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Rudi_Ratlos 6th October 2012 09:52 PM

Carl, the metal back of the MJE - drivers is connected to the collector of the drivers!
You must therefore completely isolate the drivers from the ALU - L- profile.

Best regards - Rudi_Ratlos

cjkpkg 6th October 2012 10:28 PM

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Rudi_Ratlos 6th October 2012 10:44 PM

Carl, you can use a shrinking-hose, a polyamide-screw, ...:D

Best regards - Rudi_Ratlos

cjkpkg 7th October 2012 01:08 PM

1 Attachment(s)
progress....boards are stuffed and L profiles are tapped. need to get some small screws to mount the mje's.

Rudi_Ratlos 9th October 2012 10:46 PM

2 Attachment(s)
Carl, I received the ordered thermally conductive foil this morning and finished the 1st channel of my SYMASYM.

I adjusted the quiescent current / bias to 26mV voltage drop across 2 emitter resistors (between MP1 and MP2).

The DC offset is very, very small (< 1mV).

I tested the channel using a 8 Ohm / 80W resistor and played back some sine and square-wave tracks at 16 VAC amplitude. No problem.

If I have some time tomorrow (but I believe that I will receive the FC-100 group-buy PCBs in the morning), I will try and finish the 2nd channel.

What about your build?

Best regards - Rudi_Ratlos

cjkpkg 11th October 2012 09:49 PM


I have been traveling for work a lot lately and have not done much this week.

I received my TO-220 mounting hardware with the shoulder washers today so maybe this weekend I will make some good progress.

brianco 11th October 2012 10:40 PM


Nice pics as usual. The cleanliness and tidiness of your workbench is frightening......but you have the saving human grace of smoking AND of being not very careful with the cigarette!:)

cjkpkg 13th October 2012 04:52 PM

If I am using a preamp do I put a jumper wire across the jumpers or not?

there is an excerpt in the manual that is confusing as to whether the cap multiplier is enabled with the use of a jumper or not.

By jumper I mean soldering a wire across the jumper.

Rudi_Ratlos 13th October 2012 07:11 PM

1 Attachment(s)

you are talking about 2 different things.
I explained in post #450 what to do (which resistor values to use), in case you connect the SYMASYM to a pre-amplifier.

The cap-multiplier has nothing to do with this. It simply "smoothes" the power-rail for the frontend.
If you do not want to have it this way, just put a shorting bar across Jumper 1 + 2.

Best regards - Rudi

cjkpkg 13th October 2012 08:54 PM

OK got it all wired up. One channel checks out and the other channel goes runaway.

One thing I forgot to insulate the bd139. If I fried one of them would that cause a runaway as in the potentiometer does nothing and I measured up to 900 mv before I was able to switch it off.


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