Found old thread

[mickb]

Hi everyone, i found this old thread from 2004 by priscared, he was talking about the input of his Yamaha 2001 amp.

Quote.
The input of this amp is 4dbm i believe as it is a professional amp at 230w/8ohm a channel. Now my cd player output is something like -20dbm i believe. So when i plug my cd player into it is really quiet. Any suggestions.
unquote.

I have four of these amps three 2001 and one 1002 that i bought on ebay as faulty, i repaired one of the 2001 amps and the 1002 amp, the 1002 amp is completely different to the 2001's, and although it is rated lower it seems more powerful.

I know this might be long winded, but from what priscared was talking about in 04 has got me thinking.

Anyway my point is i haven't a clue as to what he was talking about, and i wonder if anyone could enlighten me?.

 

[AudioFreak]

He was talking about the input sensitivity of the amplifier. The voltage input required to obtain the rated output.

 

[mickb]

Thank you for your reply Dan.
I'm still not sure what you mean, i'm not very clever when it comes to db stuff must be thick i suppose

Any chance you could explain please mick.

 

[KSTR]

From the YAMAHA PC2001 manual:

Rated Power: 2x 250Wrms @ 8Ohms

This equvialents to 500Wpk @ 8Ohms

Now P=U*I = U^2/R ==> U=sqrt(P*R) = 63V(peak) or 45V(rms)

Manual states a voltage gain of 32dB (= factor of 40x)

Then amp sensivity is 45Vrms/40 = 1.125Vrms

Referenced to 1V (dBV units) this is +1dbV

Referenced to 0.775V (dBu units) this is +3.2dBu. Supposedly this is the value "3dB" stated in the manual, which is meaningless without a reference (dB relative to what?).

Typical CDP output is 2Vrms = +6dBV = +8.2dBu. So a normal CDP should deliver more than enough voltage to fully drive this amp.

dBm is a power measure (power relative to 1mW -- m is the m of mW). The 0.775V reference is derived from that, this is the voltage level needed for a power of 1mW into 600ohms (sqrt(0.6)=0.7745967...)
http://en.wikipedia.org/wiki/Decibel

- Klaus

 

[mickb]

Hi Klaus
Thanks for your reply, this amp does work okay, i have tried it through a mixer with a gain control, it doesn't really make any difference.

It's pretty loud but not as loud as the PC1002 amp.
I looked up that link you put but for some reason it crashed my computer wil try again later.
Cheers Mick

 

[AudioFreak]

KSTR,

Thanks for posting in my absence.... I was just headed to bed when I made that post so didn't get a chance to make a follow up.

dBu is more or less the standard measure when talking voltage levels and sensitivity with pro sound / audio. P.A. mixers generally have much hotter output than consumer gear of yesteryear... These days, alot of consumer level equipment is also starting to use much hotter levels than was once the case.. In some cases even as hot as levels that were once only seen in the Pro Audio field.

The 1002 has a higher sensitivity than the 2001 (that is to say that the 1002 requires less voltage at the input than the 2001 to achieve rated output). With that said, the difference in sensitivity is approximately 3dB and the difference in rated power output between the 2 amplifiers is approximately 4dB. So, the 2001 should be approximately 1dB louder than the 1002 for the same input signal level. Obviously all of that only stands if you uses the same load for testing both amplifiers and until you reach the clipping point of the 1002, after which higher signal levels will result in the 1002 clipping more severely while the 2001 continues to output more power until it reaches it's clipping point. Also, for testing, the volume controls should be rotated fully clockwise on both amplifiers to ensure any volume control setting is not changing the sensitivity of either amplifier.