Ibanez SST acoustic gutar preamp

[dmeek]

dmeek, I have a Ibanez SST that has failed also. I am not a solid state electronics guy. Been following this post to see if this unit can be repaired as a new one, although available, is just too much $ for this guitar. I have removed & disassembled the unit, tried the jumper on the FET & have volume loud & clear. My question is, can I solder a jumper on it and use it that way essentially scrapping the tuner. I run through a tuner on both of my rigs so I don't care if tuner on the guitar does not function. Please advise.
D.

That will work, jumpering the FET will keep the guitar on all the time, even when the tuner is active. The tuner will still work but you would want to keep it off to save battery power.

[Stogie D]

Yeah baby!!!! Thank you dmeek. I was able to solder the jumper to the FET legs. ( I have no idea what a FET is :-) Smallest solder job I ever did! My guitar is back on track & I'm fine with the way it works with the tuner. Not an issue. Thanks again.
D.

[mmiller]

Just picked up an Ibanez acoustic bass off of CL with this SST preamp and it definitely has the volume sucking problem within a minute as described above. I haven't taken the bass apart yet (am a little leery cause I've never soldered anything this delicate before) but have several newbie questions:

Where is the "small" board as referenced above? Is it stacked on the main board? Is there a photo of the small board?

The smd emitter-base R64 47K (473) resistor replacement is a 4.7K (472) ... Is the new one a 1/4 watt resistor? Where can a novice like me pick up a few of these?

I'm kind of considering the permanent jumper semi-fix on the FET ... but if a resistor replacement is not too difficult and will fix the issue for good, I'm willing to go down that road.

Great forum all you guys! Thanks for any words of wisdom and photos if available.

Mike

[dmeek]

The smaller board plugs into the main board. It's called the Tuner Board though the leds are on the main board.
Here is a photo of the component side. You don't have to remove R64, just solder the new resistor across it.
A 10K 1/4 watt should work. When you plug the board back in double-check that the pins are in the right holes.

http://music-electronics-forum.com/a...1&d=1501788520

[mmiller]

Doug ... thanks for the really quick reply and the awesome photo! Your explanation and being able to actually see what to look for & how to fix helps a ton. I'll look on Amazon or somewhere in search of a few resistors. Also will be looking for a small soldering iron & solder to tackle this new do-it-yourself endeavor. Thanks so much!

Mike

[dmeek]

Just noticed the updated schematic I attempted to post in message #29 didn't work.
I'll try again


http://music-electronics-forum.com/a...1&d=1501856006

[leem]

Thanks dmeek for the info. I tried the mod putting a 10k resistor across R64. That fixed the problem where the sound went out. But now the tuner doesn’t work at all. Do you know if there is another way to fix it so the tuner works also? I did also notice that the layout on my board is different, and a different version.

[dmeek]

If you remove the 10K resistor does the tuner work again? That resistor shouldn't affect the tuner.
A while back I fixed an SRT preamp with a dead tuner, it was a bad crystal.
Also check the push button switch. Check voltages at pin 8 of U3 LM358 as you push the button,
+3V = tuner on, -3V = tuner off.

[jg67]

Hey there i ran into an issue with my preamp and was scouring the internet and came across this forum and thought i would give it a shot and maybe some can help me out or point me in the right direction.i have an Ibanez AEG20E acoustic electric with a fishman sst preamp with onboard tuner. So the problem is that i had left this guitar alone for about 2 years and i recently started playing again. When i changed the batteries for the tuner the tuner would respond to the strings at all however my preamp worked fine when hooked up to the amp. So me being a diy type i decided to take a closer look and so i took the preamp out along with the pickup i cleaned the volume knob phase button tuner switch and the equalizer switches with electrical parts contact cleaner. I the. Reassembled and still same result no tuner just a blinking green light and the preamp worked when connected to amp. So the I took the preamp out again this time going a little further and i took the actual circuit board out of the encasement. I separated the two boards and i had a suspicion that maybe the crystal was the culprit based on the last post. So i test for continuity of the crystal and resistance. I got a whacky reading for continuity and no resistance. I put everything back deciding i should leave it alone and now the neither the tuner or preamp work. Before the tuner would atleast flash green and the preamp gave an output when connected but now nothing and i made sue i had good batteries in there. Any thoughts on what i did wrong or what could be faulty or just replace the whole thing. Sorry for the LOOOONG post and thanks to any and all that take the time

[dmeek]

A crystal should measure open with an ohmmeter though it still may be bad. A replacement costs less than a dollar (plus shipping) so the easiest thing is to replace it.
If you have an oscilloscope and you can see the 4 MHz on either pin then it's OK.
Always double-check that the two boards are not mis-aligned and the pins are in the right sockets.

[petr_ruca]

Hey guys, first of all thanks to all of you that participated and specially dmeek who draw the schematics of this preamp. I need help with my guitar preamp, there's no sound at all but the tuner works perfectly. I tried the mods dmeek posted before to see if the problem was that the board thought it was muted all the time and still have no sound. I get -3V and 5.5V from the power supply, should this be the problem since I'm not getting those 6V? I'm also starting to think that the Op-amp is faulty because the tuner gets its signal right and the FET opens and closes normally.

Another thing that may help, when I connect the guitar to my soundcard and crank both the input and output volume, I can hear the guitar slightly with the EQ and volume affecting the sound, and this happens with tuner on or off.

Thanks beforehand!

[dmeek]

First I would check the Shape and Volume sliders. You could check with an ohmeter to make sure the wiper is not open, or with a scope see if there is signal at pin 12 of U1.
Then check for signal on pins 1 and 14. there will be about 3 volts DC on the IC pins along with the audio.
5.5V shouldn't be a problem.

[petr_ruca]

First I would check the Shape and Volume sliders. You could check with an ohmeter to make sure the wiper is not open, or with a scope see if there is signal at pin 12 of U1.
Then check for signal on pins 1 and 14. there will be about 3 volts DC on the IC pins along with the audio.
5.5V shouldn't be a problem.

Hi dmeek. All sliders and potentiometer seem to be ok with the ohmeter. I can see the signal at pin 12 but the opamp only outputs 1V DC on pins 1 and 14, so I guess this means bad IC??

I checked and -3V and +5.5V reach the opamp on pins 11 and 4 respectively.

[dmeek]

I agree, looks like a bad IC.

[petr_ruca]

Hi again, I just changed the IC and there's still no sound of the guitar but the tuner recognises correctly the notes being played. The difference now is that when the tuner is on, theres a noise whenever the green led is on. Now my guess is around Q1, C102 and C7 area. I had the signal at Q1 gate, but maybe for some reason it's burnt and it doesn't let the signal pass.

I don't have my multimeter with me right now, so I couldn't make any measures yet.

Isn't this weird?