Symasym 5.3 "AAK model" builder's thread

[LineSource]

Hi Ryssen,

There are several good threads on cascodes with supporting literature data showing that a bipolar-bipolar cascode has the lowest noise and best performance, with the JFET differential and bipolar cascode the next best performer. The MAT02-MAT03 dual low noise BJT are often used in hi-end equipment. Many favor the JFET-Bipolar - it just sound better and solves some box-to-box connect problems. The bipolar-bipolar would be better if an active crossover is right in front of the amp....maybe on the same PCB with PASS JFET opamps.

For JFET-JFET cascodes, the self biasing using the Vt difference between 170 differential and 246 cascode transistors as Borbley champions is very difficult to construct because of JFET VT matching....be prepared to purchase and hand match dozens of JFETs.

Anyway...that's what I've learned.

[Ryssen]

I will Search later and try to learn on cascading,if no one have an finished solution.Will look in the original Explendid amplifier thread,but its a Looooong thread.
The output transistors 2sc5200-OQ/2sa1943-OQ Are there any bennfits sonical to use them compared to MJL21193/94 or MJL1302/MJL3281?I have lots of them.

[AAK]

Hi MBK,

Thanks for pointing out that C18 is not listed in the BOM. It should be 0.1uf, same as C5,C6. The components that are critical on my board are R26 (150 ohms) to maintain thermal stability, R22,R23,R24 to correctly set the bias, and C14 (10pf or less for selected U3,U4) to keep the amplifier from oscillating.

It's getting late. I'll get back to answering your other questions tomorrow.

Al

[MBK]

Hi Al,

thanks, I appreciate. This is only my second discrete amp, and that is in building, not designing. My usual DIY efforts are all in speakers and op amp based signal circuits / chip amps... So while I vaguely know what the parts are for, functionally, I am not always sure of what change will affect what parameter.

[-_nando-_]

Hello !

I'm VERY interested in a higher power version of Symasym as I have 8Ohms speakers.

I built Symasym, and I'm amazed of how good it sounds, despite I still searching for a higher power version, I can't leave the good sound of Symasym.

-> So, HOW does it sound? Does it sound as good as symasym 5.3 ?

I built mine with Styroflex and Mica capacitors, Wima 3.3uF for the input, and On Semi MJL3201 and MJL1302 transistos.

-> How much power with a 8Ohms load?

-> What is the recommended supply rails for a VERY safe operation with the highest power possible at 8 ohms?

-> How much costs the PCB ?


Thank you very very much, I'm anxious for the feedback !

edit: I'd like to keep the output devices, can I use MJL1302 / 3201 ? I can use a pair if is necessary.

Best Regards

[Colescuttle]

Hi, Al:

What thermal interface material did you use when mounting the output transistors, and where did you get it?

Thanks.

George

[MBK]

Al,

did you have additional comments to the questions in my post #10 not addressed in your post #13 ?

[Ryssen]

The beginning...



Been playing with some stuff I had laying around..settled on a 2x24v trafo,good for heat if raising bias..
At least a start as I have this habbit of doing many projekts (to many)at the same time.

[AAK]

Hi Ryseen,

Nice enclosure, and heatsinks. Are the heatsinks from Conrad?

In your pic I only see one transformer. For my version of Symasym you'll need two transformers, one for each channel.

Al

[AAK]

Hi Colescuttle,

The thermal pads that I used for the output transistors are from Mouser item number 526-TP0010.

Here's a new revised BOM. The revision includes the thermal pads, and C18 that MBK brought up in post #10 that I mistakenly left out.

Al