Clipping & HK525 (1 Viewer)

[Aaron Lock]

I figured I was going to be a little bored this weekend, so I thought, hey, let's test out my HK525 and see where clipping starts. So I borrowed a o-scope from work, and thought how am I gonna do this?

I figured pumping some sine waves off a CD through the receiver and scoping the output would do the trick. I haven't done it yet, but I just wanted to know if there's a better way?

Aaron.

 

[JohnSer]

Don't know the best way, but do know that sine waves will get your amps warmed up in a hurry. I have done it with plate amps and receivers to do driver break-in. Alway had to keep the volume down. Recommend using a high wattage resister load vs your speakers. I'll be interested in your results.

JohnS

 

[Aaron Lock]

I know it is better to use a high wattage resistor, but I don't have one handy.

I just played a 1 kHz tone off a CD, turned up the volume until clipping started. About 93% of max volume. Not bad, considering most recievers I've heard of start at around 60%.

I'm sure that number will vary with frequency, but I just wanted a rough idea.

Kudos to HK.

Aaron.

 

[JohnSer]

Aaron, what impedance are your speakers at 1KHz? At the stated 93% max volume, what was the reading on your display? Did you measure the sine wave p-p out of the CD player? If you are over or under driving it, will make a differance. And one last question, was this two channel driven, or more?


Sorry, for all the questions.

JohnS

 

[Aaron Lock]

Not sure about the impedance of the speaker, didn't think to measure it.

Which display? The receiver said +4 dB.

I was playing through the DVD player, using the PCM, I'm not sure how to measure that signal.

It was two channels driven.

Aaron.

 

[AaronBatiuk]

About 93% of max volume. Not bad, considering most recievers I've heard of start at around 60%.

Meaningless. That mearly means that the gain of the receiver is less, or the output of the CD player is lower than normal, or the test tones weren't recorded at as high a volume as the others... meaningless.

What you need to measure is the voltage output of the amp at clipping. And please don't use speakers to do this test. Please.

Pick up several 10W resistors from an electronics store. Four of them should do (40 W total) for a limited period of time. If you buy 4 8 Ohm ones, connect make two sets of two in series, then connect the two sets in parallel. Note that connecting resistors in series adds the resistances; connecting in parallel (with equal resistances) will divide by the number of them in parallel. So by connecting 2 of 8 Ohms in series, you got 8+8 = 16 ohms. Then you connected two of these '16 Ohm' ones in parallel so 16/2 = 8 Ohms.
With the resistors connected instead of the speaker, turn up the volume until the sine wave on your scope flattens on the top. Determine what the peak voltage is (the voltage of the flat part). To find the RMS voltage (Vrms), multiply by 0.7071 . Now to find the RMS Power, calculate Power = (Vrms)^2 / R, where R is the resistance (8 Ohms). Do not operate the receiver in this maximum output state for very long... neither the receiver nor the resistor load will appreciate it much. Do not touch the resistors afterwards... they will be quite hot enough to burn.

 

[Aaron Lock]

For the love of your speakers, do not do this. You will blow your speakers in not time with discrete tones!!! You have probably already irreperably damaged them.

Think so? For the 20-odd seconds I ran it for, it seems doubtful. I don't hear any difference from before to after.

Aaron.

 

[Yogi]

A few seconds clipped signal is good to fry a speaker. You dont need much.

 

[JeremyFr]

Yeah you never want to run a clipped signal to a speaker because it makes for paused movement which causes the speaker to overheat. Also your receiver stating +4 db means that it is already over the point where theoretically should be clipping that you are overdriving the input stage to the amp by 4db so that means nothing and why companys like Denon & HK do that I have no clue.

 

[Guy Usher]

20 seconds is an eternity, put your finger in a light socket for 20 seconds, it only takes an instant to damage your speakers.
I guess I just dont understand. . .
Remind me not to buy any used equipment from you. . .

 

[JohnSer]

Assuming a standard 2-way speaker, most of the energy was to the woofer. Its not something I would do, but doubt that he hurt his speakers. If a frequency was picked that went to the tweeters, probably would have a couple of open voice coils right now. Might not even have to clip, just focusing full output to a high frequency band, that never happens in music, could kill the tweeters.

JohnS

 

[Michael R Price]

Aaron,

Aaron has it right here. What you need is a load resistor that approximates the impedance of your speaker (4 or 8 ohms usually) and can handle maybe 50-200 watts. You can get those for something like $10 at Parts Express, or maybe the place you work has them if they had an oscilloscope. That way you can run the tones into the load resistors and measure the output voltage. It is quite unsafe to run continuous tones through speakers at high levels. Also, what voltage did the oscilloscope show when clipping started? That is much more important than where on the volume control you were. From there we can calculate the wattage.