Assistance please

[Mogens]

Hello

I'm new here. I hope someone is willing to try and help me out a bit.

 

My high school daughter bought an old Yamaha rbx760a. She in high school and It's her first bass. She mostly plays ukulele but also has a couple of guitars and a piano. Her band needed a bass player and she wants to be able to practice at home.

 

The bass was sold a defect with a shut jack-socket.

 

When I got to look at it the pots were very worn and I decided for her it would be best to replace the electronics as well as the socket.

So I bought a cheap set: artec se2 which seems compattible https://www.thomann.de/dk/artec_se2_basselektronik.htm

The installation was pretty straight forward: 

 

I have grounded everything (bridge, backside of the volume pot and ground on the main circuit board)to the sleeve of the jack.

 

But it doesn't work.

There is absolutely no response in the amp from strumming the strings.

There is very little humming. 

It makes a lot of noise if I plug or unplug the battery.

I have tried reversing the polarity of the signal out. 

I have tried reversing the polarity of the pickups.

I have tried removing the ground wires from the sleeve, which results in a lot of humming or even buzzing.

If I unplug the balance pot and touch the pins on the mainboard I can produce noise in the amp.

The balance pots measures correctly with a multimeter.

 

It seems to me the only thing left is the pickups

 

When I measure their resistance it comes out to 240k and 1000k if I read the multimeter correctly.

 

I have no idea what to try next.

 

Oh at some point we were able to produce some horrible noise from the pickups during trial and error but I have no idea how.

 

She's really already maxed out her budget. But if the pickups are both broken we'll figure out something. But I need to exhaust all other possibilities first.

 

Can I test them by wiring them up directly to the amp? in series with a battery? Which voltage?

 

Any other suggestions. I (and her) will be so grateful for any help you can provide.

 

Best Regards Mogens from Denmark.

[BassHertz]

Have you checked the wiring of the jack plug. The wires going from the points marked 'SW' and 'GND' switch the preamp on when a jack lead is inserted into the socket. You can unplug the battery, plug the jack cable into the bass then use your multimeter and measure the resistance between SW and GND, it should read zero ohs with the cable plugged in and open circuit when unplugged.

 

 

[PaulThePlug]

A thread suggests they are passive pups with an active pre... try each pick up on its own, wired direct to the out jack... make sure you get the correct pins... as some times a stereo jack socket is used as a switch for the batt...

 

https://www.talkbass.com/threads/yamaha-rbx760a.1120089/?amp=1433947162

[MoonBassAlpha]

Hi @Mogens, welcome to the forum!

The  values you measured for the pickups are rather high,  should be in the range of 2500 to 15000 ohms,  measured when disconnected from the rest of the circuit. 

[Woodinblack]

In the first instance, I would connect each pickup directly to the jack terminals to check they work, or if you want to do both together, connect to just the balance board.

if that doesn't work, there is no point trying the preamp and it could be dead

[Mogens]

46 minutes ago, BassHertz said:

Have you checked the wiring of the jack plug. The wires going from the points marked 'SW' and 'GND' switch the preamp on when a jack lead is inserted into the socket. You can unplug the battery, plug the jack cable into the bass then use your multimeter and measure the resistance between SW and GND, it should read zero ohs with the cable plugged in and open circuit when unplugged.

 

 

Tried it and can confirm those measurements.

[Mogens]

42 minutes ago, PaulThePlug said:

A thread suggests they are passive pups with an active pre... try each pick up on its own, wired direct to the out jack... make sure you get the correct pins... as some times a stereo jack socket is used as a switch for the batt...

 

https://www.talkbass.com/threads/yamaha-rbx760a.1120089/?amp=1433947162

I'm not sure if I understand it correctly. If I connect the pickups directly to the cable going to the amp using alligator clips I get a buzzing but no response to strumming.

 

Should I connect the pickup wires directly to the socket inside the bass while the battery is connected?

[Mogens]

37 minutes ago, MoonBassAlpha said:

Hi @Mogens, welcome to the forum!

The  values you measured for the pickups are rather high,  should be in the range of 2500 to 15000 ohms,  measured when disconnected from the rest of the circuit. 

Yeah I thought so. I'm not sure if I read correctly.

I have the multimeter at 2000k-ohm. At 200k-ohm I get 1/open circuit.

 

It's pretty sad for her if she need to buy new pickups. Then she'll be so deep into this instrument she could have bought a new one instead.

[Mogens]

35 minutes ago, Woodinblack said:

In the first instance, I would connect each pickup directly to the jack terminals to check they work, or if you want to do both together, connect to just the balance board.

if that doesn't work, there is no point trying the preamp and it could be dead

Thank you for the reply. It goes in the same direction as Paul the Plug above.

[Woodinblack]

36 minutes ago, Mogens said:

It's pretty sad for her if she need to buy new pickups. Then she'll be so deep into this instrument she could have bought a new one instead.

 

You can get some pretty cheap pickups.

[Mogens]

It seems to me both pickups are gone. Is that comon?

 

What are the parameters I need to be aware of when shopping for new ones?

[Woodinblack]

It is remarkably uncommon for a pickup to break, so for both to break, very very uncommon unless something bad happened to them, but as they are just coils of wire, there is not much bad that can happen to them.

 

In the circuit for this bass it says they are just 2 wire pickups, is that true, or are there more than that?. 

 

Really, the only thing that is essential is that they fit. beyond that, it is whatever you want in a pickup. 

[Mogens]

31 minutes ago, Woodinblack said:

It is remarkably uncommon for a pickup to break, so for both to break, very very uncommon unless something bad happened to them, but as they are just coils of wire, there is not much bad that can happen to them.

 

In the circuit for this bass it says they are just 2 wire pickups, is that true, or are there more than that?. 

 

Really, the only thing that is essential is that they fit. beyond that, it is whatever you want in a pickup. 

Two wires out from each of the pickups, yes. 

 

I would also think it odd for the pickups to both be burnt out. And if they did I would either think the wire had burnt over - open circuit - or the insulation had melted - very low resistance. But I measure a very high resistance through them.

 

The pickups are completely unbranded on the front. But pictures I find online of the model of bass often has some brand printed on them. So they might not be original. Could they have been repaced with active pickups? Would that make sense? How can I check it?

 

The electronics I bought says it supports both passive and active pickups. But I see no way to change it. Like a switch or different wiring.

 

As for preference. At this point cheap and functional are the keywords. She's a newbie on the bass and just need to be able to practice. And she's on a childs budget, even though I can chip in some if need be.

 

I'm sorry for being so dumb. I just want to help her get a functional instrument.

[Jakester]

I would be massively surprised if the pickups had 'gone'. 

 

Having had a few Yamaha basses in my time, I do know some of them use pickups which are of an unusual impedance and therefore don't play nicely with aftermarket preamps without a buffer to bring the impedance to the level the preamp is expecting. 

 

See this thread on Talkbass for example:  https://www.talkbass.com/threads/help-obp-3-in-a-yamaha-bb5na.179659/

 

I don't know whether or not that is the same with your daughter's RBX 760a; I haven't been able to find a spec for the pups, but from photos I've seen it looks like they could be the same as other Yamaha pups which might suggest that could be the problem. 

 

Can you put the original pre-amp back in with the new jack socket and see if that works? If so, that could be the issue. 

[Bunion]

Could the bass have been stored in a place to cause degaussing of the pickups? 

Edited April 8, 2022 by Bunion

[BigRedX]

The most common point of pickup failure is where the wire used for the actual coils is joined to the cable that goes to the controls. If the pickups aren't sealed at the base, there should be two tags (they often look like rings) where the thin wire from coil and the corresponding wire from the cable are joined. If these are visible check that you can see the coil wires are still attached.

[John Cribbin]

Hopefully we can help you through with this problem.

 

I'll also tick the box saying the pickups are unlikely to be defective, probably the least likely scenario.

 

Bypass the electronics with wire is also a great idea. If that shows working pickups, worst case scenario, you rewire as a passive PJ.

These are great for bypass work, crocodile clip leads about £3 for a pack on eBay:

 

 

Are you able to post images of the wiring? Sometimes we can see the problem that way.

 

Working on the KISS principal, have you tried a fresh battery, that can often be the root of a problem.

 

Jack sockets are a weak point. You have a multimeter so with the lead out, do you get 9V from the battery at one of the jack connections. If so, plug the bass lead in and try again. The circuit should now be connected and you will get 9v at 2 of the 3 points on the socket.

 

Good luck.

[Woodinblack]

2 hours ago, Mogens said:

Two wires out from each of the pickups, yes. 

 

I would also think it odd for the pickups to both be burnt out. And if they did I would either think the wire had burnt over - open circuit - or the insulation had melted - very low resistance. But I measure a very high resistance through them.

 

The pickups are completely unbranded on the front. But pictures I find online of the model of bass often has some brand printed on them. So they might not be original. Could they have been repaced with active pickups? Would that make sense? How can I check it?

 

Yep, all of that is right, it odesn't sound like they should be dead.

Active pickups (which I should point out are not common and normally always EMG), would have a 3rd wire on them for power. Note that all an active pickup is that the preamp (buffer) has been potted into the actual pickup, the advantage being you can use a lot less wire and have less colouration if you buffer it straight away.

So it is unlikely you have active pickups.

 

However, if you connect the two wires from the pickup to the output socket (or the jack itself), and those wires are going to the sleve and tip (and also note that the jack socket will be stereo, so will have a ring which will be shorted by plugging a mono jack plug in). Just for clarity, if you wire the pickup to the jack and plug a jack cable in, the end wires of the jack plug that you would plug into the amp must have exactly the same resistance as measuring across the pickup, as there is nothing else connected.

 

 

2 hours ago, Mogens said:

The electronics I bought says it supports both passive and active pickups. But I see no way to change it. Like a switch or different wiring.

 

Its because it wouldn't make any difference. The output of an active pickup is the same as the output of a passive pickup (from the POV of the preamp), the only difference is the active pickups would also need power.

 

2 hours ago, Mogens said:

As for preference. At this point cheap and functional are the keywords. She's a newbie on the bass and just need to be able to practice. And she's on a childs budget, even though I can chip in some if need be.

I'm sorry for being so dumb. I just want to help her get a functional instrument.

 

None of this is dumb, and everything is making sense so far, other than why your pickups are in the state that they are.

 

Until we establish if the pickups are working, there is no point looking at the pre-amp, as it needs something to amplify!

[Mogens]

So many helpfull people here. Thanks.

 

I will see if I can get arround all suggestions and questions.

 

The battery is new and 9 volts is delivered to the main circuit.

When no jack is inserted I get arround 8 volts across signal/ground on the jack-socket. 0 when a jack is inserted. That makes me think the board detects the insertion correctly. I have no reason to think the electronics are defective or incorrectly installed. If I short the balance pot's output with some metal I can produce noise. So I assume everything up until there works.

 

I have no idea how the bass has been stored. But degaussing would probably involve some big magnet which I don't think the previous owner had. If I move a magnet across the pickups I feel resistance but no sound is produced.

 

If I connect one of the pups directly to the amp I just get at loud buzzing.

 

Pups with out of the ordinary specs sound very likely like the reason now. I will try and refit the old preamp. Though it will take me some time as I was very quick with the snips when I took it apart.

The pups have these model numbers according to the manual, though I couldn't find any specs on them: QC460500 and QC460600.

 

I can't easily get to the backside of the pups to check the connection. But as my previous post I would expect "Open circuit" on the multimeter if the wire had fallen off the coil.

 

 

[Mogens]

OH MY FREAKING DOG!!!

 

When I studied the original circuit in preparation for remounting it I noticed a couple of cables were coax.

 

So it turns out that the pups output a separate ground as well as a ground on the shield of said coax cable. I had just soldered the entire coax as one to the signal side of the balance pots. I did actually notice a little gunk but I had just switched solder, so I just assumed it was flux or something.

 

I hurriedly cut one off, stripped it properly and connected it straight to the amp. SOUND! It works.

 

The pup has a resistance of 7 k-ohm, which is much more reasonable.

 

This is by far the most embarrassing mistake I have ever made in DIY electronics. But Oh my I'm so happy at the same time and so is my daughter.

 

I can't do it right now but I will try and just wire it up correctly with the new preamp, and if that misbehaves (which it probably wont) I will install the old one.

 

A million thanks to everyone who wrote here. I don't think I would have discovered my error without you. I will report back if the new preamp turns out to be compatible or not.

[nekomatic]

I have made exactly the same mistake in my time 😁

[Mogens]

Would you imagine. Everything works when you just hook it up correctly 😁

 

I still have this weird feeling of both embarrasment and joy. 

 

She's playing now and all is well. 

 

Thank you all once again. What a lovely community. 

[MoonBassAlpha]

Fantastic!

[Woodinblack]

1 hour ago, Mogens said:

Would you imagine. Everything works when you just hook it up correctly 😁

 

I still have this weird feeling of both embarrasment and joy.

 

Embarassment is fine as long as the joy is good enough. And on the plus side, if it had worked first time, the joy would have been not nearly as good!

[Mogens]

13 hours ago, Woodinblack said:

 

Embarassment is fine as long as the joy is good enough. And on the plus side, if it had worked first time, the joy would have been not nearly as good!

I didn't mean to post any more. But there is just so much truth in what you said. 

 

I definitely wouldn't have gotten as good a hug and high fives from my daughter if it had just worked right away. 

 

I have actually made a saying and taught it to my kids. Roughly translated from danish: if you are always glad then you are never truly glad. 

 

Meaning that without downs there can't be ups. 

 

She immediately called it out when I read your message to her. (Sense of fatherly pride.) 

 

The whole thing was surely an educational experience. 

 

And by now only the joy of the sweet music reminds.