Explendid amplifier designed by Michael Bittner, our MikeB

I bought two pairs of boards, and I'm pretty certain semiconductors for two pairs as well. So I think I might spend some time reading through this thread and see if I can build a 'souped up' version sometime this year. But I also have a pair of GB150Ds that have never been powered on, so I guess those will need some love too. Amazing what happens when you clean out the garage!
 
hi everyone.

My symasym 5.3 is almost completed. But I worry about bias.
I built some classA amplifiers. They are bests. But modern technology allows classAB/B amplifiers can be so good.

MikeB recommends 55mA per channel, is there a benefit of increasing bias? for example; 150mA, 300mA, maybe 1A even 1.5A?

I also have simple capacitance multipliers and 100VA transformers per channel. I will go dual mono in one chasis.

Is the original 5.3 schematic suitable for highly biased operation?

What would be your suggests?
 
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Here is my Symasym 5.3 :)

its a dual mono in same case.
100VA transformer and simple capacitance multiplier each channel
StarGND has connected to chasis with ground-earth breaker.

there is no humm. but I hear "hiss" noise from the amplifier. When source is not connected, "hiss" is lower but still there.

is "hiss" noise normal, or can I reduce it?

my previous amp was PASS F5T and there was no hiss.
 

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I have been reading some post about this symasym amplifier but I have no time enough to read the thread completely. I want to build the second version, Symasym 5 whixh was posted in Page 1. However I would like to know if you have made a version better than the mentionated ine. Another point is the differential pair matching. Here the small transistor are false origin, and they don't work well in any part of the circuit. Thank you for your attention
 
I built Symasym using PCBs of my own design. I was also motivated by the topology which is the same as much copied Hitachi lateral MOSFET amp. This project was some kind of experiment because I wanted to see how this amp will work on the PCB using ground planes. Many people advise against ground planes for audio power amplifiers but I wanted to try it. I used two ground planes on both side of the board. One audio ground for input and feedback circuit and one for outpu Zobel and PSU bypass. Only doubt was how to connect 330pF/47k and at the end I connected it to power ground.

I did not have any problems with ground plane PCB! Everything worked OK, no stability isssues. Sound is excellent!

For my build I use dtransistors that I already have.

I/P BC550C, BC546
VAS 2SB647, 2SD667
Drivers 2SC4793, 2SA1837
Output 2SC5200, 2SA1943

There was some concern about stability with 5200/1943 pair so I used 4R7 base stoppers insted of 1R2. Also, since my drivers are not on the heatsink I use 100R instead of 33R.

Pic attached.
 

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Hi piggybladder,
Simple. The version 5.3 is the original line. There might have been a 5.4, I can't remember. The others are take-offs on the original theme, which is valid. I know Roender's work properly because I built some of those too.
(low-ish power, low part count, small form factor, cheap)?
Low-ish power? 50 watts is more than enough for most people to be honest with you. Running higher power meas higher voltages and design changes. So you are forced into a similar design, but with changes.

I built the 5.3 as a utility amplifier, and it outperformed my expectations. Then I bought Roender's design and was highly satisfied with those as well. So the quality is pretty high. I am comparing it to a Marantz 300DC (main amplifier), a Luxman C-02/M-02 combination (office system) and an Eico HF-87 tube amplifier I use. None of these amplifiers are totally stock as I have worked on all of them, including the SymAsym models. With care in matching some transistors I achieved better performance than most, and at a lower bias current. They run cool.

So for most people, the 50 watt per channel version is probably enough. If you want more, then there are those other, related projects that are spin-offs. If you are going to built one of these, read the thread for them (the whole thing) so you become aware of any tweaks to the design, or any small problems. Keep in mind you can improve the basic design by supplying the power for the voltage amplifier separately to achieve even lower distortion and freedom from what the current output is at any instant. Regulate it for even higher performance (the Marantz 300DC does this).

I think "lowish power" might apply to a 25 watt per channel amplifier, but once you reach the 50 watt level, you are capable of burning out speakers if you try. So this amplifier reaches the mid-power range, not low power. THe care and construction of these will determine "cheaply made" or something more esoteric. It lends itself to intelligent improvements while retaining it's true character.

If this is the first amplifier you are going to make, excellent choice. I recommend it to first time builders all the time.

Another good project amplifier would be the "Honey Badger" sold in the DIYAudio store. That would qualify as a good project as well, but is more advanced than the SymAsym. Read a more difficult build.

-Chris
 
Hi anatech and rest of forum friends. I had also read about the stability loss in the amplifier by using output transistors C5200 and A1943 instead of those recommended in the diagram originally but I have several of the ones mentioned firstly in my stock. I have read very good references about this symasym amp so I would like to build it. Thank you for your help
 
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Hi Elias,
Many amplifier designs do not like other output devices, same for drivers. So it isn't uncommon to have to re-stabilise an amplifier if these parts are changes. What changes in all amplifiers is the phase margin. The question then becomes, "will this affect things in operation".

I used MJW0281A and MJW0302A (obsolete now) and could run the bias at about 5 mA for minimum distortion. Others have run much higher bias current and with different driver and output transistors successfully.

-Chris
 
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Hi Elias,
You will have to change the compensation capacitor.

The bias current is a completely different thing. One thing you should know is that the higher the current in a transistor, the faster it gets up to a point. Then it decreases again. We're talking amperes, but the effect exists at bias current ranges.

Search the SymAsym thread for the output transistor types you're interested in. Bear in mind that there isn't going to be a great deal of performance differences between good quality output transistors. You would be wasting your time to locate and install the "best" output transistors. I have to admit that the On Semi devices I used are the best I have seen. But, I'm not about to try and buy (likely fake) the same parts for a couple I still have to build.

-Chris
 
Hi Chris,
The others are take-offs on the original theme, which is valid. I know Roender's work properly because I built some of those too...
The take offs are things of beauty. When/if I get time I plan to build Roender's and a couple of Ostripper's splendid versions. Not criticizing just miffed that as they've got physically bigger they're unlikely to be candidates for mounting internally in my 3 way active l/s project. So I have to pass on all the improvements :( :(
Low-ish power? 50 watts is more than enough for most people to be honest with you.
Totally agree. I'm personally unlikely to need even 50 watts. Especially in an active l/s. Only said 'low-ish' coz all the forks have gone for massive power
I built the 5.3 as a utility amplifier...
I built 3 a couple of years ago - one complete channel for an active 3-way. Tested electrically. All good. Never got to hear them tho. My tom cat pissed all over the boards. Corroded a lot of tracks :mad:
Keep in mind you can improve the basic design by supplying the power for the voltage amplifier separately to achieve even lower distortion...
Yeah, been thinking about that after reading Ostripper's fork. This had never occurred to me before. One of those damascene moments. Might achieve smaller mother/daughter board packages with all OPTs on one massive h/s attached to outside of each spkr. I'll have to brush up on cad and model this to see what's the best fit
If this is the first amplifier you are going to make
Far from the first and won't be the last I suspect :D. All the amps I've built like gainclones, Penasa's, Destroyer's are fine for mids and trebles but don't really provide the bass slam for rock music that I'm looking for. They gotta drive Audax PR240MO 10" bass drivers. Not a particularly difficult load. I noticed Rudi said somewhere in his fork that sym5.3 isn't great here either. I'll try it and see. Plan B is Sym5.3 on mids and trebles and squeezing in a slewmaster iteration on bass. Might just be do-able.

P.S. I'm broke due to disabilty. If I can't etch my own (single sided) boards or the part count's too expensive it ain't getting built :)

Thanks for all your insights.

Cheers Mark