Hair Splitting: Power Amp Edition

[Alex Kenivel]

I don't think these videos are that useful for viewing the difference. FabFilter would be more than up to the job of representing the results so more likely the issue is elsewhere.

The sweep generator, or whatever DI box you are using to capture the signal from the speaker out. I'd find some 3rd party sine sweep generator plugin for starters.

The videos are all I could show as there is no "Freeze Plot" or "Peak Hold" options in any of the other meters I have. I've also used two different sine sweep generators so far and the only thing that changes my results are using different meters

I think the default for those inputs/outputs might be set to line level. In any case, it would be most straightforward to just use output 1 or 2 to devices that expect line level signal.

The only level settings for Outs 3 and 4 are for Boost/Pad. If you could point to any definitive information I'd be glad to check it out. I went ahead and loaded a different preset that also has a split to Out3 and was able to clip the Yamaha's inputs easily (dB meter reading at over 110dB) so I don't see a point in pursuing that any further except out of sheer curiosity.

 

[Alex Kenivel]

FWIW, the sine sweeps going directly into the AFX3's RTA meter read flat

 

[laxu]

The videos are all I could show as there is no "Freeze Plot" or "Peak Hold" options in any of the other meters I have. I've also used two different sine sweep generators so far and the only thing that changes my results are using different meters


The only level settings for Outs 3 and 4 are for Boost/Pad. If you could point to any definitive information I'd be glad to check it out. I went ahead and loaded a different preset that also has a split to Out3 and was able to clip the Yamaha's inputs easily so I don't see a point in pursuing that any further except out of sheer curiosity.

See https://wiki.fractalaudio.com/wiki/index.php?title=Audio_in_and_out#Main_output_level and scroll down to boost/pad

The Boost/Pad parameter optimizes the signal level to reduce noise in certain scenarios, such as a 4CM setup (Four Cable Method), when placing the device in front of a traditional amp, or when integrating an external pedal.

The Output Boost/Pad is supported for unity gain outputs.

When putting the Axe-Fx II or III in front of a real amp using Output 3 or 4 (FM9: output 3, FM3: output 2), maximize Boost/Pad to make sure the full range of the D/A converter is used.

Again the most straightforward option would be to just connect Out 1 or 2, and make sure it is set to +4 dB Output Level setting as that's what a rack poweramp like the Yamaha likely expects.

FWIW, the sine sweeps going directly into the AFX3's RTA meter read flat

Then the sweep generator is not the issue. What are you using as a DI box?

 

[Alex Kenivel]

See https://wiki.fractalaudio.com/wiki/index.php?title=Audio_in_and_out#Main_output_level and scroll down to boost/pad

The Boost/Pad parameter optimizes the signal level to reduce noise in certain scenarios, such as a 4CM setup (Four Cable Method), when placing the device in front of a traditional amp, or when integrating an external pedal.

The Output Boost/Pad is supported for unity gain outputs.

When putting the Axe-Fx II or III in front of a real amp using Output 3 or 4 (FM9: output 3, FM3: output 2), maximize Boost/Pad to make sure the full range of the D/A converter is used.

Hmm, that hashtag marker doesn't seem to jump to any section with that name, but I did find this:

About Outputs 3 and 4:

• They are unity gain, so their output level is lower than that of Output 1 and 2 on the Axe-Fx and FM3. To achieve unity gain, set the physical OUT knob to its maximum position
• The Boost/Pad parameter in SETUP lets you fine-tune their signal level for the lowest floor noise

Again the most straightforward option would be to just connect Out 1 or 2, and make sure it is set to +4 dB Output Level setting as that's what a rack poweramp like the Yamaha likely expects.

Cool, thanks for the tip, although I gave the Yammy plenty of signal to clip the input using Out3.

What are you using as a DI box?

Behringturd Ultra-DI, DI400P. Its measuring flat with a very subtle dropoff of the high end starting at 10khz through the AFX3's RTA and Reaper's FSAM. Span and FF are still showing that upward slope.

 

[Alex Kenivel]

@laxu the hardware connectors for Output 2 on the AFX3 are XLR, now I remember why I'm using Output 3 in the first place!

 

[laxu]

@laxu the hardware connectors for Output 2 on the AFX3 are XLR, now I remember why I'm using Output 3 in the first place!

Out 1 has both XLR and 1/4".

 

[Alex Kenivel]

Out 1 has both XLR and 1/4".

Right, but just about all of the factory presets default to using a cab block routed to Out1, which I also use as the SPDIF source. Its much easier to leave all of that stuff stock and not have to reroute every preset I encounter.

I actually just found a nice little XLR/TRS patch cable in my rummaging so I'll use that with Output 2 and will only need to change a handful of presets instead! No wonder I needed to boost the shit out of Out2's mixer to get a healthy level.

Thanks for pointing out that useful detail.

 

[jay mitchell]

Bad data is bad.

 

[Boudoir Guitar]

Yamaha P3500S (PA Power amplifier, Class A/B)

Perhaps I'm doing something wrong but I'm hearing no difference between parallel and bridged modes of this stereo power amp. Without any controls on the power amp besides master volume, the output itself is pretty low when fed the same signal. I boosted the shit out of it and of course it got louder, with the clipping protection on the amp never blinking at all. I decided not to test its input limits.View attachment 57160

(1). If you aren't sending the Yammie a big ass signal compared to the other two, you're kind of crippling it -- it is a high wattage amp, but it generates that high wattage in part by starting with a pretty big signal. Wattage is not the same as "how much it can increase the level of a signal". Two amps can be designed to multiply their input by 5x, but have two wildly different (accurate) wattage ratings -- multiplying a very small signal by 5x still leads to a small output signal, and thus doesn't take a lot of wattage. Multiplying a big ass signal by 5x leads to a really big ass signal and requires a lot of watts. Feed that first amp the big ass signal and you'll either clip the input of the device, or it'll clip like crazy trying to amplify it by 5x and not be anywhere near as loud because it doesn't have enough power to output a 5xBig Ass level signal. Similarly, if you send the very small signal to the bigger amp, it would still only be able to multiply it by 5x, giving the same output of the small amp, and also only putting out the same wattage as the small amp. Give that Yammie the line level signal it was designed for. Indeed, be careful driving a greenback loaded 2x12 with that thing...I wouldn't run a "let's see how loud this fucker'll git!!!!!!" experiment.

(2). How did you have things connected for parallel and bridged mode? Assuming in both scenarios you were feeding the mono input of the cab, keep in mind that you've now doubled the load on the amp (8 ohm to 16 ohm) so there's not going to be much of a difference between bridged mono vs stereo at all. While it's a solid state amp, I'd still probably avoid running it in parallel mode if you're only going to be using one side of it.