TBA820m amp problems
- Thread starter Stephen Flynn
- Start date
Got hold of a 20k, it didn't like it..tried a 10k..still motor boating and playing up. I had a 1kb pot..it settled down with that. Not much point in having a 1k pot nothing really gained. I then submitted the pot with a resistor to ground..same result the amp only liked resistors up to 1.2k..anything higher would set it off becoming unstable, anything lower than 1k and it started lowering the output..with a small 1.5w amp..you don't want that. The charge amp circuit has a made a huge difference to capturing the missing bass frequencies. Probably a bit too much. Been reading about calculating low pass filters, and found an online calculator.
The current low pass is around 1.5hz. I think the lowest note on a guitar is 80 something, and a ukulele higher. So I think I can adjust the the low pass in the charge amp by changing the values accordingly - somewhere around 30-50hz might be better.
Just wondering, when I change those values C1 and R1...will that affect the values of the components following i.e R4 and C2...if so, is there a way to figure out what they should be????
Theres another issue I'm researching is that these piezo disc out of a typical buzzer have a resonant frequency 5k hz..so the higher string and notes set it off. Think I need to play around with a range of them some kind of EQ pot to roll off those higher frequencies. I could use the other half of the TL072 for that. If anyone has a simple way to do that effectively I would be keen to hear about it. I know on some electric guitars ( i used to have a danelectro) theres a simple pot EQ. You roll it left and you got bass..roll it right and you got treble..I think something like that would be ideal.
cheers
The current low pass is around 1.5hz. I think the lowest note on a guitar is 80 something, and a ukulele higher. So I think I can adjust the the low pass in the charge amp by changing the values accordingly - somewhere around 30-50hz might be better.
Just wondering, when I change those values C1 and R1...will that affect the values of the components following i.e R4 and C2...if so, is there a way to figure out what they should be????
Theres another issue I'm researching is that these piezo disc out of a typical buzzer have a resonant frequency 5k hz..so the higher string and notes set it off. Think I need to play around with a range of them some kind of EQ pot to roll off those higher frequencies. I could use the other half of the TL072 for that. If anyone has a simple way to do that effectively I would be keen to hear about it. I know on some electric guitars ( i used to have a danelectro) theres a simple pot EQ. You roll it left and you got bass..roll it right and you got treble..I think something like that would be ideal.
cheers
