Thanks for explaining this. Since I do not have any requirement that my amplifier function with unbalanced inputs, then I can perhaps optimize for balanced input.
If you want SUSY on the cheap, try out opa1632. It will give you an idea of the sound without much cost. One thought about using LU device in Susy, it would seem that you lose the characteristic that makes it unique. I only say this because i was asking the same questions a couple of moths ago. LU is darling in SE designs if using it for special characteristics ( triode like curve). This is only my opinion and may be incorrect. One thing I THINK Nelson is trying to do many times is find right topology for optimization of a part and its natural characteristics. Either way, I bet you have a lot of fun playing with your creation if for no other reason than it is yours. I wish you good luck and offer what little i know in help.
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Anywhere that noise might normally come from in a high power amplifier.
* Spikes or other noise on the power supply rails (although this source of error would likely affect both arms/legs equally)
* EMI or some other method for environmental noise to get into the circuit (in this example, one part of the circuit may be exposed more than the other half).
Is there an example circuit for a high power amplifier based around the OPA1632? The think about SUSY is that it does not correct errors in subsequent stages, so the power gain stage of an amplifier would not be SUSY unless you find a way to incorporate the speaker terminals into the OPA1632 feedback. It's certainly possible, but it would be a totally new design so far as I am aware. In that regard, I don't know if there is any advantage to starting with the OPA1632 versus one of the Pass circuits.
The more I think about it, the more I believe that I should just skip the LU and use a 'normal' FET. Thus, I should look at changing my layout to allow swapping in different transistors at that point in the circuit.
At the moment, the input FET is not placed where it can be mounted on the heat sink, so my question is whether a cascoded input FET would need substantial heat sinking.
It seems to me that this is not always true. I agree that some kinds of feedback will convert a current source to a voltage source. However, it would also seem possible to apply feedback in a different way and still maintain the current output amplifier.
By the way, I assume that when you say "current source" above, you're not talking about a constant current source as a sub-circuit, but a "current output stage" amplifier. At least that what I was referring to in my earlier comments.
Note that the F1 is a current output stage amplifier, a.k.a. current source amplifier, with feedback. Granted, the F1 employs DC feedback, not AC feedback, but it's still able to incorporate feedback in the circuit and retain current output.
Well, because of everything I said above about current output amplifiers, I have my doubts that SuSy must always be a voltage amplifier.
there is nothing wrong with triodes ( or triode wannabees
) in SUSY stage .whatever you do , first decision is do you need balanced or non-balanced circ ;
that way you're deciding what will be basic nature of circuit
everything after that is hard work , for finding sweet spot
maybe someone here answer you previously that you don't need cascode modulation , when going SUSY with LU+IRFP , not to not use LU .....
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Look up "UGS its UP" by cheffdegear. It shows the use of a switch to allow option of incorporatino of output stage into feedback loop. In GC suspersymmetry thread on pg 70 or so, you have Juma (maker of opa1632, i tihnk) talking about it as a FE. Yo will also find some other very dense but interesting info.
You know more than I, but i believe you may be limiting yourself because of a lack of knowledge of what is possible. Just about anything is possible, but the decision comes down to what is best for your situation. Once you hae decided what route to take, you have only begun the difficult work of optimization of that circuit. This requires measurement and tweaking and listneing. I haev started down the path 3 times and not finished. Always reverting back to known designs. Still collecting equipment for testing to make it a worthwhile endeavor.
there is nothing wrong with triodes ( or triode wannabees
whatever you do , first decision is do you need balanced or non-balanced circ ;
that way you're deciding what will be basic nature of circuit
everything after that is hard work , for finding sweet spot
maybe someone here answer you previously that you don't need cascode modulation , when going SUSY with LU+IRFP , not to not use LU .....
You tried SUSY tube FE yet. Don't know much about anything, especially tubes, but it seems possible.
yes I did
besides other things I tried , we (Juma and me) made tube-lat hybrid on Baby DiyA , for Stein .
more precisely - Juma drew circlotron output follower lat. mosfet stage , and I drew tube SUSY gain stage
Stein made it
there is nothing new under the sun , but that doesn't need to prevent us acting as lizards
besides other things I tried , we (Juma and me) made tube-lat hybrid on Baby DiyA , for Stein .
more precisely - Juma drew circlotron output follower lat. mosfet stage , and I drew tube SUSY gain stage
Stein made it
there is nothing new under the sun , but that doesn't need to prevent us acting as lizards
I want to avoid starting multiple times and never finishing. I am not opposed to op-amps, but I don't really want to start on an OPA1632-based power amplifier unless I come across a working circuit that piques my interest. I am aware that anything is possible. I'm sure that the OPA1632 feedback could be connected to the speaker terminals in a way that would make the SUSY topology function to cancel noise throughout the system. I remember an interview at Analog Devices, when I was fresh out of college, where an op-amp was used in the feedback loop of a very high voltage circuit, and it was fairly simple to imagine how to solve such a challenge. That's not want I want to do today.
Basically, I want to pick a few requirements plus a few nice-to-have features and start as close as possible to existing, proven circuits.
REQUIREMENTS:
1) Balanced input, capable of handling +26 dBu without clipping.
2) Balanced amplifier, capable of rejecting power supply and mains noise by forcing such noise to be common mode on the speaker terminals. This effectively requires floating speaker terminals, neither of which can be grounded or tied to a rail.
3) Super Symmetry, to minimize distortion.
NICE-TO-HAVE FEATURES:
A) Minimal power resistors to avoid excessive wattage losses. This basically means active current sources wherever possible.
B) Cascoding to avoid high wattage input transistors.
ZV7 has basically everything I need, and ZV9 has some nice features that are tempting me.
Rather than restarting the path several times, I'd prefer to stick with something very similar to known circuits so that I can make several amplifiers and build a surround system, rather than never even finish a mono block.
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Due to the balanced outputs of my DAC, my goal is purely balanced circuit. This amplifier will be dedicated to my DAC (both 2-channel and 8-channel models), and I have plenty of unbalanced amplifiers so I don't need to make another.
I'm hoping that I can put pads and traces for potentiometers on this board so I can find the sweet spot. I hope that I can either replace the pots with precision fixed resistors when I build additional channels, or maybe I'll be stuck tuning every single amp. I suppose some of the challenge will be matching transistors.
From memory, cascoding removes the requirement for the input transistors to carry the full power level of the output, thus making the response closer to linear. When you say I don't need cascode, is that because SUSY cancels the distortion whether cascoding is present or not? Also, if I don't cascode, then why would I still have LU+IRFP? Of course, all of the current sources are IRFP, so far, but the only signal transistors are the cascoded IRFP between the LU and the outputs. Without cascoding, I am inclined to think that the IRFP in the signal path would be gone. What am I missing?
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As Zen Mod already told you, the Doughnut offers exactly that. It is tried and tested, and if you behave yourself, you may even get a PCB layout served on a silver plate
Magura
Thanks for pointing out the distinction. There is possibly too much modulation in the circuit I pieced together above, so simplifying the cascode might be a good thing. I would like to retain the pads and traces for cascode modulation - just for the purposes of experimentation and comparison - but I will look into any changes necessary to simplify the cascode section. Suggestions are welcome.
Keep in mind that SUSY only cancels distortion within the feedback loop. There is no limitation on what sorts of outputs can be fed into an OPA1632-based circuit, but unless the feedback includes the speaker terminals, you won't get full SUSY operation as compared to ZV7. As I mentioned earlier in this thread, there should be no fundamental problem with connecting the OPA1632 feedback loop to the speaker terminals, but I haven't seen such a circuit already worked out and tested, and I'm not really too interested in heading down that path.
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Thanks for the reply. Does a giant transformer come on that silver plate?As Zen Mod already told you, the Doughnut offers exactly that. It is tried and tested, and if you behave yourself, you may even get a PCB layout served on a silver plate
Sorry, but it seems that I did not write down all of my requirements:
4) No transformers, chokes, or inductors on the outputs (call this my corollary to the "no capacitors in the signal path" philosophy), i.e., I am not interested in building ZV7-T or ZV7-E.
Admittedly, I only scanned the Choky thread until I saw that giant transformer, and then realized that it was not the design for me to build. I'm already going to have problems dealing with sourcing the heat sinks and chassis for my project, and I do not want to add a giant transformer to the list of exotic parts. Please don't think that I am criticizing the Doughnut, because I realize that it is probably an excellent continuation of the ZV7-T/E that Papa started. It's just not for me; not what I am interested in building.
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