Layman's question for the pros - diyAudio
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 Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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 20th February 2015, 04:13 PM #1 diyAudio Member   Join Date: Dec 2008 Layman's question for the pros I have Adcom GFA-565 mono blocks that are rated 300w/8-ohms. They have a 27db gain. How many mv from my amplifiers RCA pre outs do I need to reach their full potentials? Thanks
 20th February 2015, 04:28 PM #2 diyAudio Member     Join Date: Dec 2012 Location: The Jurassic Coast, England. GB Here you are; 20*log(x) = 27dB X= voltage ratio output/input Therefore X = 31,7 Voltage required for 300W RMS into 8R ( P/R = I2 = approx 6.2A __________________ Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
 20th February 2015, 04:32 PM #3 diyAudio Member   Join Date: Mar 2014 Is half the calculation missing? I make it 1.5VRMS for peak output BTW. Last edited by billshurv; 20th February 2015 at 04:34 PM.
 20th February 2015, 05:16 PM #4 diyAudio Member     Join Date: Dec 2012 Location: The Jurassic Coast, England. GB 1.5V is correct. What does BTW mean? __________________ Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
 20th February 2015, 05:27 PM #5 diyAudio Member   Join Date: Dec 2008 Yes, please. I need calculations to the mv level. Though Jon's clarification is much appreciated, it's a long time since Mr. Planks maths class (also from England) . I require something at the mv level. I'm looking at the Onkyo NR838 with an RCA line out of 200mv but a Max line out of 480?
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Join Date: May 2007
Blog Entries: 3
Quote:
 Originally Posted by Lockport Yes, please. I need calculations to the mv level. Though Jon's clarification is much appreciated, it's a long time since Mr. Planks maths class (also from England) . I require something at the mv level. I'm looking at the Onkyo NR838 with an RCA line out of 200mv but a Max line out of 480?
That seems really low for that unit.

Oh, I see, the specs say "rated" and then "maximum" ...it's a little bizarre that the two numbers they give are so far apart..guessing though, I'd say you won't have any problem driving a 565 with it.

Edit: More strange specs on that sheet, evidently the tone controls operate at 20 hz and 20 khz.

Last edited by DrDyna; 20th February 2015 at 05:34 PM.

 20th February 2015, 06:01 PM #7 diyAudio Member   Join Date: Dec 2008 .BTW= by the way Ok, Rated RCA output and impedance 200mV/470 ohms Maximum RCA output level and impedance 4.6V/470 ohms Will I obtain my 300w rms at 8ohms with this amp?
 20th February 2015, 09:01 PM #8 diyAudio Member     Join Date: May 2007 Blog Entries: 3 I would say "probably", but the way they've worded the specs is very odd to me. 4.5V seems like a reasonable maximum output, but it's odd that they included a "rated output" that's what, like, 25x lower? So, the answer is, if the maximum unclipped output is 200mV, no. If the maximum unclipped output is 4.6V, yes.
 20th February 2015, 09:20 PM #9 diyAudio Member RIP   Join Date: Nov 2003 Location: Brighton UK Hi, My best guess is input sensistivity for line inputs is 200mV. And at full gain gives 4.6V. Output = 200mV = nonsense. rgds, sreten.
 20th February 2015, 09:36 PM #10 diyAudio Member   Join Date: Oct 2008 Location: Vancouver They may be saying that the diference is the head room of the amp, a little strange but makes sense.

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