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acoustic-270-service-manual offline.pdf
Just adding some discoveries (for lack of a better term) to share as the Acoustic 270 is a bit of a bear to work on given the preamp board is not screened as well as it's upside down in the amp making it very difficult & rather precarious to work on. Also, the PCB layouts in the manual that is available are pretty impossible to follow.
Symptom:
1) no audio thru the amp. output stage is not blown
a. Q117 & Q118 FETS switch between fuzz and normal channels and are bad not allowing signal to pass
I used the original FETs but I'm sure the J11x varieties could work fine. Q117 = 2N4360 Q118=2N5457
2) Tremolo seems very weak & just not right. Makes amp 'thump or pump' but no real trem. (For reference: The trem on this amp is rather radical w/intensity turned even 1/2 way up. It completely zero's out the original signal.
a. Q114 FET 2N4360 is bad just causing the DC level of the audio to vary
b. The level trimmer R163 needs to be adjusted so that the audio level when Trem engaged is the same as main signal when not engaged and doesn't obliterate the original signal even when trem intensity turned all the way down.
I'll try to attach the manual.
In both cases once I was able to identify the position of the FETS in question, I solder-wicked them loose & pushed the leads though the board so they fell out.
I then just replaced the FETS on the foil side (up facing side since board is upside down) of course minding the proper orientation.
The FETs that came out were all NTE replacements which might indicate no NOT use those in this amp.
As mentioned above, I used original FETS that I obtained from UT Souce.com. They are a VERRRRRY reliable company as I have made many parts orders from them. They're also very responsive to inquiries as well as resolving any issues that may come up which have been very few.
Glen - Mars Amp Repair ID, USA
Just adding some discoveries (for lack of a better term) to share as the Acoustic 270 is a bit of a bear to work on given the preamp board is not screened as well as it's upside down in the amp making it very difficult & rather precarious to work on. Also, the PCB layouts in the manual that is available are pretty impossible to follow.
Symptom:
1) no audio thru the amp. output stage is not blown
a. Q117 & Q118 FETS switch between fuzz and normal channels and are bad not allowing signal to pass
I used the original FETs but I'm sure the J11x varieties could work fine. Q117 = 2N4360 Q118=2N5457
2) Tremolo seems very weak & just not right. Makes amp 'thump or pump' but no real trem. (For reference: The trem on this amp is rather radical w/intensity turned even 1/2 way up. It completely zero's out the original signal.
a. Q114 FET 2N4360 is bad just causing the DC level of the audio to vary
b. The level trimmer R163 needs to be adjusted so that the audio level when Trem engaged is the same as main signal when not engaged and doesn't obliterate the original signal even when trem intensity turned all the way down.
I'll try to attach the manual.
In both cases once I was able to identify the position of the FETS in question, I solder-wicked them loose & pushed the leads though the board so they fell out.
I then just replaced the FETS on the foil side (up facing side since board is upside down) of course minding the proper orientation.
The FETs that came out were all NTE replacements which might indicate no NOT use those in this amp.
As mentioned above, I used original FETS that I obtained from UT Souce.com. They are a VERRRRRY reliable company as I have made many parts orders from them. They're also very responsive to inquiries as well as resolving any issues that may come up which have been very few.
Glen - Mars Amp Repair ID, USA
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