Q7 has same voltage on collector as well as emitter. Either tere is a short or the transistor is defective.
If in the process of assembling, if you had fitted any of the transistors wrongly and powered the circuit, then you should replace all of them if you do not remember which one.
Check whether the transistors are properly installed.
Gajanan Phadte
If in the process of assembling, if you had fitted any of the transistors wrongly and powered the circuit, then you should replace all of them if you do not remember which one.
Check whether the transistors are properly installed.
Gajanan Phadte
Q7 is shorted with a jumper for this test per Leach instructions.
I replaced Q8 and Q9. A slight change there as a result. I changed Q12 and Q22 a few days ago with no change. As you will see I do have some new voltage readings from today which may indicate that I am getting closer. Please take a look at the new chart.
I disconnected D5, D6, D7 & D8. Looks like we may be getting somewhere. I went digging through my parts drawers and could not find any replacements for D5 and D6. That is strange because I almost always buy more than I need of everything to save on shipping. So I researched the parts lists and I noticed that for the Superamp, Leach changed D5 & D6 from 1N4148 to 1N4934. I am wondering now if I have the wrong diode in there. The one I have in there look suspiciously similar to the 1n4148's that I have a bag full of.
Anyway, The voltages match better now side to side and the DC offset on the output is way down. Please take a look at the circled numbers. These are from the same board that was in red before.
Thanks, Terry
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Still4given, use the working side to chart things then your see where the fault lays..sometimes after working on things for hours it can drive us nuts and we can't see what's what... If the circuit asked for 3o ohm two 15 ohms or 10 and a 20 would have done the trick..
With the new colour bands it's easy to mistake a ohmage we've all done that one plus a quick check if need be. If you've still got the old lower powered amp use this one just to take voltages to aid getting round this problem.
Regards A.
With the new colour bands it's easy to mistake a ohmage we've all done that one plus a quick check if need be. If you've still got the old lower powered amp use this one just to take voltages to aid getting round this problem.
Regards A.
Just reading over your new posting there.. These amps can work well with short circuit protection if there for home use as there never see the hard life of pa work, I use in4007's for such circuits and these diodes are 1000v at 1amp but its up to the builder if they wish to use better spec ones...
Hey Amptech, thanks for stopping in. I have been working on this all morning. I went digging through some more parts drawers and find a new unopened package of the proper diodes for D7 and D8. I guess I bought the right parts but must have gotten confused when installing. I understand why Leach only gave the parts that were different from the Low TIM in the Superamp docs but it made things more confusing when you were trying to fit parts. In hind sight, I should have started with the parts that were different and then did the rest from the Low TIM docs but I think I just did them in numeric number and that turned out to be a bad decision.
Anyway I installed the proper parts and it is holding voltage and looks like everything is on. With this success, I replaced the parts in the other board and hooked it up. Nope, The voltages were not right. So I changed out Q8 & Q9 but no change. Then I changed out Q13 since it was so low. Still no change so I started checking around the board for what might be causing it ans all of a sudden everything came up to voltage. Not sure what caused it but I'm going to let it burn in for a while and see if it will hold.
I do still have the Low TIM. I listen to it often. It's a nice sounding amp. The only drawbacks to trying to use it for comparison is that for one thing it is built on Jen's PCB's and it is about 64V rails. It would be a lot of work for me to just chase down devices on the board.
Blessings, Terry
Anyway I installed the proper parts and it is holding voltage and looks like everything is on. With this success, I replaced the parts in the other board and hooked it up. Nope, The voltages were not right. So I changed out Q8 & Q9 but no change. Then I changed out Q13 since it was so low. Still no change so I started checking around the board for what might be causing it ans all of a sudden everything came up to voltage. Not sure what caused it but I'm going to let it burn in for a while and see if it will hold.
I do still have the Low TIM. I listen to it often. It's a nice sounding amp. The only drawbacks to trying to use it for comparison is that for one thing it is built on Jen's PCB's and it is about 64V rails. It would be a lot of work for me to just chase down devices on the board.
Blessings, Terry
It's funny you should mention that because I had a bag of 1N4004's and a bag of 1N4007's in my hand when I found the 1N4934's. I had looked them up on Mouser and saw that they were pretty close in values. There must be some reason Leach suggested the ones he did so I just used them.
I appreciate your help. Please keep checking in. I may not be out of the woods quite yet.
Blessings, Terry
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I actually did that the other day hoping that was the problem. I had tinned all the tracks back when I first populated the boards so it was fairly easy to do it again. Thanks for the suggestion, it is a good one.
Blessings
This reminds me of a amplifier board built in the 90's, it failed to set up correctly with odd ball voltages even with all fresh parts fitted it still acted up.
So I removed all components re-cleaned the board followed by drilling the holes out plus repopulated then all worked as it should.
Still things like this test our skills of deduction to track down problems till we the light at the end of the tunnel as lots of time has been put into things already and if we run in to such faults again we can use this encounter to speed things up.
So I removed all components re-cleaned the board followed by drilling the holes out plus repopulated then all worked as it should.
Still things like this test our skills of deduction to track down problems till we the light at the end of the tunnel as lots of time has been put into things already and if we run in to such faults again we can use this encounter to speed things up.
leach superamp
just to recap on the gennie/scope.. a dummy load would be handy for power testing but if you've not got one just scope the o/p and i/p.. set your genie to 1khz sine wave and set to say 1v ac out then link to the amp and using one channel to monitor this and use the second scope channel to check the o/p of the amp. The wave should be the same as the i/p also set your scope for high volts set some settings might be 20v and the t/div to say .2 you should see clean wave.
A power o/p test can done via slowly turning the amp level until it clips then back it of for clean sine wave top and bottom and measuring the ac o/p volts from the amp..
say you had 35 volts ac out into a 8 ohm load you then divide 35 by 8 = 4.375(amps) so amps times volts would power out. 35/8 =(4.375) amps then times this by 35=153w uncliped
just to recap on the gennie/scope.. a dummy load would be handy for power testing but if you've not got one just scope the o/p and i/p.. set your genie to 1khz sine wave and set to say 1v ac out then link to the amp and using one channel to monitor this and use the second scope channel to check the o/p of the amp. The wave should be the same as the i/p also set your scope for high volts set some settings might be 20v and the t/div to say .2 you should see clean wave.
A power o/p test can done via slowly turning the amp level until it clips then back it of for clean sine wave top and bottom and measuring the ac o/p volts from the amp..
say you had 35 volts ac out into a 8 ohm load you then divide 35 by 8 = 4.375(amps) so amps times volts would power out. 35/8 =(4.375) amps then times this by 35=153w uncliped
Thanks amptech. I'm sure that will become familiar once I get to hook it up.
For now, I'm still having problems with second board. I'm checking against the good one and I've got a couple of questions for those who know how transistors work, because I don't understand it. I have replaced Q9 three times and I'm still getting the same thing so I want to ask a couple of questions. One the good board, I see a rail voltage of 87.2v and 85.8 after R33. After R12 I see 84V and after R22 I see 85.7. After R24 I see 85.1 Now, is it the resistors causing the voltage drop or is Q9 part of that. I just pulled Q9 and Q13 on the bad board then tested. I'm not seeing any voltage drop across R22 or R12 which means the voltage is getting around them somehow but I can find it. When I check with an ohm meter from trace to trace, I see just the ohms I am supposed to see. I'm completely stumped on this one.
Thanks
For now, I'm still having problems with second board. I'm checking against the good one and I've got a couple of questions for those who know how transistors work, because I don't understand it. I have replaced Q9 three times and I'm still getting the same thing so I want to ask a couple of questions. One the good board, I see a rail voltage of 87.2v and 85.8 after R33. After R12 I see 84V and after R22 I see 85.7. After R24 I see 85.1 Now, is it the resistors causing the voltage drop or is Q9 part of that. I just pulled Q9 and Q13 on the bad board then tested. I'm not seeing any voltage drop across R22 or R12 which means the voltage is getting around them somehow but I can find it. When I check with an ohm meter from trace to trace, I see just the ohms I am supposed to see. I'm completely stumped on this one.
Thanks
you can't power up the boards with missing trannies, that is simply not done..
but you can pull out Q9 AND Q8 for now, they form part of signal clipping limiting the VAS currents, the VAS is set around 5mA on the super leach.
just like the output SOA protection circuit, the amp will work even without them...
Well, I used that term loosely. I don't know for sure if it's good yet. At least the voltages are fairly even from side to side. I have been tempted to hook up the output trannies and give it a try, but my scope probes should be here any day and I really want to get the boards right first. I kinda need the "good" board for referance while I work on getting the second right. What is really weird is that the second board worked right for a few minutes and then stopped.
That's why I was hoping someone who knows transistors can help me understand how these different voltages are arrived at. If I knew that it would be a lot easier to figure out what is out of line.
i never used scopes to test my amps, never had one before, but now i have 3 of those so no more excuses for me...
but you can still make your amp work even without a scope, i built dozens of amps without scopes..
i used a Heatkit function generator, and 8 ohm dummy loads....
with everything connected, you should have no more than +-100mV output offset voltage, then you should be able to adjust bias voltage, these are two indicators that your amp is good, you can play music hence...anything less than these and you got problems...
problems can be wrong orientation of trannies, wrong trannies stuffed into the wrong spot, wires soldered in the wrong pads, or even poor soldering....
you are the one holding your boards, you are in the best position to make that thing work...
we can only give you clues....
if you followed the construction to the letter, you can get that to work the first time....
but you can still make your amp work even without a scope, i built dozens of amps without scopes..
i used a Heatkit function generator, and 8 ohm dummy loads....
with everything connected, you should have no more than +-100mV output offset voltage, then you should be able to adjust bias voltage, these are two indicators that your amp is good, you can play music hence...anything less than these and you got problems...
problems can be wrong orientation of trannies, wrong trannies stuffed into the wrong spot, wires soldered in the wrong pads, or even poor soldering....
you are the one holding your boards, you are in the best position to make that thing work...
we can only give you clues....
if you followed the construction to the letter, you can get that to work the first time....
The only other guys in my world who do DIY audio are you guys.
I built six amps, well really 7 but one played but never made it into an inclosure. It is still mounted to a pair of heatsinks. A couple of them had small issues that I worked out with help. This Superamp never made music. If you search back you can find the threads where we tried to get it going but I got tired of messing with it because I wanted to build another amp so it got set aside. I have a lot of time and money invested in this amp so I really would love to get it working.
I spent all day today fooling around with it. I have swapped out diodes, resistors,& transistors. I re-tinned all the traces and went over all of the traces very closely to look for solder bridges. The last time I powered it up I was able to get Q11&12 pretty close in voltage but now I have a huge offset on the output. Enough for today. I will look at it again tomorrow. I'm out of the TO-39 devices. I'd like to get enough to replace all of them. Probably not the problem but at least I could eliminate that.
Blessings, Terry
I built six amps, well really 7 but one played but never made it into an inclosure. It is still mounted to a pair of heatsinks. A couple of them had small issues that I worked out with help. This Superamp never made music. If you search back you can find the threads where we tried to get it going but I got tired of messing with it because I wanted to build another amp so it got set aside. I have a lot of time and money invested in this amp so I really would love to get it working.
I spent all day today fooling around with it. I have swapped out diodes, resistors,& transistors. I re-tinned all the traces and went over all of the traces very closely to look for solder bridges. The last time I powered it up I was able to get Q11&12 pretty close in voltage but now I have a huge offset on the output. Enough for today. I will look at it again tomorrow. I'm out of the TO-39 devices. I'd like to get enough to replace all of them. Probably not the problem but at least I could eliminate that.
Blessings, Terry
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