Fishman loudbox mini

[mellowamoya]

Hi all,
im looking for any technical information, schematic for a Fishman loudbox mini i have one to repair and a schematic would be a great help.
thanks
dennis

[Roly]

Hi mellowamoya, welcome.


It would, but I really doubt that you are going to find one - current model, several unfulfilled requests since 2013, etc.

What are the symptoms?

Have you had it open and had a look or taken any measurements (e.g. supply voltage(s), voltage on the output)?

Does it use a chip amp for the output stage, if so what type number?  (if it does and it's an output stage failure it is very common for manufacturers to use the typical circuit straight off the chip datasheet)

If it's just a straight failure, no output, then generally repair is pretty straightforward.

This thread may be of help;
http://music-electronics-forum.com/t23816/

[mellowamoya]

Thanks for the reply the power amp is working but nothing from the inputs. One of the op amps tl074c has a burn hole in it so I know what the problem most likely is, but I wanted to test the power supply voltages before fitting new chip or chips, chip supply voltage is 28.4v within Spec for the chip 36v max but would like to know if that is correct supply is regulated by a 317.
Thanks
Dennis

[Roly]

Assume therefore that you have fed a signal in via the Fx Return (o.n.o.) and found the power stages are working.


A TL074 (quad op amp) with a "burn hole"?  Ouch - that is very not good and suggests quite a bit of power has been fed in somewhere, possibly to an input if it's the first op-amp in the chain (or some other outside world socket), and that much energy means there is a good (bad) chance you will find other things less obviously wrong, other semiconductors blown.

This can happen if the output of another highish powered amp is directly connected to an input.

The LM317 is an adjustable regulator so its actual output voltage will be set by a couple of nearby resistors, but 28.4V looks reasonable (and not to worry as it's below the chip amp maximum).  Check the input voltage to it, it should be at least 3V higher if its working okay.

As we haven't got a circuit it would be helpful if you could post a couple of sharp well-lit pix, the whole board, and detail of where the damaged IC is.

[mellowamoya]

thanks roly,
according to the owner it just stopped while playing,im waiting on replacement 074s end of next week will get back to the amp then, one of the penalties of living on an island,have attached a couple of pics of the board and chip.
thanks
dennis

[Roly]

according to the owner it just stopped while playing

What that is possible it is also very unlikely.  People (clients) will often say something like this to hide doing something they now realise was stupid (but in reality just ignorant of things that are a bad idea).

These are Surface Mounted Devices (SMD's).  I suggest that the best way to remove the old op-amp is to use fine point side cutters to cut each of the legs, then wipe the solder and leg remains from each pad with your soldering iron (with a dab of fresh solder). Be sure you get all the remaining legs.  Good luck.


Out of curiosity, which island?

[mellowamoya]

Yes no problem I do have a good rework station and remove smd devices with the hot air iron works very well for me. I'm on the island of Trinidad in the west indies
Cheers
Dennis

[Roly]

I'm on the island of Trinidad in the west indies

Ay Rasta mon!  Lucky sod.   :dbtu:

[mellowamoya]

hi,
just an update replaced the burnt out ic and it now tested for 4hrs and it ran fine so can only think it was a faulty component.
thanks
dennis

[Roly]

Good to hear.

I always make it a point with such mystery failures to carefully go over the speaker connectors and wiring, and all too often I find something like conductors twisted together inside a plug - intermittent, but it explains everything.

Then of course there is plain bad luck.


{ahhh... Trindad.  Just looking on the map and I didn't realise you were so close to South America, mentally had you more where Martinique is, but they all look like wonderful, places to live.  I'm in a small town just north of Ballarat in the Victorian goldfields, Australia.  Not too bad I guess, but it's a long way to the beach. ;-}


I'm cool with this.


I'm cool with this.


I'm cool with this.


I'm even cool with this (got a few Huntsmen around the house and a couple of Bushies in my truck).

[Ymel]

Dear Dennis,
May I have a question? I am also living in a kinda 'island'. The nearest Fishman representative is 1200 km from here.. My speaker started to rattle at some low notes on my guitar, gain and master at 10-11 o'clock. ( I tried it with 2 different guitars). Warranty is over. I thought I take out d speaker and take it to some speaker service in d near.
How can I open this closed cabinet to get the speaker without harming it?
Thank u a lot!

[phatt]

I'd start with the 6 screws,, 3 on each side.
the chassis would then likely slip out and give access to the speaker.
Phil.

[Ymel]

I'd start with the 6 screws,, 3 on each side.
the chassis would then likely slip out and give access to the speaker.
Phil.

thanks Phatt,

I also thought that but I was afraid to face more difficulties. So it is easy. My mini started this rattling 2 months ago. But even earlier after 1'o clock with the master (guitar gain is still around 11-12 o'clock) I noticed distortion. I use it with a neck humbucker on a hollow body guitar. No additional pedals, booster or other gizmo.

The other thing I notice that if the singer raises his voice, my guitar channel reduces its volume giving priority to mic channel. Is it normal??
tks in advance

[J M Fahey]

The other thing I notice that if the singer raises his voice, my guitar channel reduces its volume giving priority to mic channel. Is it normal??
tks in advance

I bet the singer feels the same about *his*  channel  :lmao:

Fact is this Acoustig Guitar amp, same as PA, Keyboards and many Bass amps are meant to be used clean, so they incorporate a Limiter circuit which turns down overall gain to keep the mix below clipping.

So when one guy is doing his thing loud, and another enters in the mix, the overall volume will stay roughly the same, so the first user will notice his own sound going down compared to his earlier level; of course the newcomer does not have such reference.
At most, he feels he's not as loud as he expected.

[Ymel]

The other thing I notice that if the singer raises his voice, my guitar channel reduces its volume giving priority to mic channel. Is it normal??
tks in advance

I bet the singer feels the same about *his*  channel  :lmao:

Fact is this Acoustig Guitar amp, same as PA, Keyboards and many Bass amps are meant to be used clean, so they incorporate a Limiter circuit which turns down overall gain to keep the mix below clipping.

So when one guy is doing his thing loud, and another enters in the mix, the overall volume will stay roughly the same, so the first user will notice his own sound going down compared to his earlier level; of course the newcomer does not have such reference.
At most, he feels he's not as loud as he expected.

Yes, it is okay. My male singer sometimes shouts and this causes some less wanted result for a sec but the female singers are okay - I have no such phenomena with them

I meanwhile disassemblied the Mini to get the speaker:

take a hexa key to remove the 2x3 screws from both sides. Then take away the 2 small brown plastic decor plate close to the potmeters both sides. Then carefully lift up the amp part from the wooden box. Careful bc the cables are still connected to the box going to the speakerm tweater and transformator plus a ground screw. All are easy to remove u will see straight how to do that.

As the brown cover material is very weak stuff you may scratch it inside but it is not visible.
Easy to remove the speaker either, no soldering but slideable tips on it.
Repairmen said fixing speaker's rattling is about 1,5 USD. (Vietnam)