Adventures in Fractal's Dual Rectifiers

[la szum]

And then others can benefit from that, too. If that's not fostering community I don't know what is??

Thanks!

 

[Elric]

Alert: @FractalAudio

 

[0XI0]

try turning off the power amp modeling

 

[MirrorProfiles]

try turning off the power amp modeling

wouldn’t that totally remove all the impedance curve behaviour?

 

[0XI0]

wouldn’t that totally remove all the impedance curve behaviour?

yeah but you get to hear what the preamp is actually putting out in isolation, it gains a lot of top. recto power amp even on 1.0 is crazy prominent, there is a lot of low end parasitics that mess with the top end at master volumes low enough where it shouldn't yet. if you turn screen Freq and Q down to ~2/.2 it clears up a lot and gets faster.

i think the amp has a bright cap on the master too, there is a master bright cap in the model but it's not on by default. also the model bright cap defaults to 250, to my ears ~500 behaves way more like a stock dual rec. people say EMG humbuckers are dull but an 81 DI sounds like a piezo, idk where the top end goes when it gets amplified. probably some impedance conflict something or other.

 

[Whizzinby]

No sizzle in the Fractal.
Preamp page -> "High Cut Frequency" max it.
Speaker page -> "HF Reso" turn it up.

I read this and realize…

Im still on Mouth Breather Level II “Ooh, here is the saturation switch, yippee!!”

 

[SwirlyMaple]

I mentioned in the other thread about having to work a bit harder than I'd expect with the Fractal Rectifiers. I think they sound great, but the top end seems much softer than what I get from using the real amp.

To get things started......

Here is the real amp settings. B/M/T/P all at 5 (parallax making them look slightly different). Gain is at 6.5, master is about 1.8. Not exactly settings I'd use, but I think it sounds reasonable enough.
View attachment 15283

Recording the amp with it hooked up to a Mesa Oversized Straight/Slant cabinet with 2002 V30's. Tapping the amp DI signal with an Ampete switcher.

Applying an IR on the real amp DI gives this:



So when comparing with FM-3, I decided to route directly into the main input. My reamp box is calibrated for my I/O and its going through the same reamp path as the real amp did. I used Recto1 Red and Recto2 Red Modern. I started with both at the same settings, lowered the bias a bit, turned the preamp LPF all the way up, and then tried not to tweak too far from the real settings. I used the 4x12 Recto Large impedance curve (which matches the response of my cabinet closest IIRC).
View attachment 15284
View attachment 15285

That yielded this for Recto1 Red:



and this for Recto2 Red Modern:



and just as a kind of "control", here is Helix's Rectifier. I started with settings all matching the amp and just fine tuned a little:
View attachment 15286
which makes:



The Helix definitely has some signs of its trademark fizz on the top end. I believe both the Helix model, and also Fractal's Recto2 Red Modern are from a 3 channel rectifier. In my experience, its quite possible to match the tone of the real amps very close if you are careful with settings.

Even with the presence on 10 and the treble dial turned up high, the Fractal Rectifier isn't giving me the same amount of top end as the real deal. I don't think its simply a case of pot tolerances, circuit variations, or different impedance curves causing such a wild difference. I'm not saying it isn't user error either, but I'd love to determine where the difference is.

Higher quality audio can be listened to and downloaded here. I also included the amp DI signal, and guitar DI (11.4dBu input headroom) which can be downloaded if anyone wants to try matching the Fractal Rectifiers to the real amp tone.

RECTO TESTS

Listen to audio losslessly with Samply.app

samply.app

There is also a NAM model made of the real amp with this chain: https://www.dropbox.com/scl/fi/xonm...Test.nam?rlkey=3yseofmj1s6z65d3fsiqbpige&dl=0
View attachment 15287

Would be AWESOME if we're able to get these Rectifier models to match closer.

Gotta be honest... FM3 is sounding a bit TMP in this particular comparison

Helix is a lot closer in character, but has that subtle, hard-to-describe high-end harshness in its distortion.

 

[Mongillo19]

I swear Cliff mentioned really disliking real life Rectos in a comment (I could be wrong). Not that it means anything about the detail that went into it as I feel like Cliff puts 110% in every model, but maybe he wasn't as passionate about it

 

[James Freeman]

High Cut Frequency, wiki says it's the snubber cap on the phase inverter.

Why is it in the Preamp page?

Why isn't there a Suhr Reactive Load impedance curve in the Fractal? It's a useful tool.

To me it seems like the Recto model needs a refresh. Running a few sweeps and taking samples at a few critical point in the amp like before the fx loop, at PI grids, power amp grids and speaker jack with a cab load will go a long way.
I know the amp is heavey af, Cliff might not like pulling it out of storage.

Edit: It escaped me that there are two dezen Recto revisions. See Cliffs post below.

 

[FractalAudio]

What revision Dual Rectifier:
The one with the 1M gain pot instead of 250K?
The one with the 100K presence pot or the one with 25K?
The one with the bright cap on the master volume or maybe one with the treble bleed to ground on the MV?
Or maybe one of the ones with a 220pF plate cap on V2B instead of 1nF?

There have been so many changes over the years to these things. Mesa denies changing anything but their own schematics as well as "people in the know" say differently. Randall was always tinkering with the circuit. Later revisions were darker to try to tame the fizz that people complained about. But then people said they were muddy so more changes ensued.

I'll drag our reference Dual Rec. out tomorrow and measure it but I doubt it's off by much.

 

[James Freeman]

first post quoters.

 

[deathbyguitar]

I know the amp is heavey af, Cliff might not like pulling it out of storage.

I'll drive up there and carry it for him.

 

[FractalAudio]

Why is it in the Preamp page?

Why isn't there a Suhr Reactive Load impedance curve in the Fractal? It's a useful tool.

To me it seems like the Recto model needs a refresh. Running a few sweeps and taking samples at a few critical point in the amp like before the fx loop, at PI grids, power amp grids and speaker jack with a cab load will go a long way.
I know the amp is heavey af, Cliff might not like pulling it out of storage.

I'm not sure why I put it in the preamp page. Never thought about until now.

I don't own a Suhr RL and I don't want to buy one.

I take sweeps at many points in the amps as well as voltage readings and 'scope traces. That's how modeling an amp is done.

 

[dean701]

I mentioned in the other thread about having to work a bit harder than I'd expect with the Fractal Rectifiers. I think they sound great, but the top end seems much softer than what I get from using the real amp.

To get things started......

Here is the real amp settings. B/M/T/P all at 5 (parallax making them look slightly different). Gain is at 6.5, master is about 1.8. Not exactly settings I'd use, but I think it sounds reasonable enough.
View attachment 15283

Recording the amp with it hooked up to a Mesa Oversized Straight/Slant cabinet with 2002 V30's. Tapping the amp DI signal with an Ampete switcher.

Applying an IR on the real amp DI gives this:



So when comparing with FM-3, I decided to route directly into the main input. My reamp box is calibrated for my I/O and its going through the same reamp path as the real amp did. I used Recto1 Red and Recto2 Red Modern. I started with both at the same settings, lowered the bias a bit, turned the preamp LPF all the way up, and then tried not to tweak too far from the real settings. I used the 4x12 Recto Large impedance curve (which matches the response of my cabinet closest IIRC).
View attachment 15284
View attachment 15285

That yielded this for Recto1 Red:



and this for Recto2 Red Modern:



and just as a kind of "control", here is Helix's Rectifier. I started with settings all matching the amp and just fine tuned a little:
View attachment 15286
which makes:



The Helix definitely has some signs of its trademark fizz on the top end. I believe both the Helix model, and also Fractal's Recto2 Red Modern are from a 3 channel rectifier. In my experience, its quite possible to match the tone of the real amps very close if you are careful with settings.

Even with the presence on 10 and the treble dial turned up high, the Fractal Rectifier isn't giving me the same amount of top end as the real deal. I don't think its simply a case of pot tolerances, circuit variations, or different impedance curves causing such a wild difference. I'm not saying it isn't user error either, but I'd love to determine where the difference is.

Higher quality audio can be listened to and downloaded here. I also included the amp DI signal, and guitar DI (11.4dBu input headroom) which can be downloaded if anyone wants to try matching the Fractal Rectifiers to the real amp tone.

RECTO TESTS

Listen to audio losslessly with Samply.app

samply.app

There is also a NAM model made of the real amp with this chain: https://www.dropbox.com/scl/fi/xonm...Test.nam?rlkey=3yseofmj1s6z65d3fsiqbpige&dl=0
View attachment 15287

Would be AWESOME if we're able to get these Rectifier models to match closer.

sorry I'm late. lol.
what were your high treble settings on the ideal page?
I use mine at 2 o clock.

 

[MirrorProfiles]

What revision Dual Rectifier:
The one with the 1M gain pot instead of 250K?
The one with the 100K presence pot or the one with 25K?
The one with the bright cap on the master volume or maybe one with the treble bleed to ground on the MV?
Or maybe one of the ones with a 220pF plate cap on V2B instead of 1nF?

There have been so many changes over the years to these things. Mesa denies changing anything but their own schematics as well as "people in the know" say differently. Randall was always tinkering with the circuit. Later revisions were darker to try to tame the fizz that people complained about. But then people said they were muddy so more changes ensued.

Mines a Rev G, but I’ve had it side by side with others and none have been flatter in the top end like this.

I’m wondering if it’s another where it could be to do with the FX loop/channel master/global master, or whether it’s a something impedance related in the power amp.

Either way, it’s an amp that has a particular sound when paired with a Mesa cab - no load box quite does it justice in the same way because of the lack of NFB. I’m not sure if it just needs certain conditions to expose the differences.

I'll drag our reference Dual Rec. out tomorrow and measure it but I doubt it's off by much.

Thanks!

 

[MirrorProfiles]

Old photos from a few years ago, I’ll try to get close ups of the pots and some important values. Note the attached power cable and 8-16 Ω speaker taps - I think some export 240V Rectifier’s used up leftover Rev F parts, I’ve heard of others like @2112 and Lasse Lammert having Rev G’s with some Rev F leftovers.

 

[SwirlyMaple]

I tried my hand at matching @MirrorProfiles 's real Recto with my FM9, using his DI clips. Both are going through the same IR in the FM9, but it's not the same IR that he used, so it'll sound different.

The match is pretty close with these settings, though the FM9 still has less presence from about 5 to 10kHz. Increasing the High Treble or Treble knobs more than shown below just makes it sound more off in other ways. I also tried dialing up the bright cap value, but it didn't add the missing frequencies in a way that was any closer than leaving it at its default and compensating with the knobs.





These are the settings I used. Everything else was the amp's defaults, including the SIC settings. Presence had to be dimed, and that "High Treble" knob under the Ideal tab was also crucial.

 

[MirrorProfiles]

I tried my hand at matching @MirrorProfiles 's real Recto with my FM9, using his DI clips. Both are going through the same IR in the FM9, but it's not the same IR that he used, so it'll sound different.

The match is pretty close with these settings, though the FM9 still has less presence from about 5 to 10kHz. Increasing the High Treble or Treble knobs more than shown below just makes it sound more off in other ways. I also tried dialing up the bright cap value, but it didn't add the missing frequencies in a way that was any closer than leaving it at its default and compensating with the knobs.





These are the settings I used. Everything else was the amp's defaults, including the SIC settings. Presence had to be dimed, and that "High Treble" knob under the Ideal tab was also crucial.

View attachment 15331

View attachment 15332

Will listen tomorrow… this is basically how I’ve done it in the past but it always felt weird to me to have to max the presence and use the high treble control.

When using load boxes I run the presence much higher than I do with a cab load, I think load boxes roll off more on top, and the Recto presence control is basically a LPF in the preamp that’s probably balancing that roll off out a bit.

 

[dk_ace]

I can’t imagine diming the presence on the modern mode of a recto lol…

You mentioned the master volume and impact to high frequencies, one thing I seem to remember is that neither fractal nor L6 model the actual taper of the master on amps. They especially wouldn’t on the recto I imagine. Then you’ve got the different revisions and how they do things regarding the effects loop send level assuming either the model or your amp had a loop engaged. Getting the master matched to your amp is probably hard to do.

D

 

[2112]

My suspicion is it's the master volume. Here's my Recto (bold, silicon rectification) run through the X-Load UK setting against 2 instances of Recto 1 Red (same knob settings, speaker page adjusted with matching SIC and speaker parameters zero'd) - one with MV at 0.5, the other with MV at 2.



No prizes for guessing which one has the higher MV setting.