Looking Forward To Hearing Class A

engtaz

Congrats on your house warming audio purchase.

heiney9

No doubt a killer amp. Glad you are happy with it. Not to burst your bubble but there is no way that amp is Pure class A at the stated wattage. It's physically impossible considering the size of the heatsinks and chassis.

I'm sure it's heavily biased in class A up to a point but then switches to AB. That is one of the reasons it sounds so good because it stays in class A probably up to about 15-20 watts or so.

I'm really not trying to rain on your parade but just adding a little perspective. Bendini makes great stuff from what I understand. The amount of energy an amp has to dissipate while idling at max. output is huge (at 250watts). There are only a handful of manufacturer's that make high power Pure Class A amplifiers.

I suppose this all depends on your interpretation of class A.

H9

Face

engtaz wrote: »

Congrats on your house warming audio purchase.

Ain't that the truth. I should move my amps into my bedroom, I could probably go all winter without turning my heat on.

snow

heiney9 wrote: »

No doubt a killer amp. Glad you are happy with it. Not to burst your bubble but there is no way that amp is Pure class A at the stated wattage. It's physically impossible considering the size of the heatsinks and chassis.

I'm sure it's heavily biased in class A up to a point but then switches to AB. That is one of the reasons it sounds so good because it stays in class A probably up to about 15-20 watts or so.

I'm really not trying to rain on your parade but just adding a little perspective. Bendini makes great stuff from what I understand. The amount of energy an amp has to dissipate while idling at max. output is huge (at 250watts). There are only a handful of manufacturer's that make high power Pure Class A amplifiers.

I suppose this all depends on your interpretation of class A.

H9

No worries H9. Your not bursting my bubble:p Pretty much everyone I have talked to about this amp including previous owners say the same thing.

Depending on who you talk to it stays in class A 15-45 watts. The only way to find out for sure is probablly to contact Bedini electronics and ask them. There is not a lot of info on the web.

The good thing is that the SDA SRS 1.2 tls are efficent enough that most times I rarely use more than 20 watts or so im sure, considering that at 20wpc it would be over 104 DB allready.

Which considering that I am only 8-10 feet away from the speakers is usally plenty loud enough.

I figure if I play it louder than that its probally some classic AC/DC or something anyhow which sounds better louder but not really critical listening material.

Right now I am enjoying the way it provides a wide/deep rich warm detailed soundstage with more than enough ummph when called for without hesitation.:)

Thanks for all the kind words and congrats everyone.

SNOW

gidrah

You're going to love it. I'm running a BA-801 that I hope to never give back to the owner that loaned it to me about 3 years ago.

snow

gidrah wrote: »

You're going to love it. I'm running a BA-801 that I hope to never give back to the owner that loaned it to me about 3 years ago.

Thanks gidrah.:)

snow

Ok I decided to email Gary today and ask him whether this amp was A/B switching or pure class A and if he had any rack handles available, and this was his response.

Dear Daniel,

The BA-803 is using a feed-forward class A design, which means that the amplifier idles in class AB and when driven switches to full class A mode. This was designed to conserve energy, as compared to our older 25/25's, which were built in an earlier time period and stayed full-on all the time.

Unfortunately, we do not have any handles for the BA-803 series amplifiers any longer.

Best regards,
Gary

From what little I know about class A amps this allows it to have smaller heat sinks and run in pure class A mode. Supposedly it is easier on the amp and runs cooler while there is a load on it. I am sure if I am wrong in my thinking here someone will pipe up and tell me lol.


REGARDS SNOW

heiney9

snow wrote: »

Ok I decided to email Gary today and ask him whether this amp was A/B switching or pure class A and if he had any rack handles available, and this was his response.

Dear Daniel,

The BA-803 is using a feed-forward class A design, which means that the amplifier idles in class AB and when driven switches to full class A mode. This was designed to conserve energy, as compared to our older 25/25's, which were built in an earlier time period and stayed full-on all the time.

Unfortunately, we do not have any handles for the BA-803 series amplifiers any longer.

Best regards,
Gary

From what little I know about class A amps this allows it to have smaller heat sinks and run in pure class A mode. Supposedly it is easier on the amp and runs cooler while there is a load on it. I am sure if I am wrong in my thinking here someone will pipe up and tell me lol.


REGARDS SNOW

I can honestly say I'm stumped. Never heard of a design that idles in A/B and then switches to A......never. Who cares if you like it, right.

H9

snow

heiney9 wrote: »

I can honestly say I'm stumped. Never heard of a design that idles in A/B and then switches to A......never. Who cares if you like it, right.

H9

Yes thats the only thing that truly matters.:) I was able to locate this link which provides a little info on the feed forward design but not as much as i would like to know.

http://www.icehouse.net/john1/index001.html

On page 2 it has a nice write up about the 25/25 RuSsMaN's favorite amp.

REGARDS SNOW

Early B.

heiney9 wrote: »

I can honestly say I'm stumped. Never heard of a design that idles in A/B and then switches to A......never.

Heiney -- goggle it. Then tell us what it says in layman's terms. Too much techno babble for me.

Systems

snow wrote: »

The BA-803 is using a feed-forward class A design, which means that the amplifier idles in class AB and when driven switches to full class A mode. This was designed to conserve energy, as compared to our older 25/25's, which were built in an earlier time period and stayed full-on all the time.

This seems like a similar idea as to what Nelson Pass did with the Thresold STASIS series of amps.It is a dynamic bias scheme that changes according to the signal,unlike pure class a where the bias is max all the time.This improves efficiency and reduces the amount of heat generated.

Systems

Just to add a tidbit, back in the early 80's the Japanese tried to copy Thresholds sliding bias idea and several marketed amps with this,maybe you remember Technics with their New Class A and JVC had Super A.

snow

GV#27 wrote: »

This seems like a similar idea as to what Nelson Pass did with the Thresold STASIS series of amps.It is a dynamic bias scheme that changes according to the signal,unlike pure class a where the bias is max all the time.This improves efficiency and reduces the amount of heat generated.

From the last couple of hours of reading and searching my **** off lol, this appears to be what it does. it raises and lowers the bias and the amp actually runs cooler believe it or not the harder you push it.

Krell had something similar in some of there amps a while back called "Sustained Plateau Biasing'' which adjusts the bias up or down. Here is a link to an article in stereophile.

http://www.stereophile.com/amplificationreviews/404/

REGARDS SNOW

heiney9

GV#27 wrote: »

This seems like a similar idea as to what Nelson Pass did with the Thresold STASIS series of amps.It is a dynamic bias scheme that changes according to the signal,unlike pure class a where the bias is max all the time.This improves efficiency and reduces the amount of heat generated.

Nothing like STASIS the way Snow's e-mail describes it. STASIS was a heavily biased class A (A/B) amplifer and used a push-pull cascode type amplifier section with a main and bootstrap amplifer to establish linearity.

H9

cfrizz

Oh for gods sake who cares!:rolleyes:

Snow congrats! Now stop researching & questioning & sit back & enjoy some damn music!;)

heiney9

cfrizz wrote: »

Oh for gods sake who cares!:rolleyes:

Snow congrats! Now stop researching & questioning & sit back & enjoy some damn music!;)

Well we are guys, and we (I) like to figure out how things work . But in the end enjoy the amp and most of all enjoy the music.:)

H9

snow

cfrizz wrote: »

Oh for gods sake who cares!:rolleyes:

Snow congrats! Now stop researching & questioning & sit back & enjoy some damn music!;)

Lmaooo. Thanks Cathy. Ok im done searching.

H9 here is another tidbit concerning the "sustained plateau design"

I am sure it must be something similar to this.

Krell KSA-200S
Krell's new KSA-200S is a large stereo chassis, conservatively rated at 200Wpc into 8 ohms (23dBW). The rating continues to double down to a 1 ohm loading, where a 1600Wpc output is specified. Krell's proprietary output-stage bias system delivers dynamic class-A operation up to the maximum 8 ohm power rating, with an increasing proportion of class-AB operation with the higher current associated with lower load impedances. This "Sustained Plateau" biasing scheme is said to offer the sonic benefits of pure class-A without the massive energy inefficiency and correspondingly huge, hot heatsinks. The energy-conscious KSA-200S idles at 120W. If it ran in pure class-A, it would have to idle at around 1kW—over eight times as much wasted energy drawn from the wall.

Irregardless of whether this thing runs in class A or A/B or both It sounds Damn good and thats all that matters.

REGARDS SNOW

heiney9

snow wrote: »

Lmaooo. Thanks Cathy. Ok im done searching.

H9 here is another tidbit concerning the "sustained plateau design"

I am sure it must be something similar to this.

Krell KSA-200S
Krell's new KSA-200S is a large stereo chassis, conservatively rated at 200Wpc into 8 ohms (23dBW). The rating continues to double down to a 1 ohm loading, where a 1600Wpc output is specified. Krell's proprietary output-stage bias system delivers dynamic class-A operation up to the maximum 8 ohm power rating, with an increasing proportion of class-AB operation with the higher current associated with lower load impedances. This "Sustained Plateau" biasing scheme is said to offer the sonic benefits of pure class-A without the massive energy inefficiency and correspondingly huge, hot heatsinks. The energy-conscious KSA-200S idles at 120W. If it ran in pure class-A, it would have to idle at around 1kW—over eight times as much wasted energy drawn from the wall.

Irregardless of whether this thing runs in class A or A/B or both It sounds Damn good and thats all that matters.

REGARDS SNOW

What threw me initially was the way the e-mail he sent you was worded. There are probably over 50 amp topologies that have some sort of variation like this from input to output. Interesting design nonetheless and looks to be a beefy over built unit which is always cool :cool: .

H9

Systems

heiney9 wrote: »

Nothing like STASIS the way Snow's e-mail describes it.

H9

The STASIS units have a sliding bias scheme do they not?Therefore if the bias is changing dynamically with the signal it is similar in this respect to what Bedini says of his unit.:)btw.Did you email email Nelson for the technical clarification?

heiney9

GV#27 wrote: »

The STASIS units have a sliding bias scheme do they not?Therefore if the bias is changing dynamically with the signal it is similar in this respect to what Bedini says of his unit.:)btw.Did you email email Nelson for the technical clarification?

I don't think so. I admit it's been a few years since I looked at the technical papers on STASIS and I really don't know anything about the Bendini amp in question other than SNOW's e-mail response. It just struck me funny the way it read.

No doubt they are probably more similar than dissimilar. I don't think I've ever heard of STASIS refered to as "sliding bias scheme" From what I remember the bias was fairly constant, he used essentially (2) amplifiers in a cascode type scheme to allow it to be unconditonally stable and have no negative feedback in the output loop. I didn't bother Nelson this time to answer this question . STASIS runs very hot all the time and even hotter when driven hard.

snow

Let me throw this into the mix. It should either help to understand or futher confuse us all. (I) am allready confused. This is talking about the 200/200 which was the first amp Bedini made that used the feed forward, positive feedback design.

This amplifier used the first feed forward dual diff-amp front end. the output stage was a quasi-complementary design, John Bedini and Jack Strelioff were the first amplifier company to do it with this new design you could split the sing wave into a plus and minus and put it back together again in the output , with decreased distortion. These amplifiers in the 70'swere the first to drive the Infinity QSL loudspeaker systems at ear- busting levels of over 450 watts RMS. The Amplifiers were in a "Pull out Modules" The front panel included , over tempeture lights and fuse lights,and a power indictor. The output transistors that were used were the RCA 1B05's. the circuit boards were mounted inside the modules connected by Molex connectors.


The only amplifier that can challenge the Bedini Amplifier is another Bedini. The result is always a draw because every Bedini pure class A stereo amplifier has the same "Lab Standard" specifications. Whether you're listening to the low-level model 10/10 or the newest 200/200 or even the 25/25, 45/45, 100,100 models, you can rely on the same performance except for the power output. Designer John Bedini 11 years of research uncovered what others are beginning to discover: negative feedback can look good on the lab bench, but it cannot make amplifier distortion (TIM. SID) go away. Negative feedback it seems, produces it's own problems, such as frequency phase shift.

Bedini positive feedback design produces a constant source current, resulting in an amplifier unrivaled in transparency, depth of perspective, definition of inner detail and crystal smoothness of highs. Thus, Bedini's were not designed to pass sine waves in a lab. they were designed to pass musical instrumentation for musical listing enjoyment.

To prove the point that this class A series of DC-coupled amplifiers works small miracles, try a lightweight 25/25 with a pair of Quad electrostatics, Perfecto!.

Besides its sonic achievements, the 200/200 (with top open) has impressive specifications: Frequency response at 1W is flat from DC to 200Khz and at full power: DC to 40Khz: at 200 watts per channel into 8,4, or even down to 1.2 ohms ( the unit is always stable). THD from 20 to 20Khz is no more then 0.25%. It takes a mere 1/2 volt to drive the 200/200 to a full 200 watts per channel.

REGARDS SNOW

heiney9

snow wrote: »

Let me throw this into the mix. It should either help to understand or futher confuse us all. (I) am allready confused. This is talking about the 200/200 which was the first amp Bedini made that used the feed forward, positive feedback design.

This amplifier used the first feed forward dual diff-amp front end. the output stage was a quasi-complementary design, John Bedini and Jack Strelioff were the first amplifier company to do it with this new design you could split the sing wave into a plus and minus and put it back together again in the output , with decreased distortion. These amplifiers in the 70'swere the first to drive the Infinity QSL loudspeaker systems at ear- busting levels of over 450 watts RMS. The Amplifiers were in a "Pull out Modules" The front panel included , over tempeture lights and fuse lights,and a power indictor. The output transistors that were used were the RCA 1B05's. the circuit boards were mounted inside the modules connected by Molex connectors.


The only amplifier that can challenge the Bedini Amplifier is another Bedini. The result is always a draw because every Bedini pure class A stereo amplifier has the same "Lab Standard" specifications. Whether you're listening to the low-level model 10/10 or the newest 200/200 or even the 25/25, 45/45, 100,100 models, you can rely on the same performance except for the power output. Designer John Bedini 11 years of research uncovered what others are beginning to discover: negative feedback can look good on the lab bench, but it cannot make amplifier distortion (TIM. SID) go away. Negative feedback it seems, produces it's own problems, such as frequency phase shift.

Bedini positive feedback design produces a constant source current, resulting in an amplifier unrivaled in transparency, depth of perspective, definition of inner detail and crystal smoothness of highs. Thus, Bedini's were not designed to pass sine waves in a lab. they were designed to pass musical instrumentation for musical listing enjoyment.

To prove the point that this class A series of DC-coupled amplifiers works small miracles, try a lightweight 25/25 with a pair of Quad electrostatics, Perfecto!.

Besides its sonic achievements, the 200/200 (with top open) has impressive specifications: Frequency response at 1W is flat from DC to 200Khz and at full power: DC to 40Khz: at 200 watts per channel into 8,4, or even down to 1.2 ohms ( the unit is always stable). THD from 20 to 20Khz is no more then 0.25%. It takes a mere 1/2 volt to drive the 200/200 to a full 200 watts per channel.

REGARDS SNOW

Is that taken form Bendini sales literature .

H9

tonyb

cfrizz wrote: »

Oh for gods sake who cares!:rolleyes:

Snow congrats! Now stop researching & questioning & sit back & enjoy some damn music!;)

Ya hit this one Cathy!!

snow

heiney9 wrote: »

Is that taken form Bendini sales literature .

H9

Yes it was lol.:p I was hoping that it would shed a little light on how the Feed Forward and positive feedback designs worked though.

Guess I could have removed all the hype though huh.

REGARDS SNOW

Systems

heiney9 wrote: »

. I don't think I've ever heard of STASIS refered to as "sliding bias scheme" From what I remember the bias was fairly constant, .

http://stereophile.com/solidpoweramps/16threshold/
Well here is a link to a reveiw of an older Thresold amp.As mentioned apparently the older STASIS units where of the sliding bias variety.(bias dynamically changes with signal). Now I remember in the early 80's when the Japanese marketed their pseudo class A amplifiers they where commonly refered to as sliding bias designs.As they seem to do a lot back then(like China does now:eek:)they conveniently borrowed the concept from Threshold.

Sorry Snow for the hi jack but I find this amp design stuff very interesting.:)

heiney9

GV#27 wrote: »

http://stereophile.com/solidpoweramps/16threshold/
Well here is a link to a reveiw of an older Thresold amp.As mentioned apparently the STASIS circuit is of the sliding bias variety.(dynamically changes with signal) .Now I remember in the early 80's when the Japanese marketed their pseudo class A amplifiers they where commonly refered to as sliding bias designs.As they seem to do a lot back then(like China does now:eek:)they conveniently borrowed the concept from Threshold.

Sorry Snow for the hi jack but I find this amp design stuff very interesting.:)

Well in reading it I found this direct quote form the first paragraph:

The SA-1 and its lower-powered sister SA-2 are the latest from Threshold, and are the first Threshold amps to abandon sliding bias for straight class-A operation. Both use the Stasis circuit.

And this pretty much sums up STASIS and it doesn;t seem to me to use a "sliding bias scheme" to achieve the desired results. *shrug*

Normally, any attempt on the part of the voltage amp to develop an output voltage would be stymied by the current drawn off immediately by the loudspeaker load. Virtually no voltage would develop. But backing up (as it were) the SA-1's voltage amp are two banks of current-amplifying devices—output transistors—and a proprietary current-sensing circuit between the voltage amps and the loudspeaker. Whenever the sensor detects current being drawn from the voltage amplifier, it gates open the output transistors, which dump in as much current from the amp's power supply as is necessary to bring the signal voltage across the speaker up to the same level that the VA is trying to deliver.

For example, let's say the VA is trying to deliver 5 volts. Before the speaker's current drain has time to deplete this, the output transistors will dump enough current through the speaker to bring the voltage across it up to 5 volts. The voltage amp, seeing 5 volts at its output, will then deliver no current at all, just as though it were working into an open circuit.

The current gating must only be able to respond faster than the delivered voltage changes, in order to keep "on top" of the ever-changing current demands. As long as it does, the voltage amp will "see" what is essentially an open-circuit load. Thus, since we define work in terms of power consumed, it can be fairly stated that the Stasis voltage amps do no work at all, which greatly simplifies front-end power supply design. Devilishly clever, wot?

Not arguing, just getting into the conversation as I'm intrigued as well.

heiney9

nm.....

Systems

It appears that the first generation of STASIS models had the sliding bias thing going on but they changed that in later models. And it is clear that STASIS is not referencing the bias circuit but other parts of the circuit.

heiney9 wrote: »

Not arguing, just getting into the conversation as I'm intrigued as well.

No arguments here either I think we both have an interest in this stuff and I enjoy civil exchanges about all things audio.:)

heiney9

GV#27 wrote: »

It appears that the first generation of STASIS models had the sliding bias thing going on but they changed that in later models. And it is clear that STASIS is not referencing the bias circuit but other parts of the circuit.
No arguments here either I think we both have an interest in this stuff and I enjoy civil exchanges about all things audio.:)

Agreed, but as I understand a "sliding bias scheme" (or variation) was very popular in the 70's in amplifier design.

Good discussion!

Systems

heiney9 wrote: »

Agreed, but as I understand a "sliding bias scheme" (or variation) was very popular in the 70's in amplifier design.

Good discussion!

When did Threshold start mid 70's?other than them I have no idea who was doing this back then.I know several of the big JA PAN companies introduced units in about 1980 ish.

Back then when I was starting out in this hobby I made the mistake of buying one of these bad boys a Technics SU V6.I was seduced by the sexy looking aluminum face plate and by the cleverly worded spec sheet that said it was a state of the art amplifier.To this day I rank it as the worst sounding integrated amp I have ever heard but it was also the best looking component I have ever owned.I sold it and bought a little NAD 3020.Sure it was fugly but boy did it sound good.