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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: Cap coupling vs. direct coupling on vintage SS receivers posted by postjob62 on July 17, 2005 at 17:43:32:
Most of what has been posted so far is spot on-with one exception. Amplifiers with direct coupled outputs and those that are DC coupled, are not necessarily the same thing. DC coupled means that a DC voltage applied to the input will result in a voltage at the output. Direct coupled only means that the output stage does not have a coupling cap, so the output transistors are directly coupled to the load. But it can have caps elsewhere in the signal path. Even in a DC coupled amp, it's important to have an input coupling cap to prevent DC offsets from DC voltages at the input. Several amps that claim DC coupled have an input coupling cap. I guess they mean that after you get past the input cap, there are no other caps in the signal path. There are also solid state amps that have interstage ttransformers or output transformers. These behave differently than capacitively coupled amps, but cannot be called DC coupled, even though they lack coupling caps.How do you tell one? Unless the owner's manual is specific about it, or you have a schematic and can read one; you have to rely on other clues. While not 100% true, most amps that have + & - power supplies are direct coupled. Most DC coupled amps have it in the model number.
In vintage gear, if you lift the cover, look at the power supply caps. If there are two with moderate voltage ratings (35-56 volts) the amp is probably direct coupled. If there is one large cap with a 60-80 volt rating, it's an indication of a single ended power supply and the amp has to be capacitor coupled. There should also be a smaller cap in the 1-2000 uF range and a similar voltage rating for each channel. There are lots of variations on this theme, so all are just rule of thumb guidelines.I suppose, if you are in doubt, post here and ask for help.
Jerry
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Follow Ups
- Re: Cap coupling vs. direct coupling on vintage SS receivers - Bold Eagle 07/18/0517:23:26 07/18/05 (0)
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