Ba2000 right channel sounds very distorted

[sansuibutch]

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

I tried to test the bias and I don't think I'm fully understanding somthing. I did step 2 in the service manual procedure pictured. With no input and a 8 ohm load with the volume all the way up I don't get and amperage. I can turn both pots from all the way down to all the way up and nothing changed. DC offset stays the same and my milliammeter doesn't read show anything for either channel. But with no input I would kind of expect that considering amplifying nothing gives you nothing. So I played some music and whatever I do to them pots does nothing to the sound what so ever. I think I understand the concept but am not doing somthing correctly.

 

[Hyperion]

The first thing I notice... when setting the bias...
You do not need (and absolutely should not) turn the volume up, - turn it to minimum! - and disconnect the speakers.

Second thing
If you get no reading, and you are doing it the SM way - you may have a blown meter fuse. Which is why it is better to measure a voltage across the emitter resistors in mV, rather than (as the SM) a current reading in mA. But you have to know the mV reading for this amp, as converted from the 100mA bias current reading. I am afraid I have not looked at the schematic check what the voltage reading to give 100mA current reading is...

As Lee says - this amp is in a 'delicate' state and while checking to see if the bias adjusts, you should try this first on the DBT - remember to turn the pots to a minimum after checking that you get bias adjustment in this way - do not attempt to get 100mA (or mV equivalent) when on DBT ! - just check you get healthy adjustment.

 

[sansuibutch]

OK I realized why it wasn't reading. My fluke dmm I had to switch the positive lead for ma. My Klein I can leave the lead ther up to 400ma. Anyway I just checked it with the volume all the way down. With the pots all the ways down I'm getting around 1ma as I turn them up the left channel will reach 4ma and the right will get as high 3ma. And now them old readings make sense to me. Does this make any sense figuring the left channel sounds great?

 

[Overundr1]

I bet that the fluke blew the internal to the fluke ma protection fuse when you had the probes wrong. The readings from the Klein are waaaay off what you should see. Those ma readings should climb rapidly unless something else in the circuit is not right. Will have to dig up the schematic and figure out where the emitter test points are as mentioned a few posts back.

 

[sansuibutch]

I bet that the fluke blew the internal to the fluke ma protection fuse when you had the probes wrong. The readings from the Klein are waaaay off what you should see. Those ma readings should climb rapidly unless something else in the circuit is not right. Will have to dig up the schematic and figure out where the emitter test points are as mentioned a few posts back.

The fluke worked fine once I moved the + lead from the voltage port to the 300ma fused one. I have the schematic diagram but am not sure I can find the test points with it. I have a printed copy but it's not the clearest

 

[mroboto]

Didn't read all your thread, but some advices:

Keep the bias at 90mA if you want to keep it a little underbiased so he did not heat very much and when it heats, it levels up at 100 and+, but not too much, if you bias it at 100ma when unit is at 23°C , at 40°C it will easily tend to go up of a "wanted bias"..

AU-11000A is the same except 50mA or less, i would advice around 40-45mA for bias at room temperature for AU-11000A

Clic at the right of "Document joint" to see a full sized picture:

http://www.cjoint.com/c/FLFamyQm0fB

 

[sansuibutch]

Somebody mentioned bias control transistors on the driver board (Pretty sure it was Hyperion) . Can these cause my bias problem? if so would it be too weird to both have failed?

 

[Hyperion]

Somebody mentioned bias control transistors on the driver board (Pretty sure it was Hyperion) . Can these cause my bias problem? if so would it be too weird to both have failed?

Might have been me, yes a bit weird to have both fail, much much more likely are failed bias trimmers, I hope you have replaced yours?

 

[Overundr1]

Nice picture MR, often hard to describe in words what needs to be connected where and how in repair help threads, thanks.
-Lee

 

[sansuibutch]

Might have been me, yes a bit weird to have both fail, much much more likely are failed bias trimmers, I hope you have replaced yours?

I have not replaced them yet. The manual calls for 470ohm trimmers. I have some 500ohm ones on hand. They should be fine?

 

[Hyperion]

They should be fine?

Yep

 

[sansuibutch]

I ohmed out the trim pots and they work perfectly. I will change then but in the meantime I am about to submit a order to mouser for a few different things. Anyhow I can't seem to find the diodes somebody recomended I replace. This is the part number I was given (1n4148). When I search on mouser I get a bunch of different diodes and such. I allready received some that I ordered in a previous order that are tvs diodes and there not the right ones. These are for replacing the tiny ones that look like little balls with leads. Can anyone help me out picking the ones I need?

 

[Hyperion]

1N4148 is the correct type number of the diode that the vast majority on here use. To replace the small red and black 'ball' diodes of the kind you have (VD-1212 ?), just use 2 of the 1N4148's in series, have you seen this elsewhere on AK? - it is very commonly done - there must be hundreds of pictures of them on here.

 

[Overundr1]

A few questions sir. The two caps next to the vd1212 diodes are non polar caps, I cannot tell from your picture if you replaced them with non polar variants. The 4 8.2 ohm 1/2 watt resistors on each amplifier block are those nasty fuse-ables and need to be changed or setting bias will be next to impossible, finally the vd1212's if faulty will also upset the bias settings. I would not change out the trimmers just yet, as I mentioned in the rebuild I finished in another thread the originals are through hole back setting types and could make setting the bias a real chore if you replace them.

Just musing here, the ba-2000 is a traditional an amplifier design ( a very very good thing imho) and only amplifies a signal it is given, there is nothing that modifies that signal. So if you are getting a distorted output and have verified you have a clean input there are only a couple of places to look for the cause. The primary cause would be crossover distortion due to an under bias condition which you have found by the low bias setting and yes this will be audible as the finals crossover (switch) on and off. Also, with such a low bias increasing the gain (input level) will not change this behavior enough to remove the audible effects of that low bias. The other cause is in the volume potentiometers as they are the only mechanical connections in the entire audio chain.

 

[sansuibutch]

A few questions sir. The two caps next to the vd1212 diodes are non polar caps, I cannot tell from your picture if you replaced them with non polar variants. The 4 8.2 ohm 1/2 watt resistors on each amplifier block are those nasty fuse-ables and need to be changed or setting bias will be next to impossible, finally the vd1212's if faulty will also upset the bias settings. I would not change out the trimmers just yet, as I mentioned in the rebuild I finished in another thread the originals are through hole back setting types and could make setting the bias a real chore if you replace them.

Just musing here, the ba-2000 is a traditional an amplifier design ( a very very good thing imho) and only amplifies a signal it is given, there is nothing that modifies that signal. So if you are getting a distorted output and have verified you have a clean input there are only a couple of places to look for the cause. The primary cause would be crossover distortion due to an under bias condition which you have found by the low bias setting and yes this will be audible as the finals crossover (switch) on and off. Also, with such a low bias increasing the gain (input level) will not change this behavior enough to remove the audible effects of that low bias. The other cause is in the volume potentiometers as they are the only mechanical connections in the entire audio chain.

I cleaned and tested the volume pots and bias trimmers (they all passed). I replaced all the fusible resistors on the amplifier blocks and actually swapped the final stages to rule them out as a issue. The bias voltage on each channel is just about the same so I'd imagine both channels would be distorted? Yes the two capacitors you mentioned I did replace with non polar same values. I'm kind of at a loss here. I did order the predrivers and am waiting for them now

 

[sansuibutch]

A few questions sir. The two caps next to the vd1212 diodes are non polar caps, I cannot tell from your picture if you replaced them with non polar variants. The 4 8.2 ohm 1/2 watt resistors on each amplifier block are those nasty fuse-ables and need to be changed or setting bias will be next to impossible, finally the vd1212's if faulty will also upset the bias settings. I would not change out the trimmers just yet, as I mentioned in the rebuild I finished in another thread the originals are through hole back setting types and could make setting the bias a real chore if you replace them.

Just musing here, the ba-2000 is a traditional an amplifier design ( a very very good thing imho) and only amplifies a signal it is given, there is nothing that modifies that signal. So if you are getting a distorted output and have verified you have a clean input there are only a couple of places to look for the cause. The primary cause would be crossover distortion due to an under bias condition which you have found by the low bias setting and yes this will be audible as the finals crossover (switch) on and off. Also, with such a low bias increasing the gain (input level) will not change this behavior enough to remove the audible effects of that low bias. The other cause is in the volume potentiometers as they are the only mechanical connections in the entire audio chain.

I did replace the caps on the meter board with muse fg and panny fm. I figured since they were on the board with the potentiometers they would be in the signal path. Hope that wasn't a mistake but haven't fired it up since

 

[Overundr1]

General rule --- you are ok replacing polar with non polar caps, only caveat is typically non polar versions are larger and possibly will cause fitment issues.
Wish I had taken the time to measure mv across a pair of npn/pnp output resistors to give you a baseline voltage
Somewhere on AK there is a write up of this proceedure for an AU1100. Would give us a better picture of what is going on with the bias issue.

 

[sansuibutch]

1N4148 is the correct type number of the diode that the vast majority on here use. To replace the small red and black 'ball' diodes of the kind you have (VD-1212 ?), just use 2 of the 1N4148's in series, have you seen this elsewhere on AK? - it is very commonly done - there must be hundreds of pictures of them on here.

I have seem this done plenty ofor times.. my issue is when I'm on mouser and type in 1N4148 about 15 different diodes come up all with the same part number. I don't know which ones to order

 

[Overundr1]

512-1N4148

 

[sansuibutch]

512-1N4148

Thank you very much Sir