Faulty Pre-amp / Replacement needed SOLVED

lincolnblue

I have a Faith Neptune Trembesi from 2013. The pre-amp is giving me problems. It can cut out sometimes and if you touch the phase button slightly it can cut out or at least radically reduce the output until you fiddle with it again.

I've taken the preamp unit out and can't see any obvious solder issues. 

My assumption is that it'd be easier/cheaper to replace it than get it repaired. The dimensions are 5.5cmx5cm. Any suggestions of it I could get the same unit or, if not, what alternatives there are?

shufflebeat

If the phase button proves to be the only issue you could always bypass it, maybe solder a jumper across the appropriate connection to remove any doubt.

ICBM

Looks like the plastic has started to degrade as well. If you can find an identical replacement new I would do that. If the only choice is another second hand one I might think twice…

Replacing obsolete preamp units with something that doesn’t involve major surgery to the guitar is an absolute nightmare - it’s remarkable how few have compatible dimensions. This is the single biggest reason I detest onboard electronics in acoustic guitars…

Having stopped doing repair work a couple of years ago I’m not really familiar with what’s on the market now - something like the old Fishman Prefix system would fit, but would need the hole in the guitar enlarging - that’s the easier option than having a panel made to fit a smaller one though.

lincolnblue

shufflebeat said:

If the phase button proves to be the only issue you could always bypass it, maybe solder a jumper across the appropriate connection to remove any doubt.

I like the idea but wouldn't know where to begin?!

lincolnblue

ICBM said:

Looks like the plastic has started to degrade as well. If you can find an identical replacement new I would do that. If the only choice is another second hand one I might think twice…

Replacing obsolete preamp units with something that doesn’t involve major surgery to the guitar is an absolute nightmare - it’s remarkable how few have compatible dimensions. This is the single biggest reason I detest onboard electronics in acoustic guitars…

Having stopped doing repair work a couple of years ago I’m not really familiar with what’s on the market now - something like the old Fishman Prefix system would fit, but would need the hole in the guitar enlarging - that’s the easier option than having a panel made to fit a smaller one though.

I had a brief look earlier and couldn't find a same-size unit. I guess one option would be to bypass the preamp all together and fit a soundhole pickup?

thermionic

I would try cleaning the phase switch with electrical contact cleaner as a first step.

lincolnblue

thermionic said:

I would try cleaning the phase switch with electrical contact cleaner as a first step.

Good idea. I assume I take the preamp unit out then spray on both sides - from the button sure and in the circuit board?

nero1701

If you do have to fit an alternative, possibly go for a smaller one, and then 3d print the spacer for it?

maltingsaudio

Or fit a headway snake an use the hole as a sound port 
https://theartoflutherie.com/guitar-side-sound-ports/

p90fool

lincolnblue said:

ICBM said:

Looks like the plastic has started to degrade as well. If you can find an identical replacement new I would do that. If the only choice is another second hand one I might think twice…

Replacing obsolete preamp units with something that doesn’t involve major surgery to the guitar is an absolute nightmare - it’s remarkable how few have compatible dimensions. This is the single biggest reason I detest onboard electronics in acoustic guitars…

Having stopped doing repair work a couple of years ago I’m not really familiar with what’s on the market now - something like the old Fishman Prefix system would fit, but would need the hole in the guitar enlarging - that’s the easier option than having a panel made to fit a smaller one though.

I had a brief look earlier and couldn't find a same-size unit. I guess one option would be to bypass the preamp all together and fit a soundhole pickup?

The preamp died in my Faith Venus so I just wired the undersaddle piezo directly to the jack, meaning I can use it with outboard preamps instead.

This is what it sounds like with a Zoom AC-3 (ignore the soundhole pickup in the pic, that's just there as backup).

Danny1969

I've repaired a few acoustic guitar pre amps. The most common fault is the soldering on the pots and switches, they are never supported very well, often it's just the 3 little lugs supporting the pots. 

I would go over the all these joints. 
If the phase switch is faulty then you can cut and jump the PCB tracks so the switch is bypassed and the phase it static. You can always flip the phase externally. 

I repaired a pre amp on a bass mandolin once. Something had been pressing on the volume pot and had broken the end lug aways from the board. 3 months later it happened again. Turned out the women who played it was quite well endowed and the  weight of this was pressing on the pot while she played it. Luckily the repair was for the music store that sold it so I never had to get into the reasons why it failed and would always fail again unless modified. 

lincolnblue

p90fool said:

lincolnblue said:

ICBM said:

Looks like the plastic has started to degrade as well. If you can find an identical replacement new I would do that. If the only choice is another second hand one I might think twice…

Replacing obsolete preamp units with something that doesn’t involve major surgery to the guitar is an absolute nightmare - it’s remarkable how few have compatible dimensions. This is the single biggest reason I detest onboard electronics in acoustic guitars…

Having stopped doing repair work a couple of years ago I’m not really familiar with what’s on the market now - something like the old Fishman Prefix system would fit, but would need the hole in the guitar enlarging - that’s the easier option than having a panel made to fit a smaller one though.

I had a brief look earlier and couldn't find a same-size unit. I guess one option would be to bypass the preamp all together and fit a soundhole pickup?

The preamp died in my Faith Venus so I just wired the undersaddle piezo directly to the jack, meaning I can use it with outboard preamps instead.

This is what it sounds like with a Zoom AC-3 (ignore the soundhole pickup in the pic, that's just there as backup).

That sounds lovely. How easy is it to do that wiring?
I have a LR Baggs Align Series Session - would I need another pre-amp pedal or does that work as a pre-amp? (I only ever use it with acoustics with in-built pre-amps

lincolnblue

Danny1969 said:

I've repaired a few acoustic guitar pre amps. The most common fault is the soldering on the pots and switches, they are never supported very well, often it's just the 3 little lugs supporting the pots. 

I would go over the all these joints. 
If the phase switch is faulty then you can cut and jump the PCB tracks so the switch is bypassed and the phase it static. You can always flip the phase externally. 

I repaired a pre amp on a bass mandolin once. Something had been pressing on the volume pot and had broken the end lug aways from the board. 3 months later it happened again. Turned out the women who played it was quite well endowed and the  weight of this was pressing on the pot while she played it. Luckily the repair was for the music store that sold it so I never had to get into the reasons why it failed and would always fail again unless modified. 

Thanks - I'll have another look at the soldering on it

Danny1969

Take a photo in daylight of the PCB on your phone and then Magnifier up.  Then you’ll easily be able to see any issues 

lincolnblue

Well, after all that, I sprayed contact cleaner on the pots and the EQ and Phase Button  and left it 10 mins. Plugged in all in and it's working fine! So it was that simple. Thanks for all your advice but thankfully I don't have to pay for repairs or new pickup etc. 

thermionic

Always a good idea to try cleaning switches and pots before firing up the soldering iron. Glad to hear that it worked!

shufflebeat

Thanks for getting back, will be useful for others.

lincolnblue

Well, annoyingly it's still problematic. It's actually the EQ-S button, not the Phase button, but if you press it, it can work or it cuts out or, occasionally it just swells between loud and quiet. It's like the button itself doesn't fully engage if pressed or touched

digitalkettle

lincolnblue said:

Well, annoyingly it's still problematic. It's actually the EQ-S button, not the Phase button, but if you press it, it can work or it cuts out or, occasionally it just swells between loud and quiet. It's like the button itself doesn't fully engage if pressed or touched

Did you clean that too?

lincolnblue

digitalkettle said:

lincolnblue said:

Well, annoyingly it's still problematic. It's actually the EQ-S button, not the Phase button, but if you press it, it can work or it cuts out or, occasionally it just swells between loud and quiet. It's like the button itself doesn't fully engage if pressed or touched

Did you clean that too?

Yep, I gave it all a good spray of contact cleaner.