Yamaha Preamp Repair

PFAllen2 · February 2022

Some advice required, @ICBM @Danny1969 The preamp in my thin line Yamaha acoustic isn’t working and after a little investigation I conclude that there is dirt or a bad connection in the volume pot. I can occasionally get lucky by fiddling with the pot and get signal, which proves everything else is working.

I have Servisol Super 10 but where exactly should I be aiming for with this type of pot and does it need a little or a lot etc. Of course, it is the least accessible pot which needs attention.

Thanks, Paul

ICBM · February 2022

The only practical method for these is to soak the whole pot body in it and hope enough penetrates into the innards to do some good.

And it really is worth trying, since as far as I know Yamaha no longer have spares, either of the pots or the preamp boards.

If it's knackered you're probably looking at doing substantial work to fit a larger preamp unit into the guitar.

PFAllen2 · February 2022

@ICBM Thanks for the reply, I’ll give it a go. Is there any risk of damage to any other components if I go overboard?

ICBM · February 2022

Not as far as I know!

Danny1969 · February 2022

Yes unfortunately those type of pots aren't designed to be serviced. They are generally reliable in single gang but they look like dual concentric pots with a switch as well ? .... these do tend to fail more

If the soak doesn't work I would remove the faulty pot and replace it rather than junk the pre amp. You don't need the exact same one in terms of PCB pin out as you can fly wire one with a different pin out to the other board. The values and laws of the pot needs to be the same though.

ICBM · February 2022

Danny1969 said:

If the soak doesn't work I would remove the faulty pot and replace it rather than junk the pre amp. You don't need the exact same one in terms of PCB pin out as you can fly wire one with a different pin out to the other board.

The problem is that these are the special push in/out pots, which also mount the preamp to the body. You can bodge it with a different pot, but you lose that function and it’s difficult.

I have thought of scavenging them from something like a car radio which sometimes have similar pots, but never found one close enough.

Both Yamaha and Roland are a nuisance for using bespoke parts like these - the downside of having the volume and buying power to make it economical for them.

PFAllen2 · February 2022

Danny1969 said:

Yes unfortunately those type of pots aren't designed to be serviced. They are generally reliable in single gang but they look like dual concentric pots with a switch as well ? .... these do tend to fail more

If the soak doesn't work I would remove the faulty pot and replace it rather than junk the pre amp. You don't need the exact same one in terms of PCB pin out as you can fly wire one with a different pin out to the other board. The values and laws of the pot needs to be the same though.

Removing and replacing the pot would be beyond my level of expertise, any suggestions who might be able to do such a job?

JayGee · February 2022

ICBM said:

The only practical method for these is to soak the whole pot body in it and hope enough penetrates into the innards to do some good.

And it really is worth trying, since as far as I know Yamaha no longer have spares, either of the pots or the preamp boards.

If it's knackered you're probably looking at doing substantial work to fit a larger preamp unit into the guitar.

Bypass the onboard electronics altogether and use an external preamp?

TheBigDipper · February 2022

My mate recently had to give up on the preamp of his 1990s Yamaha 12-string when it stopped working. No parts available from Yamaha.

I'm not proud of this, but when he told me, I felt slightly smug for 30 seconds that I chose to go the "passive pickup in a non-electro guitar with an external preamp" route with my acoustics. And then I felt sorry for him, like I should have done from the start.

ICBM · February 2022

JayGee said:

Bypass the onboard electronics altogether and use an external preamp?

That’s a possible solution, yes. The pot mounting holes can at least be covered less obtrusively than a typical large rectangular hole.

The only other real alternatives if you want onboard electrics is to fit a different system and either choose one with a cutout large enough to remove all evidence of the original holes, or remove the pots from that one, attach body-mounted pots with wires, and mount the preamp itself to the inside of the guitar somewhere - that loses the neat push-in feature though.

Fixing obsolete electro-acoustics can be a real pain, it’s one of the reasons why like TheBigDipper I prefer to avoid them in the first place…

CavemanGrogg · February 2022

Have you tried contacting Yamaha outside of the UK? I ask because I've had nothing but terrible experiences with Yamaha UK, everything from them stating they're the only Yamaha dealers outside of Japan, from them telling me that they are the only Yamaha music school in the world outside of Japan - they're not I went to 3 outside of both the UK and Japan, graduated from one of them and taught at another of them. To me Yamaha UK seem more interested in pushing the sales of their new instruments especilly their B3's, than maintaining and repairing instruments people have already bought from them, which is very very different to all the Yamaha music stores I have visited around the world - a free set-up with a pack of strings when they're quiet is not unusual nor a free string change, and their staff really go out of the way to teach you these things. It would seriously be worth the effort of emailing around the different Yamaha distributors, not just the UK one, to see if they have or can source a replacement part for you, Yamaha are really good this way, if you own a Yamaha instrument, Yamaha doesn't care if you bought it from Yamaha UK, or Yamaha Indonesia, when it comes to customer service and after sales care. At the end of the day Yamaha is promoted very very heavily as the instrument of choice for music students of all levels, not just by Yamaha's own music school, but just about all of them, Yamaha are extremely protective over this. And if it's a very common issue, or something that comes up a lot don't be surprised if Yamaha send you or direct you to an easy to source off the self part, sure their parts are 'propriety'', but not by much, in fact barely enough to be called 'propriety' it's mainly cosmetic. I had a similar issue with the first generation of Yamaha's silent guitar, local distributor told me part was unavailable world wide, distributor in the next country over sent me over a bag of half a dozen spares.

For what it's worth I'm a huge Yamaha fan, of their instruments - my first guitar is a Yamaha classical that my parents bought for me over 30 years ago via a rental scheme which I did my music grade exams on and still have and play to this day, music schools, and the way the company does business, but there is always a bad apple, and Yamaha UK is that bad apple

PFAllen2 · February 2022

Update: the soaking of the pot with Super 10 was not successful. Annoyingly, I can get signal through the preamp at maybe 25% volume with a bit of wiggling, but it isn’t reliable even to be left as a fixed setting.

I have a K&K Mini in my other acoustic, so probably makes sense to do the same here, with an external preamp. Currently buffering with a Boss TU-2, any suggestions re preamps?

Thanks for all the replies.

CavemanGrogg · February 2022

PFAllen2 said:

Update: the soaking of the pot with Super 10 was not successful. Annoyingly, I can get signal through the preamp at maybe 25% volume with a bit of wiggling, but it isn’t reliable even to be left as a fixed setting.

I have a K&K Mini in my other acoustic, so probably makes sense to do the same here, with an external preamp. Currently buffering with a Boss TU-2, any suggestions re preamps?

Thanks for all the replies.

Contact another Yamaha distributor and explain your issue to them, from personal experience Yamaha UK are more interested in shifting B1's, B2's and B3's than offering any kind of after sales service or customer support. I truly would not be surprised if they don't send you the part or direct you to an off the self equivalent, their propriety parts tend to be propriety cosmetically only. Just like Rolls and Bently electronics, their fuses for example had the same part numbers as the exact same fuse in the Tandy electronics catalogues.

TheMadMick · February 2022

PFAllen2 said:

I have a K&K Mini in my other acoustic, so probably makes sense to do the same here, with an external preamp. Currently buffering with a Boss TU-2, any suggestions re preamps

I have a K&K mini in my Guild. It was pretty thin and weedy with the dedicated K&K pre-amp. However, plugged into an LR Baggs Para acoustic equalizer DI, it sounds fabulous into my Marshall AS50. Problem is, the Baggs ain't cheap! They go for about £100.00 2nd hand on here.

PFAllen2 · May 2022

ICBM said:

JayGee said:

Bypass the onboard electronics altogether and use an external preamp?

That’s a possible solution, yes. The pot mounting holes can at least be covered less obtrusively than a typical large rectangular hole.

The only other real alternatives if you want onboard electrics is to fit a different system and either choose one with a cutout large enough to remove all evidence of the original holes, or remove the pots from that one, attach body-mounted pots with wires, and mount the preamp itself to the inside of the guitar somewhere - that loses the neat push-in feature though.

Fixing obsolete electro-acoustics can be a real pain, it’s one of the reasons why like TheBigDipper I prefer to avoid them in the first place…

The current solution, as suggested above, is bypassing the electronics. I have partially gutted the preamp PCB, using to original connectors to and from the PCB, and hardwiring them together. I then re installed the non functioning preamp to fill the holes and leave the controls in the recessed position.

Still leaves the option of a Pure Mini install later if desired. FYI, HX Stomp makes a handy preamp, EQ , IR loader and Reverb for acoustic guitar.

Thanks for all the advice and help posted in this thread.

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