Transformer Saturation (aka GRIND)

[TubeAmpNut]

I can't seem to recreate the tone of a crying output transformer, particularly with the plexi models. There is a distinctive tone when the OT core saturates and starts to clip the output waveform. Both the Deluxe and the Plexi models are missing this pleasant artifact of a cranked non-master volume amp. Perhaps the control could be labled 'Grind'?

BK

 

[Smilzo]

:?:

How did you do to separate transformer saturation from any other kind of saturation? It could be preamp tubes, splitter clip, voltage sag, power compression... (just curios: do you swap different OT?)

 

[TubeAmpNut]

:?:

How did you do to separate transformer saturation from any other kind of saturation? It could be preamp tubes, splitter clip, voltage sag, power compression... (just curios: do you swap different OT?)

Amp techs are quite familiar with this. You can clearly see it on a scope. When the OT saturates, the waveform rapidly turns square. The OT physically and audibly 'rings' too (you only see this when the amp is on a dummy load).

Older amps with low cost, undersized output transformers grind quite easily. 50W plexis are famous for this.

My impression of the low gain non-MV models is the amp section progressively compress as expected, but also behave as if connected to a truck-sized transformer with infinite headroom (don't get me wrong, I LOVE my Ultra). I just think it would be a nice feature to be able to limit the OT headroom with a 'Grind' knob to induce the ringing and swirl you hear (or I hear?) when the OT saturates.

BK

 

[vAmp]

I'm a toob noob and I'm longing to hear what you mean...

Anyway, thx for bringing it under our attention!

 

[FreaqyFrequency]

Interesting idea indeed. Curious to see what Cliff says about this.

 

[JGR]

It would be interesting to know how in-depth each amp model's tranny was modeled. The DeYoung for instance in the SLO has a pretty big impact on the overall tone of the amp as it is more hi-fi than the normal Plexi type.

 

[Smilzo]

The DeYoung for instance in the SLO has a pretty big impact on the overall tone of the amp as it is more hi-fi than the normal Plexi type.

You talk about frequency. Play with transformer frequency in advance page.

Saturation it's a different beast. I don't have actual data to evaluate core saturation of a trafo on a musical program. I asked before, but I don't think we get there.
Phisical ringing is associated with quality of costruction... no core saturation.
Crancking the volume of a 50w and you'll see both preamp, poweramp, transformer and PT changing output waveform on a scope.
Trafo saturation is a function of core material, coil, costruction and current/voltage. DC saturation "would" be present in SE, but OT are built to avoid saturation. DC saturation in a push-pull is not an issue. I don't think AC saturation is a "missing" element in axefx rock tone. Maybe I'm wrong! :?:

 

[JGR]

The DeYoung for instance in the SLO has a pretty big impact on the overall tone of the amp as it is more hi-fi than the normal Plexi type.

You talk about frequency. Play with transformer frequency in advance page.

Saturation it's a different beast. I don't have actual data to evaluate core saturation of a trafo on a musical program. I asked before, but I don't think we get there.
Phisical ringing is associated with quality of costruction... no core saturation.
Crancking the volume of a 50w and you'll see both preamp, poweramp, transformer and PT changing output waveform on a scope.
Trafo saturation is a function of core material, coil, costruction and current/voltage. DC saturation "would" be present in SE, but OT are built to avoid saturation. DC saturation in a push-pull is not an issue. I don't think AC saturation is a "missing" element in axefx rock tone. Maybe I'm wrong! :?:

I was making a general comment about the tonality of the transformer in that amp - as you have noted, there are quite a few variables that affect a transformer's tone and behavior, and I wonder how in-depth Fractal modeled the properties of each amp's respective transformer. I started wondering based on comments of modeling an amp based on a schematic without the real thing in hand. I know they use the same tube "models" for each type of tube (rather than say modeling a JJ and an RCA) which makes sense, but the transformer can be a pretty big part of the equation, and may be more unique in some amps than others. I wonder for instance, if all the plexi's use the same transformer models, what is used in the hi gainers, etc... just curious.

 

[sjaak]

occasionally I'm using a tranformer based isolation box
not sure what's happening with saturation or phaseshift
but I like the sound of it

 

[Smilzo]

... I wonder how in-depth Fractal modeled the properties of each amp's respective transformer.... if all the plexi's use the same transformer models, what is used in the hi gainers, etc... just curious.

I got your point. Keep in mind we are talking about model: it's up to the programmer to choose it. One programmer can make "model A", "model B", "model C". Another programmer can make one model with some parameters to match 3 models, and go futher... being the algo exactly the same!
Keep also in mind that a transformer is a simple passive device: a core, some coil. There are lot of program (FEM) that model in depth the behaviour, the only issue for Cliff could be adjust some manifacturer trick used on guitar OT.

The core is made of ferrite, that is characterized by its hysterisis loop.

There are energy losses in transformers:

1) Hysterisis loss, due to energy's materials intrinsic properties used to align and re-align the magnetic domains;
2) Eddy current loss from the circulating currents within the magnetic materials inside the cores itself, high dependent upon the thickness of the cores and switching frequency;
3) Winding loss, dependent on the wire size, switching frequency, etc.

Than you can model a transfer function.

I doubt Cliff would reveal how depth is his model. If you look into advance param, you'll find some parameters that recall the properties above mentioned... hope this help.! :mrgreen:

 

[TubeAmpNut]

Trafo saturation is a function of core material, coil, costruction and current/voltage. DC saturation "would" be present in SE, but OT are built to avoid saturation. DC saturation in a push-pull is not an issue. I don't think AC saturation is a "missing" element in axefx rock tone. Maybe I'm wrong! :?:

I'm not talking about DC saturation, sag, preamp/splitter/powertube or whatever distortion. At some point the OT simply can't flux any more magnetic energy with increasing output voltage swing (inducing current through the primary) to the secondary winding. It is a frequency dependent effect, but the bass rolloff is allready accounted for in the model. When the core can't take any more it distorts. Modern/overbuilt trannys have more headroom in regard to this. Although it's not quite that simple, it should be fairly easy to approximate.

Classic non-MV amps grind with cranked. When you've heard it, you know it. When it's missing, you know it. If you don't believe me, rip out the high performance mil-spec aftermarket tranny in your homejob plexi and put in an undersized OT (which doesn't mean it will sound good). -I'm not flaming, I'm just passionate about my AxeFX!

BK

 

[Smilzo]

I'm not flaming

I know... otherwise I will not reply... ! :

At some point the OT simply can't flux any more magnetic energy

I know. It depends on core material. Core material is almost the same in OT.

Modern/overbuilt trannys have more headroom in regard to this.

I might be wrong... overbuilt OT trannies has WIDER extension, more bass.

Classic non-MV amps grind with cranked. When you've heard it, you know it.

The grind comes from phase splitter clipping. Try to increase splitter headroom, and scope.

If you don't believe me, rip out the high performance mil-spec aftermarket tranny in your homejob plexi and put in an undersized OT (which doesn't mean it will sound good).

I know what you are talking about, but to my ears it is a matter of frequency, and load on power tubes. The reflected impedance give pick attack some flavour... the NFB give distortion some clipping... I can't immagine a transformer core saturate with 50 watts of AC signal, I don't believe in cone distortion either! I heard different sound from different transformer (with same ratios), but I don't think is core saturation.

What I try to tell you is: there are some myths around tube amp. Sometimes the connection between cause and effects could be misundestood. Tube amps are simply circuit with complex interactions.

 

[TubeAmpNut]

I know. It depends on core material. Core material is almost the same in OT.

Uhh, I think you meen core size.

I might be wrong... overbuilt OT trannies has WIDER extension, more bass.

By wider, I assume you mean a lower frequency response, which is a function of both the core type and size. Since most OTs are M6 steel, size matters (and windings, blah blah). Flux density in the core is inversely proportional to frequency. i.e. Bass fluxes harder, runs out of headroom faster, distorts sooner, and as the signal strength increases, rolls off faster.

The grind comes from phase splitter clipping. Try to increase splitter headroom, and scope.

Not the grind I hear... If that were the case I would like PPIMV's. I think they suck. See quote below

[quote="BK-Amps":gky9mv6n]If you don't believe me, rip out the high performance mil-spec aftermarket tranny in your homejob plexi and put in an undersized OT (which doesn't mean it will sound good).

[/quote:gky9mv6n]

The reflected impedance give pick attack some flavour...

Come on! :shock:

the NFB give distortion some clipping...

NFB actually linearizes the power section. When the power amp clips there is no more 'excess gain' available for NFB so there is none.

I can't immagine a transformer core saturate with 50 watts of AC signal, I don't believe in cone distortion either! I heard different sound from different transformer (with same ratios), but I don't think is core saturation.

It's not the power that saturates, it's the driving voltage inducing current in the primary. I think you mean a Model 1987 Marshall saturating a transformer rated at 50W full-power bandwith at 8-ohms. Certainly not the new mil-spec high performance transformers I've previously mentioned. But old Marshall trannies weren't 50W FPBW...

What I try to tell you is: there are some myths around tube amp. Sometimes the connection between cause and effects could be misundestood. Tube amps are simply circuit with complex interactions.

The myth is OT's don't saturate! Promulgated by vendors looking to sell their expensive replacements when asked by their customers why they don't sound like old ones.

-Rock on!

 

[Smilzo]

Tnx! :mrgreen:

 

[ORDEATH]

i would like to see this continue....did cliff ever have a chance to address this shortcoming?

im no master but i think know what this sounds and feels like. ive heard something like the description on old hendrix albums before too,it feels like the tubes could break at any moment and you can hear a wierd cloudy type of swirling inside them when as you play.
but am i mistaking "grind" for a bad tube? ops

either way i would like to hear cliffs idea about this "grind"