BA115 blown tweeter

[lowell]

I just replaced a blown tweeter in this amp. The new tweeter sounds like it's getting hit w/ some bad signal. I thought maybe the crossover or tweeter driver might be bad but on review of schem I could not see anything related to a crossover. There is simply a "speaker out" on the schem. Is there no crossover for the tweeter in these amps? If I'm missing something any advice welcome... thanks!

[oc disorder]

It uses a Piezo Tweeter which doesn't require a crossover.
Google "Piezo Tweeter" for more info eg this is informative
Making piezo tweeters sound better!

http://members.misty.com/don/pzfix.html

In my opinion traditional diaphram tweeters sound better or purer but...!
they are way more expensive , require a crossover and are eaisely
overloaded and can burn out particuarly in instrument amplifiers.
As the piezos are so efficent they highlight noise (HF) which a 15" or 12"
traditional speaker cannot reproduce.

http://www.pulsardevelopments.com/products/detail/piezoan.html

This site is also informative
There may be a compromise by using a pad, reducing the output attenuates the hiss while still providing an edge to the sound .

[lowell]

I replaced the tweeter w/ new part and it is farting. Must be something wrong w/ the power amp. I then disconnected the tweeter and the woofer sounds better by itself however when the amp is turned up around 6 w/ master fully up it farts too. What shall one look for w/ this symptom. I've dealt w/ solid state amps having hum or no sound, but not this.

[Mars Amp Repair]

I just remembered that I have had a few of these amps where the bias was adjusted just a hair too low & caused weird distortion. It is a very touchy adjustment on this amp.
I'd just tweek it a hair in the clockwise position & that may clear it all up....glen

[lowell]

ok I'll try that... thanks!

[MarkusBass]

Bias adjustment procedure for this amp is described on the schematic. You have to set AP1 control for 5mV accross R61 (0.1 Ohm resistor) with no signal applied, no load. It may require fine tuning with a signal generator and an osciloscope.

Mark