Basic Audio Question

I strayed from the Dynaco Mk III's in favor of 500 watt SS Mono blocks. Amp switching for me is pain because I have setup the cross over's high pass by soldering a cap or resister to match the amps input impedance (Dynaco 500,000 ohms). My speaker are 86db and I cross over around 65hz to a SS amp.
With 500 watt monos I did not have to worry about power. Now, with the Mk III, I worry about how much power they are putting out. My maximum listening volume the preamp is around the 2 or 3 o'clock with Mk III's. Is there anyway to tell if they are being pushed too hard? Back in the day a lot of amps had meters that at least gave you some idea.

An oscilloscope is the best way. You don't even have to sync the waveform or have the display perfectly calibrated; in fact on an old, non-triggered scope you can set it to show just a fluctuating vertical line, and when it doesn't go any higher as the volume is turned up, you've hit clipping (don't run it that way for days on end, you'll burn out the phosphors on the CRT).

Old oscilloscopes can often be had cheaply at amateur radio swap meets. New, small ones can be bought for under $100.

GP49 wrote:An oscilloscope is the best way.  You don't even have to sync the waveform or have the display perfectly calibrated; in fact on an old, non-triggered scope you can set it to show just a fluctuating vertical line, and when it doesn't go any higher as the volume is turned up, you've hit clipping (don't run it that way for days on end, you'll burn out the phosphors on the CRT).

Old oscilloscopes can often be had cheaply at amateur radio swap meets.  New, small ones can be bought for under $100.

To make this really serious you could get :
http://www.ebay.com/itm/Velleman-Bausatz-K4305-Stereo-VU-Meter-2x-10-LED-Anzeige-einstellbar-Blende-/201168974751?pt=Toilettentrainer&hash=item2ed69af39f
Which is a LED VU meter.
Connect it across the speaker cables and calibrate it by the formula U = SQRT( P * R )
For R = 8 ohms you get :
U P(watt)
2.83 1
4 2
6.32 5
8.94 10
10.95 15
12.65 20
15.49 30
17.8 40
20 50
21.91 60 << this is what a Dynaco MkIII should give, calibrate the VU meter to 21V
23.66 70


For other speaker resistances recalculate the voltage that corresponds to 60w

Or just use your ears!

Cheapest way is to hook up a volt/ohms meter to the amp outputs and measure the AC output. Then plug the highest reading into the watts formula which can be found below. Or do the math yourself as peterh did above. In any case you will probably find out that the maximum volume is more determined by the limits of your speakers. The difference between 60 watts and 600 watts is 10 times and should be 10 times the output if the speakers can actually handle it. Most can't, but even if they could, 10 times louder only sounds 2 times louder to the human ear.
The setting on your preamp means nothing because it is set based on the amount of input voltage you have from your source. IE: Low input voltage to the preamp requires a high volume setting and a high voltage source will require a very low setting for the same output.

http://www.crownaudio.com/ohms-law.htm

peterh wrote:
To make this really serious you could get :
http://www.ebay.com/itm/Velleman-Bausatz-K4305-Stereo-VU-Meter-2x-10-LED-Anzeige-einstellbar-Blende-/201168974751?pt=Toilettentrainer&hash=item2ed69af39f

Eingangsempfindlichkeit einstellbar? OOooooohhhh ... pinch me, I'm dreaming!

In case anyone's wondering ... Google Translate choked, but Bing did the job ...

Stereo VU-meter with 2 x 10 LEDs (point or bar graph) and adjustable input sensitivity. Supplied with 1 front plate for horizontal or vertical mounting.

Kit K4305
Power supply: 10-15 V DC, 250 mA
Adjustable input sensitivity
Low input: 0.15 6 V RMS (47 kOhm)
High input: 1.5 60 V RMS (470 kOhm)
Range: up to 20 dB
Including front panel
Kit to the assembling, soldering skills required
Manufacturer: Velleman
Lxw: 68 x 37 mm (2 x)
Article number: 242585

I reread your post I assume you have the 500 watt amp hooked to it's own sub woofer speakers and don't have both amps hooked to the same set of speakers. That would not be healthy for your system.
Any way I have a similar set up. I use the tube amp full range on my main speakers and I use my old but trusty Adcom SS GFA555 to power the sub woofers from 80 HZ. down. The system sounds great. You do need to check to make sure all woofers are moving in and out at the same time.

sKiZo wrote:

peterh wrote:
To make this really serious you could get :
http://www.ebay.com/itm/Velleman-Bausatz-K4305-Stereo-VU-Meter-2x-10-LED-Anzeige-einstellbar-Blende-/201168974751?pt=Toilettentrainer&hash=item2ed69af39f

Eingangsempfindlichkeit einstellbar? OOooooohhhh ... pinch me, I'm dreaming!

In case anyone's wondering ... Google Translate choked, but Bing did the job ...

Stereo VU-meter with 2 x 10 LEDs (point or bar graph) and adjustable input sensitivity. Supplied with 1 front plate for horizontal or vertical mounting.

Kit K4305
Power supply: 10-15 V DC, 250 mA
Adjustable input sensitivity
Low input: 0.15 6 V RMS (47 kOhm)
High input: 1.5 60 V RMS (470 kOhm)
Range: up to 20 dB
Including front panel
Kit to the assembling, soldering skills required
Manufacturer: Velleman
Lxw: 68 x 37 mm (2 x)
Article number: 242585

aber natuerlich ist die Eingangsempfindlichchkeit einstellbar, sonst wuerde das ja keinen Sinn machen!!...........

I looked at the Velleman. It only has a max range of 20db, 10 db. for the second LED to light. That is not enough for my tastes. If set for around 25 volts you would need 2.5 volts to light the second LED. Fine for a tape recorder in record mode where you are only interested in maxing the peaks close to saturation but useless for an Amp. I suspect that is what it was originally designed for.
Just my 2 cents.

I reread your post I assume you have the 500 watt amp hooked to it's own sub woofer speakers and don't have both amps hooked to the same set of speakers. That would not be healthy for your system. wrote:

No, current configuration is the Dynacos are driving the mains and a Rotel 200wpc is driving the subs. I may download Room EQ and see where my bass is at. I tried the trail of Dirac Live room correction SW and noticed I had a hole near the cross over point. It would be nice if I could cross over higher and take off a little more demand from the Dynas.

Thanks guys