Yeah, I get that! LOL.
It's all good. Many thanks to you and the rest of the for all the help and patience. I'm having a lot of fun building up a pair of ACA v1.8 as bridged monos. 😀
The Bridged mode using a single resistor in the 1.6 and 1.8 is quite clever indeed, which is why it was Nelson who proposed using it...
As I understand it for bridged mono mode you need a signal for one channel in phase and for the other channel out of phase. Since the ACA circuit is an inverting amp, the output of a channel is out of phase with the input. So we just take a wire from the speaker output of one channel (which is out of phase compared to the input to the amp) and take a bit of it and send it to to the other channel input, wich isn't connected to the source, so the outputs combine in a "bridged Mono" way..) One channel alternates with the other, driving t he speaker. Of course the signal from the output of a channel is waay too powerful compared to an input signal so the resistor reduces it's power a bunch down to input signal level. Obviously the output stage of an amp has more distortion than an input signal, so the bridged mode does have a bit more distortion, but it's the good stuff.. Perhaps someone else can elaborate. or am I wrong?....
As I understand it for bridged mono mode you need a signal for one channel in phase and for the other channel out of phase. Since the ACA circuit is an inverting amp, the output of a channel is out of phase with the input. So we just take a wire from the speaker output of one channel (which is out of phase compared to the input to the amp) and take a bit of it and send it to to the other channel input, wich isn't connected to the source, so the outputs combine in a "bridged Mono" way..) One channel alternates with the other, driving t he speaker. Of course the signal from the output of a channel is waay too powerful compared to an input signal so the resistor reduces it's power a bunch down to input signal level. Obviously the output stage of an amp has more distortion than an input signal, so the bridged mode does have a bit more distortion, but it's the good stuff.. Perhaps someone else can elaborate. or am I wrong?....
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Variac said:
Ah...this is very useful information to help me understand what is really going on with the circuit topology.
About me: I'm a retired professional scientist; a molecular biologist working in SF Bay Area in the area of molecular diagnostics and human molecular genetics my entire career. I'm also a Design for Six Sigma Master Black Belt. So, of course, as a scientist, I want to understand the WHY behind the WHAT.
These explanations really help my understanding of what the circuit topology is doing. Thanks again! 😀
Not that I am aware of, but James (TungstenAudio) has a really good handle on the functional transformations that this specific circuit topology provides. My guess is James is a professional EE or something similar.
Yeah. That makes perfect sense.
The resistor acts to attenuate the signal back to the original amplitude.
Nelson is so bloody creative.
Amazing.
Trust me.
You can get brainy at this too.
The brain learns to think differently, and all of a sudden you want to knock yourself out for not realising it's easier in many ways than you thought, and at the same time still challenging.
There is always more to learn
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Nah, to him this is just another 1.6, which is the same circuit as the original ACA, just with some different parts values, an extra resistor, the Meanwell 24v power supply and mostly a slightly different PCB layout to fit in the awesome 2ch chassis that Jason developed with HiFi 2000, (which is what made it the 1.6) Nelson did post the bridged idea somewhere here, probably on the basic ACA thread, without explanation, I just tarted it up with some fancy switching. Any vintage ACA can easily be upgraded to current spec.although the 2ch ones are obviously easier to combine into bridged or parallel modes.
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Cheers! You can thank Variac for that.
The piece of the puzzle you're missing, which powers your completely understandable infuriation, is the thing you can't see in the wiring diagram. It's the words and lines physically printed on the rear panel.
The answer to your question is "so the rear panel can achieve its goals without being hampered by historical vestiges" or more simply, "so it can be pretty".
While keeping the old connections would have been ideal in the "if it aint broke don't fix it!" philosophy, V1.8's raison d'être is the design of the new back panel itself. A lot of thought went into the compromises involved in that design and some things had to play second fiddle, including where that resistor went. That's it (I think!).
The end result is very neat and arguable the wiring overall looks much better, at least to me who is a self-admitted symmetry freak.
Thanks, Jason.
And, just to be clear, I wasn't infuriated, just rather confused for a while there.
Your explanation about the back panel also helps to provide more context that helps to drive better understanding.
I've done a lot of professional teaching of Design for Six Sigma in my time, to very smart Phd-level scientists and engineers. As I gained more experience and thus became more effective in my teaching, I was able to provide better examples and better context as to why I was having my students do what they were doing, so they could both learn and also use that insight going-forward in their own work. This is why I was asking for explanations for why the wiring change was made.
It's all good; I understand now, and I really appreciate this community of nice folks helping out. Cheers, mate.
PS: I've been to Melbourne a couple of times; in 2004 and 2005 to photograph the MotoGP at Philip Island with credentials (I'm also a motorsports photojournalist).
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Ahhhh 🙂
Thanks for the explanation, and the Math Tungsten A, I actually found the value you specified originally to be added to R4. I"m almost ready to Build and upgrade my original 1.6. I'm just working out how to install the oversized Vishay replacement resistor for R12 while also mounting the Mica. I may wait to build until after my vacation in a week. That way I will have something cool to look forward to when I get back 🙂.
Again Thank you for your ideas for the Upgrade Path.
Mark
Thanks for the explanation, and the Math Tungsten A, I actually found the value you specified originally to be added to R4. I"m almost ready to Build and upgrade my original 1.6. I'm just working out how to install the oversized Vishay replacement resistor for R12 while also mounting the Mica. I may wait to build until after my vacation in a week. That way I will have something cool to look forward to when I get back 🙂.
Again Thank you for your ideas for the Upgrade Path.
Mark
To beat it to death, the reason the switch is wired as it is, is because it's the ONLY way I could make it work to do its tricks. Panel layout didn't affect the wiring much except IMHO making a resistor lead need to be extended a bit, which compared to all the other design issues we had, was pretty trivial.
We actually kept all the holes in the rear panel in the same positions as the 1.6, as they work well and the chassis maker doesn't have to change anything i.e. a Historical Vestige.It may appear that we could stuff like maybe move the speaker terminals closer together or other changes, but if something works well, then let me tell you even a little change can bite you on the butt! In the past we've had the unpleasant experience of finding chassis brackets interfering with holes for connectors or their diameter mysteriously changing, after production started! And that rear panel is rather small. Connectors and such are already very tightly positioned on the panel in a correct, clean way, That we were able to also fit an entire mini-manual on there regarding hook up options is a minor miracle in itself and took a lot more that 20 hours!
Sometimes people who want to know why, need to spend the time studying a new circuit to understand. (in this case what each switch position does and do stuff like trace the signal route in the different switch positions) That's really educational! Generally all the amps that Papa Pass has published to our great benefit don't explain every detail such as "why is there a resistor or JFET to ground in this particular place". and that includes the ACA. There is no explanation in previous models of exactly how each part contributes and why it is in the circuit in that exact place. There are various 500 page books available to give you a better clue.
Education is a wonderful benefit of building an amp but in our case the main goal is to produce a product that if the instructions are followed, will result in a functional amp, even for a newbie, and all parts are included to accomplish this. And just accomplishing that is incredibly and often painfully educational!
A manual explaining the reasoning behind the function, the positioning in the circuit and options for wiring every part is just way beyond the scope of what we can do. I'm sure that my post just describing the basic way the Bridging circuit works left many people more confused rather than enlightened. Give me 10 pages and 20 hours, and maybe I could do better, but you can see how a manual is a huge amount of work.
We actually kept all the holes in the rear panel in the same positions as the 1.6, as they work well and the chassis maker doesn't have to change anything i.e. a Historical Vestige.It may appear that we could stuff like maybe move the speaker terminals closer together or other changes, but if something works well, then let me tell you even a little change can bite you on the butt! In the past we've had the unpleasant experience of finding chassis brackets interfering with holes for connectors or their diameter mysteriously changing, after production started! And that rear panel is rather small. Connectors and such are already very tightly positioned on the panel in a correct, clean way, That we were able to also fit an entire mini-manual on there regarding hook up options is a minor miracle in itself and took a lot more that 20 hours!
Sometimes people who want to know why, need to spend the time studying a new circuit to understand. (in this case what each switch position does and do stuff like trace the signal route in the different switch positions) That's really educational! Generally all the amps that Papa Pass has published to our great benefit don't explain every detail such as "why is there a resistor or JFET to ground in this particular place". and that includes the ACA. There is no explanation in previous models of exactly how each part contributes and why it is in the circuit in that exact place. There are various 500 page books available to give you a better clue.
Education is a wonderful benefit of building an amp but in our case the main goal is to produce a product that if the instructions are followed, will result in a functional amp, even for a newbie, and all parts are included to accomplish this. And just accomplishing that is incredibly and often painfully educational!
A manual explaining the reasoning behind the function, the positioning in the circuit and options for wiring every part is just way beyond the scope of what we can do. I'm sure that my post just describing the basic way the Bridging circuit works left many people more confused rather than enlightened. Give me 10 pages and 20 hours, and maybe I could do better, but you can see how a manual is a huge amount of work.
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It's now clear to me as Jason pointed out, that Puma Cat was confronted with a more complicated wiring scheme in his kit, when we hadn't had time to post the new photos everywhere or explain what these new features do for you, or have a complete assembly video. and as even now we're still rolling it out.
It is a valid issue that this new model is more complicated, yet for those interested in these features, possibly in the future, it should be exciting news. We do still include the most simple wiring diagram in the online documentation, and I hope we can include that option in the online assembly instructions. It's a good idea to keep your amp as simple as possible when it's one of your first projects.
I'd be remiss not to mention 6L6's famous online assembly manuals. They are amazing, on another level! Certainly the reason so many people successfully make their own ACA.
It is a valid issue that this new model is more complicated, yet for those interested in these features, possibly in the future, it should be exciting news. We do still include the most simple wiring diagram in the online documentation, and I hope we can include that option in the online assembly instructions. It's a good idea to keep your amp as simple as possible when it's one of your first projects.
I'd be remiss not to mention 6L6's famous online assembly manuals. They are amazing, on another level! Certainly the reason so many people successfully make their own ACA.
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I would agree broadly in principal, but I'm going to gently push back on this a little bit, if I may.
I'm not a EE, and I certainly can't look at a schematic of a circuit topology and understand at a glance the functional transformations that a specific circuit topology is supposed to produce. But, when changes to a published protocol are made, e.g. the resistor value changes that Tungsten did for his premium parts enhancements, its helpful to understand the why behind what those changes bring. And Tungsten (James) very kindly and helpfully provided some info and context as to why he made those changes, and I found them to be very helpful.
Likewise, yours and Jason's explanations of why the changes to the wiring shema were made were really helpful as well. And Pico's and Jim's input was informative.
So, many thanks again to this community for being so helpful and proactive.
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