Function of AC-DC mode of Yahama M4 amp?
- Thread starter klxdrt
- Start date
Sandstrom
Seldom turns out the way it does in the song
It's my understanding that AC means capacitor coupled outputs and DC is direct (bypassing the capacitors) and possibly riskier to your speakers if something goes south in the amp. I'm am sure someone more knowledgeable than I will chime in soon...
onplane
What! No Wake???
Yes, that switch controls how the input is handled. When DC is selected, the input is routed directly to the amp. When AC is selected a blocking cap is put in series with the input to the amp.
The recommended position is DC, unless very low frequency turntable warp, wow or rumble begins to cause problems with your speakers. In this case, you should select AC and that cap will block those very low frequencies.
Regards,
Jerry
The recommended position is DC, unless very low frequency turntable warp, wow or rumble begins to cause problems with your speakers. In this case, you should select AC and that cap will block those very low frequencies.
Regards,
Jerry
pdm4606
Super Member
In other words the AC position is a high pass filter allowing the higher frequencies to pass while preventing the lower frequencies from entering the amplifier circuits.
Why not just call it a low pass/high pass or a rumble filter or a low filter???
Other Yamaha equipment has it clearly labeled as in my C-50 preamps as a "sub sonic /15hz" filter.
Why not just call it a low pass/high pass or a rumble filter or a low filter???
Other Yamaha equipment has it clearly labeled as in my C-50 preamps as a "sub sonic /15hz" filter.
onplane
What! No Wake???
Well, I wouldn't exactly call it a "high pass filter". After all, it's only a cap.
Your C-50 might actually have a 1st or 2nd order filter. I wouldn't know unless I looked at the circuit.
One thing that I just thought about is that cap might be a very good idea for those that use tube pre-amps. Tube amps have such high voltages that when warming up could expose the power amp to a significant voltage surge. If I had a tube pre-amp, I'd select the AC position.
Regards,
Jerry
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Usually there is a small value capacitor on each channel at the input of an amplifier board between the preamp stage and amp stage. Some manufacturers just put the cap in and leave it at that. Yamaha, Sony and a few others offered the choice to swith between coupled and direct on a few models. I have an early Sony direct coupled power amp with this feature. In the Sony manual it stated DC mode is to be used for test purposes only and to normally run it in AC mode.
toxcrusadr
Omelette au Fromage
My Sansui AU-517 has a switch like that on the back that selects direct or cap coupling between pre and power stages. I never really looked up the manual to see how it should be set. It's a cheap switch and will drop a channel, so the only time I mess with it is to jiggle it when that happens. I should look that up. 
stereoguy70
Well-Known Member
Yamaha put it there for when you really need to rock out!
Sorry, I couldn't resist! I figured someone was going to go there eventually,, so why not?
toxcrusadr
Omelette au Fromage
If there is a "TNT" switch back there, do not use THAT unless you are REALLY ready to Rock Out. 
whoaru99
Epic Member
It is indeed a high pass filter, despite being just a cap.
It's indicated at 10Hz.
Frankly, unless one has some super-duper speakers that dig to subterranean frequencies AND the sys op plays music that actually has that low of content, it's probably just as well to leave the setting on AC.
