converted your STC-3A into an STC-3P. (P for passive!)

- Sorry for the misque here. Actually the 250k was installed long enough to just to test the "scratchiness" I was experiencing. Since it was there with both blend pots, I reinstalled the 100k. It is back to being a STC-3A setup.

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

In that case, the critical details are;
1) What is the distance between the tops of the pickups and the underside of the strings?
2) Where have you chosen to ground the bare wires from the two pickups?

 

[super mario]

Re: Low volume output on SD STC-3A install

"Please clarify. Is that one white, one bare, one red OR one white, one bare, two red? (Only the first option makes electrical sense." - See the attached jpeg file

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

As drawn in the previous post, your Balance pot appears to lack one of the diagonal jumper connections. (Probably just an oversight.)

 

[Funkfingers]

Re: Low volume output on SD STC-3A install

the blend pot has been scratchy when dialing towards the "P" pickup has me wondering if there are other issues as well.

This alone could explain the scratchiness and the non-existent output from the P pickup.

If the P pickup is shorting somewhere, it might also explain why the J pickup is far quieter than expected.

 

[super mario]

Re: Low volume output on SD STC-3A install

As drawn in the previous post, your Balance pot appears to lack one of the diagonal jumper connections. (Probably just an oversight.)

It's there, I just did not draw it in. Sorry for the confusion....here's an updated drawing showing the ground in place..."revised" to show blend to ground connections: