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Acoustic guitar preamp not working...

Errr...what it says on the tin...

Moderator: Spike

User avatar
RichardH
Posts: 6218
Joined: Sun Apr 08, 2007 7:49 am
Location: East Sussex, UK

Acoustic guitar preamp not working...

Post by RichardH »

The preamp in a friend's acoustic guitar doesn't seem to work. It's a B-Band T35, and I have tried fresh battery etc.

The tuner doesn't light up (I have tested plugging a cable in to make sure it doesn't need a cable in to operate), and no sound comes out through an amp.

I suspect it is just a matter of replacing the unit, but anything else to try before we do that?
It's a bugger getting inside the horn when you've got the array supports in place, isn't it!

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Mottlefeeder
Junior Member
Posts: 676
Joined: Sun Sep 23, 2007 4:37 pm
Location: Warrington

Post by Mottlefeeder »

RichardH wrote:The preamp in a friend's acoustic guitar doesn't seem to work. It's a B-Band T35, and I have tried fresh battery etc.

The tuner doesn't light up (I have tested plugging a cable in to make sure it doesn't need a cable in to operate), and no sound comes out through an amp.

I suspect it is just a matter of replacing the unit, but anything else to try before we do that?
If you have access to a multimeter, you could check the resistance between the two battery contacts (with and without a guitar lead plugged in) An open circuit would indicate a faulty connection in that area, and no change when you plug a lead in might indicate a fault in the output jack socket.

David
Yamaha RBX 765 5-string fretted
Ibanez EWB205WNE 5-string fretted acoustic
Ashdown MiBass550
Hartke HA4000
BFM Jack 10 - (2)
Homebrew 1x10
Homebrew Battery Amp

User avatar
RichardH
Posts: 6218
Joined: Sun Apr 08, 2007 7:49 am
Location: East Sussex, UK

Post by RichardH »

Hmmm - that was helpful David.

I have pulled the battery box/jack socket assembly.

Image

With the multimeter I am getting a connection between B- from the battery box and the GND of the 4 pin connector (which goes off to the preamp etc).

I am not getting anything from B+ on the battery and B+ on the 4 pin connector, whether or not I have a jack plug in the socket (I am assuming that the battery is switched out when no lead is connected).

When the jack is disconnected we get

TAG1 > BATT-
TAG1 > B-

TAG2 > OUT

TAG3 > SW

BATT+ > NOTHING


When a jack socket is connected, I get signal thus:

TAG1 > BATT-
TAG1 > B-
TAG1 > SW
TAG1 > TAG3 (if mono jack inserted)
TAG1 > jack sleeve

TAG2 > OUT
TAG2 > jack tip

TAG3 > SW
TAG3 > TAG1

TAG3 > jack ring (if stereo jack inserted)

BATT+ > NOT CONNECTED


...so it would seem that the jack is not switching the +ve supply through to the 4 pin connector.
It's a bugger getting inside the horn when you've got the array supports in place, isn't it!

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RichardH
Posts: 6218
Joined: Sun Apr 08, 2007 7:49 am
Location: East Sussex, UK

Post by RichardH »

...I ran a lead round from the BATT+ to the B+ terminal on the 4 way connector, and it works! It seems that the tuner operates with the lead disconnected, but I think that is switched at the preamp end, so when tuner off the battery is disconnected.

Result! Thanks to David for encouraging me to have a tinker!
It's a bugger getting inside the horn when you've got the array supports in place, isn't it!

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oxblood
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Joined: Wed Apr 18, 2007 5:53 pm
Location: Naarch.

Post by oxblood »

Sounds like repeated plugging in/out stresses may have caused a hairline crack in one of the PCB tracks - which you've now bridged wid yer wire (sez he helpfully, after the event :D).

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Mottlefeeder
Junior Member
Posts: 676
Joined: Sun Sep 23, 2007 4:37 pm
Location: Warrington

Post by Mottlefeeder »

RichardH wrote:...I ran a lead round from the BATT+ to the B+ terminal on the 4 way connector, and it works! It seems that the tuner operates with the lead disconnected, but I think that is switched at the preamp end, so when tuner off the battery is disconnected.

Result! Thanks to David for encouraging me to have a tinker!
You're welcome. Glad you got it sorted.
Yamaha RBX 765 5-string fretted
Ibanez EWB205WNE 5-string fretted acoustic
Ashdown MiBass550
Hartke HA4000
BFM Jack 10 - (2)
Homebrew 1x10
Homebrew Battery Amp

User avatar
tauzero
Posts: 4196
Joined: Thu Dec 13, 2007 8:50 am
Location: Tamuff
Contact:

Post by tauzero »

The normal way of switching active preamps of all types is to connect the battery negative to the ring and the preamp negative/ground supply to ground, so the negative side is switched and the positive side is a permanent connection - or, in this case, permanent disconnection.
Coitum volaticum non dono

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RichardH
Posts: 6218
Joined: Sun Apr 08, 2007 7:49 am
Location: East Sussex, UK

Post by RichardH »

Yes, that is what I realised in my tinkerings. Just wondering as the tuner operates without the lead plugged in, but I suspect that is intentional, and the battery is only being used when the tuner is switched on.
It's a bugger getting inside the horn when you've got the array supports in place, isn't it!

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