Re: x0xb0x newbie: Problems with VCA BA6110 pin 4
Good morning again, saturday work, now it has to work :)
I just tested your suggested route, which does the dc offset:
R162 - R128: brings the correct 5,33 V where it should be and cuts it down to 0,7 Vafter R128, I guess this is right, but there could be a error at least.
The other route of course is the same with another middle voltage between R129 and R127 with around 3,3 V, but as it seems they only form another part of the voltage dividor.
Next step now I will desolder Pin 4 and apply a voltage directly to this pin, I hope then I wont cause that much current flow, but still will be able to produce some sound.
Just did desolder Q1, and I still have massive curretn flowing into Pin4 when supplying an external voltage supply about 1 V it begins to produce the sounds I play on the keyboard, after that curretn slowly rises sound gets louder but I got around 25 mA when supplying 1,7 V that cannot be right I assume.
So perhaps I have some broken BA6110 after all??? and worst case I cannot find the other VCA chip also supplied in my x0xb0x package, so I cannot even try the other one right now, that is really sad, gotta keep digging, perhaps I will find ich some day :)
Next step I will change the value of R131, I do believe I simply need more volatge t the base of Q3, so I will alter the settings of this npn transistor by changing the voltage. I will try this by lowering the value of R131 from 220k down to halt in first step simply by soldering another 220k at the bottom ( or whatever resistor I will find in the next 5 seconds :) )
Didnt change anything, I dont understand how the voltage on Q3 is built, but i definetly need a slightly bigger one to make this work.
I did attach my voltage supply to base of Q3 again, with a voltage of around 600 mV it works, so I do believe perhaps my transistor in Q31 is somehow a little broken or shaky, normally I will get a voltage on keyboard trigger fo around 500 mV, but this ain enough to pull the Q3 to work, so I reall do not need a lot but some changings in the resistor devidors, perhaps I could also tweak R123 and R132, i addition with R130 to pull something off.
So next I will try to get a higher voltage there, like i tried before, but hopefully it will work this time.
Ok i did lower the 1M5 Ohm R123 to half, no changes, I did highr R132 to 10 kOhm, no changes, When i look at R133 there is always 11,4 V when I push a key, on R131 on te upper side also, on the lower side it is different, the voltage goes immediatly up to around 6 V slopes down really fast around 30 ms down to under 1 V , when I keep the button pressed it will ramp up to 12 V again I guess, when realsing it gos down to 0 V.
ut all of this has absolutley no affect on the collector of Q31, how can this be how can this pnp transistor smoot down all of this and simply let 500 mV pass all the time the key is pushed, I do not udnerstand this, and I have no possibilty right now to alter this voltage I feel I really have to alter a little bit...
OK there comes light at the end of the tunnel, but I guess really at a long term cost.
I did solder 10 k parallel to R131 so i get around 9 k Ohm at this point, and now i am hearing sound for the first time without external power supply.
This is doing so by then pulling up the critical voltage behind Q31 to around 600 mV, sound is really not loud at the moment so I will play around with a poti or even with some fixed values later on, so that I can use my x0xx this aternoon at home :)
Last edited by mex
on Sat Oct 06, 2012 6:32 am, edited 2 times in total.