Ba2000 right channel sounds very distorted
- Thread starter sansuibutch
- Start date
sansuibutch
Super Member
I suggest keeping the uf value the same, its ok to go up one voltage value
i.e. 10uf 16v ok to use 10uf 25v
Also (have not looked at the schematic) there may be a few on the board that either are labled b.p. or n.p, those are non polarized caps and need to be replaced with non polar caps. Don't trust the schematics on this one.
Also, I see a couple of vd1212 diodes on that driver board (the ones that look like little balls with two leads. Might as well order a few 1n4148 diodes and change them out while you are in there, ok to ask when you get to that and guidance will follow.
Finding low level distortion is a bear without a scope, you are doing fine so far, changing out the suspect components will get you much closer then we can really dig in.
Also, the orange cap in the very bottom right of the card picture, can you reply with all of its markings, may be a low esr cap and we need to be sure you get the best replacement for it
-Lee
I'm going to order those diodes you mentioned.Are they the TVS diodes that pop up on mouser when I type in 1n4148?
super98lsc
Well-Known Member
I have a thread on here with a lot of photos of a full rebuild of one of my BA-2000 units. Feel free to ask if you need pictures of anything specific.
sansuibutch
Super Member
I changed all the caps on the PS and the driver board. Hopefully I can get it back together soon and give it a listen. I'm thinking at this point I should prolly start sourcing the big filter caps
sansuibutch
Super Member
OK it fired up just like usual. The left channel sounds great. The right channel is still distorted. Besides the four big filter caps thers only 7 little caps left in the whole amp and there on the volume and meter board. By the time I get this thing sounding right it will be a brand new amp hahah
sansuibutch
Super Member
I actually jumped that relay at one point because it was suspect. It is not my problem. Im planning on replacing the rest of the drivers and the tiny diodes and hopefully,,just hopefully I'll be getting somewhere
Have you set the bias yet? If bias is set way below the 100ma level you may be dipping into an area of output transistor operation that will introduce cross-over distortion. Also, look carefully at the mylar capacitors (the green chicklet looking ones). I have seen where they have failed and typically swell or bulge..
sansuibutch
Super Member
I measured the ohms across these and they are the same. I don't know If when they fail they start to short or not?
sansuibutch
Super Member
I have not attempted to set the bias but both channels read .1 mv so I'm guessing it would be distorted on both channels? When I tries to set the bias before it was not possible . I wrote my readings in this post somewhere. I'll dig it up
sansuibutch
Super Member
sansuibutch
Super Member
I can not remember if I had a dummy load on the outputs or the volume all the way up when I did this. It was a while ago. So I can't be positive these numbers are relevant. I defiantly remember the DC offset being in the negative on the right channel and the left channel was 11mv
And the left channel sounds perfect.
To further explain Johns reply, a transistor takes a certain voltage to turn on, in the case of those outputs you have 4, 2 npn and 2 pnp that are not 'switched on' at that low a ma value. Note, there is a way to convert that value to an mv reading but not for the sake of this discussion. Therefore they are turning on and off rapidly as the ac input value (or audio signal if you prefer) travels to the output stage. That rapid on and off switching will introduce measurable distortion which can often be seen on an oscilloscope and certainly so on a distortion meter. Sansui specs 100ma current at the test point. If you cannot adjust the amplifier channel up to that level I would look at the outputs first, remove and measure using the 6 way diode test looking for any that are not in the same ballpark reading wise, then the output resistors which should measure iirc 0.33 ohms, then the resistors just behind them then we continue on deeper into the amplifier output stage. I would expect to see hfe readings on those outputs between 450-520 mv on the diode test.
^^^
The procedure to set the bias using the output emitters and setting to a mv value was well documented by our good Dr Audio a while back. Since I do not have a ba2000 in the shop to provide test points I only provide this as food for thought. Using the I*R=V formula I come up with @66mv per emitter pair. Before using this method if necessary please ask for a more detailed look at the correct test points. This method may also give a clue as to which pair or both of the two output pairs on the right channel is misbehaving.
http://www.audiokarma.org/forums/in...au-9900-au-11000-repairs.462680/#post-5966591
http://www.audiokarma.org/forums/in...au-9900-au-11000-repairs.462680/#post-5966591
sansuibutch
Super Member
I did swap the whole output stages. The distortion stayed on the right so I'm guessing my problem is not in the output? Are you saying the bias pots being turned all the way down is possibly starving a transistor of power and causing it to turn on and off causing the distortion?
yes.
Be very careful doing this. Set your multimeter to the ma scale NOT VOLTS. Use mini grabbers to connect the probes to the test point and the wire. Once you get a reading starting to rise I would stop at 50ma and wait for a while before going up any higher as it will continue to climb as things warm up. If you get to this point then find a way to put the cover on draping the leads outside the unit and allow it to fully warm up before continuing to the 100ma value. Bad things can and will happen if you let a probe slip or a wire touch anything while doing this test.
In fact I would probably put the unit back on the dbt with a 100-200watt bulb to start with.
-Lee
Be very careful doing this. Set your multimeter to the ma scale NOT VOLTS. Use mini grabbers to connect the probes to the test point and the wire. Once you get a reading starting to rise I would stop at 50ma and wait for a while before going up any higher as it will continue to climb as things warm up. If you get to this point then find a way to put the cover on draping the leads outside the unit and allow it to fully warm up before continuing to the 100ma value. Bad things can and will happen if you let a probe slip or a wire touch anything while doing this test.
In fact I would probably put the unit back on the dbt with a 100-200watt bulb to start with.
-Lee
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