Doh! It’s All in My Head is right!
My apologies, C6 and C7 *are* the bypass caps and they are optional in the standard build. Ignore my reference to C5, sorry about that!
C5 is a 5pf cap and it is definitely required, probably for HF extension/trimming and such.
More coffee needed!
Best,
Anand.
My apologies, C6 and C7 *are* the bypass caps and they are optional in the standard build. Ignore my reference to C5, sorry about that!
C5 is a 5pf cap and it is definitely required, probably for HF extension/trimming and such.
More coffee needed!
Best,
Anand.
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At the risk of asking a silly question - is there a need to have the chassis assembled when testing amp boards? I only ask since I had the build splayed to test amp boards, but ostensibly there is nothing ground the heatsinks to chassis in that scenario save the GND to PSU board.
Furthermore, I just checked continuity and resistance across the various points, and all checks out. The only behavior that seemed off/inconsistent was the following - lets call it "right channel" amp board, when testing continuity from V+ to chassis, I get closed (0R) then it begins rise in resistance till eventually 0L. This takes about 3-5 seconds to take place. On the "left" channel I get continuity between V+ and chassis gnd, but it remains ar 0R.
Again, just sort of doing a dummy check and working through the more obvious culprits.
Furthermore, I just checked continuity and resistance across the various points, and all checks out. The only behavior that seemed off/inconsistent was the following - lets call it "right channel" amp board, when testing continuity from V+ to chassis, I get closed (0R) then it begins rise in resistance till eventually 0L. This takes about 3-5 seconds to take place. On the "left" channel I get continuity between V+ and chassis gnd, but it remains ar 0R.
Again, just sort of doing a dummy check and working through the more obvious culprits.
Your heat sinks need not be earthed for the amplifier to work. Only for safety reasons.
As long as both amp PCBs are grounded to power ground, and both have their respective +ve and -ve rail voltages connected, you should be able to bias it correctly.
BTW, have you tested to make sure you have no continuity from any of the MOSFET legs to the heatsinks?
As long as both amp PCBs are grounded to power ground, and both have their respective +ve and -ve rail voltages connected, you should be able to bias it correctly.
BTW, have you tested to make sure you have no continuity from any of the MOSFET legs to the heatsinks?
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Thank you for clarifying - yes I did just recheck all of those and no continuity across any of the the mosfets to heatsink. I ended up using ceramic pads so there is a nice margin there.
Other than that I am just waiting to set Q3, R13 and R14 back in place (already popped C1 in there) and just going over the board over and over. Dont entirely understand how the CL60 between chassis and earth functions, but wondering to what extent this is a startup current symptom. That being said, it shouldnt be completely frying that CL60 as easily as it did.
Other than that I am just waiting to set Q3, R13 and R14 back in place (already popped C1 in there) and just going over the board over and over. Dont entirely understand how the CL60 between chassis and earth functions, but wondering to what extent this is a startup current symptom. That being said, it shouldnt be completely frying that CL60 as easily as it did.
It indicates that you have probably a very low resistance through your circuit from any of the rail voltages to power ground. Temporarily remove that CL-60 and see what voltage you read at your power ground. You can also connect your amp meter in place of the CL-60 to confirm the amount of amps going through that CL-60.
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Thank you will try this tonight.
Is it possible there is no problem with construction save that the CL60 Is underrated for startup needs?
Additionally is there any chance something is off with PSU that does not present itself when powered independently until it’s feeding amp boards?
Thanks Again
For what it's worth my next build is going to be monoblocks in separate chassis, but if I were starting again I'd build one dual psu and then the M2x, AJ, USSA-5
etc in separate cases, and save a small fortune.
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Davidjt....good point....wise!
6L6....I’m leaning that way.
I think at some point I would sell - so I think all in one, whether mono or all-in-one, would be easiest for the next person. I usually build separate power supplies for tube gear but those are pretty specific to each amp/preamp. This SS gear is much easier using a single PS to experiment with....thanks for your feedback.
6L6....I’m leaning that way.
I think at some point I would sell - so I think all in one, whether mono or all-in-one, would be easiest for the next person. I usually build separate power supplies for tube gear but those are pretty specific to each amp/preamp. This SS gear is much easier using a single PS to experiment with....thanks for your feedback.
That's what I'm doing with my build. Just finished the dual PSUs and should be testing those shortly. Then I'll put the boards on the heatsinks and start biasing checks.
New Aleph J builder from Wisconsin, USA
Alright folks, doing some digging here, hopefully someone can help me read the tea leaves:
Good news - one channel is flawless. So we can table that and we have it as a good comparison for the other. The bad news is the other channel still makes the bulb glow bright. I began by checking all the solder points, etc, etc, etc. All good across the board.
Now, I went ahead and took as many measurements as I could imagine and compared them with the good channel. Unfortunately not too much here, but this is what I've got in terms of discrepancies, which is not to say that it's enough to be sure: All of these were taken in situ
Reading across the R7 in bad channel - is about 1K ohms, (reading of pot off the board was .996K ohms. In the Good channel, it reads about 100R.
Reading from the Emitter of Q3, to R12 or R11 in the bad channel, gets me about 1R, in the good one someting closer to 70R.
My current candidate for busted is Q1A - the resistances and "transistor setting" on Multimeter matches dead on with the good channel.
Any insights or ideas? Specifics to check?
BTW, with bulb in line - I took some voltages on the bad channel - Across R7 is good @ around 4.3V, and across R8 good at about 8.3V, and 4.26V between R10 and R17.
The diode and/or FETS are the most logical culprits but anyhow, advice is welcome on how to proceed from here.
Good news - one channel is flawless. So we can table that and we have it as a good comparison for the other. The bad news is the other channel still makes the bulb glow bright. I began by checking all the solder points, etc, etc, etc. All good across the board.
Now, I went ahead and took as many measurements as I could imagine and compared them with the good channel. Unfortunately not too much here, but this is what I've got in terms of discrepancies, which is not to say that it's enough to be sure: All of these were taken in situ
Reading across the R7 in bad channel - is about 1K ohms, (reading of pot off the board was .996K ohms. In the Good channel, it reads about 100R.
Reading from the Emitter of Q3, to R12 or R11 in the bad channel, gets me about 1R, in the good one someting closer to 70R.
My current candidate for busted is Q1A - the resistances and "transistor setting" on Multimeter matches dead on with the good channel.
Any insights or ideas? Specifics to check?
BTW, with bulb in line - I took some voltages on the bad channel - Across R7 is good @ around 4.3V, and across R8 good at about 8.3V, and 4.26V between R10 and R17.
The diode and/or FETS are the most logical culprits but anyhow, advice is welcome on how to proceed from here.
Hi,
Please help! I am testing the boards and one has a serious problem and the other is good and sounds great with music.
For the problem board, the speaker output voltage is 19.5v and varies little if I adjust the offset pot. The biase measure at 0.000v and doesn't change at all when changing the bias pot (R27).
Things I have done:
I build and tested the PSU first, and this works fine with expected voltages to both outputs.
When adding the transistors to the heat sinks, I tested for continuity and there was none. I have done this again after finding the problem, and again they are isolated and no continuity.
I have checked to see if the boards transistors are all the correct way round, and they are.
I have compared the problem board with the working board and see no difference.
I build both boards at the same time, putting in the same components at the same time for both and checking the values of all the resistors before using them.
What could be causing this problem and how potentially can I fix it?
Please help! I am testing the boards and one has a serious problem and the other is good and sounds great with music.
For the problem board, the speaker output voltage is 19.5v and varies little if I adjust the offset pot. The biase measure at 0.000v and doesn't change at all when changing the bias pot (R27).
Things I have done:
I build and tested the PSU first, and this works fine with expected voltages to both outputs.
When adding the transistors to the heat sinks, I tested for continuity and there was none. I have done this again after finding the problem, and again they are isolated and no continuity.
I have checked to see if the boards transistors are all the correct way round, and they are.
I have compared the problem board with the working board and see no difference.
I build both boards at the same time, putting in the same components at the same time for both and checking the values of all the resistors before using them.
What could be causing this problem and how potentially can I fix it?