Class A vs AB impact on bus compressors and use of neve cards in output buffer

[amplexus]

I officially serviced their units in the US for about 6 months as there us tech. My "official" diagnosis resource from stam was "look at the schematic on the website and figure it out". I'm sure that's no surprise to anyone here tho

I did the same as thier “official”
Canadian warranty tech for about 30 seconds until I realized what a shit show they are. I’m sure we had nearly identical experiences.

The SA4k is a gssl (but broken and I doubt they’ve fixed it) with a couple of the expat audio mods built in to the board… If you’re contemplating buying one, I’d advise against it myself.

pretty sure Stam lurks around here. Maybe he’ll show up here and answer the OP’s question

 

[Nickerz]

I did the same as thier “official”
Canadian warranty tech for about 30 seconds until I realized what a shit show they are. I’m sure we had nearly identical experiences.

The SA4k is a gssl (but broken and I doubt they’ve fixed it) with a couple of the expat audio mods built in to the board… If you’re contemplating buying one, I’d advise against it myself.

pretty sure Stam lurks around here. Maybe he’ll show up here and answer the OP’s question

Just wanted to replicate the Neve mod. Like the way it sounds.

Which mods? The turbo mod, anything else?

 

[iampoor1]

I did the same as thier “official”
Canadian warranty tech for about 30 seconds until I realized what a shit show they are. I’m sure we had nearly identical experiences.

The SA4k is a gssl (but broken and I doubt they’ve fixed it) with a couple of the expat audio mods built in to the board… If you’re contemplating buying one, I’d advise against it myself.

pretty sure Stam lurks around here. Maybe he’ll show up here and answer the OP’s question

Sounds like we did!

Oh he must lurk around here, where else do they get new product designs.

 

[FIX]

I am not sure where you got your information but it makes little sense to me. If you are talking about the BA283 class A card, the one with the 2N3055 output transistor, then this has to be run in class A, end of story, because it is a single ended output stage. If you are talking about the BA440 and friends then they are push pull output can can be run in class A/B.

I can find no info on the Stam Audio website about a B283 running in A/B.

Cheers

Ian

If we could figure out how to run a Class A amp class A/B, we would be rich!!! Think of all the power we would save...

 

[JohnRoberts]

If we could figure out how to run a Class A amp class A/B, we would be rich!!! Think of all the power we would save...

Isn't that pretty much the promise of class A/B? The best of both worlds.... while it doesn't deliver the full benefit of class A it trades a little efficiency for a lot less turn on/off misbehavior.

Back in the 80s a class D amp designer (who was smarter than me on that subject) described his class A/D amp approach where the switching devices were held on with a trickle of current to improve their full on/off switching behavior. Keep in mind the power switching devices back then were really terrible compared to modern power switching technology. Class A/D might have made sense back then, now not so much.

JR

 

[ruffrecords]

If we could figure out how to run a Class A amp class A/B, we would be rich!!! Think of all the power we would save...

You CAN run class A push pull amplifier in Class A/B. What would make you rich woulde be running a single ended class A amplifier in class A/B. On the other hand, if you want to save power then Rupert's design is pretty good because the transformer output allows the signal to swing up to twice the rail voltage. This means the theoretical efficiency of class A, instead of being the usual 25%, now becomes 50% so it is only 20% less than the 70% theoretical efficiency of full class B. Bottom line is , Rupert got is right more than 50 years ago.

Cheers

Ian

 

[stamaudio]

I wall say it again, please cut and paste where Stam says the B283 is working in class A/B. The Neve BA283 is a single ended class A amplifier. I cannot be operated in class A/B. The only thing I can find on their web site is this qquoate:

"The “British” mod adds two BV283 cards (the output section of the 1073MP preamp) as a Class A output buffer with 2 Carnhill transformers to the signal making it the perfect way to add low end and effortlessly warm up a mix." No mention of class A/B.

Cheers

Ian

Hello Ian,

I have done both. Maybe this contributes to the confusion.

The original Mod was a Class A amplifier (BA283 card) with Carnhill VTB11148 transformers. This was done "manually" in 2015-16. I added a front toggle switch to the faceplate to select the mod.

On the MK2 (2019) this changed to a 5532 operational amplifier and Carnhill transformers, I don't recall why we implemented this change back in the day but probably for a little more transparency on the mod as requested by some clients.

We have also done an American mod with 2520 op amp's and a 2503 style output transformer.

I hope this clarifies the confusion.

Josh

 

[stamaudio]

I know the guy who "designs" most of the Stam products. He himself admits that the owner is technically ignorant.

Whoever told you I am technically ignorant is absolutely right.

I thankfully have a great team of engineers these days that are both more competent and smarter than I am, we complement each other well.

 

[abbey road d enfer]

Whoever told you I am technically ignorant is absolutely right.
I thankfully have a great team of engineers these days that are both more competent and smarter than I am, we complement each other well.

There is nothing wrong with that, it just assigns a real value to any technical comment you may make.

 

[ruffrecords]

Hello Ian,

I have done both. Maybe this contributes to the confusion.

The original Mod was a Class A amplifier (BA283 card) with Carnhill VTB11148 transformers. This was done "manually" in 2015-16. I added a front toggle switch to the faceplate to select the mod.

On the MK2 (2019) this changed to a 5532 operational amplifier and Carnhill transformers, I don't recall why we implemented this change back in the day but probably for a little more transparency on the mod as requested by some clients.

We have also done an American mod with 2520 op amp's and a 2503 style output transformer.

I hope this clarifies the confusion.

Josh

HI Josh,

Thanks for the clarification. It all makes sense now. I find Facebook so confusing I never go near the place.

Cheers

Ian

 

[Nickerz]

Whoever told you I am technically ignorant is absolutely right.

I thankfully have a great team of engineers these days that are both more competent and smarter than I am, we complement each other well.

Man I want to order this compressor from you but you gotta find a way to be able to order this and have it ship after the order, not 1-2 years in the future.

 

[stamaudio]

Man I want to order this compressor from you but you gotta find a way to be able to order this and have it ship after the order, not 1-2 years in the future.

The compressor is in stock with next day shipping (4K 500 series MK2)

The rack version in sold out and I don't have any plans to build more right now. If I ever do I'll list them on the site.

The 500 series version uses the same discrete VCA's (DBX202C).

Thanks for your interest!

 

[FIX]

Isn't that pretty much the promise of class A/B? The best of both worlds.... while it doesn't deliver the full benefit of class A it trades a little efficiency for a lot less turn on/off misbehavior.

Back in the 80s a class D amp designer (who was smarter than me on that subject) described his class A/D amp approach where the switching devices were held on with a trickle of current to improve their full on/off switching behavior. Keep in mind the power switching devices back then were really terrible compared to modern power switching technology. Class A/D might have made sense back then, now not so much.

JR

My Tonelux op-amp not only shares a current source, but the output is based with 1 extra diode so it's what I call Class AAB, it's in an overlap for 1 third of the signal until it had peaks...

 

[JohnRoberts]

My Tonelux op-amp not only shares a current source, but the output is based with 1 extra diode so it's what I call Class AAB, it's in an overlap for 1 third of the signal until it had peaks...

Can't say that class AAB made it as an official amplifier class topology designation. Back last century I wrote an article for Peavey's Monitor magazine, amp class article mostly pimping Peavey amplifiers du jour.

Seriously there is a lot of work done by amplifier designers to improve upon class A/B with numerous patents. While it is relatively simple to set a simple low power A/B stage with enough class A current to operate cleanly for low level signals (crossover distortion is most apparent for low level HF signals). For power amplifiers too much class A current can result in over heating and even thermal runaway.

Another consideration in power amps providing enough class A current to operate cleanly when cold but not overheat when warmed up. Since transistor Vbe drops with increasing temperature a simple voltage bias, can result in thermal runaway.

JR

PS; There is much more on this subject, but thats enough for now. Here is MORE

 

[FIX]

Can't say that class AAB made it as an official amplifier class topology designation. Back last century I wrote an article for Peavey's Monitor magazine, amp class article mostly pimping Peavey amplifiers du jour.

Seriously there is a lot of work done by amplifier designers to improve upon class A/B with numerous patents. While it is relatively simple to set a simple low power A/B stage with enough class A current to operate cleanly for low level signals (crossover distortion is most apparent for low level HF signals). For power amplifiers too much class A current can result in over heating and even thermal runaway.

Another consideration in power amps providing enough class A current to operate cleanly when cold but not overheat when warmed up. Since transistor Vbe drops with increasing temperature a simple voltage bias, can result in thermal runaway.

JR

PS; There is much more on this subject, but thats enough for now. Here is MORE

But it's in print... Doesn't that make it fact? LOL. Thats why "I called it" AAB. Not quite A, not entirely A/B, more like aA/B. LOL

 

[JohnRoberts]

But it's in print... Doesn't that make it fact? LOL. Thats why "I called it" AAB. Not quite A, not entirely A/B, more like aA/B. LOL

Whatever floats your boat... I tend to lump class G and class H amps together as the single class G/H. The G and H were distinctions without much difference in practice.

I resisted the temptation to invent (name) a new amplifier class for my cap doubled boosted amp rails (PMA 70+). Pushing the amp rail voltages 2x transiently gave me 4x the peak power, actually a pretty good match for typical audio crest factor and signal transients.

JR

PS; My coworkers digital class AD never made it into print AFAIK.