Hi guys,
Well, this morning I decided to replace Q10 and Q11. I had recently replaced them but everything just seemed to point that way. So anyway, I swapped them out and now the little oscillation that was there is gone. Somewhere along this journey of poking and probing I must have hurt one of them. It is playing music right now and sounds quite nice. I still have about 40mv offset on that channel. I probably wouldn't think anything about it except the other channel has 000.3mv. Sure would like to figure out how to fix that.
Thanks again for all your help. You got me pointed in the right direction.
Blessings, Terry
D
EDIT: Hi Bob, you and I must have been typing at the same time. You were right on as usual. Great to see you again!
Well, this morning I decided to replace Q10 and Q11. I had recently replaced them but everything just seemed to point that way. So anyway, I swapped them out and now the little oscillation that was there is gone. Somewhere along this journey of poking and probing I must have hurt one of them. It is playing music right now and sounds quite nice. I still have about 40mv offset on that channel. I probably wouldn't think anything about it except the other channel has 000.3mv. Sure would like to figure out how to fix that.
Thanks again for all your help. You got me pointed in the right direction.
Blessings, Terry
D
EDIT: Hi Bob, you and I must have been typing at the same time. You were right on as usual. Great to see you again!
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offset at 64vdc? that will make the speaker hum and burn....remove the v limiter for now and redo measurement... I would say your under side traces are looking a tad messy or even piling by now due to so much reworking..
There are ways to solve the offset voltage problem one being selective tail pairs or even adding a trim pot within the tail pairs for zero offset there are many circuits that have this in and it's main duty is to balance the tail transistors.
Good to see things are getting there.
Good to see things are getting there.
Still,
Congrats on getting to the bottom of this! It would be interesting if you could test the bad transistor and see how it had failed...e.g. which junction(s) open or shorted.
Congrats on getting to the bottom of this! It would be interesting if you could test the bad transistor and see how it had failed...e.g. which junction(s) open or shorted.
Anything under 100 mv is good. So, unless you are going to try to match yourself a set of input devices, the one remaining question is:
How does it sound?
How does it sound?
I did try to match Q1-4. I had 25 of each. The PNP's were easy to match against each other as well as the NPN's against each other but the PNP's were all in the 260 - 290mv range and the NPN's were between 340 and 370mv.
So I used the highest value match of the PNP's and the lowest value match for the NPN's. This was his third choice.
It has been playing for about two hours now and it really does sound very nice. I have played some Jazz, Blues and Country through it and they are all well represented. Sounds similar to the Low TIM with maybe just a slight edge on the low end. Not bad considering it is all open laying on a table.
So I used the highest value match of the PNP's and the lowest value match for the NPN's. This was his third choice.
It has been playing for about two hours now and it really does sound very nice. I have played some Jazz, Blues and Country through it and they are all well represented. Sounds similar to the Low TIM with maybe just a slight edge on the low end. Not bad considering it is all open laying on a table.
Now to re-jog the memory.. resistors incorrect value then swapping out devices to the last part of vI limiter transistor and all is good to go...
We've all helped out with many comments to help solve the superleach amplifier problems..
Regards A.
We've all helped out with many comments to help solve the superleach amplifier problems..
Regards A.
Oh my, I can't even tell you how helpful all of you have been. This amp sat on a shelf for almost 8 years and that was after many trials and errors. I can't tell you how good it feels to finally have it playing music.
Tomorrow, I will sit down with it and take voltage readings for all the pertinent spots and add them to a schematic so the next guy who goes to build one of these will have them at his disposal. Hopefully the two threads will be of some help too.
If there weren't so many other amps I would like to build, I would etch some more boards and do it again so it would be more sanitary.
Thanks again to all of you who have helped.
Blessings, Terry
Tomorrow, I will sit down with it and take voltage readings for all the pertinent spots and add them to a schematic so the next guy who goes to build one of these will have them at his disposal. Hopefully the two threads will be of some help too.
If there weren't so many other amps I would like to build, I would etch some more boards and do it again so it would be more sanitary.
Thanks again to all of you who have helped.
Blessings, Terry
There's light at the end of the tunnel and there's plenty of amplifiers out there that have pushed us all to the limits so we battle on to the end that's what engineering is all about.
Expect the matching of Q1 to Q4, the matching of V D13+D14 and V D15+D16 can affect the output offset also.
John
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