SymAsym - "The Sequel", AAK's Rev_1.4 PCB Builders Thread

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#101
The amp is running fine for a couple of days now, getting pretty warm though.

No turn-on thumb or whatsoever.

The only annoying thing is the crackling sound from the speakers as the caps of the amp discharge on turn of.

I used the search function but could not find some having build a simple relay-solution for shorting the outputs on turn-off.

I don't wat to go for the Velleman solution as I need 4 of them and the price tag is a bit high, at least for me.

Any hints ?
 
#108
Version 1.3 questions

I bought 6 (and rec'd 12) of the version 1.3 amp quite some time ago. I have now returned to the project having completed all the boards(except for output transistors on 4) I have tested the 8 boards which are complete (complete with dim bulb tester).

The bad news is 3 failed the smoke test. The somewhat better news is that the other 5 all passed the smoke test (all 8 board display the correct rail voltages of +/- 52.3 V which is inline with noload conditions for a 35-0-35 transformer I'm using). Testing the 5 boards with the 100R safety resister inplace I measured voltage drops accross this resistor ranging from 1.4V tp 1.7V. The assembly manual for version 1.4 indicates this drop should be 2.5-3.5V. Should the voltage drop for version 1.3 be the same or, if not, what should it be (and do I have an issue with the 5 smoke free boards)?

Thanks,
SteveA
 
#109
"Hi SteveA, chalkandtalk,

Let me know what happens on the boards that are measuring less than 2.0V across the safety resistors if you turn pot R36 clockwise. Make sure to do it slowly. It may take several turns before you see any change. Does the voltage across the 100 ohm resistors stay the same or does it increase? If it increases make sure to keep it below 3.5V so that resistors don't over heat.

Lets continue this discussion on the Rev_1.4 builders thread here.

SymAsym - "The Sequel", AAK's Rev_1.4 PCB Builders Thread

Thanks!

Al"

I have Rev1.3 boards so I turned pot R22 clockwise (on boards with ~1.5B drops across the 100R safety resistor) and smoked the resistors. FWIW I am working from the attached BOM
 

Attachments

#111
AAK said:
That's an old BOM going back to 2007. It's for my original single transistor amp PCB. The transistors are labeled using U's not Q's like in Rev_1.3 and Rev_1.4. Are you sure you have Rev_1.3 boards? Attached is the correct BOM for Rev_1.3.

Al
Click to expand...

I must have the "old BOM boards" since it was 2007 when I bought the boards. I stuffed the boards, to a point, and they sat until recently. I completed them; started testing after finding the Rev1.4 assembly guide. That's where I stand now with eight boards, three of which smoked the saftey resistors initially and five which gave the 1.4-1.7 V drop. When advancing R22(orientation correct when compared to pic's of boards on builders thread and turned fully counterclockwise) the safety resistors smoked.



Thanks for the response.
 
Last edited:
#113
AAK said:
The Rev_1.3, and Rev_1.4 designs are completely different. The version you have is based on MiKeB's original 5.3 design.

The BOM you attached must be from an earlier version because driver transistors U5, and U6 are wrong. U5 should be the 2SA1837, and U6 should be the 2SC4793. Switching them should fix the problem.

Al
Click to expand...

Sounds good, I'll do that. Should I still use 100R safety resistor and look for the same voltage drop?
Thanks again.
SteveA
 
#119
Hi Al

It's good to talk to you again. The 5.3 symasym amps from earlier are still working very well. They are great amps. I have recently built an active crossover and have 4 of the amps in action. Now like to get a 100W version driving the woofers.

Thanks for your help here.

When I turn the pot nothing happens. The voltages across the 100ohm resistors stay constant at 2V and 1.5V. Offset stays at about 150mV 😱. I have replaced Q18, Q19, Q20 and Q21.

regards

Aidan
 
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