Reactive Load Question

Reeltarded · Post by **Reeltarded** » Sat Oct 20, 2018 1:10 pm

Do you have recording software on a computer? Uhh send amp a tone generated from software output (you can download tones of all types from a million places if you can't generate them) ...

Signal output into amp, amp drives load, load returns to a channel in software.. you can do reductive analysis using white noise, burst, and 20k sweeps.

If you don't have a setup that can do all that, let's just stick with the phone.

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 1:31 pm

martin manning wrote: ↑Sat Oct 20, 2018 11:24 am Actually, I think you can avoid making any special hook up other than finding some way to get your phone app signal into the input of an amp, and plugging the amp’s output into the load box as usual. Use a clean setting, and adjust the volume to get a couple of volts AC at the output. You already have a series resistance in your load box, which is 16.5 ohms (the 2x33 ohms in parallel), which you can use to sense current. So, you can clip one multimeter probe to the load’s input (hot), and measure voltage at the far end of the 16.5 ohms and also at the load input ground with the other probe for each frequency. To find the resonant peak clip the meter leads across the 16.5 ohms and adjust the frequency to minimize the voltage reading. That will be the frequency at the impedance peak. Then measure the voltage across the load input at that frequency and calculate the peak impedance. I’d expect the peak to occur at about 80 Hz, with a value around 100 ohms.

Great! I'm gonna try this weekend.

I understand the reasoning behind the 100 Ohm resistor tho'

It's just like when you solder a 1 Ohm resistor for biasing your power tubes.

Did you run the schematic in software to arrive at the 80 HZ at 100 Ohms ?

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 1:34 pm

Reeltarded wrote: ↑Sat Oct 20, 2018 1:10 pm Do you have recording software on a computer? Uhh send amp a tone generated from software output (you can download tones of all types from a million places if you can't generate them) ...

Signal output into amp, amp drives load, load returns to a channel in software.. you can do reductive analysis using white noise, burst, and 20k sweeps.

If you don't have a setup that can do all that, let's just stick with the phone.

Damn... you guys are good

I have Reaper and a ton of plugins.

I think I understand exactly what you're describing here, and I'm pretty sure I have an app or plug-in in my DAW that can perform that function.

Reeltarded · Post by **Reeltarded** » Sat Oct 20, 2018 1:37 pm

This is going to teach you a lot more about your software. lol

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 1:43 pm

Reeltarded wrote: ↑Sat Oct 20, 2018 1:37 pm This is going to teach you a lot more about your software. lol

I had asked a question a while back about phase - specifically between a signal coming into my DAW thru this reactive load box, and another signal coming in (same performance) thru an SM-57 on the 4x12 cab.

The guys over at TGP recording sub-forum were pretty clueless about this. I learned there was an app in my WAVES plugins for this very purpose.

Wound up learning a lot about phase issues in the process.

martin manning · Post by **martin manning** » Sat Oct 20, 2018 3:59 pm

Cathode Ray wrote: ↑Sat Oct 20, 2018 1:31 pmI understand the reasoning behind the 100 Ohm resistor tho’ It's just like when you solder a 1 Ohm resistor for biasing your power tubes.

Pretty much, but here you are wanting to measure AC current.

Cathode Ray wrote: ↑Sat Oct 20, 2018 1:31 pmDid you run the schematic in software to arrive at the 80 HZ at 100 Ohms ?

Yes, but very simply, with ideal components, so YMMV.

I don’t see how a DAW will be able to get the absolute magnitude of the impedance you are looking for, but maybe someone can explain that?

Reeltarded · Post by **Reeltarded** » Sat Oct 20, 2018 4:19 pm

Well, perfection is complicated.. direct signal straight from amp on resistive load, direct signal from amp on reactive load (this is two separate tracks done separately) then subtract the first from the second and run spectral analysis of what is left.

In this test you have to phase align the test signals. Best done if the DAW is sending a recorded signal so it's synched.

Spectral will tell you everything about resonant everything. You can even print it out.

You take your data and compare it against known engineering numbers you found on Google.

You won't get a fair answer to this question using a microphone though.

This is one of those situations where I say "Hmm.. that sounds good." or "This is a piece of shit." and move on. hehe

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 6:07 pm

martin manning wrote: ↑Sat Oct 20, 2018 3:59 pmYes, but very simply, with ideal components, so YMMV.

I've wondered about that since the guys who spec'ed out those components were trying to emulated a 4x12 cab...

Possibly they only calculated to speaker load without thinking about the closed back cabinet.

I know that (open/closed) affects the resonant peak.

Reeltarded · Post by **Reeltarded** » Sat Oct 20, 2018 7:59 pm

only a wonder why celestion speakers sound great in everything but an ev only doesn't suck in a thiele

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 8:17 pm

So, I recorded a brief track thru the reactive load onto a track in my DAW, then added Waves PAZ analyzer :

result

track used:
https://soundcloud.com/user-330384975/wiygn

Going to use the signal generator app thru my iPhone next and see what kind of result I get.

Was just curious to see what kind of waveform an actual guitar track would produce.

martin manning · Post by **martin manning** » Sat Oct 20, 2018 8:35 pm

Reeltarded wrote: ↑Sat Oct 20, 2018 4:19 pm Well, perfection is complicated... In this test you have to phase align the test signals. Best done if the DAW is sending a recorded signal so it's synched.

Ughh.. you need to sweep frequency here, and the phase shift is a function of frequency...

Cathode Ray wrote: ↑Sat Oct 20, 2018 6:07 pm
martin manning wrote: ↑Sat Oct 20, 2018 3:59 pmYes, but very simply, with ideal components, so YMMV.
I've wondered about that since the guys who spec'ed out those components were trying to emulated a 4x12 cab...

That’s not the point. Real inductors have some DC resistance, and real capacitors have some series resistance, so the impedance and frequency at which the peak occurs will be different from the theoretical value with ideal components.

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 8:39 pm

martin manning wrote: ↑Sat Oct 20, 2018 8:35 pmThat’s not the point. Real inductors have some DC resistance, and real capacitors have some series resistance, so the impedance and frequency at which the peak occurs will be different from the theoretical value with ideal components.

Understood.

Appreciate the help, guys.

On a steep leaning curve here. LOL!

Reeltarded · Post by **Reeltarded** » Sat Oct 20, 2018 10:54 pm

martin manning wrote: ↑Sat Oct 20, 2018 8:35 pm
Reeltarded wrote: ↑Sat Oct 20, 2018 4:19 pm Well, perfection is complicated... In this test you have to phase align the test signals. Best done if the DAW is sending a recorded signal so it's synched.
Ughh.. you need to sweep frequency here, and the phase shift is a function of frequency...

Yep!! That's why you use a recorded test signal and loop out of your recorder to tracks on that recorder.

Spectral analysis actually won't care as long as there is a baseline to compare both signals to. 0dbVU seems like a good enough baseline.

Reeltarded · Post by **Reeltarded** » Sat Oct 20, 2018 11:05 pm

Cathode Ray wrote: ↑Sat Oct 20, 2018 8:17 pm So, I recorded a brief track thru the reactive load onto a track in my DAW, then added Waves PAZ analyzer :

result

track used:
https://soundcloud.com/user-330384975/wiygn

Going to use the signal generator app thru my iPhone next and see what kind of result I get.

Was just curious to see what kind of waveform an actual guitar track would produce.

Looks like a fairly bright 4x12 to me. How does it feel? Lower the response time to be superfast.

Ahh also, record no hotter than -14db indicated and do not treat the signal to any normalization after the fact.

Cathode Ray · Post by **Cathode Ray** » Sat Oct 20, 2018 11:39 pm

Reeltarded wrote: ↑Sat Oct 20, 2018 11:05 pmLooks like a fairly bright 4x12 to me. How does it feel? Lower the response time to be superfast.

Ahh also, record no hotter than -14db indicated and do not treat the signal to any normalization after the fact.

Was thinking the same thing when I saw that peak...

I like the way it feel when I play thru it.

And I did think to turn off all EQ and other effects - it's a dry track coming from the reactive load being analyzed.

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