Hi everyone, could I have people's views about Mike B's Symasym. I wish to build a class AB amplifier and remember that a few years ago this amplifier was very well respected by the DIY community.
Is it still regarded this way or has it been superseded by newer / better amplifiers. ( no disrespect Mike )
I remember that it appeared to be straight forward to build and did not require any "exotic" parts which is what I am looking for.
Any assistance would be appreciated.
Alan
Is it still regarded this way or has it been superseded by newer / better amplifiers. ( no disrespect Mike )
I remember that it appeared to be straight forward to build and did not require any "exotic" parts which is what I am looking for.
Any assistance would be appreciated.
Alan
Hi,
I have built Symasym. It sounds very good. Then I have built DOGC-H by Dr. Borivoje Jagodic and this beats Symasym. DOGC-H sounds more like music, wider, deeper soundstage and more natural. So I recommend you DOGC-H, very simple design yet so effective! If you want PCB I can send you the files.
I have built Symasym. It sounds very good. Then I have built DOGC-H by Dr. Borivoje Jagodic and this beats Symasym. DOGC-H sounds more like music, wider, deeper soundstage and more natural. So I recommend you DOGC-H, very simple design yet so effective! If you want PCB I can send you the files.
OEM wise , the "symasym" is the HK680 input stage (running a triple EF).
DIY wise , I've built several versions that are superseded by my "symasui".
It ranks up with the "blameless" , leach .... can be brought down to near
single digit PPM THD. Good design.
OS
Hi Alan,
My board design based on Mike B's "SymAsym the Sequel" conceptual schematic from back in 2006 is probably the finest 100 watt/8ohm amp I've ever built. In fact it's been playing in my system for over 5 years and nothing not even several popular kits has been able to replace it.
Here's the link to my GB back in 2010 in case you're interested.
http://www.diyaudio.com/forums/soli...-sequel-aaks-rev_1-4-pcb-builders-thread.html
Best regards,
Al
My board design based on Mike B's "SymAsym the Sequel" conceptual schematic from back in 2006 is probably the finest 100 watt/8ohm amp I've ever built. In fact it's been playing in my system for over 5 years and nothing not even several popular kits has been able to replace it.
Here's the link to my GB back in 2010 in case you're interested.
http://www.diyaudio.com/forums/soli...-sequel-aaks-rev_1-4-pcb-builders-thread.html
Best regards,
Al
It requires matching of many pairs.
Input pair (cascode pair, if fitted),
second LTP pair.
mirror pair (and mirror third if fitted).
Output pair if the double version (the last of AAK's PCBs).
Collector loads and emitter resistors need matching.
BTW, replacing the input pair BJT, to become 2sk170 is a good mod. (different pin out and same with bc550)
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Hi mjona,
Good catch, but the test was done without an L/R on the output purposely. I recommended it be added externally since there's no room on the board. IMO a better place to put it anyway. 8//2uF is pretty extreme test more common in electrostatic speakers than regular speakers.
If you want to check out some stability measurements take a look below. Check pg. 1 & 6.
http://www.diyaudio.com/forums/solid-state/77562-my-killer-little-amp.html
Best regards,
Al
Good catch, but the test was done without an L/R on the output purposely. I recommended it be added externally since there's no room on the board. IMO a better place to put it anyway. 8//2uF is pretty extreme test more common in electrostatic speakers than regular speakers.
If you want to check out some stability measurements take a look below. Check pg. 1 & 6.
http://www.diyaudio.com/forums/solid-state/77562-my-killer-little-amp.html
Best regards,
Al
Member
Joined 2009
Paid Member
I posed my question about stability margins and 8 ohm plus 2 uF in parallel having looked at the claims made on Mr Bittner's website. For me this would be the quickest way to resolve what I saw as a credibility gap firstly over a figure for gain bandwidth for the 5.3 version of approximately 400 MHz and a phase margin of 90 degrees.
There is a link to a version by Mr Macura whose assessment is 1.4 MHz. He gives a stabilty margin of 56 degrees on the basis of -124 degrees at that 0 dB point. The link to the plots does not work however I think the phase shift figure is in error.
It is known that stored charge effects in Class B transistor output stages cause delays and phase shift from a point a decade in frequency ahead of the start of gain decline in loop gain. A reversal in phase to -180 degrees will always arise before the feedback gain has decined to less than one.
If the quoted phase margins have substance then the proposed test load should indicate a satisfactory result - free of significant overshoots, or ripple effects. I have strong doubts over this and no backer seems willing to take on the challenge.
Your Little Killer Amplifier does O.K. on that test load so it should handle transient signals in a real life situation.
However this follows a common practice in using a small Miller capacitor across the voltage amplifier transistor to create a single dominant pole at high frequency. This strategy has another advantage of making that stage more linear since it is an inverting amplifier.
You would perhaps want to add a low pass filter on the input to ensure the signal input does not exceed the slew rate capacity of that stage.
I suggest your Little Killer Amplifier sets your benchmark in terms of transient performance in a practical situation.
My question to you is whether or not your more complex Symasym with various forms of compensation can match this on the same bench load.
Hi alibear,
I built a few SymAsym amplifiers. I originally built one as a utility amplifier knowing it would sound good. Well, it sounds great. I have 6 more boards to build after I am finished some modifications (2SK170 pair for one). Yes, matching pairs of transistors really helps the sound quality out, but this is common to all amplifiers. My original 5.3 builds sound great even now. Do I have stuff that sounds better? Sure I do, but they are more complicated and higher power. I listen to the SymAsym, which was not the intended use when I first built one. For the money and output power, these are hard to beat. This would make an excellent first amp project that will reward you for years to come.
mjona,
People are not having a problem with these amplifiers. There was initially an issue when using different output transistors, but adjusting the compensation fixed that right away. Today there are versions that use all kinds of outputs. It is reasonably forgiving as long as you adjust the compensation if you use different outputs than they were designed with. No surprises there. I used the On-Semi MJW0281A and MJW0302A - excellent. I don't know what bugs you about the SymAsym, but give it a rest. More versions of that amp exist in the world than most any other "community kit" amp, not unless amps designed by ostripper have been more popular, and they may have as I was away for a few years.
-Chris
I built a few SymAsym amplifiers. I originally built one as a utility amplifier knowing it would sound good. Well, it sounds great. I have 6 more boards to build after I am finished some modifications (2SK170 pair for one). Yes, matching pairs of transistors really helps the sound quality out, but this is common to all amplifiers. My original 5.3 builds sound great even now. Do I have stuff that sounds better? Sure I do, but they are more complicated and higher power. I listen to the SymAsym, which was not the intended use when I first built one. For the money and output power, these are hard to beat. This would make an excellent first amp project that will reward you for years to come.
mjona,
People are not having a problem with these amplifiers. There was initially an issue when using different output transistors, but adjusting the compensation fixed that right away. Today there are versions that use all kinds of outputs. It is reasonably forgiving as long as you adjust the compensation if you use different outputs than they were designed with. No surprises there. I used the On-Semi MJW0281A and MJW0302A - excellent. I don't know what bugs you about the SymAsym, but give it a rest. More versions of that amp exist in the world than most any other "community kit" amp, not unless amps designed by ostripper have been more popular, and they may have as I was away for a few years.
-Chris
Don't pick on the original symasym !
Best amp on the forum in <2009 , that and the "blameless".
They were the only two amps back then.
Maybe Roenders folded cascode "blameless' ....
Original sym , I even have the simulation - well compensated to
be very reliable. The only improvements would to make it a higher
powered servo design (my "symasui").
All these years and I can only halve the original's THD.
Sym was one of my "nubee" amps ... helped me learn the basics.
Thanks , AAK.
OS
Best amp on the forum in <2009 , that and the "blameless".
They were the only two amps back then.
Maybe Roenders folded cascode "blameless' ....
Original sym , I even have the simulation - well compensated to
be very reliable. The only improvements would to make it a higher
powered servo design (my "symasui").
All these years and I can only halve the original's THD.
Sym was one of my "nubee" amps ... helped me learn the basics.
Thanks , AAK.
OS
You do have an excellent sales pitch. All I have asked for is for someone who has built one to post pictures of the 10 kHz square wave into 8R//2uF. That would be the perfect ending, so why not just do that.
Hi mjona,
I don't have a problem doing that, but my amps are inaccessible for a bit. If I complete another I would be very happy to post the results.
I don't know if these are the most stable amps around here, but mine have always been very "settled". Not much seems to bother that design. One thing I didn't do with it that is normal for me is to take measurements, except when I set the bias current. That was only to find the correct bias point for this amp. My measurements are back in the original thread. The bias setting is very low, maybe 15 mA +/- 5 mA for minimum THD with the clearest residuals off the THD meter.
When I get ahold of a poorly performing amplifier, that is when I go all out with measurements. I'm looking for a problem then.
I'm not trying to sell the SymAsym. It's a great little amplifier (50 wpc), and would make an excellent first project, and something that would probably be in use for years. The work that ostripper has done has me planning to build one of his next. If it sounds better than the SymAsym, ostripper has designed a giant killer! This, I want to experience. I guess I should be looking in the 150 ~ 250 wpc range of amplifiers. The Marantz 300DC (modified) is my best amplifier. Its rated output is 150 wpc, with +3dB headroom!! That and Marantz products generally can produce 10 ~ 25 % more power than the printed specs allow. That is a tough amplifier to best.
-Chris
I don't have a problem doing that, but my amps are inaccessible for a bit. If I complete another I would be very happy to post the results.
I don't know if these are the most stable amps around here, but mine have always been very "settled". Not much seems to bother that design. One thing I didn't do with it that is normal for me is to take measurements, except when I set the bias current. That was only to find the correct bias point for this amp. My measurements are back in the original thread. The bias setting is very low, maybe 15 mA +/- 5 mA for minimum THD with the clearest residuals off the THD meter.
When I get ahold of a poorly performing amplifier, that is when I go all out with measurements. I'm looking for a problem then.
I'm not trying to sell the SymAsym. It's a great little amplifier (50 wpc), and would make an excellent first project, and something that would probably be in use for years. The work that ostripper has done has me planning to build one of his next. If it sounds better than the SymAsym, ostripper has designed a giant killer! This, I want to experience. I guess I should be looking in the 150 ~ 250 wpc range of amplifiers. The Marantz 300DC (modified) is my best amplifier. Its rated output is 150 wpc, with +3dB headroom!! That and Marantz products generally can produce 10 ~ 25 % more power than the printed specs allow. That is a tough amplifier to best.
-Chris
