Output transformer for SVT-CL that doesn't limit low frequencies

[nashvillebill]

Some of the classic amps have been analyzed on this site Amp Books for Professional Builders look under the Classic Circuits tab.

With the slightly different iterations of the SVT, each one would require separate study. Look at not only the tube types--6146 versus 6550, but everything from the preamp to the PI.

The real takeaway from all this: some folks focus on stuff that's totally inconsequential: "Hey, that amp's got blue capacitors, my amp has orange caps--if I change my orange caps to blue caps that will make my amp sound like that amp!" Meanwhile they ignore obvious details--hey you think that EF86 pentode in that other amp's preamp *might* make a difference, ya think?? Circuit design (and implementation) matters far more than whether you buy vintage tubes made by virgins during a full moon (or transformers from a company with a fancy marketing department).

 

[Korladis]

Some of the classic amps have been analyzed on this site Amp Books for Professional Builders look under the Classic Circuits tab.

With the slightly different iterations of the SVT, each one would require separate study. Look at not only the tube types--6146 versus 6550, but everything from the preamp to the PI.

The real takeaway from all this: some folks focus on stuff that's totally inconsequential: "Hey, that amp's got blue capacitors, my amp has orange caps--if I change my orange caps to blue caps that will make my amp sound like that amp!" Meanwhile they ignore obvious details--hey you think that EF86 pentode in that other amp's preamp *might* make a difference, ya think?? Circuit design (and implementation) matters far more than whether you buy vintage tubes made by virgins during a full moon (or transformers from a company with a fancy marketing department).

I use Sovteks, not fancy NOS tubes.

Mainly because I play doom metal. What I am doing with my amp destroys tubes way more quickly than what most would consider regular use. I would feel bad about so rapidly using up something that cannot really be replaced, that someone else could get much, much more play time out of. There's also the expense, of course.

I just meant, while obviously the D-180 and the SVT are very different amps in lots of ways, one of the most noticeable difference is that the D-180 has much, much smaller transformers.

 

[ThisBass]

Behavior at overload range is very different. Some amps tend to generate saddle points at around 50% of rated output power, orhers don't. There is no way to tweak a power amp characteristic like that with different pentodes.
By the way the development of saddle points at overload range is often mismatched with OT saturation.

D-180 is a totally different design cause the PI directly drives the power tubes.
No way to campare this design with the svt.
I'd expect saddle points with the D-180, the svt doesn't do that.

 

[JimmyM]

Some of the classic amps have been analyzed on this site Amp Books for Professional Builders look under the Classic Circuits tab.

Not one single bass amp in the bunch.

 

[JimmyM]

I use Sovteks, not fancy NOS tubes.

Mainly because I play doom metal. What I am doing with my amp destroys tubes way more quickly than what most would consider regular use. I would feel bad about so rapidly using up something that cannot really be replaced, that someone else could get much, much more play time out of. There's also the expense, of course.

I just meant, while obviously the D-180 and the SVT are very different amps in lots of ways, one of the most noticeable difference is that the D-180 has much, much smaller transformers.

Mesa's way of making high power tube bass amps is to throw more power tubes at them and use smaller transformers, whereas Ampeg uses big transformers and fewer power tubes.

 

[ThisBass]

Mesa's way of making high power tube bass amps is to throw more power tubes at them and use smaller transformers, whereas Ampeg uses big transformers and fewer power tubes.

Indeed Ampeg amps don't show those well known "tube artifacts" of other amps.

 

[Mr. Foxen]

What I am doing with my amp destroys tubes way more quickly than what most would consider regular use.

Probably should look at the problem that is destroying valves and fix it rather than throw cheap valves at it. Flimsy cabs will do mechanical damage to valves and cab designs that don't consider impedance will be electrically hard on valves.

 

[agedhorse]

Within transformer design, the lamination material and the abruptness of the saturation curve(s) certainly affect the necessary size, as does the winding ratio and primary impedance/inductance. A lower source impedance driving the output transformer can reduce the winding ratio as well. There are a lot of tricks used by successful designers to achieve specific goals. I think it's important to recognize the track record of a particular designer before judging any design based on transformer size without considering everything else too.

 

[Korladis]

Mesa's way of making high power tube bass amps is to throw more power tubes at them and use smaller transformers, whereas Ampeg uses big transformers and fewer power tubes.

D-180 only has six power tubes, but they're 6L6... and it's only a little over half the power of the SVT, so I guess the point still stands. A closer comparison would probably be the V4B... I think... though I don't know what the V4B has for power.

Probably should look at the problem that is destroying valves and fix it rather than throw cheap valves at it. Flimsy cabs will do mechanical damage to valves and cab designs that don't consider impedance will be electrically hard on valves.

The tubes aren't getting destroyed at that rapid a rate. It's not a problem. They've lasted a few years, surprisingly, so when they go, I will be getting Sovteks again. Just, our genre is hard on amps. Running any piece of equipment cranked all the time will wear components out faster than running it in a more reasonable way will. Running an amp nearly all the way up all the time will wear out tubes faster than playing at normal volumes will. Nothing's broken, it's just the nature of the beast.

 

[Mr. Foxen]

Working properly isn't a function of genre. Volume is down to cabs too.

 

[Jeff Scott]

...(or transformers from a company with a fancy marketing department).

But................they are really stacked!

 

[Korladis]

Working properly isn't a function of genre. Volume is down to cabs too.

Not directly, but tube life is affected by how much time is spent running them hard. If it is the norm in a genre to crank the amps up all the way at every show and near all the way at rehearsals, that is going to cut down on tube life (and likely other components are going to wear out a bit faster than they otherwise would as well).

Yes, I know volume is down to cabs as well. That's why I play through a fairly loud one. But the fact of the matter is, all else being equal (which, in my case, it is, as I use the same rig), playing with my doom band is harder on my gear than playing with my folk/rock band.

My amp works fine. Last retube was about two and a half years ago, best that I can recall. But I don't think it's realistic to say that the tubes that are in it are going to last as long as they would if I were only playing with the folk/rock band.

 

[JimmyM]

D-180 only has six power tubes, but they're 6L6... and it's only a little over half the power of the SVT, so I guess the point still stands. A closer comparison would probably be the V4B... I think... though I don't know what the V4B has for power

Four 7027's for the older ones, four 6L6GC's for new ones. It's been years and years since I played one, but this band I used to play in had a D-180 and I would use it sometimes and liked it. Didn't think it was significantly more powerful than my V4B, but was a nice amp.

 

[Korladis]

Four 7027's for the older ones, four 6L6GC's for new ones. It's been years and years since I played one, but this band I used to play in had a D-180 and I would use it sometimes and liked it. Didn't think it was significantly more powerful than my V4B, but was a nice amp.

Okay, yeah, so that's actually a good illustration of what you said earlier. Comparing the D-180 and V4B, as the latter is rated not that much lower in power than the former, but has less tubes, bigger transformers, and more low end.

 

[Mr. Foxen]

Good sized iron in a 100watter:
Link Removed

 

[teemuk]

Teemuk would be far better at addressing the "musicality" of OT saturation than I, but I suspect it's rather like blocking distortion--when a capacitor-coupled tube reaches grid current limiting; not pleasant at all.

Well, just look at that scope capture and think of harmonics that kind of clipping will produce.

There's a big difference in musicality of clipping such as this...

Compared to this...

...Mainly because that hard clipping alone will only generate -some- harmonics, most still very low order, but all that odd "glitching" in addition to clipping will create plenty of -very high order- harmonic distortion. Which is just universally recognized to sound nasty.

If that kind of misbehaviour is what all clipping design dearly wants to avoid I don't understand why even more excessive and abrupt clipping from OT saturation could ever be beneficial.

Not to mention it would take place on lowest frequencies and thus intermodulation distortion would mess up practically everything when complex waves get amplified. I could imagine the effect would be similar to "farting" from intermodulation distortion distorting every other frequency as well, combined to ear-shattering "screeching" created by the high order harmonics of that kind of abrupt distortion.

 

[Mark Reccord]

And very NASTY clipping too. Basically equivalent to this:

e.g.
Amp produces full power @100 Hz with very little distortion, (upper waveform=voltage, lower waveform=current)

...But @32 Hz there's just plenty of nasty distortion from OT core saturation:

...And it worsens as frequency decreases. Here's @ 25 Hz:

It is even more evident how during saturation magnetic field just suddenly collapses. So OT saturation is pretty much just very abrupt extremely nasty distortion.

I think it's pretty much just a myth that people would actually like transformer saturation. In guitar amps the bandwidths are fortunately too narrow, in bass and PA amplification people prefer BIG rigs (sans saturation) or overall just using SS amps without transformer coupling. Makes sense to me.

Years ago I did some testing where we intentionally drove OTs into saturation and the waveforms were very much like that. When we set the circuit up so the the OT saturated before anything else, it sounded wretched. Wretched. It was a hifi application so we weren't looking to intentionally distort anything, rather we looking for the least offensive overload behaviour, which in this case was overloading the driver stage (SE output so no PI) followed by the output tubes themselves. OT saturation was by far the most offensive, much worse than even blocking distortion.

Good discussion. Love your posts @teemuk, @nashvillebill and @agedhorse! Always worth taking the time to read them.

 

[ThisBass]

Well, just look at that scope capture and think of harmonics that kind of clipping will produce.

There's a big difference in musicality of clipping such as this...

Compared to this...

.

Totally agree because there are two saddle points recognizable at trace #2. These saddle points generate additional (odd) frequency content that is obsolete at trace #1. I suppose the appearnce of these saddle points just before the signal clipps at the peak. But I have no idea about the transiation where saddle point distortion starts in realtion to peak clipping. I suppose appearence of saddle points narrow to peak clipping. But that's then unusal to tube power amps. I'm missing the 100/120 Hz riddle at the top of the signal that tube power amps normally show at overload range. Where did you picked the trace?

...Mainly because that hard clipping alone will only generate -some- harmonics, most still very low order, but all that odd "glitching" in addition to clipping will create plenty of -very high order- harmonic distortion. Which is just universally recognized to sound nasty.

That's a very valid point.
IME lots of (well known) tube power amps generate distinct amount of distortion alrready at around 50% of rated output power. No clipping nothing at all, but distortion at this 50% power point is genrated by the development of saddle points. That's a totally different Harmonic content then soft or hard clipping, but, when hard clipping comes into play it isn't as hard as it looks like because there is (at this point) already lots of THD due to distortion of saddle points. By the way ampeg svt amps are very different but that's a different story.

If that kind of misbehaviour is what all clipping design dearly wants to avoid I don't understand why even more excessive and abrupt clipping from OT saturation could ever be beneficial.

Distortion does not always mean it's clipping at the top of the signal. Saddle point "distortion" can be considered as a bias distortion that comes into play close below overload range. And indeed this kind of distortion can sound very musically in combination with "hard clipping".
Most tube power amps reduce power above a certain point of Master setting, that's then due to slightly asymmetric development of the signal at the output. At that point, although a power amp may clip hard, but due to saddle points and slightly aysymmetric signal (reduced power) a power amp can sound very musically despite of hard clipping!

Not to mention it would take place on lowest frequencies and thus intermodulation distortion would mess up practically everything when complex waves get amplified. I could imagine the effect would be similar to "farting" from intermodulation distortion distorting every other frequency as well, combined to ear-shattering "screeching" created by the high order harmonics of that kind of abrupt distortion.

Totally agree

 

[agedhorse]

Saturating an audio transformer is not unlike current clipping an inductive load in a solid state amp where the VI protection is set with inadequate margin. About the most nasty sounding of all distortion. Made even more so because it doesn't happen at zero crossing which a (just a little) more benign.

 

[teemuk]

I'm missing the 100/120 Hz riddle at the top of the signal that tube power amps normally show at overload range. Where did you picked the trace?

These are actually from a solid-state power amp. The "nasty" oscilloscope capture shows how some solid-state amplifiers can misbehave during clipping: Voltage amplifying stage is driven to deep saturation and it does not recover from it instantenously so we get that "rail sticking" hysteresis, which creates high order harmonics totally irrelevant to the signal and sounds terrible. The "clean" capture shows how the amp starts to perform once deep saturation of the voltage amplifying stage is prevented.


I mainly posted that to demonstrate "visual" difference of horrible clipping and much "nicer" clipping. It's not neccessarily "hardness" of the clipping that sounds terrible, it's all those random "glitches" and the high order harmonics created by them that start to make things sound very nasty.

Transformer saturation is not quite the same as behaviour in these waveform captures (as you can observe from the previous oscilloscope captures) but it does introduce similar random "glitching" so you can expect that it's something good design dearly tries to avoid at all costs.

Saturating an audio transformer is not unlike current clipping an inductive load in a solid state amp where the VI protection is set with inadequate margin.

Good analogy. The clipping is indeed pretty much similar as current flow just abruptly halts, and with typical VI limiting it doesn't happen "nicely" in the top portion of the wave, like it doesn't happen in transformer saturation either. Yep, many agree on that over sensitive VI limiting sounds extremely horrible. ...And OT saturation is practically analogous to it so.... You get the point.