Adventures in Fractal's Dual Rectifiers

[2112]

Doubling the stock bright cap value sounds sick. Great tip @0XI0 .

 

[SeeD]

@FractalAudio @James Freeman

So I'm working on dialling in Recto2 to match up freq. response-wise with my real amp. And tbh, with a few small tweaks I can get it close.

View attachment 15490

Red is the real amp. Greenish is Recto2.

I don't really know how to improve the closeness of the 60-80hz range. To my ears, it is quite critical.

Things I've tweaked so far:

Preamp > low cut frequency at 10hz
Preamp > high cut frequency at 40khz
Speaker > Low freq at 117hz
Speaker > LF Reso at 7.9
Speaker > LF Q at 2.096
Speaker > High Reso at 7.29

But why not just use the Tone Match block and be done ??

 

[SeeD]

Doubling the stock bright cap value sounds sick. Great tip @0XI0 .

Yeah I used to mess with the bright cap all the time, to make the amp less or more bright. Cool tool to have

 

[Orvillain]

But why not just use the Tone Match block and be done ??

Because I don't find it works particularly well to be honest. You can get the output frequency response closer, but that does nothing for the actual texture or detail of the distortion itself.

 

[SeeD]

Because I don't find it works particularly well to be honest. You can get the output frequency response closer, but that does nothing for the actual texture or detail of the distortion itself.

I see, I found that when I had my Axe Fx II it was sometimes dead on ( eq wise ) when I used the TM block, but as you say if the Drive/gain/distortion is `off` on the model vs the amp then it gets hard to match.
But i seen to remember that there was something in the low mids that the Tone Match block had a hard time matching when I did bass stuff

 

[MirrorProfiles]

Shouts to @0XI0 for the MV bright cap tip. The other tweaks were all quite subtle and I'd still have to set the amp controls a bit weird. This one kind of aligned everything with less effort.

Here is the Recto1 model, speaker controls at 0, MV Bright cap at 23.4pF. Tone controls all at 5, 4x12 Recto Large Impedance Curve. No funny business with weird amp settings, or changing the impedance curve shape, or preamp filtering.



and the original amp tone:



I opened my amp up today, the small pots/lead dress/amount crammed in made it hard to read whats on the pots. Likewise, the PCB is barely labelled, some components are buried underneath other ones, its quite hard to follow. I thought I could see 20A on my pot, so it could be that I have the same taper as the Recto1 model.

I couldn't see a cap across the MV pot itself, maybe there's one on the board somewhere. Or maybe it just happens to make the Fractal model sound more like my own amp for whatever reason. I think the only way I could know for sure is to either measure the parts or start removing stuff.

 

[Mongillo19]

Shouts to @0XI0 for the MV bright cap tip. The other tweaks were all quite subtle and I'd still have to set the amp controls a bit weird. This one kind of aligned everything with less effort.

Here is the Recto1 model, speaker controls at 0, MV Bright cap at 23.4pF. Tone controls all at 5, 4x12 Recto Large Impedance Curve. No funny business with weird amp settings, or changing the impedance curve shape, or preamp filtering.



and the original amp tone:



I opened my amp up today, the small pots/lead dress/amount crammed in made it hard to read whats on the pots. Likewise, the PCB is barely labelled, some components are buried underneath other ones, its quite hard to follow. I thought I could see 20A on my pot, so it could be that I have the same taper as the Recto1 model.

I couldn't see a cap across the MV pot itself, maybe there's one on the board somewhere. Or maybe it just happens to make the Fractal model sound more like my own amp for whatever reason. I think the only way I could know for sure is to either measure the parts or start removing stuff.

Dang those are close imo!

 

[JiveTurkey]

Dang those are close imo!

Yep. Sounds great \m/

 

[FractalAudio]

What rev is your amp? I bet you have one of the ones with 150K MV pots. That reduces the bass boost due to the treble roll-off network by about 5dB.

 

[SwirlyMaple]

What rev is your amp? I bet you have one of the ones with 150K MV pots. That reduces the bass boost due to the treble roll-off network by about 5dB.

He mentioned it was a Rev G here:

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.

And included some pics here:

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.

View attachment 15324


View attachment 15325

View attachment 15326

 

[MirrorProfiles]

What rev is your amp? I bet you have one of the ones with 150K MV pots. That reduces the bass boost due to the treble roll-off network by about 5dB.

Its a transitional (export) 1995 Rev G (RF 1G PCB). Attached power cable, 8-16 ohm taps

Was quite hard to get a clear picture, will sift through and edit to try and bring out the text. This one looked like A20

 

[MirrorProfiles]

Gain pot, couldnt quite see the values on the ceramic cap as its underneath the wires coming off the pot. This was about as good as I could do for that (was just curious if I could see the pot and bright cap value while I had the amp open).

 

[MirrorProfiles]

Red and Orange master volumes

 

[MirrorProfiles]

if my multimeter/pot reading skills are accurate (let’s assume they aren’t), I measured 190k on the MV pot. Gain pot seemed close to 250k, presence was about 100k

 

[James Freeman]

I think I see a 739, which is 1Meg Log 10%.
*Measure the two outer lugs.

 

[James Freeman]

Gain pot 794:

Pot 593794 - 270S 250K .594 Shaft 5% Audio Taper

The official Mesa Boogie online store for factory replacement parts, custom parts, hardware, shirts, hats and accessories.

store.mesaboogie.com

Master Volume pot 739:

Pot 593739 - 270S 1Meg .594 Shaft 10% Audio Taper

The official Mesa Boogie online store for factory replacement parts, custom parts, hardware, shirts, hats and accessories.

store.mesaboogie.com

 

[SwirlyMaple]

Shouts to @0XI0 for the MV bright cap tip. The other tweaks were all quite subtle and I'd still have to set the amp controls a bit weird. This one kind of aligned everything with less effort.

Here is the Recto1 model, speaker controls at 0, MV Bright cap at 23.4pF. Tone controls all at 5, 4x12 Recto Large Impedance Curve. No funny business with weird amp settings, or changing the impedance curve shape, or preamp filtering.



and the original amp tone:

Not only is the overall match super close, but it's also doing a better (perfect?) job with what I call the "Recto Clash." Certain note combinations cause this sound with Rectos, where two notes overlap in a way that they are both distinct but sound like they are clanking/colliding together. (Always hard to describe audio in words!)

Here's what I'm referring to. The "Recto Clash" is on the second stab. Real amp is first followed by the Axe-FX:

real to axe recto clash

Listen to a track by swirlymaple.

whyp.it

This particular thing is something many modelers have really struggled to get right in the past. It often gets smeared together and loses that character with lesser modelers & plugins.

 

[MirrorProfiles]

Gain pot 794:

Pot 593794 - 270S 250K .594 Shaft 5% Audio Taper

The official Mesa Boogie online store for factory replacement parts, custom parts, hardware, shirts, hats and accessories.

store.mesaboogie.com

Master Volume pot 739:

Pot 593739 - 270S 1Meg .594 Shaft 10% Audio Taper

The official Mesa Boogie online store for factory replacement parts, custom parts, hardware, shirts, hats and accessories.

store.mesaboogie.com

I just put the amp back in the box, but took a few photos when it was open again:

 

[SwirlyMaple]

Gain pot 794:

Pot 593794 - 270S 250K .594 Shaft 5% Audio Taper

The official Mesa Boogie online store for factory replacement parts, custom parts, hardware, shirts, hats and accessories.

store.mesaboogie.com

I think the pot on the left side of his image might actually be this one, if my squinty number-reading eyes are right:

Pot 592792 - 270S 1M Large Shaft 20% A-Taper

The official Mesa Boogie online store for factory replacement parts, custom parts, hardware, shirts, hats and accessories.

store.mesaboogie.com

 

[FractalAudio]

if my multimeter/pot reading skills are accurate (let’s assume they aren’t), I measured 190k on the MV pot. Gain pot seemed close to 250k, presence was about 100k

There's your answer. Some Rectos had 150K pots, most had 1M. With a 150K pot (yours is slightly out of tolerance at 190K) you get a LOT less bass out of the tone stack.

Here's a graph of the difference between a 1M and 150K MV pot:

Blue trace is 150K pot.