Layman's question for the pros

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
L

Lockport

Member
Joined 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?
 
DrDyna

DrDyna

Member
Joined 2007
Lockport said:
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?
Click to expand...

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:
DrDyna

DrDyna

Member
Joined 2007
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.
 
L

Lockport

Member
Joined 2008
At present I'm using a Sony STR-DG1000's front preamp outs to drive the Adcoms and they are rated at 2v/1 kohms and the presence of the mono blocks is non-existent. I've heard these amps driven through a laptop computer headphone out and they were stunning. They painted an audio landscape with sounds on albums I've listened to for years that I never even noticed before. The control exercised upon the drivers with remarkable clarity and once reconnected to the Sony it was, to say the least, dismal. Did I mention each amp has its own 15A arc protected circuit from the loadcenter through a surgical grade 75lbs clamping rated wall socket?

What's the end result then, albeit meaning, of the rating 200mv/470ohms vs 200mv/1kohm?
 
P

PLB

Member
Joined 2008
Hi Lockport,

Using the following equation, Vrms = SQR(W*R) shows that you will require 48.99Vrms across the speaker terminals to produce 300W into 8 ohms.
The linear gain of the amplifier can be derived by using the following equation, 10^(X/20), where X = the dB gain of your amplifier. From your data the linear gain is therefore 22.39.
Therefore the voltage required at the input of your amplifier for an output of 300W into 8 ohm will be 48.99Vrms/22.39 = 2.19Vrms which = 2190mVrms.
Any reasonable quality pre-amplifier should be able to provide this output level.

Regards

Peter
 
A

AndrewT

R.I.P.
Joined 2004
Plb is correct.

using a calculator:
Gain = inv log (dBgain/20)
Most calculators allow the dBgain/20 to be done first with an equals to reveal the answer and then type inv, then log, then equals.

BTW,
2190mVac is roughly the maximum output of a Compact Disc Player (CDP) and many other digital sources.
i.e. most digital sources can drive the amp into clipping = too loud.
 
Last edited:
A

AndrewT

R.I.P.
Joined 2004
the source resistance.impedance acts as the first part of an attenuator.
For the wideband signal feeding the typical 47K of Rin.
the attenuation is 47000/{47000+Rs).
if Rs = 1k then attenuation is ~ 0.98times (-0.2dB)

The Rs also works as an attenuator (single pole Low Pass filter) for the HF signal when considered in conjunction with the cable capacitance and the RF filter capacitor usually built into the Receiver.
1k for Rs with 1nF of cable capacitance rolls of the treble with F-3dB = ~160kHz
 
anatech

anatech

Administrator
Joined 2004
Paid Member
Well Lockport,
You have your answer and then some. You should be aware that the input levels are set to a loosely accepted value. -10 dBV should approximate 0 dB for line levels. Of course, not everyone adheres to any suggestion of a standard. That goes for input impedance too.

Anyway, I serviced Adcom under warranty for years. Almost any preamp will drive those amplifiers to full level. Of course, the woofers just might become scrap if you actually run them that hard.

What's the end effect on the signal entering the amplifier?
Click to expand...
The preamp rated to deliver its rated output and distortion level is sure to operate properly with a 470 ohm load. The one rated into a 1 K ohm load may or may not. Since in practical terms, the input impedance of the Adcom amp is much higher than those figures, either preamp would perform identically (all else considered equal).

Just relax. Adcom amplifiers have a pretty standard input impedance and similar gain to the rest of the market. Any "normal" preamp will drive them just fine. You may or may not like the sound quality, but you can have all 300 watts of sound with just about all makes.

Note on Sony. They really are not about sound quality these days. Just like so many other brands. Just concern yourself with the preamp that sounds the best and has the features you want. You have got the power covered.

-Chris
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom