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Tubes Or Solid State, A Perspective

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#81
seamonkey said:
agedhorse pointed out different facts.
Measurements will tell the truth.
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No, what he said was:

agedhorse said:
The diodes are at 0 volts DC, and there's quite a bit of local feedback in the first stage, the second stage is the phase splitter, and the third section is a cathode follower driving the grids (no voltage gain) with some bias coordination.

I do not think there's enough gain for the output stage to be driven into clipping before the diodes begin to conduct, their conduction slope (compression/limiting/distortion) along with the natural clipping of the output stage when pushed harder, will most likely result in a good part of the overdriven sound of this amp.

Sometimes there's more to a circuit than meets the eye, and in this case I think I know WHY they are there and WHY they improve things for the intended market, but since I didn't design the amp, it would be pure speculation on my part. The guys who originally designed the SVT platform are REALLY sharp guys and the one that I know is absolutely qualified to make whatever design decisions he want to... and they have earned (and continue to earn) this respect.
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and

agedhorse said:
Nope, and certainly not in any insulting or condecending way. It's just an interesting circuit with some clever (especially for it's time) twists that are not all that obvious. This is especially true with the biasing and what looks (on the surface anyway) to be some kind of bias compensation going on.

I have not analyzed this circuit, just providing some off the cuff comments based on what it looks like to me.
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The only person who has apparently actually done the measurements is the link I provided, which says the power amp only needs 0.3V to get power tube distortion, and that the diodes are acting as limiters, not there to provide intentional distortion. Agedhorse's comments seem to say that if the amp was pushed hard into distortion, the diodes would come into play, but under normal operation, as pointed out below, they aren't active:

okabass said:
HI
Sorry, that's common BS. SVT power amp needs around 300mV for full power. The pi diodes 1N456 or 1N3070 (similar to 1N4148) start to clamp around 700mV or so (the threshold voltage). So, the power amp distorts much earlier than the diodes start to distort. The diodes are merely a safeguard limiter.
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#82
After reading this thread it sounds like the "all tube" SVT is a hoax. Using semiconductor diodes as a gain stage?!?! And a diode based distortion circuit? Not cool Ampeg. I dont know whats worse. This revelation or the semiconductor rectifier. Boo.

Just kidding! Thats sarcasm. Thats also how easily internet misinformation begins. ;)
 
#83
with all due respect to andy and his level of amp designing genius (and make no mistake...he's a genius), he has already said he THINKS that is what's going on but he hasn't investigated the circuit well enough to say for sure. meanwhile, okabass built an svt clone all on his own, and he has investigated the circuit, so i'd tend to think he's got more intimate knowledge of what these diodes do.

and that is the difference between empirical knowledge and book knowledge, and why this conversation has become ridiculously stupid. okabass built an svt and knows what the diodes do. andy hasn't built an svt or investigated the circuit well enough to make a statement about what the diodes do, and he admits it. seamonkey has read a few books and thinks he knows everything about the svt without so much as being in the same room with one. nope, sorry...not gonna fly.

if you don't know something, be like andy and don't pretend you do, as you will become exposed for what you really don't know. books don't equal experience, and this conversation has become tiresome. now ist ze time on sprockets ven ve dahnce!

0.jpg
 
#84
Well now, looks like my perspective snowballed. Hmmm...
One that is certain, we all have our preferences and we all make our choices based on those preferences, whether we look for tone, weight, whatever. As long as you're happy with our path to whatever it is you look for in an amp, I guess all this is fairly immaterial!

Time to close this puppy down before bloodshed ensues.
 
#85
Back to topic somewhat (sorry about that). ;)

Will Lee said something about tubes vs ss in the BGM interview, about how he loved the sound but hated the feel. I'm very much the same way, except I tend to prefer the sound of ss, too. Until I hear something recorded through tubes - that almost always sounds great.

But the feel I just can't stand, so I stick to ss. Good thing there is SO much amazing gear to choose from these days. :)
 
#86
4-string said:
Back to topic somewhat (sorry about that). ;)

Will Lee said something about tubes vs ss in the BGM interview, about how he loved the sound but hated the feel. I'm very much the same way, except I tend to prefer the sound of ss, too. Until I hear something recorded through tubes - that almost always sounds great.

But the feel I just can't stand, so I stick to ss. Good thing there is SO much amazing gear to choose from these days. :)
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ya, vail johnson says the same thing. they both sound great to me when i hear them, so as an audience member, i couldn't care less what they use as long as they're happy. too bad extremists on both sides don't like giving others the same courtesy.
 
#89
coreyfyfe said:
No, what he said was:



and




The only person who has apparently actually done the measurements is the link I provided, which says the power amp only needs 0.3V to get power tube distortion, and that the diodes are acting as limiters, not there to provide intentional distortion. Agedhorse's comments seem to say that if the amp was pushed hard into distortion, the diodes would come into play, but under normal operation, as pointed out below, they aren't active:
Click to expand...

Well .3v is awful low. If you were to drive a power amp from the amp out of the SVT it just wouldn't be enough for the standard power amp.

So unless it's documented somewhere - I'll just wait until Unclefluffy has a chance to measure it.
 
#91
Pilgrim said:
I don't care what's inside the head - even peanut butter - as long as it sounds good to me. Tube vs solid state = whoinhellcares.

If it sounds good, it IS good. Scientific measurement is irrelevant - only your ears count.
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Oh no - Sacrilege!

That said, I think that it's fair to call folks to task who insist you MUST have a huge, heavy and usually OLD tube amp to sound good - - That's just silly.
 
#92
aborgman said:
Because anecdotal data isn't qualitative data.

Just because someone wins the lottery doesn't mean the odds aren't against winning.
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i talk to a lot of techs, and not one of them has ever told me that ss is generally more reliable, and not one of them told me that tube amps are any more prone to breakage than ss. know what they all tell me? a good design is a good design, and if you take care of your equipment, it takes care of you. anecdotal? for sure. enough for me? certainly. ymmv, and i honestly don't care if it does.

thank you.
 
#93
seamonkey said:
Consumers should should know if what they buy is labeled as "all tube" or 100% peanut free, is or isn't. Ampeg in this case has positioned that an SVT is special being "all tubes". You'd be pissed if you bought 24k gold and it turned out to be 14k. But it looks good, why care?

Ampeg in fact didn't start that way originally. You can find old advertisements. It's just what they had to do at the time to get that much power out. "SVT" was not about all tube. SS amps with that much power didn't come out until a few years after.

Only when "All Tube" became some marketing ploy did Ampeg jump on that marketing hype wagon.

If people like the sound of clipping diodes they can get that many ways. Different, more expensive, cheaper. Pedals, modeling, ... many ways.

Someone could just take a scope to the diodes and show they are or are not not coloring the signal. To me, and modeling similar amps in ltspice - Everything indicates they are. It's a terrible design for any amp protection circuit.
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Fact is a diode does not make a tube amp any less tube. Almost
every tube bass amplifier ever made has diodes in the power supply. I can only think of one or two I have ever seen that had actual tube rectification going on. Horrors!
As far as the SVT and its diodes, big deal. A diode is a passive device. It serves one of two functions, either its used for it's directionality (allowing current to only flow in one direction) or for the break over characteristic.
It does not amplify the signal, it just modifies it, same as an inductor/capacitor circuit modifies the tone. Diodes date back to the tube era and predate the transistor by about 5 decades.
Preamp tubes are still preamping, Power amp tubes are still poweramping.
But hey, if it makes you feel good to try and rain on the tube-o-philes parade, more power to ya.
pun intended.
 
#95
JimmyM said:
i talk to a lot of techs, and not one of them has ever told me that ss is generally more reliable, and not one of them told me that tube amps are any more prone to breakage than ss.
Click to expand...

You're talking right now to an electrical engineer, whose current job title is "Electronics Technician Senior" for a major research university Aerospace Engineering program... and I'm telling you that under normal, by the book, usage SS amps are GENERALLY more reliable.



JimmyM said:
a good design is a good design, and if you take care of your equipment, it takes care of you.
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I don't disagree.

Bad designs trump topology or device choice any day. You can build a turd using anything.

Given a good designed tube and SS amps, both taken care of - the average SS piece will outlast the average tube piece.
 
#96
FWIW, the first four years or so I played bass I lugged an old, Italian made all tube amp around. It was played several times every week, never had an issue. I've owned my Fender Vibrolux for 12 years or so now, never had an issue with that one either.

As far as reliability goes, I trust tube as much as ss. The modern class D stuff OTOH, not so much. Yet! I'm approaching geezer status though. :)
 
#99
aborgman said:
You're talking right now to an electrical engineer, whose current job title is "Electronics Technician Senior" for a major research university Aerospace Engineering program... and I'm telling you that under normal, by the book, usage SS amps are GENERALLY more reliable.
Click to expand...

Are we counting tubes aging and dying as the amp breaking? If people are answering that question differently that may be the cause of the disagreement.

If we're counting tube replacement as the regular cost of doing business then it could go either way.

If tube dying of old age = amp breaking, then the laws of physics are firmly behind the "SS amps are more reliable than equally well built tube amps" POV.
 
#100
Phalex said:
Yeah, I'm intrigued by class D myself. We just blew up one of our PA amps, and I'm very intrigued by class D. I'm also a bit leery, but we need a replacement amp one way or the other........
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I've seen a few issues in both directions. Had a power amp go down for unknown reasons, a power amp go down because we were running it at 2 ohms which is wasn't rated for, and a class-D powered speaker fry something in its power supply. None of this was my equipment, and some of it was user error, but it can happen to any gear, especially when not used properly.

My cover gig is currently using QSC K12s, they're loud, clear, and class-D. Definitely dig the low weight on these when we're loading out.
 
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