Symasym PCB

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I put together an "alternative" PCB for Mike Bittner's Symasym 5.3, with 2 pairs of output trannies. I do hope he won't mind me "messing" with his amp :smash:

That's about as close as i could get to having a star ground on-board. I implemented John's (MJL21193) idea of 22r//diodes for the small-signal ground "decoupler.

If anyone has ideas for improving this, don't be afraid to step forward and speak your mind :)
 

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Hi Khron,
I have not examined the PCB closely, but there are a couple things that come to mind.

Move the capacitors near your fuse holders towards the front of the PCB. This makes more room for emitter resistors and may allow the use of the "plate" types.

Use normal fuse clips for the "GMA" size fuses. The ones you have there don't look that common and may be very difficult for anyone else to source.

Allow for a single turn 300° type trimmer control. 10 turn types have small wipers and are limited in current, never mind that the single turn types are easy enough to use. I would find a 10 turn annoying as heck! I think there is a resistor in series with the control, can't remember that clearly enough to be sure.

Lastly, possibly allow for smaller input coupling capacitors. Just lay a trace in line and provide extra holes.

-Chris
 
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Hi ostripper,
It's already being done on "frugalamp2" thread.. much higher power "symasym" type amp with MUCH better performance (200-300W) with 6-8 op device scalability...
Sure, but what's wrong with the original design? I think this one might fill a nice gap in a slightly higher power bracket that also allows low impedance loads.

I think this might fill a nice gap between a 50 watt amp and the 200 + watt amp.

-Chris
 
Thanks for all the quick replies / comments :)


Anatech,

I used that type of fuse holders because i've got a bunch of them scavenged from some unused medical PSU's, just for a few of these boards. Same goes for the trimmers: i've got a few 1K or 2K's somewhere at home. Yes, there is a resistor in series with the pot. And besides, is the current going through the trimmer really "too big" for a 10-turn? And i guess a few extra pads for the input cap won't hurt :) (I've gathered a bunch of Roederstein MKT1822 caps, 1,5u-6,8u with that footprint)


OS,

I've been watching your FA2 thread these last few days, and it looks like a really good amp :) It's just those japanese transistors that kinda "scare" me :D ie. not that common, and where i might find them, they're not exactly "for free" :) One of the reasons i chose the Symasym is because of the "usual" transistors used (and getting real good performance from them :smash: )
 
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Hi Khron,
It was found that 500 ohm trimmers worked better. I can verify that as I have some built.

I used that type of fuse holders because i've got a bunch of them scavenged from some unused medical PSU's, just for a few of these boards.
That's what I figured when I saw your PCB. Can you simply add trace to allow the clips to be used? I'm just thinking that the boards are more universal then.

It's just those japanese transistors that kinda "scare" me
I think those Japanese signal transistors are the best there are. Having said that, the new On-Semi power transistors are really good too. I built my first amps with the (now discontinued :bawling: ) MJW0281A and MJW0302A. I haven't seen any transistors so far that were as good as these are. They didn't have the highest ratings, but they were all very close in parameters to each other. I would have very happily standardized these for outputs except in the much higher power ratings.

The Japanese signal transistors are not that expensive. Buy them in 50s or 100s.

-Chris
 
Rev 1, i guess :)


Anatech (i'm Chris too :D )
I tried to follow (a few of) your tips. Here's the result this far:

EDIT: There's a LOT of stuff i'd buy in 50s or 100s, but i'm (still) a mere student, so... Sometimes, that's not an option and / or i have to make do with what i can get my hands on at little or no cost :) I'm sure you've "been there, done that", some time ago :D
 

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Hi Chris,
Much better, thank you.

I guess the board needs to be checked in detail now.

Sometimes, that's not an option and / or i have to make do with what i can get my hands on at little or no cost I'm sure you've "been there, done that", some time ago
Some time ago?? That's a permanent condition.

Or you can overspend and end up with a horrible bill like I did.

-Chris
 
I meticulously simulated the original "symasym" and have
knowledge of it's "big brother" , Ampslab's Bi120.

My answer to this is the FA2, while saluting mike B's contribution
to DIY, and not infringing on Ampslab's IP, offers a very
superior Alternative to both. (prototyped and simulated symasym and found stability problems which were only balanced
by "gross compensation" at OP stages):(

I know you all like your symasym's and I would not want to "bastardize" a good design, but I think there is MUCH room
for improvement ,as some have bet their business on it.
(M. Chua - Ampslab)
OS
 
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Hi ostripper,
My answer to this is the FA2, while saluting mike B's contribution to DIY, and not infringing on Ampslab's IP, offers a very superior Alternative to both. (prototyped and simulated symasym and found stability problems which were only balanced by "gross compensation" at OP stages)
I am always interested in amplifier designs. I can't prove or disprove what you say. However, my comments were simply to encourage Chris' efforts. I think there is a place for the original SymAsym, and also this slightly beefed up version.

Most of my comments directed to you were because you were in effect saying that Chris should simply stop and go with your design. However, that may not be in his best interest and certainly would eliminate the pride and confidence this project brings. It is everyones right to be able to create and build. This is the main point of DIY. I am unlikely to bin my SymAsym amplifiers.

I know you all like your symasym's and I would not want to "bastardize" a good design, but I think there is MUCH room for improvement ,as some have bet their business on it.
Well, yes. Exactly.

Mine were built to drive wall speakers. Once I fired one up, I immediately realized that the basic design was very good, better than it looked (and I expected them to sound good). Once I found this out, my intentions turned to using these amps as a test bed to try different things out with them. Remember, it's just as easy to ruin the performance of the original design. I have even gone so far as to try them with both matched and unmatched parts. The diff pair always being matched. The original SymAsym is an excellent standard to judge other amplifiers on. You do understand that I am not saying they are the best. They are, however, much better than most commercial designs out there.

I am very interested in seeing your design, and may build it also. Your design will be competing with a Marantz 300DC and a pair of new Cyrus Mono X amplifiers. Those are high marks to hit or exceed, partly because I went over the Marantz matching parts and replacing capacitors. ;) It's a much better amp now.

I will similarly encourage you to excel with your design. My hopes are that it should perform better than your expectations, and better than my commercial amplifiers.

-Best, Chris
 
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Khron said:
I implemented John's (MJL21193) idea of 22r//diodes for the small-signal ground "decoupler.


Hi Khron,
I can't take credit for that but I feel honoured that you would attribute it to me :)

I'm not sure what I'm seeing here. Is this a resistor in series with the output? Perhaps you left the load resistor in when making the board layout?
 

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ostripper said:

My answer to this is the FA2, while saluting mike B's contribution
to DIY, and not infringing on Ampslab's IP, offers a very
superior Alternative to both.

:)
Doing a bit of the old soft sell OS?

The Symasym may look like it has problems in simulation, but it is a proven design. Many of the things that make an amp sound good or special may be wrapped up in irregularities that show up during simulation. Who knows. I don't, that's for sure.
I haven't heard the Symasym to make a judgment on it's SQ, not that I'm any kind of discerning listener. I attempted to bend the design a while back to suit the parts that I had at the time but I didn't have the know-how. I met with a lot of opposition to my meddling and I dropped the idea and carried on on my own.
It's good to see others exercise their creativity and do something that could well go down as a worthwhile contribution. There is much to learn from all of these efforts.
 
Since our fellow member , Andy C. introduced me to the "finer aspects" of spice I have modeled ALL the amps offered here.

Having only built quasi, DX, P3a,leach, symasym ...I wanted
something more. All the above relied on the accepted norms
of standard topology. As there are a lot of "off the wall"
ideas thrown around DIY land, I decided to see if any good
"hybrids" could be realized from all of this.

With a buffered widlar CM VAS in my "symasym clone" I've
totally done away with H3-5-7 leaving only minute H2 to
deal with. This amp does not need any comp. "after the fact"
The better aspects are related to the buffer which "ultra
linearizes" the VAS at ANY frequency.

As far as Scalability , I've run the first amp from 25v to
70v with no issues. FA2, (I shouldn't call it a clone) can do
40 to 100v no problem.
I won't go as far to say say the symasym is "flawed"
but we (MJL21193/myself) had a go at it and wondered
how it could be so revered.
OS
 
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Let's stay on track please ....

Hi ostripper,
I won't go as far to say say the symasym is "flawed" but we (MJL21193/myself) had a go at it and wondered how it could be so revered.
I don't think it is revered. I do think it is straight forward to build with a high chance of success. What you get out of it depends on how much skill you can build it with. As I said earlier, the SymAsym is a good reference amplifier. Many people across the world have built them with success.

Now, I would really like to focus on Chris' version of the SymAsym. He started this thread for assistance with his version. Let's stay on track from here on please. I may be forced to do some cleaning here, just to preserve Chris' ideas. He seems to be directly building on the original design - and that is great!

-Chris
 
MJL21193

I'm not sure what I'm seeing here. Is this a resistor in series with the output? Perhaps you left the load resistor in when making the board layout?

That's the 10 ohm // output inductor.

ReiMomo

I think it needs a resistor for each base of the outputs.
oh wait thats the foil side!!! but you still need to fix the emmiter resistors then.

I'm gonna have to ask you to be a bit clearer, please :xeye:


OS,

I never said this Symasym is the "be all, end all" holy grail of amplifiers, but it's just about the best (free, diy) design i've seen, buildable with "normal" parts, many of which i already have. Of course, if you have the knowledge, willpower and available funds, nothing's stopping you from designing and building an amp able to crush all "opposition" :)

I'm just a student trying to make the best of what i have available :smash:
 
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