Brian,
I didn't offer matched devices (transistors) for the SYMASYM in the past.
What I offered was "hard-to-get" parts, like my favourite DC-blocking capacitor on the input, Vishay's MKT1822 / 10µF, or MPC74 0R22 / 5W resistors.
If you talk about matching the SYMASYM transistors: it is not as essential as you think.
I have once compared my own, highly-matched TO3-SYMASYM to a totally unmatched SYMASYM and could hardly hear any difference.
If you want to match transistors: go and use BJTs for the input differntial pair (f.e. MPSA18, if you do not use a Pre-AMP, or 2N5551, if you use a Pre-AMP)
and match them with your DMM.
Talking about the output-transistors: I recommend you to use NJW0281 / NJW0302.
The OnSemi NJW0 have a very small COB, and - this may answer your question: they have a very small Hfe deviation, when you buy them (from MOUSER for example).
I bought a bulk of 75 pcs. of each several months ago and matched them for some German DIY- friends.
The max. deviation within this bulk has been < 5%!
Best regards - Rudi_Ratlos
P.S. Have a look at my current SYMASYM-build (Post #515). I am using BJTs for the differential input pair.
I didn't offer matched devices (transistors) for the SYMASYM in the past.
What I offered was "hard-to-get" parts, like my favourite DC-blocking capacitor on the input, Vishay's MKT1822 / 10µF, or MPC74 0R22 / 5W resistors.
If you talk about matching the SYMASYM transistors: it is not as essential as you think.
I have once compared my own, highly-matched TO3-SYMASYM to a totally unmatched SYMASYM and could hardly hear any difference.
If you want to match transistors: go and use BJTs for the input differntial pair (f.e. MPSA18, if you do not use a Pre-AMP, or 2N5551, if you use a Pre-AMP)
and match them with your DMM.
Talking about the output-transistors: I recommend you to use NJW0281 / NJW0302.
The OnSemi NJW0 have a very small COB, and - this may answer your question: they have a very small Hfe deviation, when you buy them (from MOUSER for example).
I bought a bulk of 75 pcs. of each several months ago and matched them for some German DIY- friends.
The max. deviation within this bulk has been < 5%!
Best regards - Rudi_Ratlos
P.S. Have a look at my current SYMASYM-build (Post #515). I am using BJTs for the differential input pair.
Yes Mr. Rudi,, I,ve made a number of changes to the circuit..First change r20=22ohm +r19=22ohms change to 47 ohms. this change is good to 45vdc.above this voltage you should put a power diode in series with the resistor. Across the drivers a 100pf cap from base to collector gets rid of any nasty rf garbage. Sit back listen,,check your bias I set mine at about 60ma and adjust to find the sweet spot..ENJOY Regards Evette
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
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
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Carl,
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
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
