Ba2000 right channel sounds very distorted

[Hyperion]

OK, have you checked R01 and R02 recently? they are 8.2 ohm resistors near TR01 and TR02 ? - please do check them.

I was only going to suggest changing TR23 (either swapping with TR24) or for 'new' - so only one replacement unless you want a spare?

Problem is Mouser is out of KSC1845 at present - to replace the other transistor.

 

[sansuibutch]

OK, have you checked R01 and R02 recently? they are 8.2 ohm resistors near TR01 and TR02 ? - please do check them.

I was only going to suggest changing TR23 (either swapping with TR24) or for 'new' - so only one replacement unless you want a spare?

Problem is Mouser is out of KSC1845 at present - to replace the other transistor.

R01 and r02 seem to 470kohms by the stripes on them. I didn't take them out of circuit but they don't read anywhere near 8 ohms. I'll take em out and check them. I saw that on mouser. I seen two variations of it also. I couldn't see much difference besides the casing.

 

[Hyperion]

Might be 4.7 ohms perhaps? - 470K is far too much - please measure them.

NB: TR01 and TR02 are 2 of the OP transistors - on the heatsink.

 

[sansuibutch]

Might be 4.7 ohms perhaps? - 470K is far too much - please measure them.

NB: TR01 and TR02 are 2 of the OP transistors - on the heatsink.

Oh okay, I thought you meant on the driver board . Yes the 8.2 ohm resistors were fusible if I can remember and I did replace them and just checked theme, they are all good. Looking over those I looked real close and I can see a gap in between the OP transistors and the heatsink. I didn't use a ton of thermal past but I thought it was plenty. Should I pull these out and use more? And if so are the mica's reusable? Seems the heatsinks are just not perfectly flat there

 

[Hyperion]

Were the mounting surfaces perfectly clean before you re-mounted the OP transistors, and you aren't using any washers except the mica ones - correct?

If everything was totally clean (no old compound) I am not sure what you can do about that except use bergquist pads which give me the impression that they might be better here, more white heatsink compound is not the answer. Yes, the mica washers can be re-used unless they are damaged, in which case they should be replaced. NB: FYI in case you didn't know you don't use bergquist pads AND mica washers - its either/OR.

Anyone else have any suggestions or comments about the above?

 

[mroboto]

I think only the rim have a gap, under the transistor, this might be tight.

 

[sansuibutch]

I think only the rim have a gap, under the transistor, this might be tight.

I cleaned it before hand, it was spotless whene I installed them. Just mica's, no washers. I understand how the paste works and rally don't know what to do here. I snugged them down decent and wouldn't say I over tightened theme by any means.

 

[sansuibutch]

Is there anywhere to source KSC1845? I see digikey has them but they have seven variations of it. I don't have a clue?

 

[Overundr1]

Had not noticed the scarcity of that low noise transistor
Anyways, Digikey only has one gain code of ksc1845 in stock with an hfe of 300. Will have to do, and will do fine in that part of the circuit. Gain codes become much more critical in tone and phono stage circuits.

 

[sansuibutch]

Had not noticed the scarcity of that low noise transistor
Anyways, Digikey only has one gain code of ksc1845 in stock with an hfe of 300. Will have to do, and will do fine in that part of the circuit. Gain codes become much more critical in tone and phono stage circuits.

Thank you ,I ordered a bunch. Hopefully they will be here soon

 

[sansuibutch]

So I replaced that transistor. Also the same one in the other channel. I made sure the bias trimmers where all the way down and hooked it up to some speakers. I fired it up and to my surprise and amazement I finally have clean sound on both channels. Later on is will check dc offset and go from there. I must admit it feels pretty good to hear clean music out of this thing. This amp has put me through some paces to say the least. Before I opened it I really didn't have any clue what I was doing . You guys are AWSOME!!!!!!!! thank you all so much for the help and advice

 

[Hyperion]

I think Lee, Overundr1 should take all the kudos here - he stuck with you by far the longest.

 

[Overundr1]

Almost home now, see if you can set the bias. Thanks John, long road warrior week last week for me.

 

[sansuibutch]

Lee did guide me through a lot of issues. I'm very happy he is so familiar with this amp and for the guidance. I thank you both very much for all the help. This is one of them times this line is very accurate ( I couldn't of done it without you guys). So I listened to this amp for about 20 mins before trying to set bias to heat is up. The amp won't get warm at all still and here are the ma readings I get turning the trimmers all the way down to all the way up

Right channel 4.69ma - 12.10ma
Lfet channel 4.61ma - 10.82ma

There pretty close to even so that's cool but still no way of getting it up to or even near 100ma. I knew these would still be low. More fun time. Any suggestions?

 

[Hyperion]

Those readings are encouraging - real progress, time to switch on 'ultra careful mode' and take it slow and easy. As you say Lee knows these units well - as he has one, usually the kind of readings you have there are caused by very low gain transistors, or wrong value or drifted value resistors.

I'll let Lee take it from there.

 

[Overundr1]

Yes, encouraging. Now its time to re-check your work on all the resistors you replaced. The circuit IS working, something is holding back voltage from reaching the adjusters, since both channels are showing the same error there is a duplicated error on both sides of the driver board. Here is a picture of my working board after I rebuilt it. Note, your amp will function fine with those low readings however there will be a measure of crossover distortion, perhaps inaudible but would bug me no end. If you post up your board in the next post we can eyes on the two looking for differences.
-Lee

 

[Overundr1]

Knew I saw this listing somewhere, thanks to Mroboto

http://audiokarma.org/forums/showpost.php?p=4889674&postcount=41

 

[Hyperion]

Those 'green' and same shape 'dark grey/black' transistors with tabs are 'UniWatt' types and are known to go low gain with age.

 

[sansuibutch]

Thats awsome. When I replaced the fusible resistors I followed Mroboto's link that you shared. I replaced all the uniwatt transitors also. Ignore the yellow circles

 

[sansuibutch]

These pics are so much clearer before I upload them