dolbyscat Posted May 4, 2005 Share Posted May 4, 2005 I have a Marantz 1152dc amp,on the rear is a switch for a/c or d/c,can anybody educate me on the need or use of this function.I have switched it and can hear no audible difference.thanx. Quote Link to comment Share on other sites More sharing options...
markus111 Posted May 4, 2005 Share Posted May 4, 2005 As I remember, this was a fad for a couple of years where they advertised direct coupled output. Don't quote me on this, but I believe it let them advertise that the response was DC (zero Hz) to 30khz, or something ridiculous like that. I remember having a discussion with a pretty knowledgable Marantz guy who said there are times when you shouldn't use it, and it really doesn't have any benefit sonically. He recommended leaving it off all the time. Mark Quote Link to comment Share on other sites More sharing options...
markus111 Posted May 4, 2005 Share Posted May 4, 2005 Sorry - off meaning leave it on a/c. Mark Quote Link to comment Share on other sites More sharing options...
dolbyscat Posted May 4, 2005 Author Share Posted May 4, 2005 Thanks Mark,i'll just carry on ignoring it 'till someone tells me different. Quote Link to comment Share on other sites More sharing options...
PrestonTom Posted May 5, 2005 Share Posted May 5, 2005 This is curious. If what Mark is remembering is correct, then a DC switch could be a real hot potato. On electronic measurment equipment (o'scopes) and sometimes wave generators and filters there is frequently an otption for coupling the input or output. AC coupled effectively removes any DC component (a non alternating current or biasing voltage). If that is what this switch is doing, I have no idea why they would ever think of providing such an option on home audio (I would be curious to know). Normally the source and preamp would not be sending DC so there would no reason to amplify it (unless there was a microphone preamp that was sending a biasing voltage - although I imagine that would be through a different wire). The reason it could be a hot potato is that if there were ever a glitch you would not want to send much DC to a speaker - this would be a bad thing! Perhaps it was meant for some kind of an electrostatic speaker?? I am curious about this one. -Tom Quote Link to comment Share on other sites More sharing options...
Mark Hardy Posted May 5, 2005 Share Posted May 5, 2005 Interestingly: in this context "DC" means both Direct Current and Direct Coupled. The "AC" position will presumably insert a DC blocking capacitor into the output. "DC" will bypass the cap and direct couple the outputs to the speakers. The theory is that the LF response will be better (flatter) and there'll be little or now LF phase shift in the absence of an output cap. The "problem" with direct coupling is: if anything goes wrong in the amp (esp. the output stage) and there's no (or insufficient) protective circuit to stop it, DC voltage will be present on one or both outputs, with frequently disastrous results for the speakers' voice coil(s). Ask me how I know this! :-( Quote Link to comment Share on other sites More sharing options...
markus111 Posted May 5, 2005 Share Posted May 5, 2005 ---------------- On 5/5/2005 10:44:52 AM Mark Hardy wrote: Ask me how I know this! :-( ---------------- Boy, that is a drag! I thought that's what I remembered. It probably sounded great in their marketing hype - until the phones started burning off the hook. I wonder how many voice coils they fried before they pulled this from the market? Seems I remember this option from several of the manufacturers during that time. I wish I could remember what "that time" was. Was it 1982 - 1984? A mind is a terrible thing to lose........ Mark Quote Link to comment Share on other sites More sharing options...
Mark Hardy Posted May 6, 2005 Share Posted May 6, 2005 Here is a really poor scan from the contemporary Marantz full line brochure (unfortunately a small, almost pocket-sized pamphlet) showing the 1152 and another similar Marantz amp. Quote Link to comment Share on other sites More sharing options...
djk Posted May 7, 2005 Share Posted May 7, 2005 The caps in question are on the amplifier input, and not the speaker output. For testing purposes the caps are bypassed so squarewave tests do not have 'tilt' to them. Quote Link to comment Share on other sites More sharing options...
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