It has reached our shores! (Warning: This is about Bugera/Behringer)

[gigslut]

Originally Posted by fdeck

@gigslut, thanks for that nice explanation. Though I'm not a tube player, I'm curious about all types of bass gear, and enjoy reading about tube technology. The SVT is how I would design an amp if I didn't know about transistors.

I worked out that the input diodes don't go into conduction until the output is well past clipping. I was always curious why there's not a blocking capacitor in the input circuit -- something that I would have added out of force of habit. Perhaps the diodes provide some protection to the signal source in case the first triode breaks or develops a short.

Also, the Bugera is Boring. Focus groups are all well and good, but couldn't they think up anything new? Like a sweepable mid?

I would assume the blocking caps would be in the preamp chassis (not shown) so you aren't carrying DC plate voltage from the previous stage through the cable connecting the chassis.

The fact that the diodes allow the amp to be driven well past clipping before conduction also indicate that the cathode followers are indeed intended to push the amp into AB2 operation, though with those big grid stoppers, it would probably compress a lot.

[Downunderwonder]

The voice control is basically a mid shift iirc from the old bashfest.

[fdeck]

Originally Posted by gigslut

I would assume the blocking caps would be in the preamp chassis (not shown) so you aren't carrying DC plate voltage from the previous stage through the cable connecting the chassis.

The fact that the diodes allow the amp to be driven well past clipping before conduction also indicate that the cathode followers are indeed intended to push the amp into AB2 operation, though with those big grid stoppers, it would probably compress a lot.

I've always been curious how much compression there is, when the amp has negative feedback. This is one of the mysteries of tube amps that I've never been able to delve into.

[gigslut]

Originally Posted by fdeck

I've always been curious how much compression there is, when the amp has negative feedback. This is one of the mysteries of tube amps that I've never been able to delve into.

NFB can only do so much and when the output section has no more to give, gain rises substantially in the PI in amps with heavy NFB, which can cause things to get ugly. That's one of the the issues Aiken talks about, and he recommends reducing NFB in amps. The NFB resistor is a 47k that feeds a voltage divider that dumps most of it to ground, and the rest to the cathode of the driver side of the cathodyne PI. I'm not good at doing math on NFB circuits, but it looks to be minimal. With that 120pf cap in there it looks more of a presence circuit than NFB.

Here's a good article on cathodyne that may shed some light on the purpose of the cathode followers in the SVT. It outlines some of the frailties of the cathodyne phase inverter and offers some unique solutions.

http://www.freewebs.com/valvewizard/cathodyne.html

[Downunderwonder]

Originally Posted by fdeck

.....

Also, the Bugera is Boring. Focus groups are all well and good, but couldn't they think up anything new? Like a sweepable mid?

BVV3000’s 5-position FREQUENCY selector lets you choose the center frequency that best suits your playing style, or the one that brings out your instrument’s true personality. Just select from 220 Hz, 450 Hz, 800 Hz, 1.6 kHz and 3.0 kHz and turn the MIDRANGE knob to boost or cut by as much as 15dB—and that’s a lot! And if you want even more tone-sculpting options, engage the ULTRA-LOW switch for an additional +2 dB boost @ 40 Hz, or the ULTRA-HIGH switch for a soaring top-end boost of +9 dB @ 8 kHz

Sweepable would be better.

[JimmyM]

Hey, what a coincidence! Their 5-position mid switch works just like the SVT-CL's! And wouldn't you know it, but so do the ultra-lo and ultra-hi switches! I guess great minds do think alike. Awesome creativity.

[gigslut]

Originally Posted by JimmyM

Hey, what a coincidence! Their 5-position mid switch works just like the SVT-CL's! And wouldn't you know it, but so do the ultra-lo and ultra-hi switches! I guess great minds do think alike. Awesome creativity.

They say imitation is the sincerest form of flattery. If that is so, the folks at Behringer are the sincerest flatterers around.

[guy n. cognito]

Meh, they know their market. Their selling look-a-likes to people that can't or won't buy the real thing.

[JimmyM]

I see they don't give up nearly as many specs as Ampeg does, either.

[rodl2005]

Originally Posted by gigslut

They say imitation is the sincerest form of flattery. If that is so, the folks at Behringer are the sincerest flatterers around.

+1 this & their SVT3PRO copy are SO blatant it's darn near silly.

It's a wonder that Ampeg can't get em....?
Sure it's an old design etc etc.....
But with THAT many "coincidences" one would think it a few TOO many??

[fdeck]

Originally Posted by JimmyM

I see they don't give up nearly as many specs as Ampeg does, either.

Let's see if 300 Watts is given as an RMS rating.

[calypsocoral302]

Well, I'd like to thank Chef for trying to keep this on-topic.

On the topic of outsourcing, I'll steer clear, except for one, and only one, point... at one point in time, I was vehemently against it. Then, I found out that the American practice of purchasing Chinese-made goods helped lift 20% of the Chinese population out of poverty (not the "Boo-Hoo, I don't have an iPad to compliment my iPhone" kind of "poverty" we have here in the U.S.A, but the "I don't have enough money to feed my children" kind of poverty that most of the rest of world experiences on a daily basis).

While I'd prefer to help my fellow American make a living, if a company selling Chinese-made goods can make an awesome product, well, let's just say I'm not going to feel too bad-- American or Chinese, my fellow man is my fellow man.

That said, I am pretty confident that Bugera was able to copy the specs of the Ampeg SVT-CL pretty accurately-- it's only a 35-year-old-design, after all. My only concern is-- how does the microprocessor-controlled bias affect the signal path? How transparent is it?

[Downunderwonder]

Biasing correct all the time should be invisible from what little I know.

[Arjank]

Originally Posted by rodl2005

+1 this & their SVT3PRO copy are SO blatant it's darn near silly.

You mean their BVP5500 right?
It may look like the SVT3pro but technically it's different, I have the schematics of the SVT3pro and the BVP5500 is not a copy.
The BVP5500 is a very good amp, I do not think it will sound less then the "real" thing. I did not do a direct comparison with the SVT3pro, but I did compare the BVP5500 to a Eden Navigator + poweramp over my 210+8"coax cab. Tone wise it held it's own against the navigator but on high volumes the BVP5500 loses a bit of control over the woofer's compared to the poweramp but that is what you expect from an amp that has a few times less power. For an all in one package and for that price it's a steal!

[Son of Bovril]

Well, the Infinium technology is kinda similar to the Markbass tube amp they brought out that did self biasing, although the ability to run different tubes together does look quite interesting...

I've heard that KT88's can allow for a bit more wattage and headroom than 6550's, if thats true and the circuit is "designed & built correctly" it's possible that this head could give a bit more clean headroom than the average 300watt tube head

[aborgman]

Originally Posted by Mr. Foxen

Always considered the cathode followers to be down to the amount of current you need to drive that many output bottles.

Yeah that is what he's talking about. They're really over voltage protection diodes more than clipping diodes. I usually use back to back zeners or actual TVS diodes for the purpose - but if you're wanting to limit at a single diode drop, Ampeg picked the cheapest and easiest way.

[aborgman]

Originally Posted by JimmyM

Hey, what a coincidence! Their 5-position mid switch works just like the SVT-CL's! And wouldn't you know it, but so do the ultra-lo and ultra-hi switches! I guess great minds do think alike. Awesome creativity.

Eh... and every Ampeg tube amp (and Fender and Marshall and pretty much every other tube amp) works exactly like a reference design put out by RCA in the 1940s.

The Ampeg tone stack? Thank James and Baxandall for their work in the late 1940s/early 1950s.

If we're going to talk innovation in tube amplifier design- we need to go back about 20 years before the SVT, and look at RCA not Ampeg.

[username1]

It was hard to see but looking at the speaker connection it appeared to be able to only handle a 2 ohm load? Is it switchable like an svt?

[rodl2005]

Yes, 4 & 2 ohm switchable, just like an SVT. Strange that,

[JimmyM]

Originally Posted by aborgman

Eh... and every Ampeg tube amp (and Fender and Marshall and pretty much every other tube amp) works exactly like a reference design put out by RCA in the 1940s.

The Ampeg tone stack? Thank James and Baxandall for their work in the late 1940s/early 1950s.

If we're going to talk innovation in tube amplifier design- we need to go back about 20 years before the SVT, and look at RCA not Ampeg.

No, we need to go back to Edison and his light bulb. That's where it all started.