BillFitzmaurice.info

Hi there,

I just finished my T39 (20" wide with 3012LF) and have been playing with the set up. I built an Omni 10 a couple of years ago and for the time being I was planning on using the O10 as my top and the T39 as the bottom. I have a GK 800RB (bi) amp which delivers 100 watts into 8 ohms for the top (or 60W into 16 ohms) and 200 watts into 8 ohms into the bottom (or 300W into 4 ohms). The crossover is variable from 100 hz up to 1000 hz.

I suspect that the amp or crossover might be not functioning correctly because no matter where I set the crossover frequency there doesn't seem to be much difference in output between the top and bottom - or at least it doesn't change much.

Can I simply hook up the top amp (then later the bottom amp) to my little analog volt meter and measure the voltage as I sweep the frequency? Will that damage the amp? I have the Blink Audio test CD so I'm thinking I should be able to construct the crossover curves for the top and bottom and make sure that the crossover is working and also perhaps determine the slope. One of my concerns is that since this is an old amp that the crossover slope is pretty flat thus much of my bass signal is sitting in the crossover range and muddying things up.

I think I should also be able to measure the output voltage of the amps to make sure that they are within the safe limits of the two cabs, although the plans indicate that the T39 should be able to handle 450W or 60V so I'm not too worried about that side.

Thanks in advance for any advice.

Doug

DrDoug018 wrote: Can I simply hook up the top amp (then later the bottom amp) to my little analog volt meter and measure the voltage as I sweep the frequency?

Yes.

DrDoug018 wrote: Will that damage the amp?

No.

DrDoug018 wrote:
Can I simply hook up the top amp (then later the bottom amp) to my little analog volt meter and measure the voltage as I sweep the frequency?

Just run pink noise into the amp and do the frequency sweep. The shift of the crossover frequency, or lack of it, will be very obvious.

Bill Fitzmaurice wrote:

DrDoug018 wrote:
Can I simply hook up the top amp (then later the bottom amp) to my little analog volt meter and measure the voltage as I sweep the frequency?

Just run pink noise into the amp and do the frequency sweep. The shift of the crossover frequency, or lack of it, will be very obvious.

Thanks WB and Bill for the help. I ran the sweep and the crossover seemed to shift but I was not clever enough to figure out how to automatically capture the data. Therefore I manually measured the voltage from the top and bottom amps while applying the various frequencies. Here's what I got.
Seems like the crossover is working but is not very accurate above 100 Hz or so. As I increased the dial from 100, 200, 300, 400, 500, 600, the crossover increased from 100, 125, 175, 225, 275, 325. Also seems like the slope is sorta shallow but I have not calculated it yet (not exactly sure how). At any rate, it seems like an awful lot of the frequencies I will be playing on bass will be provided by both the top and bottom cabs and I'm not sure how that will affect the clarity or sound.

Thanks again the help.

Doug

With the O10 as a top you don't need a very steep slope. Just set it where it sounds best.